Top 18 low-carb & keto controversies

Top 18 low-carb & keto controversies

It is common for people to be skeptical of a low-carb diet in the beginning, especially since high-carb, low-fat advice has been so prevalent for decades.1
We don’t want any unsubstantiated fears to get in the way of people reaping the benefits of a low-carb diet. On this page you can learn why many of these controversies are based on misunderstandings or incomplete knowledge – those are nothing to worry about.

However, our goal of making low carb simple also requires us to be very upfront and honest about potential problems and how to handle them. Some problems can and do occur on low carb, and it can be helpful to know what they are and what can be done about them.

Here are the most common controversies about low carb, and what the current best available scientific evidence can tell us about them.


1. Will saturated fat clog my arteries and give me a heart attack?

time-saturated-fat-butter-cover-smNo. This is probably one of the biggest nutrition myths of the last few decades.2

First of all, heart disease doesn’t work the same way a clogged sink does! There are many potential contributing factors to the development of heart disease, including genetics, inflammation, and metabolic health conditions, such as diabetes.3 How diet interacts with these other factors can vary greatly from one individual to another.

In terms of scientific evidence, links between saturated fat and heart disease are weak and inconsistent. Although other reviews reach different conclusions, some reviews of current science indicate there’s no connection between saturated fat and heart disease.45 The weakness of the evidence against saturated fat is catching on in the mainstream media as well.6

Because the evidence is so weak and because the individual response to dietary fats varies significantly, population-wide recommendations to avoid saturated fat appear to have been a mistake.

Fortunately, during the last several years more and more experts and organizations have realized that natural saturated fats – despite their reputation – appear to be neutral from a health perspective.7

It’s natural to eat saturated fats, as they are found in natural foods that we have eaten throughout evolution.8 This includes human breast milk, and the multiple foods that sustained our ancestors as adults.9

Don’t fear fat. Updated experts don’t.

A user guide to saturated fat

Watch doctors explain why saturated fat is neutral

Vegetable oils: What we know and what we don’t

Read recent news about saturated fat

2. Does a low-carb diet cause high cholesterol?

LDL cholesterolLow-carb diets tend to improve the cholesterol profile by increasing levels of HDL (“good”) cholesterol, and decreasing levels of potentially harmful triglycerides.10 They may also improve the size profile of the LDL.11

These appear to be beneficial changes that are associated with decreased insulin resistance and improved health.

Regarding LDL (“bad”) cholesterol, most people experience no significant changes on low carb.12 However, in some people, LDL levels decrease or (more often) increase somewhat.13

For a small minority of people however, cholesterol may go up abnormally high on a low-carb, high-fat diet.14 In those situations it maybe worth an experiment to adapt the diet to lower the LDL cholesterol levels. Depending on your overall risk profile, you may want to work closely with your doctor to monitor for any evidence of cardiovascular disease.

Controversy exists about the absolute risk of elevated LDL in all people, as some observational studies show that higher LDL levels in the elderly are associated with living longer, and others report no increased risk as long as HDL and triglycerides are normal.15 While this does not prove cause and effect, it raises the question if LDL is a concern for everyone.

Taken together, studies show that low-carb diets on average improve risk factors for heart disease for the majority of people, including cholesterol.16

The bottom line: Low-carb and high-fat diets on average improve the cholesterol profile and reduce most risk factors for heart disease. The effect of this has been demonstrated in a 2010 study that showed a reduction in atherosclerosis after two years on a low-carb, high-fat diet.17

Low carb and cholesterol – the full guide

Learn how to handle elevated cholesterol on low carb

Read recent news about cholesterol

3. Doesn’t the brain need carbs?

No. On a strict low-carb diet the brain can be primarily fueled by fat – or technically, by ketones. When carb intake is very low, your liver converts body fat or fat from the food you’ve eaten into ketones, which can be used by the brain as fuel.18

brainThis means that fat-burning goes up significantly – a big plus for people who want to lose excess weight.19

Furthermore, your body can produce any glucose it needs through a process called gluconeogenesis, converting other nutrients to glucose – even if you don’t eat any carbs at all.20

There is no need for carbohydrates in the diet, and the brain functions fine without it.

Learn more in our full guide:

Food for thought: Does the brain need carbs?

Learn more about ketones and ketosis

4. Is low carb bad for the environment?

No. It’s a common misunderstanding that a low-carb diet requires eating a lot of protein, including meat, making it bad for the environment. This is simply not true.

A low-carb diet is just that — low carb. You can otherwise eat whatever you want be it vegan, vegetarian, carnivore, or anything in between.

The amount of protein usually stays moderate – about 1.5 grams per kilo per day.21 So there’s no need to eat more meat just because you’re on a low-carb diet. In fact it’s very possible to even eat a vegetarian or vegan low-carb diet, should you want to.

cowFurthermore, the impact of meat production on the environment depends on many factors. Do you buy locally raised, grass fed or pasture raised meat or poultry? If so, these can be raised in a manner that is environmentally friendly! They may potentially reduce the pesticide burden and nutrient depletion of soils, as well as allowing for more carbon dioxide to be stored in the ground.22

The environmental benefit of having carb-rich monocultures such as soy, sugar and corn is also overstated. These pesticide-heavy crops reduce biodiversity and contribute to pollution to a much greater extent than, let’s say, a biodynamic cow farm.23

Finally, a low-carb diet often results in people eating less food, as it’s so satiating.24 After significant weight loss people need even less food. Needing less food, and needing to eat less often, is of course good for the environment.

Bottom line: A low-carb diet is moderate in protein and it’s no different for the environment than most diets. If you still choose to eat more meat than usual, the impact on the environment depends a lot on how the animals were raised.

Six ways to stay environmentally friendly on a low-carb or keto diet

The green keto meat eater

Diet Doctor Podcast with Professor Frank Mitloehner and another with Diana Rodgers.

TED / Allan Savory: How to fight desertification and reverse climate change

Watch one of the smartest men in the world explain the real problem for the environment (Hint: it’s fossil fuels)

5. Can you get nutrient deficiencies on low carb?

NutritentsProbably the opposite is more often true. The foods consumed on a low-carb diet are highly nutritious.25 For example, eggs (a staple for many people on low carb) may provide the most complete nutrition of any food on the planet.26

Consider that a complete chicken can be formed from the nutrients inside the egg. There’s no way for the chicken to pop out and get some vitamins and minerals while growing in the egg; everything has to be there. And by eating an egg, we humans get all those nutrients.

Meat, fish, and vegetables are also highly nutritious foods. And many people eating low carb tend to replace nutrient-poor pasta, rice, and potatoes with more nutrient-rich vegetables.

Studies show that a low-carb diet can be nutritionally complete.27

Compared to the more complete nutrition of a low-carb diet, refined flour is more or less devoid of any nutrition apart from pure starch. Usually, it’s legally required to add vitamins to flour, so that people who eat a lot of it do not get vitamin deficiencies.

Also, grains like wheat are high in phytic acid that can potentially reduce the absorption of many minerals.28

Another concern with low-carb diets is the lack of fruit, often thought to be necessary for proper nutrition. This is a misunderstanding. Apart from vitamin C, there are very few nutrients in most modern fruit.29 These days, they are modified to be large and very sweet. We think of fruit as candy from nature, and should probably be eaten in moderation. Fruit juice is even worse, given the concentrated sugar and lack of fiber to help slow the absorption.30

Modern fast food and snack food also contain a lot of calories and minimal if any nutrition.31 And low-fat products are low in essential fat-soluble vitamins, which are found in full-fat versions of yogurt, cheese, and other whole foods.

Bottom line: Switching from a standard Western diet to a low-carb diet based on real foods is likely to significantly increase the amount of vitamins and minerals you get from your diet.


6. Can low carb damage your thyroid?

thyroid2Not likely. If you eat a well-formulated low-carb diet, it’s very unlikely it will affect your thyroid negatively.32

Although some studies may show a decrease in the active thyroid hormone T3, it is not clear that this represents a problem.33 For instance, some hypothesize that our bodies become more sensitive to thyroid hormones, and therefore have a different “normal” range. Others suggest fat is more metabolically efficient, and therefore less thyroid hormone is required to metabolize it.34 While these are just theories at this point, they highlight how a change in a single lab value does not by definition signify a problem or deleterious change.

In fact, some people who lose significant amounts of weight on low carb may end up needing less thyroid medication, and a few individuals may even be able to stop taking it completely.35 This may just be an effect of a smaller body needing less thyroid hormone – there isn’t any research showing that carbohydrate reduction itself can improve thyroid function.

This means that if you have hypothyroidism and supplement with thyroid hormone you can start a low-carb diet like anybody, and continue to do regular checkups as usual. If you lose a lot of weight it may be wise to do an extra check of your thyroid hormones once in a while, e.g. every time you’ve lost 30 pounds (15 kilos). It’s not impossible that your dose may need to be adjusted.

Bottom line: Eating a healthy, low-carb diet should not negatively affect your thyroid.

Learn how to eat more fat

7. Can low carb damage your kidneys?

Highly unlikely.36 Many people still believe that a low-carb diet or even a high-protein diet could put a strain on the kidneys. This is a myth based on two misunderstandings.

kidneysFirst, a well-formulated low-carb diet is moderate in protein — around 1.5 grams per kilo per day.37

As a low-carb diet doesn’t need to be very high in protein — for example, 3 grams per kilo per day — the whole “problem” behind this controversy simply does not exist.

Secondly, people with normal kidney function can handle high amounts of protein without any problem for the kidneys.38

Even if people choose to eat excessive protein, this will only be a problem if the kidneys are already severely damaged. An example of this would be end-stage kidney disease that is close to requiring dialysis. If you have severe kidney disease and you’ve been told to limit protein, you should of course do so.39 But that would still make it possible for you to successfully eat a low-carb, high-fat diet.

To summarize: For people without kidney disease there’s no reason to worry about the effect of excessive protein on your kidney health.

Bottom line: A low-carb diet is fine for your kidneys.

In fact, by lowering elevated blood sugars a low-carb diet may actually protect the kidneys from one of the most common causes of damage. Especially for people with diabetes, low carb might help protect their kidneys, by helping control their blood sugar levels.40

What you need to know about a low-carb diet and your kidneys

Watch doctors explain how low carb affects your kidneys
How to reverse your type 2 diabetes

8. Can low carb make you depressed?

depressionNot likely. But during the first week, or two, of a low-carb diet, it’s common to experience symptoms similar to those of depression (such as lethargy, tiredness, irritability, brain fog).41

These problems usually disappear within a few days or a couple weeks. They can often be avoided for the most part by getting enough fluid and salt – for example a cup of bouillon 1-2 times a day.

Long term, a low-carb diet often has the opposite effect. Getting into ketosis can make some people feel very energetic and might increase mental performance and endurance.42 People sometimes mention the “mental clarity” they feel.

Studies of the mental state on low-carb diets generally, and on average, show either no clear change or a slight improvement, compared to before starting the diet.43 Note that studies show the average result for a group of people. A few individuals may feel worse, while others feel better.

One reason that some people may feel depressed is if they have an addiction to reward from high-carb, sweet foods.44 Removing such foods when people are addicted to them may result in temporary feelings of loss and sadness, similar to symptoms of a depression. It may be similar to the effect of withdrawing from nicotine or alcohol when addicted to these substances.

Fortunately, after early withdrawal symptoms have passed, getting free of an addiction is incredibly liberating and enables people to lead fuller and happier lives.45 So it can definitely be worth the struggle.

Finally, to make a low-carb diet feel great long term requires tasty food and a simple and enjoyable lifestyle. Feel free to use our resources to speed up the process.


Check out awesome low-carb recipes

Make low carb simpler using our low-carb living guides

9. Is low carb bad for exercise?

Exercise and low carbLow carb can be good, bad, neutral or even fantastic for exercise. It depends.

During the first couple of weeks when you’re switching from a diet rich in carbs to a low-carb diet, your capacity in the gym will most likely go down.46 This is due to the low-carb flu, but it will likely pass within one or two weeks.47

After a few weeks of adaptation, people often report feeling at least as good as before when exercising, especially if they make sure to get enough fluids and salt.48

Furthermore, for endurance athletes, there are many potential benefits to being fat-adapted and eating LCHF.49 For instance, this is demonstrated by the fact that the two top performers in Tour de France 2016 were on some form of low-carb diet.

But the findings are not universal. Two studies out of Australia report that race walk times decrease after 12-weeks of eating a keto diet, despite improved fat oxidation.50

Benefits have also been seen for powerlifting and weightlifting athletes.51 Additionally, following a ketogenic diet might improve body composition when combined with resistance training.52

However, more carbs may be needed for non-endurance sports such as sprinting etc.53 In these cases, it might be a good idea to take in some more carbs on the day when you need to perform, such as during a game day.

The bottom line is that scientific evidence is mixed on how ketosis affects athletic performance. Individual variability, different effects for different exercises, and the importance of adaptation all need to be taken into consideration.


Watch doctors explain how low carb can be good for exercise

Learn more about how to increase physical performance on low carb

10. Is low carb bad for your gut bacteria?

Gut bacteriaProbably not. There is currently a lot of research being conducted on gut bacteria and microbiome.54 The main problem with much of the reporting on gut bacteria and diet is confusing statistical correlations with causality, i.e. taking weak clues and mistakenly calling it proof.55

Not much, if anything, can yet be said about the health effects of changes to the microbiome on a low-carb diet, only that it changes.56 However, many people report that they have less gastrointestinal stress and bloating after starting a low-carb diet. Additionally, the ketogenic diet may lead to beneficial changes in the microbiome in people with certain health conditions, such as multiple sclerosis and epilepsy.57

Probably the best things to do for your gut bacteria are to avoid refined, simple sugars and try to avoid antibiotics unless you absolutely have to.58

Watch a presentation on the possible benefits of slow carbs to feed the microbiome

11. Can you get constipated on low carb?

Yes. Constipation is a possible side effect that can occur, especially during the first time on a low-carb diet, as your digestive system may need time to adapt.59

It can usually be alleviated by either drinking more water and increasing salt intake, taking in more fiber or, if necessary, adding Milk of Magnesia.60

Note that just because some people have a bowel movement less often does not mean they are constipated. Many people report decreased stool frequency on low carb, but as long as they don’t feel bloated or abdominal pain, there is no concern with this.61

If you suffer problems with constipation when starting low carb, it is usually temporary.

Learn more about preventing or curing constipation on low carb

12. Can you get osteoporosis on low carb?

osteoporosisNo. There is a lingering idea that eating low carb could result in osteoporosis, due to making the blood “acidic” and leaching minerals from the bones. But this theory has been disproven in several ways.

For example, under normal circumstances the pH of the blood does not change depending on what you eat.62 Blood pH is tightly controlled within a very narrow range – otherwise, we’d die.

This theory is usually based on the idea that a diet rich in protein would make the blood acidic, making it bad for the bones. This is the opposite of what studies show – people who eat more protein tend to have stronger bones.63 Looking at all available science, higher protein intake hasn’t been shown to harm bone health and may potentially even help protect against bone loss in the lower spine.64

Finally, repeated studies show no effect on bone density in people eating low carb, even after several years.65

Low carb does not negatively affect the bones.

Read our complete guide on bone health and low-carb diets.

Learn more about low carb, blood pH and bone strength

13. Does low carb cause hair loss?

hairOccasionally. Temporary hair thinning can occur for many different reasons, including any big dietary change. This is especially common when severely restricting calories (e.g. starvation diets, meal replacements) but it can also occasionally happen on a low-carb diet.66

This kind of temporary thinning of the hair67 typically occurs 3-6 months after a big dietary change or any other kind of stressful experience for the body. After a period of losing more hair than usual, the lost hairs then grow out again, so that the hair ends up as thick as before.

It’s safe to say that the large majority of people who try a low-carb diet never experience this. Furthermore, it’s likely possible to minimize the risk by not doing a low-carb and low-fat diet at the same time, i.e. by avoiding starvation. Make sure to eat enough fat to feel satisfied, and a moderate amount of protein.68 Learn more about low carb & temporary hair loss

Learn how to eat more fat

14. Does low carb cause ketoacidosis?

KetoacidosisNo. Many people mix up ketoacidosis with ketosis.

Ketoacidosis (also known as diabetic ketoacidosis, or DKA) is a rare and dangerous medical condition that mainly occurs in people with type 1 diabetes if they don’t take insulin, especially if they are ill.

People with type 2 diabetes who take certain medications (eg SGLT2 inhibitors) can also develop DKA, although this is relatively rare.69 However, eating a ketogenic diet while taking these medications might potentially increase the risk of DKA.70

Also, in rare cases, women eating a very low-carb diet can develop ketoacidosis while breastfeeding.71

Ketosis (sometimes referred to as nutritional ketosis), on the other hand, is a 100% natural and safe state for most people, under full control by the body.72

It can be caused by a low-carb diet or by a brief period of fasting.73

Under normal circumstances, a strict low-carb diet never results in ketoacidosis. It results in ketosis, a natural and safe state that enables the body to quickly burn fat.74

Learn more about ketosis and ketoacidosis

15. Do you get a shortage of whole grains on low carb?

Do you need to eat whole grains – like bread or pasta – to stay healthy? While the fiber in whole grains may slow down the absorption of glucose and lower the glycemic index (possibly a good thing), it’s less clear what the benefit is on a low-carb diet.75 There’s likely much less benefit of slowing down the absorption of carbs if you don’t eat many carbs.

Furthermore, there no high-quality science proving a need to eat whole grains to prevent disease or prolong life. The most recent Cochrane review of high-quality nutrition science found no evidence for that idea.76

There’s a widely-held belief that people need to eat grains to get specific nutrients. However, other foods that are lower in carbs are often more nutritious.

Finally, there’s an idea that the microbiome in our guts may benefit from the fiber in whole grains. This is still a controversial topic with a lack of high-quality science. However, there are many other sources of fiber that are far lower in carbs than whole grains.

Learn more about whole grains and health

16. Is salt dangerous for your health?

A low-carb diet is not necessarily higher in salt than other diets. But it’s often recommended to increase salt intake when starting, to reduce the risk of side effects. So is salt dangerous?

Actually, the science for this common piece of health advice is quite weak and misguided.

Read more detail in our comprehensive guide on salt.

You can also read more on our news post detailing how salt restriction lacks credible evidence

17. Is red meat dangerous?

A low-carb diet is not necessarily higher in red meat than other diets. It’s even possible to eat a vegetarian low-carb diet. However, many people eat a low-carb diet with red meat. Here’s our guide to what the scientific evidence tells us about it:

Guide to red meat – is it healthy?

  1. This advice may have contributed to the obesity epidemic first seen in the US, which is now a global health issue.

    Nutrition 2015: Statistical review of US macronutrient consumption data, 1965-2011: Americans have been following dietary guidelines, coincident with the rise in obesity [overview article]

    Some argue that very few individuals actually adhered to the dietary recommendations, and therefore we cannot blame them for the rise in obesity and metabolic disease. However, it does seem clear that the advice to cut calories and lower fat at a minimum created the environment for increased hunger and as a result increase carb and calorie consumption which likely contributed to the overall decline in health.

  2. Current Nutrition Reports 2018: Saturated fat: part of a healthy diet [overview article]

  3. Journal of Natural Science 2017: Linking chronic inflammation with cardiovascular disease: From normal aging to the metabolic syndrome. [overview article; ungraded]

    Frontiers of Endocrinology 2018: Type 2 diabetes mellitus and cardiovascular disease: Genetic and epigenetic links.
    [overview article; ungraded]

    The following observational study reported a much greater risk of developing heart disease for those with metabolic disease, such as diabetes or having insulin resistance, than traditional measures like elevated LDL cholesterol. You can read our review of the study here.

    JAMA Cardiology 2021: Association of Lipid, Inflammatory, and Metabolic Biomarkers With Age at Onset for Incident Coronary Heart Disease in Women [observational study with HR>2, weak evidence]

  4. Here are five meta-analyses showing no connection between saturated fats and heart disease:

    And one 2020 Cochrane review of RCTs showed a reduction in cardiovascular events for lower saturated fat intake, but this effect was modest. This study also found no difference in cardiovascular death or all-cause death.

    Interestingly, of the 12 studies analyzed, 9 showed no significant difference in heart disease risk, whereas 3 did show a difference, and the pooled analysis showed a small difference. In addition, there was no documentation of the types of saturated fats consumed.

    Cochrane Database of Systemic Reviews 2020: Reduction in saturated fat intake for cardiovascular disease [systematic review of randomized trials; strong evidence]

    Learn more about the science of saturated fat

  5. Beyond studies on saturated fats, there’s no good support for natural foods containing plenty of saturated fats being a concern. For example, butter, meat, coconut oil, etc. In studies, these foods have not been proven to increase heart disease risk:

    American Journal of Clinical Nutrition 2017: Total red meat intake of ≥0.5 servings/d does not negatively influence cardiovascular disease risk factors: a systemically searched meta-analysis of randomized controlled trials [strong evidence]

    PloS One 2016: Is butter back? A systematic review and meta-analysis of butter consumption and risk of cardiovascular disease, diabetes, and total mortality [very weak evidence]

    Indian Heart Journal 2016: A randomized study of coconut oil versus sunflower oil on cardiovascular risk factors in patients with stable coronary heart disease [moderate evidence]

    Dairy fat including yogurt and cheese has been shown to be protective against heart disease in observational studies.

    Advances in Nutrition 2019: Effects of full-fat and fermented dairy products on cardiometabolic disease: Food is more than the sum of its parts [nutritional epidemiology study; very weak evidence]

    As leading scientists claimed in their 2020 review paper, we should discuss health implications of specific foods rather than lumping them all together as “saturated fats.”

    Journal of the American College of Cardiology 2020: Saturated fats and health: A reassessment and proposal for food-based recommendations: JACC State-of -the-Art Review [overview article; ungraded]

  6. Here are a few examples.

    TIME: Eat butter. Scientists labeled fat the enemy. Why they were wrong.

    WSJ: The dubious science behind the anti-fat crusade

    The Washington Post: ‘Carbohydrates are killing us’

  7. For example, The Academy of Nutrition and Dietetics has publicly stated that saturated fat should no longer be considered a nutrient of concern, given the lack of evidence connecting it to heart disease. See the references above for more examples.

  8. Humans and our ancestors have been eating natural saturated fats for millions of years:

    Nature Education Knowledge: Evidence for meat-eating by early humans [overview article]

  9. About 50% of all the fat in breast milk is saturated fat.

    Lipids 2010: Saturated fats: a perspective from lactation and milk composition [overview article]

  10. Nutrition Reviews 2018: Effects of carbohydrate-restricted diets on low-density lipoprotein cholesterol levels in overweight and obese adults: a systematic review and meta-analysis [strong evidence]

    Annals of Internal Medicine 2010: Weight and metabolic outcomes after 2 years on a low-carbohydrate versus low-fat diet: a randomized trial [moderate evidence]

  11. Lipids 2009: Carbohydrate restriction has a more favorable impact on the metabolic syndrome than a low fat diet [moderate evidence]

    A nonrandomized trial showed a ketogenic diet reduced the percentage of smaller LDL and increased the larger LDL. This trial also showed no significant increase in atherosclerosis in the carotid artery at two-years, even in the hyperresponders.

    Cardiovascular Diabetology 2020: Impact of a 2-year trial of nutritional ketosis on indices of cardiovascular disease risk in patients with type 2 diabetes
    [nonrandomized study, weak evidence]

  12. A meta-analysis showed no significant change on average.

    Nutrition Reviews 2019: Effects of carbohydrate-restricted diets on low-density lipoprotein cholesterol levels in overweight and obese adults: a systematic review and meta-analysis [systematic review of randomized trials; strong evidence]

    Another study in people with type 2 diabetes found that LDL cholesterol increased by just 9%, on average, after one year on a very-low-carb diet.

    Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study [weak evidence]

  13. This can vary quite a bit from person to person. For instance, in a 3-week study of healthy people who followed a low-carb diet, LDL cholesterol levels increased by as little as 5% in some and as much as 107% in others.

    Atherosclerosis 2018: Effect of low carbohydrate high fat diet on LDL cholesterol and gene expression in normal-weight, young adults: A randomized controlled study [moderate evidence]

  14. These individuals are often referred to as “hyper-responders,” which Dave Feldman of Cholesterol Code has written about extensively: Hyper-Responder FAQ

  15. BMJ Open 2016: Lack of an association or an inverse association between low-density-lipoprotein cholesterol and mortality in the elderly: a systematic review [weak evidence]

    Canadian Journal of Cariology 1988: Cholesterol and lipids in the risk of coronary artery disease–the Framingham Heart Study [observational study; weak evidence]

    Metabolic Syndrome and Related Disorders 2003:
    Triglycerides, high-density lipoprotein cholesterol, and risk of ischemic heart disease: a view from the Copenhagen Male Study
    [observational study; weak evidence]

  16. British Journal of Nutrition 2016: Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomised controlled trials. [strong evidence for improved risk factors]

    Cardiovascular Diabetology 2018: Cardiovascular disease risk factor responses to a type 2 diabetes care model including nutritional ketosis induced by sustained carbohydrate restriction at 1 year: an open label, non-randomized, controlled study [weak evidence]

    Progress in Lipid Research 2008: Dietary carbohydrate restriction induces a unique metabolic state positively affecting atherogenic dyslipidemia, fatty acid partitioning, and metabolic syndrome [overview article]

    Learn more about this and other studies on low carb and risk factors

  17. All three diets induced weight loss and resulted in signs of reduced atherosclerosis, compared to baseline.

    The low-carb, high-fat diet – defying expectations – did not do worse. Instead the non-significant trend was towards a stronger positive effect on low carb:

    Circulation 2010: Dietary intervention to reverse carotid atherosclerosis [moderate evidence]

  18. Although the brain always requires some glucose, a portion of its energy needs can be met by ketones.

    Critical Care 2011: Clinical review: ketones and brain injury [overview article]

    Journal of Cerebral Blood Flow & Metabolism 2017: Inverse relationship between brain glucose and ketone metabolism in adults during short-term moderate dietary ketosis: a dual tracer quantitative positron emission tomography study [weak evidence]

  19. Research has shown that people who consume ketogenic diets often experience an increase in fat burning and fat loss.

    Diabetes and Metabolic Syndrome 2017: Induced and controlled dietary ketosis as a regulator of obesity and metabolic syndrome pathologies [moderate evidence]

    BMC Proceedings 2012: Medium term effects of a ketogenic diet and a Mediterranean diet on resting energy expenditure and respiratory ratio [moderate evidence]

    Military Medicine 2019: Extended ketogenic diet and physical training intervention in military personnel [weak evidence]

  20. American Journal of Clinical Nutrition 2009: Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet [moderate evidence]

  21. In many LCHF studies showing health benefits, people are advised to eat a moderate amount of protein and as much fat as needed to feel satisfied.

    Diabetes Therapy 2018: Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: an open-label, non-randomized, controlled study [weak evidence]

    Applied Physiology, Nutrition and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence]

  22. Environmental Health 2017: Human health implications of organic food and organic agriculture: a comprehensive review [overview article]

    Nature Communications 2015: Emerging land use practices rapidly increase soil organic matter [weak evidence]

    Agricultural Systems 2017: Impacts of soil carbon sequestration on life cycle greenhouse gas emissions in Midwestern USA beef finishing system [weak evidence]

  23. Science of the Total Environment 2018: Environmental and health effects of the herbicide glyphosate [overview article]

    Global Food Security 2017: Livestock: on our plates or eating at our table? A new analysis of the feed/food debate [overview article]

  24. Many studies have shown that when people eat low-carb high-fat diets, their appetite decreases. As a result, they naturally eat end up eating less without consciously restricting how much they eat.

    Obesity Reviews 2014: Do ketogenic diets really suppress appetite? A systematic review and meta-analysis [strong evidence]

  25. These include natural fats, meat, poultry, sea food, eggs, vegetables and berries.

    Learn more about low-carb foods

  26. Nutrients 2015: Egg and egg-derived foods: effects on human health and use as functional foods [overview article]

  27. For example this one:

    BMJ Open 2018: Assessing the nutrient intake of a low-carbohydrate, high-fat (LCHF) diet: a hypothetical case study design [weak evidence]

  28. Phytic acid binds to important minerals like calcium, iron, potassium, and magnesium, which impairs your body’s ability to absorb and use them.

    Journal of Zhejiang University. Science. B 2008: Phytate: impact on environment and human nutrition. A challenge for molecular breeding [overview article]

  29. Here are the nutrition profiles for commonly consumed modern fruits. Fruits are also high in sugar, with the exception of avocado: nutrition in fruits

  30. Studies have shown that consuming fruit juice results in greater weight gain than consuming fresh fruit.

    Obesity (Silver Spring) 2012: Beverage vs. solid fruits and vegetables: effects on energy intake and body weight [moderate evidence]

    The Lancet Diabetes and Endocrinology 2014: Fruit juice: just another sugary drink? [overview article]

  31. The Journal of Clinical Lipidology 2015: JCL roundtable: fast food and the American diet [overview article]

  32. There aren’t any studies showing that a low-carb or ketogenic diet with adequate calories can cause hypothyroidism, a condition reflected by elevated levels of thyroid stimulating hormone (TSH) and low levels of T4 hormone.

    In a study of overweight diabetic men without hypothyroidism who consumed less than 20 grams of carbs per day for 16 weeks, TSH levels remained the same or decreased slightly by the end of the study.

    Nutrition & Metabolism 2005: A low-carbohydrate, ketogenic diet to treat type 2 diabetes [weak evidence]

  33. Metabolism 1980: The role of dietary fat in peripheral thyroid hormone metabolism [nonrandomized study with only 4 participants, weak evidence]

    Clinical Endocrinology 2001: Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men [nonrandomized study, weak evidence]

  34. [mechanistic opinion; very weak evidence]

  35. Anecdotal stories, i.e. very weak evidence.

  36. A 2018 review of 12 randomized controlled trials in people with type 2 diabetes concluded that low-carbohydrate diets do not jeopardize kidney function.

    Diabetes Metabolism Research and Reviews 2018: Effect of low-carbohydrate diet on markers of renal function in patients with type 2 diabetes: a meta-analysis [strong evidence]

  37. Keeping protein intake moderate and eating enough fat for enjoyment are the hallmarks of a LCHF diet.

    Diabetes Therapy 2018: Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: an open-label, non-randomized, controlled study [weak evidence]

    Applied Physiology, Nutrition and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence]

  38. Medicine (Baltimore) 2015: Long-term effects of a very low carbohydrate compared with a high carbohydrate diet on renal function in individuals with type 2 diabetes: a randomized trial [moderate evidence]

    Nutrition & Metabolism 2005: Dietary protein intake and renal function [overview article]

  39. There’s some evidence that this can slow progression of the disease:

    American Journal of Kidney Disease 1996: Effects of dietary protein restriction on the progression of advanced renal disease in the Modification of Diet in Renal Disease Study [moderate evidence]

  40. A 2018 comprehensive review of 12 RCTs found no evidence that low-carbohydrate diets are harmful for kidney health in people with type 2 diabetes.

    Diabetes Metabolism Research and Reviews 2018: Effect of low-carbohydrate diet on markers of renal function in patients with type 2 diabetes: a meta-analysis [strong evidence]

    Furthermore, clinicians have reported improvements in renal function in their diabetic patients who follow carb-restricted diets, as documented in this case report:

    Nutrition & Metabolism 2006: A low-carbohydrate diet may prevent end-stage renal failure in type 2 diabetes. A case report [very weak evidence]

  41. Nutrition X 2019: Effects of differing levels of carbohydrate restriction on mood achievement of nutritional ketosis, and symptoms of carbohydrate withdrawal in healthy adults: A randomized clinical trial [randomized trial; moderate evidence]

  42. This is mainly based on anecdotal evidence from people in nutritional ketosis. [very weak evidence]

  43. Here’s a recent example, showing similar improvements on two different diets, including a very low-carb diet.

    Both diets showed improvements that may at least partially be due to a simultaneous exercise program. The point is, though, that there is no obvious difference between the diets:

    Journal of Internal Medicine 2016: Long-term effects of very low-carbohydrate and high-carbohydrate weight-loss diets on psychological health in obese adults with type 2 diabetes: randomized controlled trial [moderate evidence]

    In an earlier study comparing a ketogenic diet to a low-fat diet without an exercise component, the ketogenic diet group reported a greater reduction in depression and fatigue than the low-fat diet group, although both groups experienced overall improvement in these and other symptoms.

    Obesity (Silver Spring) 2007: The effects of a low-carbohydrate ketogenic diet and a low-fat diet on mood, hunger, and other self-reported symptoms [moderate evidence]

  44. Frontiers in Psychiatry 2018: Sugar addiction: from evolution to revolution [overview article]

  45. This is based on consistent clinical experience of low-carb practitioners. [weak evidence]

  46. In a two-week study, overweight adults who consumed a ketogenic diet reported greater fatigue during exercise than those who ate a moderate-carb diet.

    Journal of the American Dietetic Society 2007: Blood ketones are directly related to fatigue and perceived effort during exercise in overweight adults adhering to low-carbohydrate diets for weight loss: a pilot study [moderate evidence]

    However, such studies have been criticized for not allowing enough time for proper keto-adaptation prior to testing exercise capacity.

  47. According to ketogenic researcher Dr. Steve Phinney, although it takes only a few days to get into nutritional ketosis, it can take 3 to 4 weeks to become fully keto-adapted, regardless of body weight, composition, or fitness.

    Nutrition & Metabolism 2004: Ketogenic diets and physical performance [overview article]

  48. [anecdotal reports; very weak evidence]

  49. Metabolism 2016: Metabolic characteristics of keto-adapted ultra-endurance runners [weak evidence]

  50. You can read our article on the topic here.

  51. Journal of Strength and Conditioning Research 2018: A low-carbohydrate ketogenic diet reduces body mass without compromising performance in powerlifting and Olympic weightlifting athletes [moderate evidence]

  52. Journal of the International Society of Sports Nutrition 2018: Efficacy of ketogenic diet on body composition during resistance training in trained men: a randomized controlled trial [moderate evidence]

    Journal of Strength and Conditioning Research 2017: The effects of ketogenic dieting on body composition, strength, power, and hormonal profiles in resistance training males [weak evidence]

  53. At this time, it’s unclear how performing high-intensity sports like soccer and basketball would be affected in people who’ve been eating LCHF long term, for example, six months or more.

    Journal of Human Kinetics 2017: Low-carbohydrate-high-fat diet: can it help exercise performance? [overview article]

  54. The gut microbiome is the entire collection of bacteria and other organisms living in your digestive tract.

  55. For instance, in a 2018 review of studies looking at the effects of different types and amounts of fat on gut health, results from most observational studies found weak associations between self-reported high fat intake, gut bacteria imbalances, and metabolic dysfunction (e.g. insulin resistance).

    However, the controlled trials (higher-quality evidence) found that fat intake didn’t have a significant effect on gut bacteria or metabolic health:

    Clinical Nutrition 2018: Dietary fat, the gut microbiota, and metabolic health: a systematic review conducted within the MyNewGut project [moderate evidence]

  56. Nutrients 2019: The impact of low-FODMAPs, gluten-free, and ketogenic diets on gut microbiota modulation in pathological conditions [overview article]

    Some of the changes may be uniquely beneficial such as having an anti-inflammatory effect.

    Cell 2020:
    Ketogenic Diets Alter the Gut Microbiome Resulting in Decreased Intestinal Th17 Cells
    [animal and human mechanistic study; very weak evidence]

  57. Frontiers in Microbiology 2017: Reduced mass and diversity of the colonic microbiome in patients with multiple sclerosis and their improvement with ketogenic diet [weak evidence]

    World Journal of Gastroenterology 2017: Ketogenic diet poses a significant effect on imbalanced gut microbiota in infants with refractory epilepsy [weak evidence]

  58. Science 2016: Antibiotic use and its consequences for the normal microbiome [overview article]

  59. This can be somewhat individual, though. For instance, in a 6-month study where people with type 2 diabetes ate fewer than 25 grams of total carbs per day, 68% of the study participants reported that they became constipated at some point during the study.

    American Journal of Medicine 2002: Effect of 6-month adherence to a very low carbohydrate diet program [weak evidence]

  60. This is mainly based on the consistent experience of experienced clinicians. [weak evidence]

  61. Between three times a day to three times a week is considered a very normal range for bowel movements.

    Cleveland Clinic: Frequent bowel movements

  62. This includes diets in which very few carbs are consumed, e.g. ketogenic diets.

    Endocrine 2017: Acid–base safety during the course of a very low-calorie-ketogenic diet [weak evidence]

    Nutrients 2018: Chronic ketogenic low carbohydrate high fat diet has minimal effects on acid-base status in elite athletes [weak evidence]

  63. Computational and Structural Biotechnology Journal 2019: High versus low dietary protein intake and bone health in older adults: a systematic review and meta-analysis [meta-analysis of randomized controlled trials; strong evidence]

    Current Opinion in Lipidology 2011: Dietary protein and skeletal health: a review of recent human research [overview article]

  64. The American Journal of Clinical Nutrition 2017: Dietary protein and bone health: a systematic review and meta-analysis from the National Osteoporosis Foundation [strong evidence]

  65. Here are three examples:

  66. Journal of the American Medical Association 1976: Alopecia in crash dieters [weak evidence]

    This is based on reports from people who’ve experienced hair loss after beginning a low-carb or ketogenic diet, rather than published research. [very weak evidence]

  67. In medical terms it’s called telogen effluvium.

  68. This is the safe, effective and sustainable way to follow a low-carb diet.

    Diabetes Therapy 2018: Effectiveness and safety of a novel care model for the management of type 2 diabetes at 1 year: an open-label, non-randomized, controlled study [weak evidence]

    Applied Physiology, Nutrition and Metabolism 2017: A 12-week low-carbohydrate, high-fat diet improves metabolic health outcomes over a control diet in a randomised controlled trial with overweight defence force personnel [moderate evidence]

  69. Diabetes Research and Clinical Practice 2017: Effects of SGLT-2 inhibitors on diabetic ketoacidosis: a meta-analysis of randomised controlled trials [strong evidence]

  70. Lakartidningen 2018: Life-threatening ketoacidosis in patients with type 2 diabetes on LCHF diet [very weak evidence]

  71. Case Reports in Nephrology: Ketogenic diet-induced severe ketoacidosis in a lactating woman: a case report and review of the literature [very weak evidence]

  72. In rare cases, being in ketosis can be dangerous for certain people; for instance, those who are deficient in certain enzymes needed to use ketones effectively. Although disorders like this are typically diagnosed in childhood, one condition (porphyria, a blood disorder) can happen at any time. Other conditions require consulting with a doctor to ensure that being in ketosis is safe.

    Who should not follow a ketogenic diet?

  73. Journal of Nutrition and Metabolism 2018: Nutritional ketosis and mitohormesis: potential implications for mitochondrial function and human health [overview article]

  74. Several studies have shown that diets that cause nutritional ketosis often accelerate fat loss, among other benefits.

    British Journal of Nutrition 2013: Very-low-carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomised controlled trials [strong evidence]

    Diabetes and Metabolic Syndrome 2017: Induced and controlled dietary ketosis as a regulator of obesity and metabolic syndrome pathologies [moderate evidence]

    Journal of the International Society of Sports Nutrition 2014: The effects of ketogenic dieting on skeletal muscle and fat mass [weak evidence]

  75. For instance, a grain-free, very-low-carb diet was shown to be much more effective for weight loss and decreasing blood sugar in overweight people with type 2 diabetes compared to a low-glycemic-index (low-GI) diet that included whole grains:

    Nutrition & Metabolism 2008: The effect of a low-carbohydrate, ketogenic diet versus a low-glycemic index diet on glycemic control in type 2 diabetes mellitus [moderate evidence]

  76. Cochrane Reviews 2017: Whole grain cereals for the primary or secondary prevention of cardiovascular disease [strong evidence for lack of any proven effect]