Top 17 low-carb & keto controversies
Of course, we don’t want any unsubstantiated fears of the past get in the way of people reaping the benefits of a low-carb diet. So here’s a short Q&A explaining why most of these controversies are nothing to worry about.
We also want to make low carb simple, and this includes being very upfront and honest about potential problems and how to handle them. Some problems actually can occur on low carb, and it can be very 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 currently best available scientific evidence says.
Will saturated fat clog my arteries and give me a heart attack?
No. This is one of the biggest nutrition myths of the last few decades.1 Fortunately, during the last several years more and more experts and organizations have realized that natural saturated fats are completely OK and healthy.
Saturated fat is found in real foods that we’ve consumed throughout evolution.2 It’s natural to eat saturated fats, it’s found in lots of natural foods, even human breast milk is full of it.
During the last ten years or so, many reviews of all available science have come to the conclusion that there’s no connection between saturated fat and heart disease.3 This fact has also been recognized in many high-quality newspapers, such as TIME.4 It’s simply been a mistake.
Don’t fear fat. Updated experts don’t.
A user guide to saturated fat
Does a low-carb diet cause high cholesterol?
Low-carb diets tend to improve the cholesterol profile by increasing levels of the “good” HDL cholesterol, and decreasing levels of harmful triglycerides. These are both good changes, associated with improved health.
Regarding the “bad” LDL cholesterol, most people experience no significant changes on low carb. However, some people can lower or (more often) increase LDL levels somewhat. Note that studies show that at least people over 60 years of age tend to live longer with higher LDL levels.5
Taken together, studies show that low-carb diets generally improve risk factors for disease, including cholesterol.6 For a small minority of people however, cholesterol may go up abnormally high on an LCHF diet. In those situations it could be worth adapting the diet to normalize the cholesterol levels.
The bottom line: Low-carb and high-fat diets on average improve the cholesterol profile and reduce most risk factors for 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.7
Doesn’t the brain need carbs?
This means that fat-burning goes up significantly – a big plus for people who want to lose excess weight.
Furthermore, our body can produce the glucose it needs through a process called gluconeogenesis, converting other nutrients to glucose.
There is no need for carbohydrates in the diet, and the brain functions fine without it.
Learn more in our full guide:
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 supposed to contain more fat, not more protein. This is why it’s often called an LCHF diet (low-carb, high-fat).
The amount of protein should stay moderate – about the same as on other diets. 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 low-carb diet, should you want to.
Furthermore, the impact of meat production on the environment depends on many factors. Do you buy organic, pesticide-free, locally-grown and grass-fed food? That’s very environmentally friendly! It reduces the pesticide burden, doesn’t deplete soils of nutrients and allows for more carbon dioxide to be stored in the ground.
The environmental benefit of having carb-rich monocultures such as soy, sugar and corn is also clearly overstated. These pesticide-heavy crops reduce biodiversity and contribute to pollution to a much greater extent than, let’s say, a biodynamic cow farm.
Finally a low-carb diet often results in people eating less food, as it’s so satiating. 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 should only be moderate in protein – e.g. meat – and thus it’s no different for the environment than most diets. If you still do choose to eat more meat than usual, the impact on the environment depends a lot on how the animals were raised.
Watch one of the smartest men in the world explain the real problem for the environment (Hint: it’s fossil fuels)
Can you get nutrient deficiencies on low carb?
Probably the opposite. The foods consumed on a low-carb diet are highly nutritious.8 For example, eggs (a staple for most people on low carb) may provide the most complete nutrition of any food on the planet.
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 while growing in the egg, everything has to be there. And by eating an egg we 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.
Compared to that, modern flour is more or less devoid of any nutrition whatsoever 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.
On top of that problem, grains like wheat are high in phytic acid that can reduce absorption of many minerals.
Fruit is often thought to be very nutritious. This is a sad misunderstanding. Apart from vitamin C, there are very few nutrients in most modern fruit. These days, they are modified to be very sweet and mostly supply nutrients in the form of sugar. Fruit is basically candy from nature, and should probably be eaten in moderation. Juice is of course even worse.
Modern fast food and junk food also contain a lot of calories and not much nutrition. And low-fat products are low in essential fat-soluble vitamins.
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.
Can low carb damage your thyroid?
Not likely. If you eat a well-formulated low-carb diet, meaning you replace carbs by eating more healthy fat, it’s very unlikely it will affect your thyroid negatively.
Long-term starvation or calorie restriction diets can lead to hypothyroidism (an underactive thyroid). But you won’t be starving on low carb as long as you eat enough fat to feel satisfied.
In fact, many people who lose significant amounts of weight on low carb end up needing less thyroid medication, and occasionally they can stop taking it completely. But this is probably just a positive effect of a smaller body needing less thyroid hormone.
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). Perhaps by then it could be time to lower your dose.
Bottom line: Eat enough to feel satisfied, and your thyroid will be fine.
Can low carb damage your kidneys?
Highly unlikely. Many people still believe that a low-carb diet necessarily is very high in protein, that could put a strain on the kidneys. This is a myth based on two misunderstandings.
First, a well-formulated low-carb diet is high in fat, not protein. The amount of protein – like meat – should be moderate, just like in most diets. There’s no benefit of eating excessive amounts of protein. It can even be detrimental on a low-carb diet, as excess protein gets converted to glucose, just like most dietary carbohydrates.
As a low-carb diet is not high in protein, the whole “problem” behind this fear simply does not exist.
Secondly, people with normal kidney function can handle plenty of excessive protein without any problem for the kidneys.10
Even if people would 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. Basically, if you have severe kidney disease and you’ve been told to limit protein, you should of course do so.11 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 excessive protein. And, most importantly, there’s no need for anyone to eat excessive protein on low carb in the first place.
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 can save their kidneys, by helping control their blood sugar levels.12
Can low carb make you depressed?
Not 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).
These problems usually disappear within a few days or a week. 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 often makes people feel very energetic and can increase mental performance and endurance. People very often 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.13 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. 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’s just like the effect of withdrawing from nicotine or alcohol when addicted.
Fortunately, after early withdrawal symptoms have passed, getting free of an addiction is incredibly liberating and enables people to lead fuller and happier lives. So it can definitely be worth the struggle.
Is low carb bad for exercise?
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. This is due to the low-carb flu, but it will pass in one or two weeks.
After a few weeks of adaptation, people often feel at least as good as before when exercising. Especially if they make sure to get enough fluids and salt.
Furthermore, for endurance athletes, there are many benefits to being fat-adapted and eating LCHF. For instance, this is seen in the fact that the two top performers in Tour de France 2016 were on some form of low-carb diet.
However, more carbs are probably needed for non-endurance sports such as sprinting etc. 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.
Is low carb bad for your gut bacteria?
Probably not. There is currently a lot of research being conducted on gut bacteria. The main problem with a lot of the reporting on gut bacteria and diet is confusing statistical correlations with causality, i.e. taking weak clues and mistakenly calling it proof.
Not much, if anything, can yet be said about the health effects of changes to the microbiome14 on a low-carb diet, only that it changes. However, many people report that they have less gastrointestinal stress and bloating after starting a low-carb diet.
The number one thing to do for your gut bacteria is to never use antibiotics unless you have to. And even then less is often more.
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.
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.
If you suffer problems with constipation when starting low carb, it is usually temporary.
Can you get osteoporosis on low carb?
No. 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. Blood pH is tightly controlled within a very narrow span – 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.15 Looking at all available science in 2017 there’s a total lack of support for the idea that eating protein is anything but fine for your bones.16
Finally, repeated studies show no effect on bone density in people eating low carb, even after several years.17
Low carb does not affect the bones.
Does low carb cause hair loss?
Occasionally. 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.
This kind of temporary thinning of the hair18 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.
Does low carb cause ketoacidosis?
Ketoacidosis is a rare and dangerous medical condition that mostly happen to people with type 1 diabetes if they don’t take insulin.
Ketosis, on the other hand, is a 100% natural and safe state, under full control by the body. It can be caused by a low-carb diet or by a brief period of fasting.
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 large amounts of fat.
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. 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.19
There’s an idea 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.
For more answers to common low-carb fears from some of the leading low-carb doctors20 in the world, then check out our Q&A video series:
Low-carb side effects & how to cure them
Common early problems
Later potential issues
Practical low-carb guides
The only other myth that comes close to being as harmful is the idea that we should fixate on calories for weight control – and that it doesn’t matter what we eat.
Together, the myths about saturated fats and calories may be in large part responsible for the simultaneous epidemics of obesity and type 2 diabetes. ↩
For example butter, lard, tallow, meat, coconut oil, cream, cheese etc. ↩
Here are three of the most recent meta-analyses showing no connection between saturated fats and heart disease:
- Open Heart: Evidence from Randomised Controlled Trials Does Not Support Current Dietary Fat Guidelines: A Systematic Review and Meta-Analysis (2016)
- Annals of Internal Medicine: Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-Analysis (2016)
- PLOS ONE: Is Butter Back? A Systematic Review and Meta-Analysis of Butter Consumption and Risk of Cardiovascular Disease, Diabetes, and Total Mortality (2016)
Here’s one recent example:
Natural fats, meat, poultry, sea food, eggs, vegetables and berries.
For example this one:
Here’s an overview of scientific studies on this topic:
There’s some evidence that this can slow progression of the disease:
Here’s one case report, just as an example:
Here’s one 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] ↩
Microbiome is a fancy word for gut bacteria. ↩
Here are three examples:
- Nutrition 2016: Long-Term Effects of a Very Low Carbohydrate Weight Loss Diet and an Isocaloric Low-Fat Diet on Bone Health in Obese Adults
- Annals of Internal Medicine 2010: Weight and Metabolic Outcomes After 2 Years on a Low-Carbohydrate Versus Low-Fat Diet
- The Journal of Pediatrics 2010: Efficacy and Safety of a High Protein, Low Carbohydrate Diet for Weight Loss in Severely Obese Adolescents
Dr. Sarah Hallberg, Dr. Ted Naiman, Dr. Jason Fung, Dr. Peter Brukner, Dr. Eric Westman, Dr. Cate Shanahan, Dr. Rangan Chatterjee ↩