Is a low-carb or keto diet right for you?
You can also read about a scientific paper exploring the potential contraindications for a keto diet.
1. Do you need low carb?
Do you have health concerns that a low-carb or keto diet might help?
Reducing carbohydrate intake – a little or a lot – can be an important first step in improving a number of health issues, especially obesity and metabolic issues. These health improvements can be achieved often by diet alone, without medications or other interventions that may have serious side effects.1
A low-carb or keto diet is not a “cure-all,” but it can be a very effective first-line intervention or a complementary addition to therapies prescribed by a healthcare provider.
If you are already on medication — especially medications that lower blood sugar or blood pressure — or have other serious health concerns, you should seek the support of a healthcare provider when making any significant changes to your diet or lifestyle.
Can a low-carb or keto diet benefit you in other ways?
Dietary changes can affect other aspects of your life besides health, such as athletic performance, hunger levels, and the time you spend cooking. Although these areas are seldom investigated in scientific trials, many individuals and clinicians learn about these effects when using a low-carb or keto diet for other reasons. Their experiences can help you make informed choices about these issues as well.
You might not need a low-carb or keto diet if:
- You have no metabolic issues, are at a healthy weight for you, and otherwise tolerate carbohydrate foods easily
- Diabetes and other metabolic diseases do not run in your family.
- You do not like to eat the kinds of foods that are encouraged on a low-carb or keto diet (although you can still do a keto diet even if you are vegetarian or vegan).
- You feel that reducing your intake of favorite carbohydrate foods would negatively impact your quality of life, no matter what health benefits might occur.
Some people may not have reason to limit dietary carbohydrate, especially minimally processed carbs such as root vegetables, fruit, and legumes. They feel great eating carbs, are at a healthy weight, and have no discernible health concerns, issues, even with a thorough evaluation of glucose and potential insulin resistance issues.2
While carbohydrates are not needed for essential nutrition, they are in many foods that some people prefer to keep in their diets, such as fruit, whole grains, and below-ground vegetables.3
No diet is one-size-fits-all, and no dietary pattern is a magic “cure-all.” Reducing dietary carbohydrate has noticeable, significant, and proven benefits for many people, but that doesn’t mean it is the “right” diet for everyone.
Follow the links to learn what science says about how a low-carb or keto diet can (or cannot) help:
Follow the links for a discussion about how reducing dietary carbohydrates may (or may not) positively affect other aspects of your life, apart from health concerns.
2. Moderate low-carb or keto: how low-carb do you need to go?
A keto diet and a generic low-carb diet are similar, but not the same. The distinction is the amount of carbs you consume each day.
A keto diet is typically 20 grams of net carbs or fewer per day — although the exact amount may vary between individuals. At this level, most people will achieve a level of nutritional ketosis, which means their bodies have converted to burning fat for energy needs, rather than glucose.4 See our ketosis guide below.
However, not everyone needs to reduce carbohydrates to this level in order to benefit.
Although not universally agreed upon by experts, at Diet Doctor we believe a low-carb diet can include any range of carbohydrate intake from zero up to 100 grams of net carbs per day. See our guide on ketosis and our visual guide to various levels of carbs in a meal:
What level is right for you?
How do you decide which level of carb consumption is right for you? Once you pick a level, should you stick to it all the time? The answer varies among individuals, depending on their starting point, goals, health history, and other considerations.
The simple recommendation is this:
- If you are treating, reversing, or adding a complementary therapy to an established medical condition (type 2 diabetes, dementia, seizures, cancer, etc.), a strict ketogenic diet may be the most effective way to start.5 If you have other wellness or lifestyle concerns, then a low-carb approach of under 100 grams a day may be equally effective.6
- If you are trying to lose a lot of weight, a strict ketogenic diet will likely be faster and more effective.7 If you are trying to maintain weight, a more liberal low-carb diet may be equally effective.8
- If cutting carbohydrates in your diet will impact other aspects of your life in positive or negative ways, consider the level of carbohydrate reduction that is personally and socially feasible. A person is not just a medical condition or a number on a scale. Enjoyment of food, social activities that center around food, food cultures and traditions — these are all part of a person’s relationship with food. Taking these concerns into account can help you decide what level of carbohydrate reduction is right for you.
3. Where to start
If you decide that a low-carb or keto diet is right for you, here are some resources to help you get started:
4. Weight loss
Individuals can lose weight on a variety of diets. When comparing weight loss outcomes after a year or more, differences in diets often disappear.9 In this case, it is worth asking some other questions when choosing any diet for weight loss:
- Does this diet require “calorie counting” to deliberately restrict calories?
- What effect does the diet have on hunger and satiety?
- What effect does the diet have on your resting metabolic rate?
- Can you maintain weight loss long term on this diet?
Here is how the keto and low-carb diet both stack up against those questions:
1) No need to count calories: You may have heard that keto or low-carb diets are just another way of reducing calories to lose weight. At Diet Doctor, however, we recommend that people starting the keto diet do not count calories, that instead you eat when you are hungry and stop when you are full — provided that the foods you are eating are on the keto foods list or part of our keto or low-carb recipes.
This approach usually has people feeling satisfied and full at lower calorie levels. In fact, in experimental settings, individuals who were put on a ketogenic diet had less hunger and a reduced appetite, which spontaneously reduced their calorie intake even though they were told to eat as much of the allowed foods as they would like and were not told to count or restrict calories.10 If you are not a fan of keeping track of your calories in-calories out, you may prefer to follow a low-carb or keto diet where you pay attention to what kinds of food you eat, rather than how much.
2) Reduced hunger, more satiety: Why do people on low-carb diets eat less without deliberately restricting calories? Making protein a priority can lead to feeling satisfied sooner.11 In addition, low-carb and keto meals may help trigger hormones that lead to a natural reduction in calorie intake, especially in those who are overweight or insulin resistant.12
Studies comparing eating eggs to eating a bagel for breakfast show that the low-carb, higher protein egg breakfast increased satiety and reduced calorie intake for up to 36 hours; one study showed that eggs for breakfast also led to a beneficial lowering of insulin and ghrelin, hormones known to affect hunger levels and food intake.13 Although each meal contained an identical amount of calories, individuals who consumed the egg breakfast stayed full longer and ate fewer calories for the rest of the day than the bagel group did.
3) Higher metabolic rate: You may have heard that “all diets fail” or that “the best diet for you is the one you can stick to.” While the second statement is certainly true, whether or not a diet “fails” may have to do with its effect on metabolic rate. Choosing a lower-carb diet that increases resting energy expenditure may make it easier to maintain weight loss over the long-term.
Recent studies have shown that a lower carb diet (10 – 20% of total calories) increases resting energy expenditure during weight loss maintenance, whereas a higher carbohydrate diet (60% of calories) decreases metabolic rate.14 One of these studies also showed a beneficial lowering of insulin and ghrelin (a “hunger hormone”).
4) Lasting results: A lower-carb diet can help maintain weight loss not only because of increased energy expenditure, but because the foods recommended on a low-carb diet are ones that many people enjoy ― and even miss when they are trying to count calories and reduce dietary fat. Keto and low-carb diets are full of above ground vegetables, full-fat dairy, eggs, meat, fish, cheese, butter, and more.
Any diet can be boring and monotonous, and only you can decide whether you prefer the recommended foods for a low-calorie, reduced-fat diet or a low-carb diet. But the many delicious and satisfying foods included in keto and low-carb diets can make these diets easy to “stick to” long term.
How low to go for weight loss?
No clinical studies as yet have compared low-carb to keto diets to determine which approach is better for weight loss. Clinical experience and opinion favor a keto diet for faster results.15 However, in most people a low-carb approach may also lead to weight loss, although usually not as dramatically.
You may want to start with a ketogenic diet of fewer than 20 grams net carbohydrates and see how you do. Then, after a few months, if you want to transition to a 50- or even 75-gram carbohydrate diet, you can experiment with that. Just remember to focus on higher quality, minimally processed sources of carbohydrates. If you find your weight loss stalls or reverses, then you know a keto diet is more effective for you. If your weight loss continues at a pace you are happy with, then you can stick to a low-carb diet with slightly more carbs.16
If a more liberal but still low-carb diet fits best into your food preferences and social life, you may choose slower weight loss. In addition, if you are currently following a high-calorie, high-carb, low-quality standard American diet, either approach will likely lead to weight loss. The key is finding which level of carbs helps you feel the best, is easiest for you to follow, and gives you the greatest chance for long-term success.
Where to start: For more information on losing weight with a keto or low-carb diet, see our guide:
How to lose weight
Guide Do you have trouble losing weight? Or would you like to lose faster? You’ve come to the right place. Your weight is hormonally regulated. If you reduce the levels of your fat-storing hormone, insulin, you’ll have a way easier time losing excess weight. Get ready for weight loss without hunger.
5. Diabetes or pre-diabetes
Dr. Sarah Hallberg and her colleagues at Virta Health showed that a ketogenic diet is effective at reversing type 2 diabetes and eliminating the need for expensive and potentially dangerous medications.17
Within just 10 weeks, patients receiving the ketogenic diet and Virta coaching intervention significantly reduced their HbA1c, weight, and medication use. More importantly, after one year, 60 percent were still free of the metabolic signs of diabetes, had removed or greatly reduced their need for medication, and had improved many other health issues, including their blood pressure, insulin resistance, inflammatory markers, and blood lipid profiles.
By contrast, the majority of the usual care subjects saw most of their health issues worsen.18
Smaller randomized studies, which are a higher level of evidence, also support ketogenic diets for improving diabetes control.19
GuideAs we base our guides on scientific evidence, it is important to have a clear policy for how to grade the strength of different kinds of evidence. Our policy is in many ways similar to other documents of its kind.
The Diet Doctor policy for grading scientific evidence
GuideAs we base our guides on scientific evidence, it is important to have a clear policy for how to grade the strength of different kinds of evidence. Our policy is in many ways similar to other documents of its kind.
Other studies have shown that different dietary and lifestyle approaches can improve type 2 diabetes, but the results of these studies are not as dramatic as the results from Virta’s use of a ketogenic diet, which showed an A1c reduction from 7.6 to 6.3 in one year.20 While we cannot directly compare different trials since they differ in subject population, protocol, and other factors, it is hard to ignore the vast difference in success rate.
In 2008, Dr. Eric Westman led a randomized study that showed a ketogenic diet had more robust results than a low glycemic index diet for diabetes control, although both had positive effects.21
A year later, another randomized trial of a low-carb Mediterranean diet also showed more effectiveness than a low-fat diet.22 However, another randomized trial showed that at one year, the low carb group (33 percent of total calories, or 165 grams on a 2,000 calorie diet) was similar to the low-fat group in terms of diabetes control. Randomized trials of a vegan diet showed marginal improvements in diabetes markers and blood sugar control, with a reduction in HbA1c from 8.05 to 7.71 after a 74-week intervention.23 A paleo diet also showed modest improvement in diabetes markers and blood sugar control compared to a standard diabetes diet.24
In fact, any improvement upon a standard American diet is likely to show some benefit for type 2 diabetes, but when it comes to degree of improvement, it appears that low-carb and ketogenic diet get top marks.
How low to go for diabetes?
Currently, available data suggests that a keto diet of less than 20 net carbs per day may be the most beneficial approach for treating type 2 diabetes and potentially reversing the disease process. That does not mean that a low-carb diet of less than 100 grams of net carbs is completely ineffective in type 2 diabetes. More randomized trials are needed to compare low carb and keto diets for a definitive answer. However, the data does suggest that keto diets will achieve more complete and faster improvement than other dietary interventions.
Where to start: For more information on treating or reversing type 2 diabetes with a keto or low-carb diet, see our guide:
How to reverse your type 2 diabetes
GuideDo you have type 2 diabetes, or are you at risk for diabetes? Do you worry about your blood sugar? Then you’ve come to the right place. You can normalize your blood sugar naturally as needed – without pills, calorie counting or hunger.
6. High blood pressure
When it comes to hypertension, most guidelines focus on the DASH (Dietary Approach to Stop Hypertension) diet, a diet which is low in fat and salt, with an abundance of fruits and vegetables. In the initial trials, compared to a standard American diet, the DASH diet did show a small reduction in systolic blood pressure (SBP).25
However, low-carb and keto diets have a similarly powerful positive effect on blood pressure (BP). In fact, in one study, the very low-carb Atkins diet had twice the improvement in BP reduction as Zone, LEARN, and Ornish diets: it reduced SBP by 7.6 points, compared to 2-3 points for the other diets.26
Generally speaking, any diet that reduces weight should reduce blood pressure, but the improvement in BP seen with low-carb diets may not simply be a function of weight loss but instead may be related to the diet itself. A randomized study showed that both a keto diet and a low-fat diet plus the weight loss drug orlistat resulted in weight loss.27 However, the keto diet reduced SBP by 6 points while a low-fat diet plus orlistat increased SBP by 1.
Finally, a study on a Spanish Mediterranean keto diet reduced SBP from 125 to 109.28 This study was not randomized and had no control group, yet it did show an impressive reduction in SBP.
Finding ways to lower BP without medications is important. Current controversial guidelines recommend aggressive treatment of high blood pressure. Unfortunately, studies investigating more aggressive control of blood pressure with medications show an increased risk of falls, kidney injury, lightheadedness, and other adverse effects.29
If you want to try a low-carb or keto diet in order to get the beneficial effects of lower blood pressure without the drug-induced adverse effects, consult with your doctor first.
How low to go for hypertension?
There is a lack of trials comparing a keto diet to a low-carb diet for control of blood pressure. The data above suggests you may wish to start with a keto diet (less than 20 grams of net carbs) for maximum effect in lowering blood pressure without medication. However, losing weight with a low-carb diet is also likely to have beneficial effects.
Where to start: For more information on controlling high blood pressure with a keto or low-carb diet, see our guide:
How to normalize your blood pressure
GuideElevated blood pressure is a common health issue today. Almost a third of U.S. adults have high blood pressure – perhaps you or someone in your family does? High blood pressure isn’t necessarily something you can feel, but it increases the risk of serious conditions such as strokes and heart attacks.
7. Irritable bowel syndrome (IBS)
Over the last decade, one of the accepted evidence-based treatments for irritable bowel syndrome (IBS) has been a low FODMAP diet.30 FODMAP is an abbreviation for “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols,” which are different types of short-chain carbohydrates (except for polyols, which are sugar alcohols).
If the removal of various short-chain carbohydrates has been proven in multiple studies to improve IBS symptoms, it makes sense, that a general low-carb diet could be beneficial for IBS, too.
Dr. Eric Westman and his team published a small study in 2009 showing significant improvement in IBS symptoms in 77 percent of participants with documented IBS who followed a keto diet.31 Aside from this study, however, data to support a keto or low-carb diet for IBS is scarce.
How low to go for IBS?
Not enough scientific evidence exists to support a definitive recommendation for keto or low-carb in the treatment of IBS. However, anecdotal evidence, clinical experience, and findings related to FODMAP diets suggest that a keto diet or a low-carb diet that focuses specifically on limiting FODMAP foods could be beneficial and is a reasonable approach.32
This may be a case where your own experience with dietary changes provides you with information and positive results not currently available from science.
Where to start: For more information on treating IBS with a keto or low-carb diet, see our guide:
IBS and the keto diet
GuideWhen Audra Atkins-Reeves started the low-carb keto diet in October 2016, her only aim was to lose weight — and happily she found within five months she had lost 40 lbs (18 kg). She discovered another welcome, unexpected benefit: Within a month of starting the keto diet her gut was remarkably calm, quiet, and cooperative for the first time in decades.
8. Polycystic ovary syndrome (PCOS)
PCOS is the most common endocrine condition in women of reproductive age and is marked by hormonal disturbances that create higher circulating male hormones, irregular or absent menstrual periods, and cysts on the ovaries.
Women with PCOS are often overweight, have elevated insulin levels and documented insulin resistance.33 Additionally, some may tend to eat a higher glycemic index diet.34 The condition also puts women at much higher risk of both gestational diabetes and future type 2 diabetes.35 It makes sense, then, that a low- carb or keto diet might improve symptoms of PCOS. Weight loss and treatment with metformin (a drug that enhances insulin sensitivity) have both shown success in treating PCOS, yet the question remains if low-carb and keto diets would be just as, or even more, effective.36
Clinical trials have shown that modest restriction of dietary carbohydrate (41 to 43 percent of calories, not technically a low-carb diet and certainly not ketogenic) reduced markers of insulin resistance and decreased testosterone and cholesterol levels in women with PCOS.37 In another study, restricting carbohydrate to 40 percent of calories improved loss of fat mass in women with PCOS.38
One small 2005 study followed 11 women with PCOS as they went on a ketogenic low-carb diet for six months.39 The five women who completed the study greatly improved their weight, hormonal status and perceived amount of body hair. Two of them became pregnant during the study, despite previous infertility problems.
In addition, a 2020 study showed 14 women with PCOS showed a significant improvement in hormone levels and markers of insulin resistance.40
Some evidence also exists that fertility and reproductive health improves with a low-carb diet even in women without diagnosed PCOS. A systematic review of low-carb diets (defined as less than 45% of calories from carbs) in overweight and obese women showed positive effects on fertility hormones, ovulation, and pregnancy rates.41
Although these studies fail to compare moderately reduced carbohydrate diets to low-carb or keto diets, taken as a whole the data suggest that low-carb diets may be beneficial for treating PCOS and improving reproductive health and fertility.
How low to go for PCOS?
Any diet that leads to weight loss may be beneficial for PCOS, but lower carb diets have been shown to be successful at treating markers of PCOS and improving outcomes. More data are needed for a conclusive recommendation. No data exist comparing the effects of low carb and keto diets.
Where to start: For more information on treating or reversing PCOS with a keto or low-carb diet, see our guides:
9. Cholesterol abnormalities
Low-carb and keto diets may improve many people’s overall cholesterol measures by reducing triglycerides (TG), raising HDL (high-density lipoprotein), and improving the size and density of LDL (low-density lipoprotein).42 Changes in these markers may, or may not, all be related to insulin resistance, which is important as a standalone marker as well.
Many people don’t know they have insulin resistance as standard blood tests are poor at detecting it.43 Yet, they may know that they have low HDL and elevated TG. Meta-analyses of randomized trials consistently show better reduction of TG and increase in HDL with low-carb compared to low-fat diets, along with greater weight loss.44
Published in 2018, the one-year data from Virta Health’s non-randomized trial showed a 24 percent decrease in triglycerides, 18 percent increase in HDL (with an impressive 29 percent decrease in the TG/HDL ratio), 20 percent reduction in small dense LDL, and multiple other beneficial effects.45 And it’s worth noting that, although LDL increased slightly, LDL particles decreased by 5 percent―showing that LDL became larger and less dense ― and the 10-year ASCVD (Atherosclerotic Cardiovascular Disease) risk score improved by 12 percent.
Some individuals see a dramatic rise in LDL and increases in LDL particle size on ketogenic diets. It is not clear how often this happens, but is estimated that between 5 and 30% of individuals who use a low-carb diet will respond with higher LDL levels.46 However, whether this is a concern or not is uncertain. This is outside the current available evidence, and therefore needs to be an individualized decision made with your healthcare provider.
How low to go for cholesterol issues?
For blood lipid markers, it’s not clear that there is a significant difference between a ketogenic (<20 g net carbs) diet or a low carb (<100 g net carbs) approach as scientific studies have not compared the two approaches. It is clear that a low-carb diet can improve these markers and that a ketogenic diet can have a dramatic impact on them.
Where to start: For more information on addressing cholesterol issues with a keto or low-carb diet, see our guide:
Cholesterol and low-carb diets
GuideLearn what cholesterol is, how your body uses it, why low-carb and keto diets may lead to a change in blood cholesterol levels, and whether you should be concerned if your cholesterol increases with a keto or low-carb lifestyle.
Ketogenic diets have been used as a treatment for childhood epilepsy (seizure disorder) since the 1920s and are still successfully used today for this purpose.47 The advent of seizure drugs often makes nutritional ketosis a second line treatment, but the development of safe, effective, consistent protocols has revived interest in these diets for seizure disorders.48
How low to go for epilepsy?
Specialists in treating childhood epilepsy with dietary interventions typically find that the higher the fat and lower the carb content, the more effective the diet. Therefore, a strict keto diet is likely to produce the most benefit by providing the brain with a steady supply of ketones it can use for fuel. In fact, there are some who experiment with exogenous ketones in this setting to supply the brain with higher levels of this alternative fuel, although there are no convincing studies to support this.49
Where to start: For more information on treating epilepsy with a keto diet, watch this video:
11. Cognitive decline, Alzheimer’s disease, and other neurological conditions
In treating existing cognitive decline, whether it is Alzheimer’s disease or other forms of dementia, switching your brain’s fuel from glucose to ketones appears to have a positive effect.50
Alzheimer’s disease is sometimes referred to as “Type 3 Diabetes” as it appears to include insulin resistance of the brain and a reduced ability for brain cells to take up glucose.51 So switching fuel sources may be beneficial from a mechanistic point of view.
The biggest potential for using a ketogenic diet as a therapy may be in mild cognitive decline, but the lack of alternative treatments for severe cognitive decline make dietary changes attractive, although improvement has been difficult to demonstrate.52 This may also be an area where ketone supplementation could be beneficial, but again the level of evidence about consuming extra ketones over and above dietary changes is still low.53
Ketones appear to have a protective effect on the brain in general, and therefore we can speculate that a ketogenic diet may possibly benefit various neurological conditions such as traumatic brain injury, stroke, and other causes of nerve cell damage.54 This remains a hot topic of research.
How low to go for cognitive issues?
Early, limited data suggest a keto diet, which switches the brain’s fuel from glucose to ketones, may be beneficial in improving symptoms of Alzheimer’s dementia. While still highly exploratory, some individuals may want to try a ketogenic diet to see if their cognitive function improves when they remain in ketosis. To achieve this, most people would need to routinely stay under 20 grams of carbohydrate a day.
In theory, shifting the brain’s metabolism from glucose to ketones could offer protective effects for other neurological conditions. While ketogenic diets for posttraumatic brain injury, spinal cord injury, and Parkinson’s disease are now being actively researched, the data is so far very early and not yet conclusive to indicate it as a therapy.
Where to start: Diet Doctor has written some articles about the burgeoning, but still controversial, area and we have also published a video presentation about insulin and the brain by psychiatrist Georgia Ede below:
The ketogenic diet for Alzheimer’s prevention and treatment: can it help?
GuideAlzheimer’s disease and other related neurodegenerative conditions, which impact memory, behavior and decision-making, are now an epidemic hitting all Western societies.
12. Cancer adjunctive therapy
Ketogenic diets have the potential to assist in the treatment of certain cancers. Some cancer cells have an abnormal metabolism such that they depend completely on glucose for their fuel and are unable to oxidize fatty acids.55 Theoretically, switching the body’s metabolism from glucose to fatty acids, as happens in a ketogenic diet, could potentially help treat some types of cancer.56
Based on the need for an altered metabolism, low-carb diets likely would not be as effective as keto diets. In addition, a ketogenic diet may help sensitize cancer cells to make radiation and chemotherapy more effective. Although the ultimate effect is speculative, this could help reduce the required dose to allow for adequate treatment with fewer toxic side effects. 57
Animal research and limited human data suggest that a ketogenic diet may be beneficial when combined with traditional therapies for treating brain, prostate, colon, pancreatic and lung cancer.58 However, we should recognize that forms of cancer may differ greatly, and for some cancers, a ketogenic diet may not be the best approach to use, even in conjunction with medical treatment.59
Importantly, the amount of human evidence supporting a ketogenic diet for cancer treatment is limited, and this evidence supports a ketogenic diet combined with traditional treatment such as surgery, radiation and chemotherapy. No convincing data exists yet to support that a ketogenic diet is superior to traditional therapy, or that it should be used as a solitary treatment.
This should be considered a scientific field in its infancy, with more information to come. You can learn more details in this podcast episode with cancer scientist Angela Poff, PhD.
How low to go?
It is too early to conclusively say keto diets help treat cancer, but preliminary evidence points to potential benefits when combined with traditional cancer therapies.
Furthermore, although no studies of this have been done, for an individual who is controlling type 2 diabetes or other conditions with a keto or low-carb diet, continuing this diet while undergoing cancer treatment might help to maintain overall health.
Where to start: For more information about how diet and cancer may be related, see Diet Doctor’s introductory discussion about the Warburg effect and cancer and the Diet Doctor article discussing existing science and debate around using the ketogenic diet as an addition to standard therapy for the brain cancer, glioblastoma.
13. Lifestyle concerns
Athletic performance on a keto diet remains a controversial subject with conflicting data.60 Issues of adaptation time, type of exercise, differences of training and racing diets, and baseline fitness all play a role in measuring response. Some studies that found a negative response investigated the effect of a keto diet on performance over as little as four days.61 That is a woefully inadequate time to allow for adaptation to a keto diet.
However, others show reduced competitive athletic performance after 25 days of a ketogenic diet, which still is questionable if there was enough time for adequate assessment.62
Fully adapting to a keto diet may take a lot of time, something many athletes may not have in preparation for an event. Yet to see maximal benefit, there needs to be a shift in fuel metabolism to ketosis and adequate adaptation to this state.63 It is estimated that this adaptation period typically lasts four to six weeks, but in some cases may take much longer.64
The leading book on the keto diet and athletic performance is The Art and Science of Low Carbohydrate Performance by Jeff Volek PhD, RD and Dr. Stephen Phinney, MD, PhD.65 The authors note on the book’s website: “The key fact underlying this book is that you can train your body to burn fat by simply changing your diet over a period of a few weeks, thereby turning blood sugar and glycogen into secondary fuels. Once you make this transition, you can then train harder, perform longer, and recover faster.“
Based on anecdotal reports, it appears there are subsets of endurance athletes who thrive on a ketogenic diet, just as there are subsets who do worse.66 As of now, the science does not adequately define a way to predetermine who will do well and who will not. If one is willing to do a self-experiment for a minimum of six months, then a trial of a ketogenic diet seems reasonable.
For those who struggle, transitioning to a non-ketogenic low carb diet, such as 150 grams of carbs per day, might allow athletic performance to improve, especially for the more glycolytic (glucose burning) activities such as sprinting or interval demands (for example, jiu jitsu). We don’t have solid evidence to compare a non-ketogenic low-carb diet to a high-carb diet, so again self-experimentation is likely the key to finding the best individualized approach.
Verdict: In theory, endurance exercise performance could improve with a keto diet after a prolonged adaptation period, but the data are inconclusive.
Mental health, performance, and attention
This is an area full of anecdotal reports but with a shortage of scientific evidence. In theory, shifting the brain’s metabolism from glucose to ketones could be beneficial for cognitive function in general. Therefore, a ketogenic diet of under 20 grams is required. Even then, however, there is no consensus as to improved cognition. This is an era best left to self-experimenters to see if they happen to see improved mental clarity and less brain fog.
Verdict — No clear evidence. Self-experimentation with a keto diet is reasonable, as carbohydrate is a non-essential nutrient. Diet Doctor has written a few articles that explore the nature of the evidence so far for both mental health conditions and for attention deficit disorder.
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This has been shown in meta-analyses of randomized controlled trials — considered the strongest, most robust type of evidence — comparing low-carb diets to low-fat and other diets:
The British Journal of Nutrition 2015: Effects of low-carbohydrate diets v. low-fat diets on body weight and cardiovascular risk factors: a meta-analysis of randomized controlled trials [systematic review of randomized trials; strong evidence] ↩
Frequently doctors do not monitor for insulin resistance, so even when blood glucose is normal, insulin resistance could be progressing. A thorough health evaluation that includes measures of insulin resistance can help determine whether reducing dietary carbohydrate would be a helpful intervention for you.
Journal of Diabetes Research 2016: Assessment of Insulin Resistance in Subjects with Normal Glucose Tolerance, Hyperinsulinemia with Normal Blood Glucose Tolerance, Impaired Glucose Tolerance, and Newly Diagnosed Type 2 Diabetes (Prediabetes Insulin Resistance Research) [nonrandomized study, weak evidence]
In their 2005 textbook, the U.S. Food and Nutrition Board of the Institute of Medicine states:
“The lower limit of dietary carbohydrate compatible with life apparently is zero, provided that adequate amounts of protein and fat are consumed.”
Institute of Medicine of the National Academies 2005:Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids [textbook chapter; ungraded] ↩
The digestible, non-fiber portion of carbs is often referred to as “net carbs,” which are calculated by subtracting fiber from the total carbs a food contains. It’s generally accepted that fiber isn’t digested and absorbed by the human digestive tract:
At less than 20 grams of carbs, you’re pretty much guaranteed to be in ketosis https://www.dietdoctor.com/low-carb/ketosis — a state where your body burns mainly fat for fuel. However, some people may be able to achieve and maintain ketosis even at higher carb intake levels. In one study, healthy volunteers remained consistently in ketosis while consuming about 50 grams of net carbs per day:
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]
However, those who are overweight or have baseline insulin resistance may require a stricter approach, limiting net carbs to 20 grams per day. ↩
In many studies, restricting carbs to less than 50 grams per day has been found to greatly aid weight loss:
The 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 [systematic review of randomized trials; strong evidence]
In a meta-analysis of 45 trials, average weight loss among people eating low-carb or low-fat diets was virtually the same at one year:
Journal of the American Medical Association 2014: Comparison of weight loss among named diet programs in overweight and obese adults: a meta-analysi [systematic review of randomized trials; strong evidence]
However, this needs to be interpreted with caution as many trials, such as the DIETFITS trial, start with a very low-carb intervention but then liberalize the carb intake as the trial moves on. At the end of the DIETFITS trial, the “low carb” group was eating 130 grams of carbs per day and the “high carb” group was at 210 grams.
JAMA 2018: Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion: The DIETFITS Randomized Clinical Trial [randomized trial; moderate evidence]
Nutrients 2018: Protein from meat or vegetable sources in meals matched for fiber content has similar effects on subjective appetite sensations and energy intake-a randomized acute cross-over meal test study [randomized trial; moderate evidence]
Nutrition Research 2010: Consuming eggs for breakfast influences plasma glucose and ghrelin, while reducing energy intake during the next 24 hours in adult men [crossover trial; moderate evidence] ↩
Remember to also pay attention to your health markers. After all, the best weight loss is one that also improves your overall health! ↩
The Virta trial enrolled 262 adult volunteers with type 2 diabetes who were coached and supported to achieve nutritional ketosis by the Virta program — called a continuous care intervention (CCI). For comparison, the study also enrolled 87 adult volunteers who received the typical care and support for treatment of type 2 diabetes. This included appointments with their physician and consultations with registered dietitians focusing on the American Diabetes Association guidelines.
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 stud [non-randomized trial; weak evidence] ↩
It is worth noting that the Virta study was not a randomized controlled trial, as its participants were not randomly compared at the same time to participants using another intervention or a placebo. As such, it does not prove it is better than any other intervention and is therefore considered a lower level of evidence. But it does clearly show in their select population, their treatment intervention was very successful for reversing diabetes. ↩
Nutrients 2020: Impact of a ketogenic diet on metabolic parameters in patients with obesity or overweight and with or without type 2 diabetes: A meta-analysis of randomized controlled trials [systematic review of randomized trials; strong evidence]
Nutrition & Diabetes 2017: Twelve-month outcomes of a randomized trial of a moderate-carbohydrate versus very low-carbohydrate diet in overweight adults with type 2 diabetes mellitus or prediabetes [moderate evidence] ↩
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 [randomized trial; moderate evidence] ↩
Annals of Internal Medicine 2009: Effects of a Mediterranean-style diet on the need for antihyperglycemic drug therapy in patients with newly diagnosed type 2 diabetes: a randomized trial [moderate evidence] ↩
American Journal of Clinical Nutrition 2009: A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial [moderate evidence] ↩
The BP lowering effects were more pronounced in those who already had hypertension and in those who ate a low potassium diet.
Journal of the American Medical Association 2007: Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women [randomized trial; moderate evidence] ↩
Clinical Gastroenterology and Hepatology 2009: A very low-carbohydrate diet improves symptoms and quality of life in diarrhea-predominant irritable bowel syndrome [nonrandomized study, weak evidence] ↩
Minerva Endocrinology 2015: Obesity and polycystic ovary syndrome [discussion of mechanisms; ungraded]
American Journal of Clinical Nutrition 2006: Separate effects of reduced carbohydrate intake and weight loss on atherogenic dyslipidemia [randomized double blind crossover study; moderate evidence] ↩
Journal of Diabetes Research 2016: Assessment of Insulin Resistance in Subjects with Normal Glucose Tolerance, Hyperinsulinemia with Normal Blood Glucose Tolerance, Impaired Glucose Tolerance, and Newly Diagnosed Type 2 Diabetes (Prediabetes Insulin Resistance Research) [nonrandomized study, weak evidence] ↩
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 [experimental trial; weak evidence] ↩
Epilepsia Open 2018: Optimal clinical management of children receiving dietary therapies for epilepsy: updated recommendations of the International Ketogenic Diet Study Group [protocol; moderate evidence] ↩
Journal of Diabetes Science & Technology 2008: Alzheimer’s disease is type 3 diabetes – evidence reviewed [discussion of mechanisms; ungraded] ↩
Nutrition and Metabolism 2009: Study of the ketogenic agent AC-1202 in mild to moderate Alzheimer’s disease: a randomized, double-blind, placebo-controlled, multicenter trial [randomized trial; moderate evidence] ↩
Journal of Sports Medicine & Physical Fitness 2018: Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial [randomized trial; moderate evidence] ↩
PLoS One 2020: Crisis of confidence averted: Impairment of exercise economy and performance in elite race walkers by ketogenic low carbohydrate, high fat (LCHF) diet is reproducible [randomized trial; moderate evidence] ↩
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