Ketogenic Diet Myths vs. Facts

A slew of articles in recent months have referred to the ketogenic diet as a “fad” or “trend.” It’s “dangerous,” claimed one article, and an anonymous post by the Harvard Public School of Public Health said the diet “comes with serious risks.”1 Yet strangely, these critics seldom cite scientists or doctors who work with the diet, and many—including the Harvard article—cite no medical literature to substantiate their allegations. Without substantiation, many simply rehash long-contradicted, outdated claims.

A ketogenic diet is high in fat and low in carbohydrates. It’s called “ketogenic” because people on this diet shift from using glucose (a type of sugar) as their main fuel source to ketone bodies, which are derived from fat. In other words, people on the ketogenic diet can use their bodies’ fat stores as fuel—and this is why many studies show that this diet is superior for sustainable weight loss.

Still, the headlines keep coming. Men’s Health declared, “Ketogenic Diet Side Effects: How the Trendy Low-Carb Diet Can Give You Acne.” The health and fitness website warned about “The Ketogenic Diet and Insomnia.” Other articles raised fears of bloat and constipation or cautioned that the regimen requires inhuman willpower from its followers.

Full disclosure: I have followed a low-carb diet for nearly a decade and find no problem adhering to it. I’ve lost weight and all my cardiovascular biomarkers have improved. Moreover, I’ve studied the science and history behind low-carbohydrate diets, so beyond my personal experience, I bring an evidence-based perspective. (Previously, for 25+ years, I adhered faithfully to a “mostly plants” regimen of fruits, veggies, and whole grains, including my own homemade 7-grain bread, while exercising religiously. Yet during that time my blood lipids were unhealthy, and I never could shake an extra 10-20 pounds.)

To be clear, I am not suggesting a ketogenic diet for all. However, this diet is clearly a safe and highly effective option for people with metabolic diseases (obesity, diabetes, heart disease, etc.), and therefore should not be falsely portrayed as a dangerous fad.

In this article, I address the 13 most common anti-keto claims found in the media.

My principal hope in this article is to provide journalists with a resource to do what basic journalism demands, namely to ensure that stories are scientifically balanced and accurate. At the end of this post I provide contacts for some of the credentialed experts who helped me compile this research. Reporters, please seek out these or other low-carb diet experts so you can provide accurate, up-to-date information for your readers.

Claim #1. Keto is bad for athletes

This Keto diet can definitely help one lose fat, but the resulting lack of carb fuel makes one tired and unable to perform at desired levels.” -Lewis Maharam, M.D. and Daily News columnist2


Numerous studies show that the ketogenic diet has helped athletes improve their body composition, trim fat, maintain performance and improve recovery. These studies have included marathon runners,3 triathlon competitors,4 CrossFit athletes,5 gymnasts,6 and other athletes performing high intensity7 and interval8 exercises.

One study found that after 12 weeks eating a ketogenic diet, endurance athletes cut body fat, increased oxidation and sprint power, and performed better overall on a critical power test compared to athletes on high-carb diets.9

Claim #2. Keto is dangerous if you have diabetes

“New research published in the Journal of Physiology indicates that ketogenic diets, which are low carbohydrate high fat eating plans that are known to lead to weight loss, may cause an increased risk of Type 2 diabetes in the early stage of the diet.” Medical Xpress10


First, that study, which was reported upon widely, was on mice. Mice are not like humans in the way they fatten or contract metabolic diseases. Journalists/media should stop reporting on mice stories as if they were applicable to humans, especially when there is such a large body of clinical trial data on humans. Let’s be clear: rigorous clinical trial data on humans trumps any data on mice. Every time. And what does the rigorous data on humans say?

The ketogenic diet is actually the most promising diet for people with Type 2 diabetes. Some studies have shown that extreme caloric restriction can reverse diabetes, but continued starvation is largely unsustainable.

The other nutritional remedy for T2 diabetes is carbohydrate restriction. In a large, ongoing university-based study, 60% of patients with Type 2 diabetes reversed their diagnosis of diabetes after just one year on a ketogenic diet, supplemented by support via a mobile phone app.11 On this protocol, 94% of participants reduced or eliminated their need for insulin medications while improving the vast majority of cardiovascular risk factors.12

No other diet has demonstrated such promising results for Type 2 diabetes.

Moreover, upwards of 17 scientific studies13 support the idea that carbohydrate restriction works to manage blood sugar, or glycemia, in patients with diabetes.

Claim #3. Keto causes fatigue and flu-like symptoms

That totally miserable feeling is actually called the ‘keto flu’ and it’s basically a bunch of flu-like symptoms that often appear at the beginning of a keto diet overhaul.” -Sarah Bradley, Women’s Health reporter14


Upon starting the diet, some patients report symptoms like fatigue, headaches, and muscle aches. However, these short-lived symptoms are, in fact, a sign that the diet is working, and the body is switching over from burning glucose as fuel to burning fat. This transition involves upregulating certain enzymes and down-regulating others; it is a profound shift for the human body that can have uncomfortable symptoms. However, these side effect usually last only 3-4 weeks. They can be ameliorated in most cases, by drinking several cups of bouillion broth during the day until the transition is completed.15

The idea of the “keto flu,” which used to be previously known as the “Atkins flu,” is an old concept that has been addressed, in the scientific literature and in practice, for more than two decades now.16

Claim #4. Keto is bad for heart health and will raise your cholesterol

“However, saturated fat has long been lauded as a heart-harming macronutrient; the American Heart Association recommends no more than 13 grams of saturated fat per day. In fact, Nieca Goldberg, M.D., medical director of the Joan H. Tisch Center For Women’s Health at NYU Langone Medical Center, said saturated fats can increase bad cholesterol.” -Christina Stiehl, PopSugar reporter17


One meta-analysis18 incorporating data from 447 participants found that low-carbohydrate diets not only helped individuals lose weight, but also improved their cholesterol. And another meta-analysis,19 citing 17 clinical trials, found that low-carb diets protected against major cardiovascular risk factors. A third study20 including 119 participants found that low-carbohydrate dieters had lower cholesterol than low-fat dieters after one year.

While it’s true that low-carb diets do raise the so-called bad LDL-cholesterol in some people, it’s important to note that LDL-C, when influenced by diet, has never been shown to have any effect on cardiovascular risk. Large clinical trials and observational studies show that one’s level of LDL-C and the lowering of LDL-C through diet is not reliably linked to cardiovascular outcomes.21, 22, 23

Moreover, the ketogenic diet also reliably raise the “good” HDL-cholesterol, while also improving most other cardiovascular markers, including blood pressure, as this study shows.24 Thus, the overall effect on cholesterol and other markers for heart disease is positive. In some lean hyper-responders, a keto diet will increase LDL particle number, and this effect needs further investigation.

Claim #5. Keto will make you break out

“The skin is a temperamental beast. Any change in your diet, but particularly one that turns our usual percentages of fats, carbohydrates, and proteins upside down, can be inflaming.” -Ross C. Radusky, M.D., dermatologist, Men’s Health25


One study26 found carbs to be the “main culprit” in causing acne. And another study found that low-glycemic diets lessened acne.27

What’s more, a review28 conducted by Italian researchers suggested that the keto diet could target acne by reducing inflammation and levels of insulin and IGF-1 — all known causes of acne.29

Claim #6. Keto is not good for your gut

Most ketogenic diets are very low in fiber, and fiber is usually integral for gut health, as it is the food that good bacteria eat.” -Charlie Seltzer, M.D., Insider30


In fact, patients with gastroesophageal reflux disease (GERD) have been shown to improve after eating very low carbohydrate diets.31, 32 Another study found increased carb-intake worsened GERD, while a high-fat, low-carbohydrate diet reduced symptoms.33 And two studies have linked esophageal diseases, including Barrett’s esophagus (BE)34 and GERD,35 to sugar and carbohydrate intake.

Claim #7. Keto causes, or worsens, fatty liver disease

“Keto is not desirable for people with most stages of diabetes, kidney disease, or other liver conditions,” -Kelly Boyer, nutritionist, This is Insider36


The European Association for the Study of the Liver actually cites a low-carbohydrate diet as a way to treat the disease.37 Studies show that cutting carbohydrates38 and particularly fructose,39 or sugar from plants, works to improve liver fat metabolism.

What’s more, high-carbohydrate diets have been associated with worsening non-alcoholic fatty liver disease. Find evidence here,40 here41 and here.42

Claim #8. You’ll lose sleep on a ketogenic diet

…May also lead to health problems, including insomnia or poor quality sleep.” -Lucy Burns, reporter, Livestrong.com43


There seems to be no foundation for this claim. People eating diets very low in carbohydrates and high in fats and proteins have been found, in one study,44 to enjoy better sleep quality, meaning they spent more time in deep sleep than those on high-carbohydrate, low-fat diets.

A survey of 1,580 low-carb consumers published in late 2017 by the Journal of Insulin Resistance45 found that while more than 11% of respondents reported using sleep-aids before beginning their low-carb diet, less than 5% reported using them after their diet. Moreover, nearly seven in 10 reported improved quality of sleep after dieting while only 3.4% said their sleep quality had worsened.

Claim #9. Keto causes gallbladder problems

The ketogenic diet can affect the gallbladder in a few ways. Frequent fasting has the effect of slowing bile production and usage. This leads to stagnant bile that eventually turns to sludge and gallstones.” ‘Doctor Eden,’ commercial blog46


Multiple studies have found that diets higher in fat prevent gallstone formation. Examples are here47 and here.48 Meanwhile, diets low in fat actually increase gallbladder volume49 and may increase the risk of gallstone development, as do diets high in sugar and carbohydrates.50

Claim #10. It reduces lean body mass

We generally see greater lean body mass (LBM) loss in ketogenic diet groups” -Adam Tzur, Brandon Roberts and Alex Leaf, contributing authors, SciFit.net51


A three-month trial52 found the keto diet had no impact on the lean body mass of CrossFit participants.

Claim #11. Keto is not good for long-term weight management53

Because the diet requires diligent monitoring, diet planning and is very restrictive in nature, it is not recommended at this time for long-term use for weight management” -Kelcie Atkin, R.D., L.D., C.D.E.54


Studies have demonstrated that the keto diet may in fact be ideal for long term weight management. One meta-analysis55 found that individuals following very low-carbohydrate ketogenic diets lost more weight in one year than those on low-fat diets.

A survey published in the Journal of Insulin Resistance56 found that three of four respondents on a low-carb diet reported losing 10 pounds or more; one-third reported losing more than 30 pounds. Six out of 10 respondents who were on the diet two years or more reported losing 20 pounds or more and 46% said they lost 3 inches from their waists.

Claim #12. People just can’t stay on keto

“[I]t is hard to follow…it’s so hard to stick with that people can’t eat this way for a long time.” -Marcelo Campos, M.D., Harvard Medical School57


The ketogenic diet does not limit calories; people can eat as much as they like so long as they restrict carbohydrates. This means that people don’t have to endure long periods of feeling hungry—which is why the ketogenic diet tends to be sustainable.

The survey in Journal of Insulin Resistance found that before respondents started their low-carb diets, nearly nine of 10 experienced intense hunger between meals. Once on the diet, only 3.5% said they grew hungry between meals. Respondents reported similar improvements in other aspects of their physical and psychological well-being.58

Of the 1,580 survey participants, more than half reported staying on a low-carb diet for at least one year, and 34% reported more than two years. Further, those on the diet for two years or more said that they had largely maintained their weight loss. This is a self-selected sample, with an obvious bias for people who are experiencing success (dieters are less inclined to report on their failures). However, this data does show that long-term adherence is possible.

“These overwhelmingly positive changes suggest that a low-carbohydrate diet may be especially sustainable,” the study’s authors concluded.

Further evidence comes from a large, university-based study on patients with Type 2 diabetes, which showed an exceptional 84% adherence to a ketogenic diet at 1 year.59

Claim #13. Keto Kills

“Low-carb diet linked to early death, medical study suggests.” USA Today, citing a study mainly by Harvard researchers published in The Lancet Public Health60


As I wrote in op-eds for the Wall Street Journal61 and Medscape,62 the Lancet Public Health study is based on very thin data. The questionnaire underlying the report left out questions regarding popular foods, such as pizza and energy bars, and did not consider alcohol consumption. Moreover, the “low-carb” diet group in this study included people eating up to 37% of calories as carbohydrates—not low-carb according to the latest science. Ultimately, this is the kind of data that can show association but not establish causation, which means it is the kind of data one can use to generate hypotheses but not prove them. This kind of data would never be considered sufficient to approve a drug, for instance. The same standards should be applied to diet. Quite a few researchers, including myself, had our critiques published in Lancet Public Health.63 The authors replied but did not respond to most of the criticisms.

Meanwhile, more than 70 trials have examined the health effects of a low-carb diet. They attest to the benefits64 associated with ketosis and low-carb diets, including a reduction in body weight and body mass index, improved cardiovascular risk factors including blood pressure, and the reversal of Type 2 diabetes. It is virtually impossible to imagine that a diet with so many health improvements in the ‘near term’ (2 years) could ultimately shorten life—and the study authors offer no possible mechanism to explain how this might happen.

I think the larger question is why we are seeing such a sudden rash of anti-keto stories. So many of them quote no experts sources and do not provide citations for their claims. Skeptics with little acquaintance with the diet are quoted exclusively instead. From a journalistic perspective, this lack of balance of viewpoints and the failure to back up claims with evidence falls below basic reporting standards. Offenders on this list include even the Harvard School of Public Health, which recently published more than one  unsourced, one-sided article on the keto diet (This is in addition to the Lancet Public Health article cited above, by Harvard researchers, which suggests that a low-carb diet kills you). These stories could reflect lazy reporting or they could very well be scare tactics to steer people away from the keto diet.  Why would reporters or scientists at Harvard be doing such a thing? That’s material for another post. Stay tuned.

Expert contacts who helped compile source material for this article:

Tro Kalayjian, D.O., Internal Medicine, Yale New Haven Health

Shebani Sethi, M.D., MS: Psychiatry & Obesity Medicine,, Stanford University Department of Psychiatry

Angela A Stanton, Ph.D. independent researcher, migraine specialty

Col. Rob Oh, M.D., MPH, CAQSM –   Family Medicine, Sports Medicine

Many other low-carb practitioners who have familiarity with the scientific research can be found here:

Other experts can be found by going to and searching for “keto” or “ketogenic” to find scientists who are studying this diet. 

4 year=2018&issue=05001&article=01656&type=Fulltext
16 See discussion of this in Teicholz, N. The Big Fat Surprise (Simon & Schuster 2014), pp; 304-306. 
21 Teicholz, N., The Big Fat Surprise (Simon & Schuster) 2014, pp. 316-318
63 (scroll down to “Correspondence”)

36 thoughts on “Ketogenic Diet Myths vs. Facts”

  1. Thanks Nina for dispelling some of these myths. I believe the keto diet has been around for decades to treat epilepsy so there should be long term data in that population.

    How do you define the keto diet? I’ve seen many ranges in marcronutritent intake such that I can’t imagine the outcomes are consistent across all of them.

  2. Dear Nina,

    Thank you for sharing this insightful article. I notice that you have quoted me in Claim #2 following an interview I gave to a magazine some months ago. I hope you will permit me to clear up any misconceptions about my stance.

    I’m an advocate of the keto diet and I have noticed significant benefits amongst my patients, and indeed myself. The point I attempted to make in the article was that people on medication for chronic conditions such as hypertension or type 2 diabetes should ideally proceed in a collaborative manner with their primary care physician.

    For purposes of clarity, I did not state that “You shouldn’t try keto if you have diabetes.”

    With best wishes,


    Dr. Shan Hussain

  3. I am an MD Anesthesiologist from India. Thanks for this brilliant compilation. I am a low carb practioner and I face these accusations daily.

  4. Dear Nina Teicholz,
    I’m a brazilian doctor very interested in keto diet. In fact, i’ve been following keto diet for almost one year.
    Concerning your response to claim #6, is a fact that keto diet improves GERD disease. But the gut health goes beyond GERD disease. In my experience, keto diet does cause constipation, mainly due to low fiber content. As an attempt to alleviate this side effect, we can increase the consumption of water and low carb seeds.

  5. Nina, this is a brilliant article, thank you. I have shared it with my Low Carb & Keto Facebook US & UK groups, many of whom are new to this way of eating for weight loss, reversing Diabetes, preventing Diabetes and improving their health. My members receive regular low carb recipes and support but articles like this, really do reinforce their reasons for staying low carb and helps them justify their lifestyle to family, friends and some Medics!
    We’d love you to visit us ➡️
    Thanks again
    Jan Rose

  6. I tried the keto diet a couple years ago and about 6 weeks in of following it closely I started having significant episodes of lightheadedness and anxiety like symptoms. The coach I was working with said it was keto flu so I continued on the diet for a couple more weeks but it was making life difficult so I stopped. Now every time I try to go low carb the symptoms come back. Sometimes I wonder if it’s just anxiety response or all in my head. I would love to eat low carb but haven’t ever been able to figure out why this happens. I read somewhere that keto can be harder for women’s bodies and affect their adrenal glands. Would this increase anxiety symptoms.

  7. I would like clarification on “gut” heath. The info listed above is about stomach issues, which would agreee with as far as lowering GERD symptoms. I’m curious about lower digestive micro biome information for those eating less/low/zero carbs?

  8. Great article. Reminiscent of Ancel Keys days where the sugar is good for you myth went as high as being legislated as being a healthy product. Begs the question, what shenanigans go on behind the scenes with institutions like Harvard presenting unsourced papers and reports. Will stay tuned. Love your work.

  9. Another big claim in the biology literature is that the brain runs best on glucose and it’s bad to run the brain on ketones for long. Thoughts?

  10. The response to claim No 6 “………is not good for your gut” misses the point. The claim points to the gut microbiota not GERD or Barrett esophagus. Green leafy vegetables are part of a (at least: of my) lowcarb eating pattern, they are full of fibers.

  11. Regarding #2, mice on a “keto” diet.
    I recall a study on mice or rats that claimed that a high fat caused diabetes-2.
    But there was a serious snag. When the chow that the animals ate was investigated closer it wasn’t high fat at all, at least not low carb. It was found that the chow contained about 20% sugar.
    The chow manufacturer explained that it was correct, but necessary to mix in the sugar. Else the mice would not eat it at all!

  12. If we really take a good look at who it is that is claiming keto as bad / an unhealthy lifestyle/an unsafe or unsustainable diet, it makes perfect sense, really.

    Fitness providers such as Jillian Michaels who rely on sales of her exercise programs, apps, paraphenalia, , etc.; doctors who treat patients with medical conditions that are positively affected by the keto WOE, drug producers, etc. etc.

    Biggest lesson that comes from this is when reading negative comments, reports, etc. about Keto, consider first and foremost the source – what have they got to lose/gain by this destroying the faith in this process??

    I say Keto on 🙂

  13. TAKE THE OPPOSING POINT OF VIEW and see if THAT is healthy. If a LOW CARB diet is BAD, is a HIGH CARB diet GOOD? Well, America and all nations that follow the American diet ARE GETTING FATTER and suffering the consequences of obesity and we are currently on that high carb diet plan. So, there will always be naysayers even when Jesus comes back to put us on the right track.
    From the founding of the United States to about the 1940’s, obesity wasn’t a problem for the average American. There just wasn’t that many pastries, desserts and junk foods around. Only the rich could afford to be fat. The rest of the folks ate meats, vegetables, fats and had very little sugars. Mom cooked everything with bacon fat. That’s a rationale Keto diet. Poor folks were always slim in those days. Now, with the proliferation of CHEAP junk food, everyone is fat.

  14. This article is a must read for everyone who wants to start Keto diet. I’m skeptical to try it because of claim #6, so I’m glad this is just a myth. I can’t wait to start my Keto journey. Thank you.

  15. I just lost +- 15 lbs in 3 weeks. Felt pretty bad a couple of times but it did not last over a day. Goal is no carbs every day but some sneak in occasionally. Exercise some, walks and weights. Sleep great, giving up wine and booze contribute to that. Constipation some days but try to eat salads to avoid that along with remembering drinking water and stool softeners. I am a 64 year old football watching kind of guy that turns up his nose at kale and tofu but has had no problems with just an avacado, cheese stick and a hard boiled egg in my lunch bag.
    “I’ll have a tossed salad with blue cheese dressing, then that porterhouse with a side of creamed spinach” I said to the waiter at Morton’s.
    Man, I feel better.

  16. You did not mention the positive of a Keto flex diet as recommended by Dr. Dale Bredesen (neurologist, UCLA), which helps prevent and reverse Alzheimer’s when combined with following an optimum nutrition plan including exercise. For full information go to AHNP, and also read Dr. Bredesen’s book, and professional publications.

  17. I have been a Pilates instructor for almost a decade two years ago one of my students told me that about ketogenic diet and i have started sharing a custom diet plan with my class and they have started getting outstanding results. Even after doing years of research i had many questions but with this article i have learned everything that was left behind. Thank you

    • That is great to hear. Thank you for staying open to your own observations. Many scientists cannot do this very thing–simply to trust what they see.

  18. i have been a fitness trainer for more than a decade and i could clearly see that most of these myths does not make any sense. A diet couldn’t do all that to a person until and unless he is already going through some medical condition 🙂

  19. Thanks for the article, very informative! I’m recently involved in exploring and education myself about the diet and I am very passionate about the topic.

  20. My wife and I have been on a low carb ketogenic diet since January 7, 2019. The results have been astounding. We each lost fifteen pounds of stubborn and unhealthy abdominal fat. We feel incredible and wholeheartedly endorse your debunking of the keto myths listed based solely upon our personal experiences. This will be a permanent lifestyle change for us.

    As an aside, on my day off yesterday, I finished reading the Big Fat Surprise which led me to find your webpage this morning. I had read Gary Taubes’ The Case Against Sugar just prior. Talk about a double whammy. Upon completion of your book, as I’m sitting in my home office recliner, sipping coffee spiked with heavy whipping cream and monk-fruit sweetener, I gazed over at the numerous medical texts lining the bookshelves next to me. I am a board certified emergency medicine and urgent care physician. Although I hold a master of public health degree from a prestigious university, I have devoted my decade plus of clinical practice entirely to community medicine, not to research oriented academia. Yet, the doctors and scientists I learned from specifically taught me to base my principals of practice whenever possible upon solid clinical data using randomized controlled trials as the gold standard in proving causation. For your many years of research in realizing and reinforcing this principal, I salute you.

    On page 297 of the Big Fat Surprise, the sentence “While Pennington’s analysis…” literally sums up for me the sheer enormity (and tragedy) of what has happened over the past 60 years. Total bombshell. It’s so difficult to believe we were born into becoming unwitting participants in what was in fact an epic national medical and dietary experiment albeit one with good intentions initially. At age 50 now, I feel quite duped. My wife is an internist and she feels even more duped. Nonetheless, we are armed with sound clinical principals and shall both continue to walk the talk as well as practice what we preach. Most importantly we aspire to be living, breathing examples of healthy minds, bodies and spirits who enjoy a balanced existence. Thanks again and take care, W.

    • Thank you for your comment! It is indeed hard to believe that we were all so throroughly duped–and probably we’d remain so today if our own experience in improved health were not such hard proof to the contrary.

  21. This is very well-written and informative! Keto diet seems to be the trend for weight loss nowadays. My friend’s brother started following a Keto diet and we’ve seen significant changes in his physique since then. I just think it requires discipline and commitment to be able to do this properly.

  22. This article is an unquestionable requirement perused for everybody who needs to begin a Keto diet. I’m mindful so as to attempt it as a result of case #2, so I’m happy this is only a fantasy. I can hardly wait to begin my Keto venture. Much obliged to you

    • Actually, the brain runs very well on ketones. In low-carb experiments, mood and clarity of mind consistently improve.

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