by Ya’el Courtney

In 2022, the majority of Americans (52%) followed a particular diet or eating pattern, primarily motivated by two things: a desire to protect long-term health and a desire to lose weight. According to data from the International Food Information Council, 23 million Americans chose to follow a ketogenic, or “keto”, diet last year to work towards these goals. This number has more than doubled since 2018, when only 10 million Americans chose keto. The business world has not missed this momentum – the keto diet market was valued at $10.22 billion in 2019 and is expected to grow 5.3% annually, reaching a value of $15.27 billion by 2027. It’s clear that the ketogenic diet is becoming increasingly popular, but should it be? Does it meet dieter’s main goals of long-term health and weight loss? Scientific research conducted over the last two decades says no, not really, and that this diet may be harmful for most people.

What is a ketogenic diet? 

Among dieting categories, methods that encourage low carbohydrate consumption and high protein consumption are increasingly popular. This includes things like Paleo, the South Beach diet, and the Atkins diet, which people sometimes mistakenly refer to as ketogenic diets. A true ketogenic diet is different. The ketogenic diet is a high fat, moderate protein, low carbohydrate eating pattern that differs from general healthful eating recommendations (set forth by the U.S. National Academy of Medicine) (Figure 1). Keto typically reduces total carbohydrate intake to less than 50 grams a day, with some people adhering to less than 20 grams a day. For context, one six-inch banana has 30 grams of carbohydrates, and one cup of cooked pasta has 45 grams. Keto dieters are encouraged to break down their daily caloric intake into approximately 70-80% fat, 10-20% protein, and 5-10% carbohydrates.

The ketogenic diet aims to induce weight loss by reducing the body’s supply of glucose, which is the primary source of energy for all cells in the body and is derived from consuming carbohydrate-rich foods. Instead, the diet encourages the production of an alternative fuel source called ketones from stored fat, hence the name “keto”-genic. The brain requires a steady supply of glucose, about 120 grams daily, and cannot store glucose. Therefore, when carbohydrate intake is minimal or during fasting, the body initially obtains glucose from liver stores. After 3-4 days, if stored glucose is depleted, the body enters a state called ketosis. During ketosis, the liver becomes able to produce ketone bodies, a type of fuel made from stored fat. In theory, the body will then eat away at its stored fat to meet its energy demands, leading to fat loss in an individual. 

Is the keto diet effective for weight loss? 

While the theory behind fat loss resulting from a keto diet is appealing, it does not hold up well in practice. While keto dieters often experience a satisfying initial weight loss, this is a short-term result from the loss of body water that accompanies lower carbohydrate intake, not fat loss. This is because when we eat carbs, the energy that we do not use immediately is stored as glycogen molecules, and each gram of glycogen is stored with 3 grams of water attached to it. When you cut down on carbs, you quickly use up your glycogen stores, losing that water weight. Furthermore, the ketogenic diet’s restrictive nature makes it unlikely that people will follow it correctly, with over 50% of people failing to adhere to a ketogenic diet in many medical studies, which negates any short-term weight loss effects. Even if properly followed, a ketogenic diet is not intended to be adhered to long-term, nor is it uniquely effective. Studies show that after 6 months, a ketogenic diet does not lead to significantly higher weight loss than other weight loss approaches.

What health risks are associated with a ketogenic diet? 

So, if a ketogenic diet isn’t particularly effective for weight loss, how does it measure up to dieters’ second main objective: protecting long-term health and preventing future health conditions? Studies conducted over the last 10 years suggest that keto is likely riskier for most people than calorie-reduction approaches with moderate carbohydrate intake (Figure 2). 

First, while of course there is individual variability in food intake, the macronutrient ratios demanded by a ketogenic diet tend to lead to a general nutrient imbalance with glaring deficiencies. Many adherents curtail or eliminate fruits, vegetables, whole grains, and legumes while increasing consumption of animal products. This leads to deficiencies in thiamin, folate, vitamin A, vitamin E, vitamin B6, calcium, magnesium, iron, and potassium. These deficiencies can lead to a host of frustrating daily health issues. For example, common symptoms of potassium deficiency – referred to medically as hypokalemia – include constipation, heart palpitations, and extreme fatigue. Magnesium deficiency leads to fatigue, muscle twitches and cramps, apathy, and high blood pressure. Even when dieters focus on nutrient-dense foods, a ketogenic diet is reported to have multiple micronutrient shortfalls, often lacking in vitamin K, linolenic acid, and most water-soluble vitamins. Ketogenic diets are also typically low in the fiber needed for healthy intestinal function, nutrient absorption, and immune function. It is not yet known whether fiber supplements can counter these effects. Keto is also not conducive to optimal kidney function, as it significantly increases the occurrence of kidney stones. 

People who are pregnant or may become pregnant should be especially wary of following a ketogenic diet, as carbohydrate-restricted diets have been clearly associated with birth defects. This applies even if people follow carbohydrate-restricted diets before becoming pregnant and stop immediately upon learning they are pregnant. If the pregnancy was planned, people who followed keto in the year prior to conception were 30% more likely to have a child with a neural tube defect, specifically anencephaly or spina bifida. Additionally, in the 40% of pregnancies that are unplanned, there is an 89% increase in risk of neural tube defects if a carbohydrate-restricted diet was followed for the preceding year. This is likely related to decreased folate intake, since many carbohydrates are fortified with folate. 

Finally, a long-term health metric that many people who choose to lose weight are concerned about is cardiovascular risk, since it is well-established that obesity directly contributes to many incident cardiovascular risk factors. Unfortunately, emerging research shows that a ketogenic diet actually increases the risk of cardiovascular disease. In a young, fit population of CrossFit athletes, following a keto diet for 12 weeks led to an average weight loss of 6 pounds but increased “bad cholesterol” (LDL-C) by a whopping 35%. Typically, you would expect to see LDL-C levels drop when you lose weight. LDL-C has long been associated with cardiovascular risk because it forms arterial plaques (a cholesterol build-up in the inner lining of arteries), and emerging research that followed people for 12 years has now directly linked long-term ketogenic dieting with a 2x higher risk of heart disease or other negative cardiac events. More longitudinal research is being done on these risks, but many doctors are now stepping up and advising people to follow other weight-loss approaches to preserve their cardiovascular health. 

Is a ketogenic diet good for anyone?

Interestingly, the keto diet was not originally intended for the everyday dieter, as it was designed and used in clinical settings since the 1920’s to treat seizure disorders. Countless studies over the years support that keto often yields a significantly positive outcome for the treatment of refractory epilepsy in children and adults. Even in these cases, when it significantly reduces seizure incidence, keto is associated with adverse effects including dehydration, hypoglycemia (low blood sugar), lethargy, metabolic acidosis, gastrointestinal symptoms, and elevated cholesterol. However, the quality of life improvements brought about by seizure reduction are compelling enough for some patients to continue to follow the diet. 

Keto is being tested as an intervention for a host of other afflictions with mixed results. For example, this diet may be useful for the treatment, but not the prevention, of Alzheimer’s disease (AD). It seems to yield mild cognitive benefits for AD patients, though saturated fat intake, which typically increases on a ketogenic diet, is strongly associated with the risk of developing Alzheimer’s, and more research is underway to understand the nuances of this effect. It has been tried, but is now discouraged, for patients with Type 1 diabetes. Additionally, studies are underway regarding the impact of a ketogenic diet on Type 2 diabetes, non-alcoholic fatty liver disease, and a variety of cancers, but potential benefits remain unclear. 

Though more longitudinal studies are still being conducted, early conclusions already suggest that a ketogenic diet does more harm than good for almost everyone. Rather than a one-size-fits-all miracle weight loss approach, a ketogenic diet should be considered as a medical intervention only to be undertaken upon specific recommendation from a physician. 

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Ya’el Courtney is a fourth-year PhD candidate in the Neuroscience program at Harvard University. You can find her on Twitter as @ScienceYael. 

Figures created with biorender.com.

Cover image by AbsolutVision on pixabay.

For more information: 

• For a series of reviews from the Harvard T.H. Chan School of Public Health on the research behind popular diets, click here.
• Check out a long-term weight management program created by a team of weight-loss experts at the Mayo Clinic that is generally safe for most adults here.
• To learn about the history of the ketogenic diet, read this article.
• To read about how the ketogenic diet might work to reduce seizures in patients with epilepsy, click here.