Introduction

Lebron James. Halle Berry. Kourtney Kardashian. Megan Fox. Tim Tebow. Vinny “Keto Guido” Guadagnino of Jersey Shore fame. A growing list of celebrities and athletes have embraced the ketogenic diet, a high-fat low-carb diet trend, and have seen some impressive weight loss.

But is the ketogenic diet better than other diets? What does the science actually say?

What Is A Ketogenic Diet?

The ketogenic diet focuses on high fat, moderate protein, and low or very low carbohydrate intake, and typically has no restrictions on total calories. This ratio of macronutrients is proposed to help induce a state of ketosis, where the body essentially switches fuel sources. When deprived of carbohydrates, the body starts burning more fat.

Molecules called ketone bodies are produced as a product of all the fat-burning, and these molecules are utilized for energy in your brain instead of glucose. As you might expect, the promise of some extra fat-burning has made “going keto” ostensibly appealing to dieters.

The diet was originally created to help control and modify symptoms of epilepsy in children in the 20s and 30s, but it has since spread into popular culture with other purposes. Since then, the ketogenic diet has been the subject of much research, celebrity and blogger buzz, as well as reasoned criticism.

What Is The State Of The Research?

Much of the research has focused on epilepsy, as well as weight loss, diabetes, cardiovascular disease, and other neurological diseases. A search on PubMed for “Mediterranean diet” reveals 5,389 matches, while one for “ketogenic diet” reveals only 2,278 matches.

Does The Ketogenic Diet Help For Weight Loss?

Like most diets, going “keto” has generated buzz on the basis of its potential for weight loss.  Is there any reason to believe severely restricting carbs, getting the majority of your calories from fat, and not counting calories is the best way to lose weight? The answer, as you might imagine, is complicated.

The ketogenic diet, like many extreme diets, limits an entire food group from consumption, and thus limits the overall amount of food available to you. Therefore, it’s not surprising when much of the research suggests that following the ketogenic diet may help you lose some weight over varied time periods (4, 5, 9, 10, 11, 25, 26, 28, 29, 32, 37). However, a curious dieter may want to know if it has any advantage over other diets.

One study from 2006 looked to compare a ketogenic diet to a non-ketogenic low-carbohydrate diet to assess if going into ketosis was critical for significant weight loss. All food was provided by the researchers and strictly prepared, and they measured blood glucose, cholesterol, triglycerides, insulin, ketone concentration, and body weight. After six weeks, both groups lost the same amount of weight, despite the ketogenic group achieving a state of ketosis (15).

The researchers concluded “patients should know that there is no apparent metabolic advantage associated with ketosis during dieting” (15).

Another study from 2006 looked at the effects of very low-carbohydrate, very low-fat, or high unsaturated fat diets, while controlling for total number of calories for 83 subjects. The researchers found that all three groups lost about the same weight after 12 weeks, with a slight edge to the very low-carbohydrate group when comparing percentage of weight lost (26).

One study from 2010 compared a low-fat diet to a low-carbohydrate diet for weight loss and found there were no differences between each approach over a period of two years, although there was a slight trend favoring the low-carb group (8).

In a study of 58 obese children and adolescents, participants were randomized to either a ketogenic diet without restriction of daily calories or a standard diet in line with the American Heart Association, with the goal of reducing their intake by 500 calories daily. After six months, both groups lost weight, but the ketogenic group lost slightly more (28).

Complicating matters, an analysis of 13 studies found that those on a ketogenic diet lost significantly more weight than those on a low-fat diet (2).

Bottom Line

Following a ketogenic diet may help you lose weight, but its advantage over other diets has not been conclusively demonstrated and the research is mixed.

Does It Help Fight Neurological Diseases?

Epilepsy

The ketogenic diet was originally created to help control symptoms of epilepsy in children who would not respond to medication, and as such, a major focus of the research is on this subject. A literature review from 2003, a meta-analysis from 2005, and systematic reviews from 2000 and 2006 all found that the existing literature demonstrated a ketogenic diet can help to reduce seizure symptoms by varying amounts.

However, none of the studies the reviewers found were of high quality; they generally lacked control groups, placebo groups, randomization or anything else to help reduce bias (20, 33, 13, 16).

A very thorough Cochrane review came out in 2016 that was able to find seven randomized controlled trials with a total of 427 children. Despite some methodological concerns of the studies, they found that 10% to 55% of patients were seizure-free, and 38% to 85% reduced their seizure frequency by half (24).

Another meta-analysis from 2018 of 16 studies echoed these results and found that the ketogenic diet is effective for reducing seizures in adults as well. 13% of patients eliminated their seizures completely, 53% of patients reduced them by 50% or more, and 27% reduced them by 50% or less (22).

Other Neurological Disorders

One study investigated the effects of a very low-carbohydrate diet compared to a high-carbohydrate diet on 23 older adults with mild cognitive impairment. They found that the very low-carb group had elevated ketones as well as improved performance on verbal memory tests, but there were no changes in working memory, depressive symptoms, or mood (19).

Another study investigated the effects of a ketogenic diet on 30 children with autism. They found 18 children were able to maintain the diet for six months and had some improvements in their symptoms. The biggest changes were seen in those with mild cases of autism, with smaller changes seen in those with moderate and severe cases of autism (7). However, the small study group, lack of blinding, lack of control or sham groups, and significant percentage of children that could not complete the diet make the results only preliminary.

The effects of a ketogenic diet on headaches and migraines have also been investigated. One study from 2015 looked at 96 women with migraines, and half started a very low-calorie diet that was designed to induce ketosis while the others started a “standard” diet with a higher percentage of total energy coming from carbohydrates.

After four weeks, the experimental group transitioned back to the standard diet. The researchers found that the experimental group had a sharp decline in migraine frequency and pain medication use after the first month, but this increased again after transitioning back to the standard diet (23).

Many have suggested that the ketogenic diet may be helpful for patients with Alzheimer’s disease (AD). This claim stems from a 2009 study where 152 patients with the disease were given either a ketogenic compound in pill form or a placebo. The researchers measured their performance on a few measures designed specifically for AD patients. They found that the pill was able to induce ketosis and resulted in slightly improved scores on a portion of a cognitive test compared to the placebo (12). This study leaves room for doubt, however, as the difference was very small.

There is one study on Parkinson’s disease which only had seven subjects, and one study on ALS that was performed with mice (34, 38). Both of these studies were not of sufficient quality or of appropriate methodology to suggest that the ketogenic diet can help with these conditions.

Bottom Line

The ketogenic diet may help significantly reduce or eliminate seizures for patients with epilepsy who do not respond to medication, but the research on other neurological conditions is much more preliminary.

Does It Reduce The Risk Of Diabetes?

The elimination of carbohydrates in the ketogenic diet has made it an attractive option for those with Type 2 Diabetes, and seems like a reasonably plausible option to manage blood sugar appropriately. There is strong research that suggests utilizing a ketogenic diet is associated with positive changes related to diabetes including decreased blood glucose, improved A1c, (an average of blood glucose over three months), improved insulin resistance, and reduced diabetic medication usage (4, 5, 9, 10, 14, 37, 28, 32, 30, 35).

Some research even suggests that a ketogenic diet performed better than:

  • both a normal diet, and a normal diet plus exercise, at lowering A1c levels over 10 weeks (9)
  • a low-calorie diet with macronutrient ratios of less than 30% fat, 10-20% protein, and 45-60% carbohydrates, when looking at A1c levels over 4 months (10)
  • A low-calorie diet for lowering blood glucose over 24 weeks (14)
  • a low-fat diet and a high unsaturated fat diet for lowering insulin and glucose levels over 12 weeks (26)
  • a hypocaloric diet at improving diabetic parameters, although they had statistically close results (28)
  • a low-glycemic diet for reducing diabetic medication usage in a 2008 study over 24 weeks (35)
  • the “Create Your Plate” plan put forth by the American Diabetes Association for reducing A1c and medication usage over 32 weeks (30)

Bottom Line

Reducing carbohydrate and sugar intake as recommended by the ketogenic diet can help diabetics reduce blood glucose, improve their A1c, and lose weight.

Does It Reduce The Risk Of Cardiovascular Disease?

The relationship between the ketogenic diet and cardiovascular disease has also generated significant interest. Cardiovascular disease is a leading cause of death, and dietary interventions may be helpful in mitigating the risk factors associated with it, including obesity, diabetes, high cholesterol, and high blood pressure.

As mentioned above, following a ketogenic diet may help you lose weight and manage diabetes effectively, although diets with similar levels of calories and reduced (but not eliminated) carbohydrates may be just as successful.

Two informal reviews of the literature from 2015 and 2017 both suggested that eating a ketogenic diet can result in favorable changes to total cholesterol, high-density lipoproteins (HDL), low-density lipoproteins (LDLs), and triglycerides, although some studies report negative changes, particularly in LDLs (27, 18). In a more thorough meta-analysis of 13 studies, the ketogenic diet was shown to be better than low-fat diets for raising HDL levels, decreasing LDL levels, and reducing diastolic blood pressure (2).

However, one informal review on the ketogenic diet for children found that six of the seven studies they looked at showed it was associated with negative changes in cholesterol levels. The discrepancy may be due to differences in the types of fats utilized in each diet (18).

Bottom Line

The ketogenic diet may improve cardiovascular risk factors, but the research is mixed when it comes to cholesterol. There is no long-term data on ketogenic diet adherence and the development of cardiovascular disease.

Does It Help With Cancer?

The ketogenic diet has gained considerable interest in its potential for treating cancer. The basic premise is that cancer cells feed on sugar, and reducing your sugar intake may help starve the cancer and slow it down or eliminate it.

The research thus far is still in the preclinical stage and only basic science studies, animal studies, and small case studies have been done (1, 36). According to one review, 72% of animal studies that were found showed a ketogenic diet can have antitumor effects (17). However, small human trials have not shown any substantial benefit (31, 39, 3).

Despite a potentially plausible mechanism, the ketogenic diet has just not been tested enough in humans to know if it can be recommended to help slow down cancer (6). One author writes

“In contrast, to the considerable attention from researchers, physicians and the media for its potential role in cancer treatments, evidence on benefits regarding tumor development and progression as well as reduction in side effects of cancer therapy is missing” (6).

Bottom Line

Despite interesting preclinical research, there is no sound scientific evidence that the ketogenic diet can help with cancer, and thus cannot be recommended.

Feasibility and Safety Of The Ketogenic Diet

The elimination of carbohydrates and high fat consumption that the ketogenic diet proposes has naturally led to concerns about its long-term feasibility and safety. Eliminating entire food groups simply makes it a hard diet to follow. In the majority of studies available, there were significant percentages of subjects who simply could not stay on the diet.

One meta-analysis from 2005 found that in a total of 1,084 patients over 19 studies, half of them dropped out, citing ineffectiveness, the diet being too restrictive, illness or side effects, or poor compliance (13). In another meta-analysis from 2016, the authors reported 10-20% dropout in children due to lack of efficacy and refusal to eat, among other reasons (24).

The ketogenic diet is not without side effects. Two reviews reported that the most common side effects were increased LDLs, increased cholesterol, and gastrointestinal discomfort (diarrhea, constipation, vomiting, and nausea). (22, 24). One study reported children being treated for epilepsy on the diet experienced poor growth, altered cholesterol levels, and kidney stones (21). In addition, eliminating carbohydrates may be associated with inadequate fiber and other vitamin and mineral intake, which must be taken into account.

Bottom Line

Because of significant concerns with long-term feasibility and side effects, it is best to consult with your doctor or a registered dietician if you choose to utilize the ketogenic diet.

Conclusions

  • The ketogenic diet can be effective for weight loss, diabetes management, and epilepsy.
  • The ketogenic diet has not been conclusively shown to be better than other diets for weight loss, when controlling for total calories, and may result in missing nutrients.
  • One feature it has in common with other diets, reducing sugar intake, is a reasonable recommendation for most people.
  • There are potential side-effects to consider and it is best to consult a doctor or registered dietician if you start the ketogenic diet.
  • The science is simply not there yet for some of the bolder claims like treating cancer, migraines, Alzheimer’s disease, autism, ALS, or Parkinson’s disease.

The ketogenic diet has its ardent defenders and its critical cynics, but the science leads us to somewhere in the middle. It is not conclusive, but it cannot be dismissed either.