The ketogenic diet is one of the most popular diets out there, generating nearly $10 billion in global sales in 2019.
The diet’s core focus is eating foods high in fat and very low in carbs.
There are some health benefits to the diet, including weight loss, epilepsy management, and reduction in A1c and triglycerides, but researchers call into question its risks, long-term effects, and sustainability.
Certain health trends just seem to catch on with the general public and become a sort of holy grail of lifestyle shifts. The ketogenic diet (KD) is one of them. In fact, Americans searched for KD more than any other diet in 2020, according to Missouri Medicine. The global market for KD brought in $9.57 billion in 2019. However, a new study finds that the KD diet may be harmful to certain people, causing cardiac issues. 
This diet emphasizes high fat and low carbohydrate intake, intended to mimic a fasting state metabolism. The goal is to induce ketosis, the metabolic state which burns fat rather than glucose. People who use KD are intended to eat somewhere between 10–15 grams of carbohydrates per day, with nearly 90 percent of food intake coming from fat. There are several variations of the KD. Adopting the KD has its benefits and drawbacks.
Potential benefits of KD
As outlined in a review in Missouri Medicine, people often turn to KD for weight loss—which is probably the diet’s biggest draw. How? There are a few potential mechanisms at play here. The authors posit that “insulin inhibits lipolysis, and decreased insulin in low-carb diets causes increased fat breakdown.”
Yet another theory is that with carbohydrate intake, “the body will have to undergo increased amounts of gluconeogenesis [a metabolic state] to provide glucose to the brain.” Other theories suggest that in ketosis, the appetite decreases.
While weight loss is certainly possible with KD, your patients may need help to adhere to its strict rules. Mary Wirtz, MS, RDN, CSSD, a clinical dietitian and board-certified specialist in sports dietetics, says that the keto diet has definitive limitations.
“The ketogenic diet may be a tool for short-term weight loss and improving motivation for individuals discouraged by weight loss programs….but it is no more effective than a calorie-controlled diet for long-term weight loss and weight loss maintenance. Furthermore, a calorie-controlled diet (versus ketogenic) is certainly more balanced and sustainable,” she says.
A review in Cureus commented on the issue of compliance, noting that “long-term compliance with KD is a limiting factor. The sustainability of the diet has been called into question, and the prognosis of the diet’s effects after discontinuation must be examined.”
People also turn to KD for other health benefits, including the management of diabetes. However, the review found that “significant caution would need to be observed in patients with type 1 diabetes who wish to follow a ketogenic diet.”
In people with type 2 diabetes, the review authors wrote, “it is likely that any weight loss achieved with the ketogenic diet could lower A1c and help reduce the medication burden. Care must be taken to taper diabetes medications appropriately to reduce the risk of hypoglycemia.” The review also shared that these results were seen in the short term and seemed to wane after a year.
For patients with cardiac health issues, the researchers found that KD does decrease blood triglycerides and increase HDL-cholesterol. Its effects on LDL-cholesterol are variable, however—a main concern for physicians. Increased LDL may be due to the kind of fats patients are eating, so it’s important that you talk to your patients about healthy food sources.
“I always encourage individuals to optimize heart-healthy unsaturated fat sources versus saturated fat sources and work hard at increasing vegetable intake while adhering to the diet. These factors are crucial for optimizing long-term health and chronic disease mitigation,” Wirtz says.
More on the potential risks associated with KD
According to Wirtz, physicians should discuss the potential limitations of KD.
While KD may increase HDL and decrease blood triglycerides, studies have shown that it may increase LDL. One 2023 study presented by the American College of Cardiology found that KD and keto-like diets (which are slightly higher in carbohydrates and lower in fat that a traditional KD) may be associated with higher blood levels of LDL cholesterol, as well as two times the heightened risk of cardiovascular events. The study found that KD may increase the risk of “angina, blocked arteries requiring stenting, heart attacks, and strokes.”
The study itself does have its limitations, though. One issue is that the study subjects self-reported dietary information at one point in time rather than over time. More information would lead to a more robust understanding of the subjects’ food intake patterns.
Health risks may be heightened due to the kinds of food people eat when they’re eating KD or KD-like foods, Wirtz suggests. “I always encourage individuals to optimize heart-healthy unsaturated fat sources versus saturated fat sources and work hard at increasing vegetable intake while adhering to the diet. These factors are crucial for optimizing long-term health and chronic disease mitigation,” Wirtz says.
“There are inter-individual differences in how people respond to this dietary pattern that we don’t fully understand yet. One of our next steps will be to try to identify specific characteristics or genetic markers that can predict how someone will respond to this type of diet,” the authors wrote.
The researchers concluded, “The findings merit further research in prospectively designed studies, especially when approximately one in five Americans report being on a low-carb, keto-like or full keto diet.” The researchers suggested people have their cholesterol levels monitored while doing KD and to talk to their doctors about other risk factors for heart disease or stroke.
Another downside, Wirtz says, is that some people on KD “are not meeting non-starchy vegetable intake recommendations, and their dietary fiber intake is therefore poor.” She also states that vitamin and mineral intake is relatively low. “Furthermore,” she observes, “ these individuals often struggle with severe constipation, decreased energy, and exercise levels, and significant mood changes.”
Some of these issues may be part of what KD users refer to as the “keto flu.” Australian researchers reported on this complication in Frontiers in Nutrition. The keto flu is described as a cluster of transient symptoms that include “headache, fatigue, nausea, dizziness, ‘brain fog,’ gastrointestinal discomfort, decreased energy, feeling faint, and heartbeat alterations.” It generally occurs two to seven days after beginning the KD. Keto flu is not a recognized medical condition, although there are countless Internet searches and blog pages describing its effects.
The review also stated that KD is not recommended for pregnant women.
What your patients should consider before trying KD
You should encourage your patients to work with a professional if they’re interested in trying KD. “I would highly recommend that if a patient is interested in adhering to a ketogenic diet, they consider a referral to a registered dietitian, who can provide more individualized and comprehensive recommendations,” says Wirtz.
For patients you think may benefit from KD but who might struggle with the diet’s hard and fast rules, research shows that a less restrictive approach can result in weight loss. Specifically, people who followed a diet plan cycling between short periods of a ketogenic Mediterranean diet followed by longer periods of a traditional Mediterranean diet achieved substantial weight loss.
In the end, more research on KD is needed. As the review authors concluded, “Although ketogenic diets are popular and patients show great interest, their use must be approached with caution.”