New Research Sheds Light on Keto’s Scary Downsides—Here’s What Registered Dietitians Have To Say

Here's what to know about this new study—and the diet you may want to try instead.

The ketogenic, or "keto" diet has been around for years now. This popular diet, which consists of a range of high-fat foods, has led to successful weight loss for some, but the findings of a new study show a reason why you might want to skip it: a potentially higher risk of heart disease.

Researchers presented the data, which has not been peer-reviewed, at the American College of Cardiology’s Annual Scientific Session Together With the World Congress of Cardiology in late February. They say that a low-carb, high-fat diet, which aligns with keto, could be associated with higher LDL ("bad") cholesterol levels and double the chances for cardiovascular events, including heart attack and stroke.

The keto diet has actually been around for more than a century and was initially used to treat epilepsy in children. But it's resurfaced over the years as a way to lose weight, a concern for experts given potential health risks. Registered dietitians say research like the new study is essential in reducing these risks.

"With the increase in individuals adopting the keto diet for weight loss and blood sugar control, it is important to look into the long-term effects of the diet on the heart," says Anastasia Gialouris, MS, RD, a registered dietitian in Brooklyn, New York. "Cardiovascular disease is the leading cause of death in America, and so it is important to study what role the keto diet may have in this health crisis."

Experts delved further into the keto diet, why it may affect heart health, and more effective eating plans.

Related: What Is The Keto Diet and How Does It Work?

About the New Research

The researchers set parameters for low-carb, high-fat diets (LCHF): 45% of the participants' daily calories would come from fat, with 25% comprising of carbs.

The scientists used health information from UK Biobank, a United Kington database that evaluated people for at least 10 years. They compared 305 following an LCHF diet with 1,200 people eating a regular diet.

The results didn't bode well for keto. Among the findings, people following an LCHF diet had:

  • Higher levels of low-density lipoprotein (often referred to as LDL or "bad" cholesterol)

  • Higher levels of apolipoprotein B, an LDL-coating protein (apolipoprotein B levels serve as a better predictor of heart disease than LDL)

  • Ate more total and saturated fat

  • Consumed twice as much food from animal sources than those following a standard diet

Researchers controlled for risk factors like heart disease, diabetes and hypertension. But at a follow-up 11.8 years later, people following an LCHF diet were twice as likely to have a cardiac event, artery blockage, heart attack, stroke and peripheral heart disease, according to a press release.

"This study suggests that overall health can be harmed by following a ketogenic diet due to the high level of saturated fat the participant consumes," says Beth Czerwony, RD, a registered dietitian with Cleveland Clinic’s Center for Human Nutrition.

People often follow a keto diet for weight loss, and Czerwony says some people may achieve that. Generally, weight loss can reduce heart disease risk. Still, this research shows that the dangers of keto-induced weight loss don't outweigh the benefits.

"Overall, cholesterol, triglycerides and 'bad' cholesterol increase," Czerwony says. "This study would suggest that ketogenic diets, although allowing for desirable weight loss, does not improve overall cardiovascular health."

The study has some limitations, and even the authors noted that it could show a correlation between the keto diet and cardiac event risk. A favorite phrase in the scientific community is "correlation does not equal causation." But one dietitian thinks the study has its merits.

"Even with the potential flaws, the findings of the study are still certainly worth paying attention to," says Danielle Smith, RD, a registered dietitian with Top Nutrition Coaching. "Logically, it would stand to reason that consumption of high amounts of saturated fats could increase the risk of cardiovascular disease based on what research has shown about saturated fats clogging arteries. It is known that high cholesterol levels do increase the risk of cardiovascular diseases and complications such as heart attack and stroke."

Related: What Is the Mediterranean Diet?

Experts Agree: It May Be Worth It To Skip the Keto Diet

This research isn't the first to point out the potential health risks of keto. Another study from 2019, which was peer-reviewed, found an association between diets that call for low or moderate carbohydrate intake and atrial fibrillation, which can up the risk of heart failure and stroke.

And research from 2021 indicated that the risks of the keto diet outweighed the benefits, even though it's also been promoted as a way to treat obesity, diabetes and liver disease. Gialouris warns of other issues from restricting the intake of carbohydrates, which the body uses for energy.

"Short-term negative side effects of the keto diet include ​​dehydration, constipation, fatigue, headaches, brain fog, insomnia and difficulty exercising," Gialouris says. "Overly restrictive diets, like keto, can also lead to social isolation and disordered eating.

Smith understands the desire to lose weight but believes there are other ways to go about it. "Fully excluding nutrient-dense carbohydrates [is] not necessary to still experience those positive benefits," says Smith.

What's more, keto-induced weight loss is often short-term because the diet is so restrictive. "Most often, participants will follow the keto diet for several months up to a year, allowing for the desired weight loss to be achieved and then going back to their normal baseline diets," Czewony says. "Often participants also will stop the diet due to several factors including diet boredom and cost of groceries."

Related: 100+ Delicious Mediterranean Diet Recipes

What To Do Instead of Keto

"The Mediterranean diet has been touted in multiple studies to be the best diet for heart health and long-term weight loss due to its variety of fruits, vegetables, whole grains, lean proteins and limited intake of concentrated sweets while utilizing healthy fats," says Czerwony.

The Mediterranean doesn't cut out any food groups and promotes omega-3 fatty acids found in foods like salmon, walnuts and sardines, Smith notes.

If you're concerned about your weight or diet, Czerwony recommends speaking to a healthcare provider.

"Any time you are concerned about a health condition, most times it can be improved with a healthy diet and lifestyle change," Czerwony says. "Talking with your PCP or a dietitian will give you the opportunity to review your overall intake, medications, and level of physical activity in order to customize an individualized program to suit your personal situation."

Next up: 40 Best Foods for Weight Loss