The diet deprives the body of carbohydrates in a bid to force it to burn fat for fuel, with 75% of calorie intake coming from fats. That means people following the keto diet eat foods like fatty fish, eggs, dairy, meat, butter, and low-carb vegetables like asparagus and spinach.

Keto has skyrocketed in popularity thanks to books, celebrities, and social media stars touting its alleged benefits, which are said by backers to include rapid weight loss and hormonal balance. Aside from weight loss, keto diets are sometimes used as a treatment option for people with epilepsy.

On TikTok, the keto hashtag has been viewed more than 10.3 billion times.

However, in a new study presented Sunday at the American College of Cardiology’s 2023 Scientific Session, which is being held in New Orleans until March 6 together with the World Congress of Cardiology, researchers argued the strict keto lifestyle may not be as healthy as some nutritionists and influencers might want you to believe.

Findings

They found that low-carb diets that encouraged high fat intake may be linked to elevated levels of “bad” cholesterol in the body—and could double the risk of major cardiovascular health problems like artery blockages, heart attacks, and strokes.

Researchers led by Dr. Iulia Iatan of the University of British Columbia’s Centre for Heart Lung Innovation, who is also an attending physician-scientist at the St. Paul’s Hospital Healthy Heart Program Prevention Clinic, designed a diet that would see at least 45% of daily calories come from fat and no more than 25% come from carbohydrates.

Using data from the U.K. Biobank database, the research team compared the diets of 305 people whose eating habits were close to the diet they drew up with the diets of around 1,200 people who ate a standard diet.

Biobank recorded participants’ data for at least a decade.

The study—which is not yet peer-reviewed—found that after an average 11.8 years, people on the low-carb high-fat diet were more than twice as likely to suffer from several major cardiovascular events. These included blockages in the arteries, heart attack, stroke, and peripheral arterial disease.

However, its authors noted that they could only show an association between dietary habits and health risks, rather than a causal relationship, because the study was observational in nature.

It was also limited by a small sample size and the self-reporting of food intake.

Is the keto diet safe?

The study unveiled on Sunday isn’t the first instance in which scientists have thrown cold water on the keto regime as a diet that is beneficial to health in the long term.

Some researchers have argued that the diet isn’t sustainable for people to follow over long periods of time, with Harvard health experts pointing out that the faster rate of weight loss achieved through sticking to a keto diet compared with others appears to dissipate over time.

Last month, an international research team found that artificial sweeteners commonly used in keto-friendly products were linked to an increased risk of heart attacks, strokes, and blood clots.

Meanwhile, dietitians at the University of Chicago Medicine labeled the diet “extremely strict and difficult to maintain” in an article in January, warning that it could come with a multitude of negative side effects including low blood pressure, kidney stones, constipation, nutrient deficiencies, and an increased risk of heart disease.

“Strict diets like keto could also cause social isolation or disordered eating. Keto is not safe for those with any conditions involving their pancreas, liver, thyroid or gallbladder,” they said.

“Someone new to the keto diet can also experience what’s called the ‘keto flu’ with symptoms like upset stomach, dizziness, decreased energy, and mood swings caused by your body adapting to ketosis.”