Following a 'Keto-Like' Diet Linked to a Higher Risk of Heart Disease, Study Shows

  • Eating a low-carb, high-fat diet—similar to the keto diet—may increase a person's risk of heart disease.
  • Low-carb, high fat diets have spiked in popularity in recent years—about 7% of the U.S. population followed some sort of high-fat diet as of 2022.
  • The primary concern for following a low-carb, high fat diet is that it may lead to an increase in LDL, or "bad" cholesterol levels, which carry an increased risk of heart disease and stroke.

Eating a low-carb, high-fat diet—similar to what’s known as the keto diet—has been linked to a higher risk of heart disease for some people, new research shows.

The study, which is awaiting publication and has not yet been peer-reviewed, was presented at the American College of Cardiology’s 2023 Annual Scientific Session. It found that people on a low-carbohydrate, high-fat (LCHF) diet that included no more than 25% of their daily calories from carbs had increased LDL cholesterol and were over twice as likely to experience one or more major cardiovascular events, during an approximately 12-year follow-up period.

bacon and eggs cooking on stove

Natalie JEFFCOTT/Stocksy

Low-carb, high-fat diets have spiked in popularity in recent years as a means of achieving weight loss. According to survey data from the International Food Information Council, about 7% of the U.S. population followed a ketogenic or high-fat eating plan as of 2022. But experts have wondered whether following this unusual macronutrient breakdown could cause problems in the long term, especially for heart health.

In fact, the study was driven by observations by the researchers themselves that this type of diet was indeed associated with cardiovascular risk factors.

“Our study rationale came from the fact that we would see patients in our cardiovascular prevention clinic with severe hypercholesterolemia after following a LCHF dietary pattern,” said lead study author Iulia Iatan, MD, PhD, attending physician-scientist at the Healthy Heart Program Prevention Clinic, St. Paul’s Hospital and University of British Columbia’s Centre for Heart Lung Innovation in Vancouver, Canada. “This led us to wonder at the relationship between these LCHF diets, cholesterol levels, and cardiovascular disease.”

Here’s a closer look at what the study found and what it means for people on a low-carb, high-fat diet.

Low-Carb, High-Fat Diets and Heart Disease Risk

Dr. Iatan and her team of researchers didn’t set out to examine how a keto diet, specifically, could affect heart health. Rather, they were interested in the effects of a variety of low-carb, high-fat diets—defined as more than 45% of total daily calories coming from fat and under 25% coming from carbs.

She noted that these numbers do not meet “official” parameters for a ketogenic diet, which typically involve consuming at least 70% of calories from fat and under 10% from carbs.

“We chose to look at this broader LCHF dietary pattern because the keto diet can be very restrictive and difficult to maintain long-term,” Dr. Iatan told Health. “We also wanted to have enough participants on the LCHF dietary pattern to be able to draw meaningful conclusions,” she explained.

That said, even a diet somewhat higher in carbs and lower in fat than traditional keto appeared to have significant effects on heart health.

To conduct their analysis, Dr. Iatan’s team used data from the UK Biobank, a database of over 70,000 participants whose health information has been tracked for over 10 years. They identified 305 subjects whose self-reported diet information met the criteria for a LCHF eating pattern and compared them with 1,220 subjects whose diets were considered “standard” (i.e., a more balanced macronutrient ratio). The average age of subjects was 54 and 73% were female.

The research revealed that those who followed a low-carb, high-fat eating pattern had a significantly elevated risk for heart disease. “What we reported was an association between this dietary pattern, increased levels of LDL-cholesterol, and apolipoprotein B (a protein on the surface of cholesterol, which may be a more accurate indicator of cardiovascular risk than LDL alone), and an increased risk of cardiovascular events,” Dr. Iatan said. These risks played out in serious ways: people following this dietary pattern had twice as many cardiovascular events like angina, blocked arteries, heart attack, and stroke.

Interestingly, however, Dr. Iatan said that a LCHF diet did not have the same effect on all subjects. “We showed that the hypercholesterolemia effect is not uniform, but that there is a sub-group of people that will have severe hypercholesterolemia while on a LCHF diet. This is the group in whom the greatest increase in cardiovascular risk was observed.”

It’s worth noting, too, that the study had some limitations. Besides being conducted on a relatively small sample of 305 subjects, it only analyzed British participants. Individual dietary choices were also self-reported, which can muddy accuracy. Meanwhile, Dr. Iatan pointed out that “this is an observational study, so a causal relationship between a LCHF diet and heart disease cannot be inferred. Therefore, it shows correlation but not causation or cause and effect.”

How a Keto-Like Diet Can Affect Heart Health

Ever since keto and keto-like diets burst on the scene as a trendy means of weight loss, their high fat content has been a topic of discussion among heart health professionals.

“The primary concern is that a high-fat, low-carbohydrate diet may lead to an increase in ‘bad’ cholesterol,” Veronica Rouse, RD, MAN, of The Heart Dietitian, told Health. “When blood cholesterol levels are elevated, it can increase the risk of developing atherosclerosis, a condition in which plaque builds up in the arteries and restricts blood flow to the heart. Atherosclerosis can lead to heart disease, heart attack, and stroke.”

Rouse also said that a high-fat diet can drive inflammation. “Inflammation is a natural response to injury or infection,” she said, “but when it becomes chronic, it can lead to a range of health problems, including heart disease.”

According to Dr. Iatan, the saturated fat (especially from animal sources) in many study participants’ diets was another particular concern.

“[Participants’ diets were] high in saturated fat, with a double consumption of animal sources at 33.2% in the LCHF group vs. 16.8% in the standard group,” she said. “When people shift their caloric intake from carbs to fat, and especially if it is predominantly saturated fat (such as from animal products), LDL cholesterol and apoB will go up. This has been well documented.”

The American Heart Association, for example, recommends that people who need to lower their cholesterol limit saturated fat consumption to 6% of total calories.

What This Means for People on a Keto-Like or Other LCHF Diet

If you’ve been following a low-carb, high-fat diet, this study’s findings may sound alarming—but it’s important to remember that the science isn’t necessarily settled on macronutrient ratios and heart health.

“Each patient responds differently. There are inter-individual differences in how people respond to this dietary pattern that we don’t fully understand yet,” said Dr. Iatan. Whether you’re following a keto-like eating pattern for weight loss—or even for epilepsy, diabetes, or any other health goal—it’s best to consult with your doctor or dietitian to determine whether its potential risks outweigh its benefits.

There could also be ways of following a LCHF diet that don’t necessarily raise cholesterol. “It is well known that including healthy unsaturated fats like olive oil, avocado, and nuts can lower LDL cholesterol, improve blood pressure, and reduce heart disease risk,” Rouse said. “So perhaps including more unsaturated fats, and less saturated fats like animal meats may provide more positive outcomes when following a keto-like diet.”

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  1. American College of Cardiology. ‘Keto-like’ diet may be linked to higher risk of heart disease, cardiac events.

  2. International Food Information Council. 2022 Food and health survey.

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