The ketogenic or “keto” diet, which involves consuming very low amounts of carbohydrates and high amounts of fats, has been gaining popularity.
However, a new study presented at the American College of Cardiology’s Annual Scientific Session suggests that a “keto-like” diet may be associated with higher blood levels of “bad” cholesterol and a twofold heightened risk of cardiovascular events such as chest pain (angina), blocked arteries requiring stenting, heart attacks and strokes.
Previous studies have shown that a low-carbohydrate, low-fat diet (LCHF) can lead to elevated levels of LDL cholesterol in some people. While elevated LDL cholesterol is a known risk factor for heart disease (caused by atherosclerosis, a buildup of cholesterol in the coronary arteries), the effects of such a diet on risk for heart disease and stroke have not been well studied.
About the new study
The study was conducted by researchers from the Healthy Heart Program Prevention Clinic, St. Paul’s Hospital and the University of British Columbia’s Centre for Heart Lung Innovation in Vancouver, Canada.
A LCHF diet was defined as consisting of no more than 25% of total daily calories from carbohydrates and more than 45% of total daily calories from fat. A “standard diet” was defined as ones as a diet that did not meet these criteria and were more balanced in carbohydrates and fat.
Proponents of a ketogenic diet generally recommend limiting carbohydrates to 10% of total daily calories, protein to 20% to 30% and consuming 60% to 80% of daily calories from fat.
The research team analyzed data from the UK Biobank, a large-scale database with health information from over half a million people living in the United Kingdom who were followed for at least 10 years. Upon enrollment in the biobank, 70,684 participants completed a one-time self-reported 24-hour diet questionnaire and, at the same time, had blood drawn to check their levels of cholesterol.
The researchers identified 305 participants whose questionnaire responses indicated that their diet during the 24-hour reporting period met the study’s definition of an LCHF. These participants were matched by age and sex with 1,220 individuals who reported eating a standard diet.
The findings
Compared with participants eating a standard diet, those who followed a LCHF diet had significantly higher levels of both LDL cholesterol and apolipoprotein B (ApoB), the main protein found in LDL cholesterol, also known as "bad" cholesterol because high levels of it can damage the arteries.
Previous studies have shown that elevated ApoB may be a better predictor than elevated LDL cholesterol for risk of cardiovascular disease.
After an average of 11.8 years of follow-up—and after adjustment for other risk factors for heart disease, such as diabetes, high blood pressure, obesity and smoking—people on an LCHF diet had more than two-times higher risk of having several major cardiovascular events, such as blockages in the arteries that needed to be opened with stenting procedures, heart attack, stroke and peripheral arterial disease.
In all, 9.8% of participants on an LCHF diet experienced a new cardiac event, compared with 4.3% of those on a standard diet, a doubling of risk for those on an LCHF diet.
The findings suggest that people who are considering going on an LCHF diet should be aware that doing so could lead to an increase in their levels of LDL cholesterol. “Before starting this dietary pattern, they should consult a health care provider”, the researchers said. “While on the diet, it is recommended they have their cholesterol levels monitored and should try to address other risk factors for heart disease or stroke, such as diabetes, high blood pressure, physical inactivity and smoking.”
Individual variation found
The study’s findings also suggest that not everyone responds to an LCHF diet in the same way.
“On average, cholesterol levels tend to rise on this diet, but some people’s cholesterol concentrations can stay the same or go down, depending on several underlying factors,” the lead researcher said. “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.”
Study limitations
Participants provided dietary information at only one point in time. Moreover, self-reports of food consumption can be inaccurate.
Because the study was observational, it can only show an association between the diet and an increased risk for major cardiac events, not a causal relationship.
However, the researchers said the findings merit further research, especially considering that approximately 1 in 5 Americans report being on a low-carb, keto-like or full keto diet.
Source: American College of Cardiology Annual Scientific Session, 2023.
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