As many as 9.8% of study participants who followed this type of diet experienced a cardiac event, compared with 4.3% of those on a standard diet – a doubling in risk.
“Our study found that regular consumption of a self-reported diet low in carbohydrates and high in fat was associated with increased levels of LDL cholesterol – or “bad” cholesterol – and a higher risk of heart disease,” said lead author Iulia Iatan, 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.
The findings were presented at the American College of Cardiology’s Annual Scientific Session and World Congress.
Low-carbohydrate, high-fat diets linked to elevated cholesterol
Low-carbohydrate, high-fat (LCHF) diets, like the keto diet, restrict consumption of carbohydrates, forcing the body to start breaking down fat for energy instead. The breakdown of fat in the liver produces ketones, chemicals that the body uses as energy in the absence of carbohydrates.
Proponents of a ketogenic diet suggest limiting carbohydrates to 10% of total daily calories, protein to 20% to 30%, and obtaining 60% to 80% of daily calories from fat.
Previous studies have shown that an LCHF diet can lead to elevated levels of LDL cholesterol in some people. While elevated LDL cholesterol is a known risk factor for heart disease, the effects of an LCHF diet on risk for heart disease and stroke have not been extensively studied.
‘Keto-like’ diet doubles risk of cardiovascular events
For this study, the researchers defined an LCHF diet as consisting of no more than 25% of total daily energy or calories from carbohydrates and more than 45% of total daily calories from fat. They dubbed this “keto-like” because it is higher in carbohydrates and lower in fat than a strict ketogenic diet.
They analysed data from the UK Biobank, a large-scale prospective database. Upon enrolment, participants completed a one-time self-reported 24-hour diet questionnaire and were blood tested for cholesterol levels. The team identified 305 participants whose responses indicated that their diet met their definition of an LCHF.
Compared with those following a standard diet, participants on an LCHF diet had significantly higher levels of both LDL cholesterol and apolipoprotein B (apoB), a protein component that is a known indicator for risk of cardiovascular disease.
After an average of 11.8 years of follow up, and after adjustment for other risk factors, people who followed an LCHF diet had more than two-times higher risk of having several major cardiovascular events, such as angina, heart attacks, strokes, and peripheral arterial disease.
Not all participants respond to LCHF diet in the same way
“Among the participants on an LCHF diet, we found that those with the highest levels of LDL cholesterol were at the highest risk for a cardiovascular event,” Iatan said.
The findings also suggest that not everyone responds to an LCHF diet in the same way, she explained.
“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,” she added. “There are inter-individual differences in how people respond to this dietary pattern that we don’t fully understand yet.”
‘Keto-like’ an inadequate definition
However, critics drew attention to the use of the phrase “keto-like”, saying that this failed to adequately define a true keto diet.
Robert Lustig, professor emeritus of paediatrics at the University of California, San Francisco, highlighted the lack of follow-up monitoring.
“Were the subjects actually on a ketogenic diet? I doubt it,” he wrote in a LinkedIn post. “Every ketogenic diet without monitoring regresses to the mean in just two months. If you start out on keto, and you're not checking your blood or urine or breath ketones, carbohydrate will sneak back into your diet, insulin will start to rise, lipolysis will be shut off, and soon you'll be on a high-fat, medium-carbohydrate diet, which is the worst diet on the planet.”
Iatan admitted that the fact that participants provided dietary information at only one point in time was a limitation of the study but said the findings merited further research.
She added: “Our 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 healthcare provider. 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.”