Consumption of a low-carbohydrate, high-fat diet, dubbed a “keto-like” diet, was associated with an increase in LDL levels and a twofold increase in the risk for future cardiovascular events, in a new observational study.
“To our knowledge this is the first study to demonstrate an association between a carbohydrate-restricted dietary platform and greater risk of atherosclerotic cardiovascular disease,” said study investigator Iulia Iatan, MD, PhD, University of British Columbia, Vancouver.
“Hypercholesterolemia occurring during a low-carb, high-fat diet should not be assumed to be benign,” she concluded.
Dr. Iatan presented the study March 5 at the joint scientific sessions of the American College of Cardiology and the World Heart Federation.
The presentation received much media attention, with headlines implying a causal relationship with cardiac events based on these observational results. But lipid expert Steven Nissen, MD, of the Cleveland Clinic, warned against paying much attention to the headlines or to the study’s conclusions.
In an interview, Dr. Nissen pointed out that the LDL increase in the “keto-like” diet group was relatively small and “certainly not enough to produce a doubling in cardiovascular risk.
“The people who were on the ‘keto-like’ diet in this study were different than those who were on the standard diet,” he said. “Those on the ‘keto-like’ diet were on it for a reason – they were more overweight, they had a higher incidence of diabetes, so their risk profile was completely different. Even though the researchers tried to adjust for other cardiovascular risk factors, there will be unmeasured confounding in a study like this.”
He said he doesn’t think this study “answers any significant questions in a way that we want to have them answered. I’m not a big fan of this type of diet, but I don’t think it doubles the risk of adverse cardiovascular events, and I don’t think this study tells us one way or another.”
For the study, Dr. Iatan and colleagues defined a low-carbohydrate, high-fat diet as consisting of no more than 25% of total daily energy from carbohydrates and more than 45% of total daily calories from fat. This is somewhat higher in carbohydrates and lower in fat than a strict ketogenic diet but could be thought of as a ‘keto-like’ diet.
They analyzed data from the UK Biobank, a large-scale prospective database with health information from over half a million people living in the United Kingdom who were followed for at least 10 years.
On enrollment in the Biobank, 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 they followed a low-carbohydrate, high-fat diet. These participants were matched by age and sex with 1,220 individuals who reported being on a standard diet.
Of the study population, 73% were women and the average age was 54 years. Those on a low carbohydrate/high fat diet had a higher average body mass index (27.7 vs. 26.7) and a higher incidence of diabetes (4.9% vs. 1.7%).
Results showed that compared with participants on a standard diet, those on the “keto-like” diet had significantly higher levels of both LDL cholesterol and apolipoprotein B (ApoB).
Levels of LDL were 3.80 mmol/L (147 mg/dL) in the keto-like group vs. 3.64 mmol/L (141 mg/dL) in the standard group (P = .004). Levels of ApoB were 1.09 g/L (109 mg/dL) in the keto-like group and 1.04 g/L (104 mg/dL) in the standard group (P < .001).
After an average of 11.8 years of follow-up, 9.8% of participants on the low-carbohydrate/high-fat diet vs. 4.3% in the standard diet group experienced one of the events included in the composite event endpoint: Angina, myocardial infarction, coronary artery disease, ischemic stroke, peripheral arterial disease, or coronary/carotid revascularization.
After adjustment for other risk factors for heart disease – diabetes, hypertension, obesity, and smoking – individuals on a low-carbohydrate, high-fat diet were found to have a twofold risk of having a cardiovascular event (HR, 2.18; P < .001).