Low-carb, high-fat diet: Friend or foe?

Revered by diet enthusiasts as a godsend in the weight loss arena, a low-carbohydrate, high-fat (LCHF*) diet appears to take the opposite pole from a cardiovascular (CV) standpoint, as researchers from Canada found high levels of bad cholesterol and apolipoprotein B (apoB) in individuals who adhered to this dietary pattern.

“[Our study showed that] habitual consumption of a self-reported LCHF was associated with increased LDL-C** and apoB levels and a greater risk of incident CV events,” said Dr Iulia Iatan from the University of British Columbia, Vancouver, British Columbia, Canada, at ACC23.WCC.

Compared with participants on a standard diet (SD), those on LCHF diet had significantly elevated mean levels of LDL-C (3.80 vs 3.64 mmol/L; p=0.004) and apoB (1.09 vs 1.04 mmol/L; p<0.001), as well as total cholesterol (6.08 vs 5.85 mmol/L; p=0.002), HDL-C** (1.62 vs 1.56 mmol/L; p=0.039), and non-HDL-C (4.46 vs 4.29 mmol/L; p=0.03). [ACC.23/WCC, abstract 407-10]

Participants adhering to the LCHF diet also had significantly higher levels of ketone bodies such as ß-hydroxybutyrate (BHB), acetone, and acetoacetate (p<0.001 for all) compared with those on SD. “[The BHB level met] concentrations compatible with nutritional ketosis,” said Iatan.

Incident ASCVD*** event rate was twofold higher with LCHF vs SD (9.8 percent vs 4.3 percent; p<0.001). This effect was seen even after adjusting for covariates^# (adjusted hazard ratio, 2.18; p<0.001).

“LCHF or ketogenic diets have become increasingly popular due to their purported health benefits for a variety of conditions,” said Iatan. In 2021, ~16 percent of American adults – which translate to about 160M individuals – reportedly followed a low-carb dietary pattern in the previous year.

However, the health benefits that most followers rave about are countered by its CV effect, given the high intake of saturated fats and carb restriction to induce ketogenesis. “We would see patients following this diet in our clinic with severe hypercholesterolaemia,” said Iatan. “This led us to wonder about the relationship between the LCHF diet, lipid levels, and CVD.”

Iatan and colleagues selected individuals from the UK Biobank cohort. After exclusions and age- and sex-matching, they had 305 participants on LCHF and 1,220 on SD (mean age 54 years, 73 percent female).

Those on LCHF had substantially lower mean TDE^## (1,449.9 vs 1,992.1 kcal/day) and carb intake (23.2 vs 51.0 %TDE) as expected but had higher protein (22.2 v 15.8 %TDE), total fat (52.3 vs 30.7 %TDE), and cholesterol intake (0.31 vs 0.098 %TDE; p<0.001 for all). Their animal fat consumption was twice as much as in the SD arm, and the cholesterol intake was “well above the guideline-recommended levels”, Iatan noted.

A timely topic

Discussant Dr Alison Bailey from Parkridge Health System, Chattanooga, Tennessee, US remarked that this was a “great analysis on a very timely topic” considering the throngs of proponents of the LCHF diet. “Many patients believe they are improving their health by following this diet. I think this puts a lot of data into our hands to suggest otherwise.”

“[Overall, our] findings highlight the potential CV risk of this dietary pattern and suggest that hypercholesterolaemia occurring during LCHF diets should not be assumed to be benign,” Iatan stressed.

“People considering going on LCHF should be aware that doing so could lead to an increase in their LDL-C levels. Before starting this dietary pattern, they should consult a healthcare provider,” Iatan said. “While on the diet, [they should] have their cholesterol levels monitored and try to address other risk factors for heart disease or stroke, such as diabetes, hypertension, physical inactivity, and smoking.”

“What is important to remember is that each patient responds differently, so there is interindividual variability between responses,” she continued. While LDL-C could account for the increased CV risk, other studies are needed to confirm this and to determine other potential mechanisms at play.

“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,” she said.