Genetics May Decide Whether a Low-Carb Diet Sends Your Cholesterol Soaring

New research presented at NUTRITION 2026, the flagship annual meeting of the American Society for Nutrition, suggests that genetics may help explain why low-carb diets raise low-density lipoprotein (LDL) cholesterol, the "bad" cholesterol linked to heart disease, in some people but not others. The findings, presented by Alexa Barad, a postdoctoral scholar at Stanford University School of Medicine, have not yet been peer-reviewed and should be considered preliminary.

The analysis drew on DIETFITS, a randomized controlled trial in which more than 600 adults followed either a healthy low-carb or a healthy low-fat diet for a year; the original trial found no significant weight-loss advantage for either diet. For the new study, researchers examined 431 of those participants for whom genetic data were available, looking at how genotype, saturated fat intake, diet type and changes in LDL cholesterol from baseline to six months were related.

Among participants on the low-carb diet, those with a greater genetic predisposition to higher LDL cholesterol were more likely to see it rise, and this pattern was strongest in those who also ate more saturated fat. The same relationship did not appear among people on the low-fat diet. Rather than looking at single genes, the researchers combined thousands of genetic variants into a "polygenic score" to estimate each person's overall tendency toward higher or lower LDL cholesterol.

Barad said genetic testing is not required to draw a practical lesson: people can respond very differently to the same dietary change, so monitoring individual cholesterol matters more than assuming one diet works the same for everyone. Current guidance recommends keeping saturated fat below 10% of daily calories; for those on a low-carb diet, Barad suggested favouring nuts, seeds, olive oil and avocado over butter, beef tallow, fatty cuts of meat and processed meats.