A new study looked at why some people see their 'bad' cholesterol rise when following low-carbohydrate or keto diets. The study followed 431 adults who ate either a healthy low-carb or a healthy low-fat diet. Researchers found that people with genes linked to high LDL cholesterol were more likely to have a bigger increase in LDL, or 'bad', cholesterol if they ate more saturated fat on a low-carb diet.

The main cause is genetics. Some people have genes that make them react more strongly to saturated fat, which is found in foods like butter and fatty meat. When these people eat fewer carbohydrates and more fatty foods, their cholesterol can rise much more than others.

Because of this, experts say people who choose low-carb or keto diets should carefully watch their cholesterol levels. Choosing foods with unsaturated fat, such as olive oil, nuts, and avocado, may be a safer way to follow a low-carb diet for people worried about high cholesterol.