What does a low-carbohydrate diet do to your LDL cholesterol in the long term?

A ketogenic diet noticeably raises LDL cholesterol in the short term. In a randomised trial (n=33), LDL rose by an average of 10% after 12 weeks of ketogenic eating, while the Mediterranean diet actually lowered it by 5%. In people with diabetes, another study found an additional rise of more than 0.37 mmol/L after six months compared with a high-carbohydrate diet.

After one to two years, however, that difference largely disappears. A Cochrane analysis of 61 randomised studies (nearly 7,000 participants) found little to no long-term difference in LDL between low-carbohydrate and balanced-carbohydrate diets, both in people with and without diabetes. This aligns well with the diabetes study, in which the LDL effect was no longer demonstrable after nine months.

There is an important nuance: not every low-carbohydrate diet works the same way. A strongly calorie-restricted ketogenic diet actually showed a decrease in LDL, but that decrease was no greater than with other diets with the same calorie deficit. It is therefore plausible that weight loss itself, rather than the elimination of carbohydrates, is responsible for this.

Beneficial for the heart, however, are the effects on triglycerides (fats in the blood) and HDL, the so-called 'good' cholesterol. Ketogenic and low-carbohydrate diets consistently lower triglycerides and raise HDL, which is considered favourable for cardiovascular risk.

Some authors argue that high LDL on a low-carbohydrate diet is not necessarily dangerous, provided triglycerides are low and HDL is high. That is a plausible argument, but it runs counter to current guidelines and has not been tested in clinical outcome studies. If you have significantly elevated LDL in combination with other risk factors, always discuss this with your doctor.