We have heard it time and time again. High-fat diets cause heart disease. Sure, they improve metabolic syndrome, insulin resistance and diabetes… they lower blood pressure and improve weight loss. But they might cause heart disease, so we shouldn’t recommend them.
Sometimes this sort of “logic” makes me ashamed to call myself a doctor.
Fortunately that debate is actively changing.
I was optimistic that a recent study on coronary artery calcification (CAC) and low-carb diets was going to speed up that change. Unfortunately, that doesn’t seem to be the case.
The study was just published in The British Journal of Nutrition and is the first to investigate whether or not low-carb diets are associated with the progression of cardiovascular disease as measured by CAC score. A CAC score is a simple, non-invasive test using a CT scan. It takes about 10 seconds, has a low level of radiation (about the same as a mammogram) and tells us if there is any calcium in the walls of the arteries in and around your heart. Although it does not tell us if you have blockages inside your arteries, it is an excellent marker of the presence of coronary artery disease and a very good predictor for risk of heart attacks in the next 10 years.
This was a prospective, observational study (a weak level of evidence based on Diet Doctor’s policy for grading scientific evidence) where they enrolled over 5,000 individuals, average age 63, and followed them with a baseline CAC and a repeat study 2.4 years later. They collected data about fat and carbohydrate consumption and in the end, they found no difference between the various levels of carbohydrate or fat intake in terms of development or progression of CAC.
While on the surface this seems like it should exonerate low-carb diets of any cardiovascular concern. Unfortunately, this wasn’t the study to set the record straight.
For starters, they relied upon food frequency questionnaires, the same unreliable method that many nutritional epidemiology studies use.
Secondly, the results are muddied by the same confounding variables and healthy-user biases from which all epidemiological studies suffer.
Thirdly, the lowest carbohydrate cohort ate less than 43% of their calories from carbohydrates and more than 40% from fat, and the highest carbohydrate group ate more than 65% from carbohydrates and less than 22% fat. Those percentages don’t truly represent those following a very low-carb, ketogenic diet or even a moderately low-carb diet (less than 100 grams of carbs per day).
Finally, 2.4 years is too short of a follow-up period to realistically reach conclusions about coronary disease progression based on CAC.
Although this may be an encouraging start, higher-quality, longer-term studies that investigate the effects of a well-formulated ketogenic diet are needed to ultimately answer this question. In the meantime, the best evidence we have on the safety of a low-carb diet is its effect on surrogate markers such as blood pressure, insulin resistance, metabolic syndrome, HDL and triglyceride levels, size of LDL particles and others.
For me, that’s good enough to keep recommending low carb to most of my patients.
Thanks for reading,
Bret Scher MD FACC