The Low-Carb / Low-Fat Debate and Heart Health

Thursday, September 6, 2007 - 2:12pm

By Donna Feldman, MS, RD

The ongoing debate about low-carb versus low-fat diets for weight loss sometimes seems like religious strife. Both sides are convinced that the other is completely wrong. One of the main attack points from the low-fat camp is that low-carb/high-fat diets increase heart disease risk because, obviously, they are higher in fat. The American Heart Association's most liberal diet limits dietary fat to 30% of calories, while low-carb diets can include more than 50% fat. This is a significant difference, and potentially a reason to be concerned about heart disease risk factors.

Is heart disease linked to high-fat diets?

Thanks to the ongoing controversy, researchers have tackled the question of whether heart disease risk is linked to high-fat diets. The Nurses Health Study at Harvard has 20 years of data on diet and health for thousands of women. Analysis of data on lower- carbohydrate/higher-fat diets indicated that risk of heart disease was not elevated compared to lower-fat diets. The diet type that did increase risk was one with high glycemic load, which means higher sugar and refined carbohydrates and lower fiber. The diet that helped lower risk was one that emphasized vegetable sources of fat and protein-in other words, a more vegetarian diet.1

Other low-fat/low-carb studies

Intervention studies, where subjects are fed experimental diets and tested for cardiac risk factors, provide insight. While low-fat diets positively affect some of the parameters, like LDL cholesterol, they do not improve others, like triglyceride levels. Low-carb diets, by contrast, improved risk factors for metabolic syndrome, like glucose and triglycerides.2

One thing to keep in mind, though, is that study diets were reduced in calories, meaning the subjects were losing weight. Weight loss alone can improve heart disease risk factors, regardless of type of diet.

Should you change to a low-fat or low-carb diet?

For short-term weight loss, a low-carb diet is not likely to exacerbate your heart disease risk. If you are overweight, and you successfully lose weight, your risk factors are likely to improve. The important point many people forget is that "low-carb" does not mean license to gorge on fatty meats and cheese. Even the Atkins diet recommends a certain amount of vegetables. Most people find that a strict low-carb diet is hard to follow for too long, and they add more carbohydrate foods. Make sure the carbs you add are vegetables, fruits, and whole grains, rather than sweets, snack foods, and soft drinks.

Likewise, a "low-fat" diet should not be high sugar, since this can aggravate coronary risk factors. Unfortunately, it is easy to eat an unhealthy low-fat diet if you don't focus on vegetables, fruits and whole grains. It's probably easier to stick to a low-fat diet in the long run, so make it heart healthy by avoiding excess sugar and choosing lean meats and lowfat dairy products.

Conclusion: the effect of long-term use of a low-carb diet is still unknown

Research shows that short-term use of a low-carb weight loss diet does not increase heart disease risk, despite the higher fat content. Some risk factors even improve, although those improvements might be caused by the weight loss itself rather than the type of diet. The effect of long-term use of this type of diet is not known. Most health professionals do not recommend sticking to a low-carb diet for a long period of time.

  1. N Engl J Med. 2006 Nov 9;355(19):1991-2002.
  2. J Nutr. 2004 Apr;134(4):880-5. J Am Coll Nutr. 2004 Apr;23(2):177-84.