The Diet Wars: Low Carb or Low Fat?

Woman looking at food labels

If you want to lose weight and improve your heart health, a recent study concludes that limiting carbohydrates works better than limiting fat intake.

The study, published in the Annals of Internal Medicine, examined the effects of the two diets on weight loss, lean body mass, and heart-disease risk factors such as cholesterol, and inflammatory markers.

Here's What the Study Found

Low-carb dieters:

  • Lost 8 more pounds than the low-fat group.
  • Lost “fat weight,” not the lean muscle mass seen with the low-fat group.
  • Had increases in HDL (good cholesterol) and decreases in triglycerides (another important fat that affects heart-disease risk).
  • Had decreases in two important markers of long-term cardiovascular risk—C-reactive protein and the 10-year Framingham score (how likely you are to have a heart attack in the next 10 years).
  • Saw not much change in LDL (bad cholesterol) in either group, although it would have been expected in the low-fat group.

The low-carb dieters (eating mostly protein, unsaturated fats, olive oil, and nuts) were instructed to limit their carbs to less than 40 grams a day; the low-fat group (eating more grains, cereals, and starches), to less than 30 percent of their daily calories from fat and less than 7 percent from saturated fats. There was no restriction on calories.

While the beneficial effects seen in this study, funded by National Institutes of Health, can definitely improve your overall cardiovascular risk, a closer look might help us assess the potential benefits more clearly.

Study size. It was a small study with only 148 obese men and women who were followed for one year. Usually, studies to assess benefits to the general population have hundreds or thousands of participants and a fairly equal gender and ethnic distribution.

Fat intake. Even though the low-carb group could eat more fat, they were instructed to increase the monounsaturated fats and unsaturated fats (healthier fats) and limit or eliminate trans fats. They did increase saturated fats to more than twice the limit recommended by the American Heart Association but the majority of the fat intake was the healthier unsaturated fat.

Cardiovascular profile. None of the participants had known heart disease, heart attacks, strokes, or had undergone leg circulation or heart bypass surgeries. There is ample data showing that limiting fats, particularly saturated fats, trans fats, and cholesterol can decrease the risk of further events and procedures. And so, people who have had heart disease or undergone the procedures noted should be careful in limiting saturated fats even further.

What we can all take away from the study is that significant weight loss is possible by decreasing your carbohydrate intake and using primarily unsaturated or monounsaturated fats—and that the benefits extend to your cardiovascular health.

Lifestyle change: Finally, it’s important to remember that the low-carb diet should actually be a lifestyle change and not only a way to lose weight. Talk to your doctor about this and other important lifestyle factors which should include a daily walking or aerobic exercise program, discontinuation of smoking, and taking care of your high blood pressure and diabetes.

author name

Joseluis Ibarra, MD

Joseluis Ibarra, MD, FACC, is a cardiologist with The Heart Group of Lancaster General Health.

Education: Dr. Ibarra earned his medical degree at Southwestern Medical School of the University of Texas and he performed his internship and residency at the University of Pittsburgh's Presbyterian Hospital.

Call: 717-544-8300

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