In the May issue of Annals of Internal Medicine, two studies compared low-carb to low-fat diets. In both studies, participants on the low-carb diet lost weight but also improved their triglyceride levels and HDL (good cholesterol).
Low-carb diets are hugely popular. According to this month's Time cover story, sales from low-carb related products are expected to hit $30 billion this year. A recent poll estimates that 26 million Americans are on a strict low-carb diet and 70 million consciously restrict carbohydrate intake. However, the fad took off without supporting scientific research. This is what has compelled two different institutions to conduct long-term (12 months) studies on the effects of low-carb diets on health and weight loss.
The Early Show medical correspondent Dr. Emily Senay says in the study conducted by the Philadelphia Veterans Affairs Medical Center, 132 severely overweight adults were selected for the trial. The researchers assigned patients to either a low-carb diet or a conventional low-fat weight loss diet. They instructed the low-carb group to eat no more than 30 grams of carbs per day. The conventional diet group received instructions to decease calorie intake by 500 calories per day and have less than 30 percent of total calories from fat. The researchers collected information about weight at the start of the diet, after 6 months, and after 1 year.
The second study conducted by Duke University and sponsored by the Robert C. Atkins foundation (the study authors have no financial interest in Atkins Nutritionals, Inc.) assigned 120 relatively healthy, mildly to moderately obese people to two randomly assigned groups: either low-carb or low-fat. Both were given diet instructions and exercise recommendations. Twice a month, the participants attended group meetings, in which they received additional dietary instructions and psychological support, while the researchers collected measurements of their physical condition. All participants bought and prepared their own food according to the instructions they had received.
The low-carb diet group also received vitamins and nutritional supplements. The low-fat diet group was instructed to eat 500 to 1,000 calories less than they needed to maintain their usual weight. The researchers measured each person's weight; they also determined how closely each person had followed the diet. Because low-carb diet changes chemicals in the urine, urine was tested to assess adherence to the diet. In addition, levels of fat in the blood were periodically measured.
In both studies, low-carb dieters lost weight and had better blood triglyceride and high-density lipoprotein (HDL or "good" fat) levels than the low-fat dieters.
In one study two low-carb dieters dropped out because of increases in their "LDL" low-density lipoprotein level. The low-carb group also reported more adverse side effects, like, constipation, bad breath, headaches, muscle cramps, diarrhea, rash, weakness -- unlike the low-fat group.