A high-carbohydrate, low-glycemic index diet both decreases fat mass and maximizes cardiovascular risk reduction, compared with three other weight-loss diets, reported Joanna McMillan-Price of the University of Sydney (Australia) and her associates.
A low-fat, high-carbohydrate diet is still considered the “best practice” among physicians. In contrast, high-protein and low-glycemic index diets have caught on with the public, but “clinicians and health professionals remain skeptical, calling for greater scientific evidence on which to base” their advice to patients who want to lose weight, the researchers said.
They conducted a 12-week, randomized, controlled trial of four weight-loss diets that all aimed for the same fat content (30% of total energy intake), the same moderate fiber content (30 g/day), and the same daily caloric goals (1,400 kcal for women and 1,900 kcal for men). The carbohydrate and protein contents of the four eating plans varied. The participants comprised 129 overweight young adults. The 98 women and 31 men were aged 18–40 years and had a body mass index (kg/m
Diet 1 was a conventional weight-loss eating plan: a high-carbohydrate (55% of energy intake) and average protein (15% of energy intake) diet that relied on high-glycemic index whole grains, such as fiber-rich breakfast cereals and breads. Diet 2 was a high-carbohydrate but low-glycemic index eating plan, which had the same proportions of protein and carbohydrates but relied on low- instead of high-glycemic index carbohydrates.
Diet 3 was a high-protein (25% of energy intake), low-carbohydrate (45% of energy intake) eating plan that relied on lean red meats and high-glycemic index whole grains. Diet 4 had the same proportions of protein and carbohydrates but relied on low- rather than high-glycemic index carbohydrates.
All four diets reduced weight by 4%–6%, and all reduced fat mass and waist circumference. Weight loss of 5% or more occurred in 31% of subjects on diet 1, in 56% on diet 2, in 66% on diet 3, and in 33% on diet 4.
All four groups reduced fat intake, but the high-carbohydrate groups ate the most fiber and consumed less fat overall, less saturated and polyunsaturated fats, and less cholesterol than did the high-protein groups. Thus, diet 2 produced “the best clinical outcomes, reducing both fat mass and LDL-cholesterol levels,” Ms. McMillan-Price and her associates said (Arch. Intern. Med. 2006;166:1466–75).
“Our findings suggest that dietary glycemic load, not just overall energy intake, influences weight loss and postprandial glycemia. … Diets based on low-glycemic index whole-grain products (in lieu of whole grains with a high glycemic index) maximize cardiovascular risk reduction” as well as weight loss.
In an accompanying editorial, Dr. Simin Liu of the department of epidemiology at University of California, Los Angeles, said that physicians should encourage patients' use of “glycemic index” and “glycemic load” concepts along with caloric count and nutrient composition, because these designations are superior to the “simple” or “complex” carbohydrate classifications in predicting glucose and insulin responses.
“We need to teach our patients to identify low-glycemic index foods within different food groups. Typically, foods with a low degree of starch gelatinization, such as pasta, and those containing a high level of viscous soluble fiber, such as whole grain barley, oats, and rye, have slower rates of digestion and lower glycemic index values,” Dr. Liu noted (Arch. Intern. Med. 2006;166:1438–9).
“Without any drastic change in regular dietary habits, for example, one can simply replace high-glycemic index grains with low-glycemic index grains, and starchy vegetables with less starchy ones, and cut down on soft drinks that are often poor in nutrients yet high in glycemic load,” Dr. Liu added.