Based on the findings, the researchers advise consuming mostly what's known as low-glycemic index carbohydrates, such as whole-grain breads. The glycemic index (GI) is a measure of the ability of carbohydrates to increase blood glucose levels; those with a low GI cause blood levels to increase more slowly, explained Dr Thomas Meinert Larsen, a co-author of the study, published in the New England Journal of Medicine.
What is it about the high-protein, low-glycemic index carbohydrate diet that keeps weight under control? "Possibly a stronger satiating effect and more balanced blood sugar regulation," Larsen hypothesised.
With his colleagues, Larsen evaluated 938 adults with an average body-mass index (BMI) of 34, which is considered obese. In all, 773 completed the initial weight-loss phase and then were assigned to one of five different maintenance plans:
- Low-protein diet, (13% of energy) with a high GI
- Low protein, low GI diet
- High protein (25% of energy), low GI diet
- High protein, high GI diet
- Control group, which got no special instructions
During the weight-loss period of eight weeks, participants lost an average of 11kg. All five maintenance diets had a moderate fat content, about 25% to 30% of total calories. After six months, Larsen's team found that the 548 who completed the programme had an average weight regain of 500g.
Low protein diets no good
Those in the low-protein/high-GI group showed the worst results, the researchers found, with a weight gain averaging 2kg. Those on the low-GI diet had an average weight regain of 900g less than those on the high-GI diet.
"Thus, we have ourselves been quite hesitant to advocate the use of glycemic index," Larsen said. "But our new data, based on the largest randomised study on this topic ever, shows that, indeed, GI is of importance."
So what is a typical high-protein, low-GI diet? According to Larsen:
- Breakfast of natural, unflavoured yogurt low in fat and fairly high in protein, with muesli, whole-grain crisp bread with low-fat cheese and an orange.
- Vegetable sticks and low-fat cheese sticks for a snack.
- Lunch of whole-grain rye bread with lean meat or chicken cold cuts, mackerel in tomato sauce and vegetables
- Whole-grain rye bread with low-fat liver pate and cucumber for a snack.
- Dinner of stir-fried turkey with vegetable and whole-grain pasta; avocado salad with feta cheese and sugar peas.
"These newer approaches may be more effective than conventional approaches in weight maintenance," said Dr David Ludwig, director of the Optimal Weight for Life Program at Children's Hospital in Boston, who wrote an editorial to accompany the study.
Low-GI really works
"There has been considerable controversy over the role of glycemic index in general, and obesity treatment in particular," he said. "This study provides very strong, supportive evidence for the importance of this low-glycemic concept."
It's not difficult, he said, to shift from high-glycemic foods to low-glycemic foods. "It's shifting to somewhat less processed carbohydrates and, importantly, not making the carbohydrate the only thing you are having at the meal."
As for boosting protein, he said, "we're not talking about a 450g slab of prime rib" or the very high levels of protein popularised in some low-carb diets.
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