Protein's satiating power puts a new spin on weight management

Research conducted at the University of Washington and the Oregon Health and Science University sheds new light on the optimal ratio for macronutrient distribution in a weight-reducing or weight-maintaining diet. It is seemingly paradoxical that both lowfat diets and low-carbohydrate diets, high in fat and protein, have resulted in decreased ad libitum caloric intake as well as significant weight loss. The conclusion has been that diets with fat contents at both intake extremes have shown beneficial results. The goal of the study was to determine if increased protein intake, while maintaining carbohydrate intake, could be the source of the benefits attributed to the popular low-carbohydrate diets.

Nineteen subjects were sequentially assigned to the following diet regimens:

• 2 weeks of a weight-maintenance diet - energy distribution of 15% protein, 35% fat, and 50% carbohydrate

• 2 weeks of an isocaloric diet - energy distribution of 30% protein, 20% fat, and 50% carbohydrate

• 12 weeks of an ad libitum diet - energy distribution of 30% protein, 20% fat, and 50% carbohydrate

The researches found that the increase in dietary protein, without change in dietary carbohydrate intake, resulted in rapid weight loss and decreased body fat. The ability of dietary protein to increase energy expenditure was examined as a potential cause for this effect, but the researchers determined that the overall weight loss during the ad libitum regimen was fully explained by the cumulative effect of reduced caloric intake. After transitioning to the isocaloric higher-protein diet, subjects reported an increased sensation of fullness and a decrease in hunger. Within 24 hours of starting the ad libitum diet, subjects confirmed the increase in satiety by spontaneously reducing their caloric intake by 494 +/- 74kcal/day. As subjects continued to self-regulate energy intake throughout the 12-week regimen, they sustained the caloric intake decrease at 441 +/- 63 kcal/day which resulted in a constant rate of weight loss.

The researchers concluded that a 15% increase in dietary protein, with a constant carbohydrate intake, can result in clinically significant weight loss.  This protein effect may help to explain the weight loss observed in low-carbohydrate diets because the increased protein offsets the higher fat content of such diets.  By providing increased satiation and weight loss benefits, while minimizing the higher fat consequences, a high-protein diet, with constant carbohydrate intake, may be an effective weight management tool.

Citation:
A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations.  Weigle DS, Breen PA, Matthys CC, Callahan HS, Meeuws KE, Burden BR, Purnell JQ. American Journal of Clinical Nutrition:2005;82(1):41-48.

To read the abstract, go to A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in kiurnal plasma leptin and ghrelin concentrations.

An accompanying editorial "The satiating power of protein - a key to obesity prevention" by Arne Astrup in the July issue of the American Journal of Clinical Nutrition discusses the challenges facing modern society in confronting the obesity crisis.  Providing effective tools for weight management is complicated because our regulatory systems have evolved to prevent energy depletion.  The author supports the current focus of nutrition science to increase the satiating power of the diet.  The remaining unanswered question regarding the benefits of the higher protein diets is concern for possible long-term ill effects.  The Institute of Medicine concluded that there is no confirmatory evidence that a high-protein diet increases the risk of renal stones, osteoporosis, cancer, or cardiovascular disease and set a range for optimal protein intake at 10% to 35% of calories for adults.  The European Union has just funded a large multicenter trial of high- compared with low-protein diets and of high- compared with low-glycemic-index diets in overweight and obese families.  This study should provide the needed information for a more complete evaluation of these diets.  The author suggests that perhaps the time has come "to consider the economic and environmental consequences of increasing the population's intake of protein from fish, meat, and vegetables and how this increase can be incorporated into the local cuisine."

To read the editorial, go to "The satiating power of protein - a key to obesity prevention."

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