By Katrina Woznicki,
Published: July 27, 2005
Reviewed by Robert Jasmer, MD; Assistant Professor of Medicine, University of California, San Francisco
SEATTLE, July 27-It seems that it may be the high-protein--the byproduct of a low-carb diet--that is key to promoting weight loss by boosting satiety, researchers here reported.
Action Points
* Inform patients that diets high in protein may lead to moderate weight loss by boosting satiety.
* Discuss with patients that the key to potential weight loss is to consume a balanced diet of protein, carbohydrates, and fat rather than eliminating any main food group.
Cutting carbs may not even be necessary, said David S. Weigle, M.D., a professor or medicine at the University of Washington School of Medicine here and colleagues. The idea is to boost protein intake.
Comparing different diets, all with the same percentage of carbohydrates, the researchers found that satiety was significantly higher when daily intake was almost one-third protein. The participants even lost weight on a diet of 30% protein, 20% fat, and 50% carbohydrates, according to the study in the July American Journal of Clinical Nutrition.
For two weeks, 19 healthy individuals were placed on a weight-maintaining 2,000-calorie diet that consisted of 15% protein, 35% fat, and 50% carbohydrates.
Then for the next two weeks in another 2,000-calorie diet, protein was doubled, replacing some of the fat. The participants ate a high-protein diet, consisting of 30% protein, 20% fat, and 50% carbohydrates.
Finally, these diets were followed by 12 weeks of a diet in which they were allowed to eat as many calories as they wanted, but had to consume the same percentages of protein (30%), fat (20%), and carbohydrates (50%) as in the high-protein diet.
The study excluded individuals with a body mass index of 30 or higher, those who did aerobic exercise for more than 30 minutes three times a week, and those who used tobacco, alcohol, or had diabetes or any other medical condition.
During the study, all participants kept a daily diet diary and were asked to rank their responses to the questions "How hungry have you felt between meals today?" and "How full have you felt after eating meals today?"
In addition to the food logs, the investigators collected blood samples at the end of each diet to measure any changes in insulin, leptin, and ghrelin levels.
Satiety was greatest during the two weeks on the high-protein diet despite no significant change in leptin levels at this point, the researchers reported.
"The subjects reported a clear decrease in hunger and an increase in fullness during weeks three and four after the transition to the isocaloric high-protein diet," Dr. Weigle and colleagues reported. This rise in satiety was confirmed by a drop in spontaneous caloric intake of 494 ± 74 kcal/d within 24 hours of starting the 12-week high-protein ad libitum diet, they wrote.
Even during this phase, during which participants ate as many calories as they wanted while maintaining the 30% protein intake, they took in an average of 450 fewer calories per day and lost almost five kilograms (about 11 pounds) overall.
During the ad libitum phase, the researcher found hormonal changes: Leptin levels decreased, and ghrelin levels increased. Fat mass declined by 3.7± 0.4 kg.
How the high-protein ad libitum diet produced these effects is unclear, the researchers said. But it appears protein plays a role.
Doubling dietary protein while keeping carbohydrates a constant "produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin and results in significant weight loss," they wrote.
The results, they said, "suggest substituting protein for fat in the diet may lead to greater weight loss than can be obtained by substituting carbohydrate for dietary fat."
In an accompanying editorial, Arne Astrup, M.D., of the Royal Veterinary and Agricultural University in Copenhagen, agreed that the study showed protein is more satiating than fat and carbohydrates. Yet he, too, said scientists do not know how protein increases satiety.
The study found "that the effect could not be explained by changes in the hunger hormone ghrelin or in the satiety hormone leptin," Dr. Astrup wrote.
High protein recommendations are centerpieces of fad diets like the Atkins Diet, The Zone, and The South Beach Diet, and there is some evidence showing these approaches have led to moderate weight loss, Dr. Astrup said.
"Should we advise the public to increase their intakes of meat and dairy products?" he asked. "The answer depends on the potential adverse effects of a high-protein diet."
Primary source: American Journal of Clinical Nutrition
Source reference:
Weigle et al, "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," AJCN, July 2005; 82; p. 41-48.
Another great article from a couple years ago, but the information does not change!
A.J. McAlendin
