Protein is often touted as the key to healthy weight loss. But a talking point repeated by protein promoters—that the nutrient fills you up—has remained up for scientific debate.
The authors of the meta-analysis wanted to focus on one specific question: what effect does protein have on fullness? They sifted through thousands of studies and settled on five strong ones to analyze. Each study that made it into the final analysis used a similar experimental design, where people came into the lab after fasting and were given food with protein, then monitored for how full they felt over a period of time.
“Our paper did show that indeed, higher protein intake led to greater sensations of fullness,” says study co-author Richard Mattes, distinguished professor of nutrition science at Purdue University. To confirm that finding, the authors broadened their scope by including 28 papers in a secondary analysis and they came to the same conclusion.
Mattes points out that more rigorous research is needed, since a set of five studies, however carefully chosen, may not reflect the totality of scientific literature. There are also many other questions about protein that need to be investigated, like whether vegetable protein has the same effect as animal protein or whether protein delivered in a shake is less satisfying than the kind you eat.