Studies reveal a satiating effect both from one meal to the next, and over the course of a day. “Research by Dhurandar and Campbell has shown that high-protein foods such as eggs and lean ham eaten at breakfast influence calorie intake throughout the day, providing a feeling of satisfaction from hunger,” says Greenblum. A 2005 study published in the
Journal of the American College of Nutrition (24(6):510-515) followed 30 overweight and obese women who consumed either a bagel or an egg breakfast and found that participants reported greater satiety during the pre-lunch period after the egg breakfast and consumed significantly less energy for lunch. What’s more, she notes, “energy intake following the egg breakfast remained lower for the entire day, as well as for the next 36 hours.”
Pikosky adds that “in addition to meal-by-meal effects of protein on satiety, studies have shown higher-protein diets also to have a satiety effect.” A review published in the May 23, 2008, Physiology & Behavior (94(2):300-307) found the satiety effects of high-protein ad libitum diets lasted from one to six days, and up to six months. “In terms of the total diet, studies using approximately 30% of total calories from protein have been shown to be beneficial in promoting satiety and, in the ad libitum situation, a reduction in energy intake,” he says.
Raging hormones
Protein’s slower rate of digestion and its ability to pace food’s passage through the gut may be at work here—as, too, may be its lower glycemic index and glycemic load. But, what’s really caught researchers’ attention is the relationship between proteins and intestinal hormones. As Pikosky says, while “the specific mechanisms contributing to protein’s impact on satiety are yet to be determined, it has been hypothesized that one of the mechanisms is changes in certain ‘satiety hormones,’ whether they be appetite-stimulating hormones such as ghrelin, or appetite-suppressing hormones such as glucagon-like peptide-1, cholecystokinin, or PYY.”
Bargetzi points to whey, as well as some of its peptide fractions, as generating just such effects. She singles out one fraction, glycomacropeptide (GMP), for potentially suppressing appetite by stimulating cholecystokinin. However, she cautions, “the GMP levels in whey protein can be influenced by how the whey protein is manufactured.” What she describes as the “special cross-flow filtration process” and “patented fractionation process” that her company uses to manufacture and isolate its whey protein isolates gives them “some enhancements in bioactive fraction, including a high level of GMP,” she says.