vidence suggests that high protein diets are beneficial for weight loss. A number of intervention studies have assessed different types of high protein diets and generally the result show that they cause weight loss when compared to high carbohydrate alternatives. Protein may aid weight loss because the presence of undigested protein in the stomach is the rate limiting step in the release of food to the duodenum, and this is thought to decrease nutrient absorption rates and favourably modulate insulin release. However, some evidence also suggests that protein may also suppress the release of ghrelin, a gut hormone that plays a key role in upregulating appetite. Protein may therefore decrease appetite undependably from its ability to regulate insulin. However, liquid whey protein is highly insulinogenic and more quickly digested than solid protein, and so the appetite regulator ability of whey protein is more controversial.
For example, one group of researchers1 compared the appetite responses to glucose, fructose and whey protein in obese men. Drinks of 50 grams whey protein, 25 grams whey and 25 grams fructose, 50 grams fructose or 50 grams glucose where administered to the subjects and then the plasma concentrations of gut hormones measured. The whey protein produced a significantly lower response for ghrelin, suggesting that whey, like other proteins, is able to regulate gut hormone involved in appetite. However, when the subjects were allowed access to ad libitum amounts of food 4 hours later, there was no difference in the energy consumed by the glucose, fructose or whey protein groups. Interestingly, addition of fructose to the whey protein (50 / 50 mix) ameliorated the inhibition of ghrelin. Therefore increased protein intake in the presence of fructose may not be beneficial to appetite regulation.