It seems that the jury is out on protein increasing satiety, especially if taken early in the morning. The results of several studies on the timing of protein consumption are being claim that consuming approximately 25% of the total breakfast calories from protein compared with 15% results in greater feelings of fullness, a feeling which can last up to 4 hours (or right around lunchtime). Participants in the study consumed calorically equal diets with treatment variations in fat and protein while calories from carbohydrates were kept constant at 55% of total dietary calories. Wayne Cambell, PhD, lead researcher and Professor of Food and Nutrition at Purdue University stated, “There is a growing body of research which supports eating high-quality protein foods when dieting to maintain a sense of fullness.” In a study at Purdue University overweight or obese men were put on calorically equivalent reduced calorie diets. One diet consisted of 11-14% of calories from protein while the other contained 18-25% of calories from protein. The experimental groups were further subdivided according to whether the higher protein meals were added at breakfast, lunch, or dinner. The feeling of satiety was highest and most sustained when breakfast contained the higher percentage of protein. “This study is particularly unique in that it looked at the timing of protein intake and reveals that the timing of protein consumption may be a critical piece of the equation,” according to Dr. Cambell.

Careful interpretation of these data should be employed as this does not necessarily mean that substituting fat with more protein facilitates weight loss. In fact, a study at the Maastricht University, Netherlands reported that “In conclusion, a breakfast with 25% of energy from casein is rated as being more satiating than a breakfast with 10% of energy from casein at 3 and 4 hours after breakfast, coinciding with prolonged elevated concentrations of plasma amino acids, but does not reduce subsequent energy intake.” Proponents of the “calories in vs. calories out” theory will likely argue that this finding will have limited, if any, implications for weight loss. As a matter of fact, one should be careful when adding protein to the diet beyond 2.0g per kg of bodyweight as this may lead to hepatotoxicity and stress the renal system as well, possibly leading to severe medical complications if chronically applied. The recommendation for protein intake for most adults should be between 1.2-1.4 grams per kg of bodyweight. It should be noted that one study examined an overweight/obese sample on a reduced calorie diet while the other study’s sample consisted of individuals with average BMI consuming a normal calorie diet. Overweight and obese individuals have different levels of “satiety” markers (leptin, ghrelin, orexins, etc) when compared with average individuals and the interactions of these biochemicals with higher amino acid concentrations and/or lower fatty acid concentrations will likely be affected. Also, the fact that these individuals were on a reduced calorie diet should be taken into account when interpreting study findings. Finally, satiety is not the only factor that plays a role in weight loss and weight gain. However, this may be a tool worth utilizing or at the very least warrants further investigating.