Many research papers investigate macronutrient ratios and their effects on various physiological parameters. However, there is a tendency to oversimplify the categories and treat protein, fat and carbohydrate as single uniform macronutrients. This oversimplification does disservice to the science of nutrition because within each single category are a plethora or structurally different compounds that can have quite different effects on physiology and metabolism. For example, whey protein offers some unique properties that make it of interest, particularly its cost, effects on insulin and convenience as a powdered supplement. However, other proteins offer other benefits and can have wide ranging metabolic and physiological effects. In particular, protein can influence the glycaemic effects of a meal and the satiety of the individual. These are important because evidence is accumulating that protein is beneficial in weight loss, and this benefit might be related to these effects.
For example, researchers1 have investigated the metabolic and physiological effects of whey, casein and soy protein in 23 lean healthy subjects. In particular, the researchers were interested in the effects of protein on energy metabolism, satiety and glucose control following consumption of an isocaloric test meal. The test meals were administered in a randomised, double-blind, crossover design with three of the meals containing 50% protein (whey, soy or casein), 40% carbohydrate and 10% fat, and one of the meals containing 95.5% carbohydrate as a control. The thermic effect of whey, casein and soy were 7.7, 5.4 and 4.9% higher than the carbohydrate meal, respectively. As has been reported previously, the glycaemic response to glucose was attenuated 32% by addition of protein to the meal. Whey protein produced a greater insulin response compared to the glucose control, with casein and soy producing the smallest insulin response.
These results suggest that protein is able to alter metabolism in the postabsorptive state, and this is further influenced by the type of protein that is ingested. Protein has shown benefits in weight loss because of its ability to increase satiety, and the results of this research support this view. Both casein and soy produced increase satiety compared to whey, but subjects reported preferring the taste of the whey protein. The ability of protein to reduce the rise in blood sugar (glycaemic response) following a test meal is due to the delayed gastric emptying caused by the presence of amino acids and proteins in the stomach. In addition, whey protein can further lower the glycaemic response by causing an increased release of insulin. The thermic effects of proteins, coupled with their satiety inducing effects and control of blood sugar levels explains their effects in benefiting weight loss.
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