Thursday, January 13, 2011

Which protein is best for appetite control? by Jerry Brainum

For purposes of bodyfat loss, most studies show that low carbohydrate diets provide the most rapid effects. While some critics of low carb diets have said that the initial weight loss seen during low carb diet plans consists of mostly water, more sophisticated body composition tests have shown that on a calorie for calorie basis, low carb diets do promote a greater loss of bodyfat compared to low fat, high carb diets. One reason often stated for the superiority of low carb diets is that such diets modulate insulin release. Insulin is a storage hormone, and has potent effects on promoting bodyfat synthesis, particularly when excess caloric intake is consumed. Since carbs promote the greatest release of insulin, controlling insulin release by consuming less carbs should promote more effective fat loss. But low carb intake is only part of the reason why low carb diets appear to be so effective. Such diets also feature a higher protein intake. This increased protein consumption not only serves to protect vital lean tissue mass, but also provides an increased satiety effect. In other words, it helps to control appetite so you don't overeat.Protein also provides a thermogenic effect, fostering the conversion of fat calories into heat. But which protein sources are best for this purpose?
   This was the focus of a recent study that featured 23 lean, healthy subjects. They consumed four meals, all containing the same amount of calories, but differing in the protein source. The meals consisted of 50% protein, 40% carbohydrate, and 10% fat. The protein sources varied with each meal, with the sources being whey, casein from milk, and soy. A fourth meal used as a control consisted of 95.5% carbohydrate. The results showed that the whey meal provided the greatest thermic effect followed by casein and soy. Fat oxidation after the meal was highest in the whey meal, followed by soy, and was higher in the protein meals compared with the high carb meal. The high protein meals lowered the glycemic response (how high the blood glucose level rose) by 32%, with whey showing the highest insulin release, which accounted for the blunted glycemic response of the meal. Subjective appetite responses from the study subjects indicated that casein and soy proved more satiating than did whey. But the subjects liked the taste of whey more than casein and soy.
     An interesting aspect of this study was the high insulin response produced by the whey meal. Since insulin is blamed for increased fat synthesis, doesn't this mean that whey should promote fat gains? It doesn't work like that. While the high amino acid content of whey, which is rapidly absorbed, does promote an insulin release, it does not result in increased fat synthesis as is the case for processed carbs. But the higher insulin release promoted by whey does blunt appetite, accounting for the increased satiety effect shown by whey. This also explains why large amounts of fructose tend to produce higher bodyfat levels. Fructose doesn't promote an insulin response, so appetite isn't blunted when you consume large amounts of fructose, which in turn tends to promote overeating, and subsequently, increased bodyfat synthesis.

Acheson KJ, et al. Protein choices targeting thermogenesis and metabolism.Am J Clin Nutr 2011: in press.

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