Evidence suggest that high protein diets are beneficial to the health. The health benefits of high protein diets are numerous and the benefit conferred on the individual depends largely on the starting point of their health. In developing countries, low protein diets, or low animal protein diets, are recognised as being responsible for an increased risk of infection, particularly upper respiratory tract infections. In Western nations, the risk of upper respiratory tract infections is low and mortality from infection drops as nations develop and the access to cheaper food increases. Instead this population may benefit from high protein intakes because they appear to have weight loss effects. As body weight increases are associated with increased mortality, the weight loss effects of high protein diets may confer significant benefits to those who are overweight. The exact reason for the benefits of high protein diets on weight loss are not fully understood. However, a number of possible mechanisms exist that may explain their effects.
In the short term, high protein diets may cause thermogenic effects. Dietary protein requires around 20 to 30 % of its usable energy in order for it to be absorbed, metabolised or stored, whereas the figure for carbohydrates is just 5 to 10 %. Eating more protein therefore necessitates are larger percentage of the ingested energy be utilised for metabolic needs and this can increase the thermic effect of food considerably. High protein diets are therefore metabolically wasteful. In the short term, high protein diets may also decrease appetite. There is a requirement for protein and consumption of energy has been shown to be related to this requirement for protein. Eating higher protein foods satisfies the protein requirement sooner, decreasing subsequent energy intake. Such an appetite for protein has been described as the protein leverage hypothesis (here). Protein also appears to have a more general appetite suppressive effect, and this effect may be due to the inhibition of stomach emptying rates displayed by protein.
Dr Robert Barrington’s Nutritional Comments: The appetite regulatory effects of high protein diets are well reported in the literature and perhaps the most significant of the short term benefits. The less efficient metabolism of protein however, may also contribute significantly to the weight loss effects of higher protein intakes. However, one of the most overlooked mechanisms by which protein may cause short term weight loss effects is through the restriction of carbohydrate foods. By definition high protein are low in carbohydrate, and restriction of carbohydrates, particularly if this carbohydrate is composed of refined starch and sugar, may have significant weight loss effects. Protein of course is also required for the synthesis of new skeletal muscle and in this way is an excellent adjunct to a resistance training regimen. That the effects of high protein intakes are multifactorial in nature may explain the consistently good result in terms of weight loss that they provide.
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