igh dietary protein intake is associated with weight loss. This is likely because protein dictates the gastric emptying rate, slowing the speed of digestion, which lowers the glycaemic effects of food. This may modulate blood glucose levels and improve the efficiency of energy partitioning in the postabsorptive state. The benefits of weight loss on long-term health suggest that higher protein diets may considerably reduce all cause mortality. High protein intakes may also be able to lower blood pressure, although this effect is more controversial. The mechanisms by which this happens is not clear, but may relate to a reduction in concomitant intakes of carbohydrate foods which subsequently modifies nutrients intake and alters digestive and postabsorptive metabolism. That refined carbohydrates increase the risk of weight gain and insulin resistance suggest that reducing intake, through an increased protein content to the diet, may provide multiple health benefits.
Recent research1 published in the American Journal of Clinical Nutrition investigated the effects of protein or maltodextrin on the blood pressure of 90 overweight men and women aged 20 to 70 years. For 2 weeks subjects consumed a diet composed of 15 % energy from protein, 30 % energy from fat, and 55 % energy from carbohydrate, as well as a 20 g sucrose drink with each meal (three times per day). For the following 4 weeks of treatment the subjects maintained their diet but replaced the sucrose drink with 20 g maltodextrin or 20 g protein (three times per day). The protein contained 20 % pea, 20 % soy, 30 % egg and 30 % milk protein isolate (creating a 40:60 plant to animal protein ratio). Following the 4 week treatment, the systolic blood pressure was 4.9 mm Hg lower and diastolic blood pressure 2.7 mm Hg lower in the protein group, when compared to the maltodextrin group. When measured in a non-research setting, the systolic blood pressure was 4.6 mm Hg lower in the protein group.
The protein supplements increased protein intake to 25 % of energy and decreased carbohydrate to 45 % of energy. This suggests that the effect of the higher protein diet may have been due to the lowering of the carbohydrate content of the diet. Interestingly, the sodium excretion rate was higher in the maltodextrin group when compared to the protein group. This supports other evidence that shows sodium intakes and excretion rates are poor predictors of blood pressure in healthy individuals. There were no changes in body weight in either group during the study, which suggests that the weight loss effects of protein are not responsible for the blood pressure lowering effects. The authors estimated that the ~5 mm Hg reduction in systolic blood pressure would equate to a 14 % decrease in mortality from stroke and a 9 % reduction in mortality from coronary heart disease, if the results were extrapolated to the population as a whole.
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