High protein, low carb diets cause the greatest appetite reduction.
Low carbohydrate, restricted calorie diets have successfully been shown to enhance weight loss compared to standard or higher carbohydrate intakes, because they work indirectly by dramatic food restriction via appetite suppression. One of the theories behind high protein, low carb diets is the increased thermic effect of protein. According to a few studies, the thermic effect of protein is 25-35 percent of calories, but it is only 5-15 percent for carbohydrates. Fat is about equal to or less than carbs, depending on the type. In a meta-analysis of 1,416 subjects, low-carb diets (50-150g of carbs per day) led to more fat loss compared to placebo. There has been debate as to what macronutrient is causing the most significant reduction in appetite: is it protein or carbs?
Carbohydrate and protein proportions
Researchers analyzed which combination of the carbohydrate and protein proportions in the diet would show the greatest bodyweight and fat loss. Appetite, caloric intake, body weight, and fat mass were measured in 19 subjects placed sequentially on the following diets:
- High-protein, low-carbohydrate/high fat of 20 percent protein, 25 percent carbohydrates, 55 percent fat.
- High protein, normal carbohydrate, normal fat of 20 percent protein, 50 percent carbs, 30 percent fat.
- Normal protein, low carbohydrate/high fat of 10 percent protein, 25 percent carbohydrates, 65 percent fat.
- Normal-protein, normal carbohydrate, normal fat of 10 percent protein, 50 percent carbs, 40 percent fat.
At the end of the study, all four diets contributed to weight loss; however; it showed irrefutably, that, despite the success all-over with all four diets, the answer is that it is the relatively high-protein content per se, that supports the even greater success, and not the relatively lower carbohydrate content. Appetite suppression was markedly increased with the isocaloric high-protein diet. After the research was crunched, the specific comparisons showed that the two high protein diets, namely high protein, normal carbohydrates vs. high protein, low carb and the two standard protein diets, namely normal protein/normal carbohydrates vs. normal protein/low carb did not show significantly different effects. Both high protein diets resulted in enhanced fat loss and body weight loss compared to the normal protein diets. In sum, the researchers showed that body-weight loss and weight-maintenance depends on the high-protein (a relatively high-protein content of 1.1 vs. 0.7 g/kg BW), but not on the ‘low-carb’ component of the diet, while it is unrelated to the concomitant fat-content of the diet.
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