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High-Protein Diets Yield Mixed Results

Popular weight loss strategy improves satiety and decreases fat mass, but increases risk of metabolic disease…

Some of the potential mechanisms that account for weight loss associated with high-protein diets involve increased secretion of satiety hormones (GIP, GLP-1), reduced orexigenic hormone secretion (ghrelin), the increased thermic effect of food and protein-induced alterations in gluconeogenesis to improve glucose homeostasis.

There are, however, also possible caveats that have to be considered when choosing to consume a high-protein diet. A high intake of branched-chain amino acids in combination with a western diet might exacerbate the development of metabolic disease.

A diet high in protein can also pose a significant acid load to the kidneys. Finally, when energy demand is low, excess protein can be converted to glucose (via gluconeogenesis) or ketone bodies and contribute to a positive energy balance, which is undesirable if weight loss is the goal.

In a review of study data, researchers explored the mechanisms whereby a high-protein diet may exert beneficial effects on whole body metabolism while presenting possible caveats associated with the consumption of a high-protein diet.

Diets high in protein have been shown to be a potential tool for weight loss. General dietary guidelines for adults suggest an acceptable macronutrient distribution range (AMDR) of 45–65% of total energy from carbohydrates (CHO), 20–35% from fat (F), and 10–35% from protein (P) with a recommended dietary allowance (RDA) of 46 and 56 g/d or 0.8 g/kg body weight (BW) of P for females and males, respectively.

A diet is therefore considered high in protein if it exceeds 0.8 g/kg BW or the habitual 15–16% of total energy. High-protein (and low CHO) diets have recently received much attention in form of the Atkins diet which is a non-energy-restricting, low CHO (as low as 30 g/day), high-protein/high-fat diet, the South Beach diet (low CHO/high protein diet), the Stillman diet (low CHO/high protein/low fat) or the Zone diet (low CHO/high protein). But also diets high in protein but containing a normal amount of CHO (20% P, 50% CHO and 30% F) have been successfully used to improve metabolic parameters, suggesting that weight-maintenance depends on the protein content but not necessarily on a low CHO content.

A recent study showed that GLP-1 blunted postprandial glucose response and reduced insulin release by reducing gastric emptying at physiological doses in response to a mixed meal. This increased gastric retention, lowered hunger and the desire to eat and augmented satiety. The process of gastric emptying might play an important role in the perception of hunger and satiety.

High-protein diets can help preserve lean body mass during weight loss. With regard to the macronutrient distribution, it appears that there is a difference whether protein is increased at the expense of CHO or fat. Increasing protein at the expense of CHOs leads to increased contribution of amino acids to energy expenditure with a concomitant decrease in lipogenesis due to decreased supply of dietary glucose and likely has a negative impact on exercise performance and training intensity. Carbohydrate supply is critical for strength and endurance performance. Athletes should therefore be aware about limited energy intake and maintenance of training levels.

Whereas diets high in protein have considerable beneficial effects on satiety and weight control, which is of great interest to e.g. obese individuals, there are some caveats to high protein diets such as increased acid load to the kidneys or high fat content of animal proteins. Awareness of these caveats enables individuals choosing to consume a high-protein diet to get the most benefit from it.

Practice Pearls:

  • Diets high in protein have been shown to be a potential tool for weight loss.
  • Whereas diets high in protein have considerable beneficial effects on satiety and weight control.

A high-protein diet for reducing body fat: mechanisms and possible caveats, Nutrition & Metabolism 2014, 11:53 doi:10.1186/1743-7075-11-53, Nov 19, 2015