High-protein diets: How they affect weight, energy, and blood sugar levels

By Tarun Sai LomteReviewed by Benedette Cuffari, M.Sc.Aug 21 2024

Interest in dietary protein for improving health outcomes has significantly increased over the past two decades. A recent study published in Frontiers in Endocrinology reviews the effects of dietary protein on energy intake, appetite, and postprandial glycemia.

Study: Impacts of dietary animal and plant protein on weight and glycemic control in health, obesity, and type 2 diabetes: friend or foe? Image Credit: nadianb / Shutterstock.com

The acute effects of protein intake

Current evidence suggests that high-protein diets facilitate weight loss, attenuate weight gain, and improve glycemic control. Protein also reduces postprandial glycemia and suppresses energy intake, which may be attributed to its capacity to stimulate gastrointestinal (GI) hormones and postabsorptive mechanisms. The ability of protein consumption to reduce hunger and induce satiety in healthy and obese individuals is dose-dependent.

One meta-analysis found reductions in hunger food consumption, desire to eat, and an increase in fullness that was accompanied by reduced postprandial glycemic levels. These effects of increased protein consumption may only be sustained for six to 12 months.

Comparisons of preloads containing milk proteins like casein or whey, turkey, egg, tuna, or soy proteins have revealed that the whey protein had the most profound effects, whereas other studies reported that whey protein was less satiating than others. Nevertheless, milk proteins are more potent in reducing blood glucose than pea, egg, or fish proteins.

Proteins and their digestion products stimulate GI hormones such as incretins, cholecystokinin (CCK), glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP-1), and peptide tyrosine-tyrosine. These hormones are transported to peripheral organs and stimulate pyloric pressure and insulin secretion, thereby reducing postprandial glycemia.

These protein effects on GI functions similarly vary based on the type of protein, with whey more potent in its effects than other protein sources. One previous study reported that intraduodenal whey protein infusion stimulated plasma CCK, GLP-1, and pyloric pressures in a dose-dependent manner in both lean and obese individuals. Increased content of branched-chain amino acids in whey protein, particularly isoleucine and leucine, contributes to reducing glycemia and energy intake.

Intermediate- and long-term effects

Weight loss with a high-protein diet has primarily been examined through ad libitum and energy-restricted diets. Regardless of the approach, protein-rich diets facilitate more weight loss than standard diets in interventions lasting up to six months. However, high-protein ad libitum diets have been consistently more effective.

A meta-analysis of 24 trials found a modestly higher reduction in weight and fat mass with an isocaloric energy-restricted high-protein diet as compared to the standard diet over an average period of 12 weeks. Another meta-analysis of 74 trials observed decreased body weight, waist circumference, and body mass index (BMI) with a high-protein diet over six months.

Long-term studies are limited and, to date, have not identified a sustained effect of high protein intake. For example, one previous meta-analysis on 15 clinical trials with at least one year of intervention did not identify any benefits or detrimental effects associated with high-protein intake on weight loss. A 12-month study found modest improvements in weight maintenance with a high-protein diet compared to a high-fat or -carbohydrate diet.

Plant vs. animal protein

Importantly, the wide range of potential dietary protein sources must be considered, as several studies have reported an increased risk of diabetes with animal protein consumption. In contrast, protective effects have been associated with plant protein.

Various epidemiological studies have consistently reported associations between high animal protein intake, weight gain, and, as a result, an increased risk of obesity. In one study, higher daily consumption of total and animal protein, which was primarily obtained from chicken and red meat, was associated with weight gain over 6.5 years.

No protective or adverse associations have been observed with plant protein consumption. In one study examining relationships between different protein sources and long-term weight gain across three cohorts, independent associations were observed between animal protein sources and weight gain over four years. In contrast, plant protein sources were associated with weight loss.

Most studies have observed that long-term animal protein consumption increases the risk of diabetes, whereas plant proteins have neutral or protective effects. The mechanisms involved in the differential impact of proteins from distinct sources remain unclear; however, differences in glycemic load, amino acid composition, and deleterious effects of insulinotropic characteristics of animal protein may be involved in the health benefits associated with plant protein consumption.

Conclusions

Robust evidence has demonstrated that increasing protein consumption improves glycemic control in diabetes and supports weight loss. Nevertheless, there remains a lack of sufficient data supporting the long-term health benefits of increased protein intake; therefore, future longitudinal studies on heterogeneous and larger populations are needed.