Protein is a key macronutrient, essential for physiological functions such as healing, supporting the immune system, and maintaining metabolic health. Beyond these foundational roles, clinical trials consistently show that high-protein diets, exceeding the recommended dietary allowance (RDA) of 0.8 grams per kilogram of body weight per day (g/kg BW/d), promote weight loss and weight loss maintenance by reducing fat mass while preserving lean body mass.^1-6

Mechanistically, high-protein diets enhance satiety and reduce food intake by increasing appetite-suppressing hormones (glucagon-like peptide-1/GLP-1, cholecystokinin/CCK, and peptide YY/PYY) and lowering hunger-stimulating ghrelin hormone levels.^1-6 This, combined with diet-induced thermogenesis – the energy required to digest and metabolize protein – can create a calorie deficit that’s more sustainable than simply reducing calories, which can increase hunger signals.^1,2,4,6

There are many mechanisms and well-documented research behind why higher protein intake helps increase satiety and promote weight loss, which is why this dietary strategy is an important option for healthcare practitioners to educate their patients focused on weight loss or weight loss maintenance. 

Definitions and Mechanisms of a High Protein Diet

Research shows that Americans often meet their protein needs at 0.8 g/kg BW/d (about 46g/day for females and 56g/day for males) from meat, poultry, and egg sources.  The Dietary Guidelines for Americans 2020-2025 estimate that up to 90% of US adults are not meeting their protein recommendations for dairy foods or dairy alternatives, plant-based proteins like soy foods, nuts and seeds, and protein from seafood sources.⁷ 

There is no standard definition of a high-protein diet. Researchers generally define it as a pattern where protein intake is higher than standard dietary recommendations, either as g/kg BW/d or as a percentage of total daily energy intake. Meta-analyses such as one by Wycherley et al. (N=24 clinical trials/1063 participants) reported high protein diet levels ranging from 1.07–1.60 g/kg BW/d, while a systematic review by Carvalho et al. (N=10 studies/1079 participants) compared high-protein diets (>1.2 g/kg BW/d or ≥25% of total daily energy intake) to normal-protein diets (0.8–1.2 g/kg BW/d or 15–20% of total energy).^3,8 High-protein diets are generally characterized in clinical studies as ≥1.2–1.60 g/kg BW/day or 16%–45% of total daily energy intake as protein, which consistently exceeds standard recommendations of 0.8 g/kg BW/day or 10% – 15% of total energy.^1,3,6,8

High protein diets work in multifactorial ways as they help promote weight loss and improve body composition. The overarching systems that work together for your patients on a high-protein diet are increased satiety via increased satiety hormones, hunger hormone suppression, and increased energy expenditure through increased thermogenesis. 

Protein and Satiety Hormones

Dietary protein promotes fullness and reduces food intake by influencing hunger-related hormones released by cells in the digestive system. High-protein diets increase levels of anorexigenic hormones GLP-1, CCK, and PYY, which suppress appetite and signal satiety. At the same time, a high-protein dietary pattern reduces ghrelin levels, an orexigenic hormone that stimulates hunger. 

Research suggests that free amino acids and bioactive peptides (the products of protein digestion) play a role in regulating food intake by influencing areas of the hypothalamus responsible for appetite control. Elevated plasma levels of individual amino acids like tryptophan, histidine, and tyrosine contribute to this process by acting as precursors to neurotransmitters like serotonin, histamine, dopamine, and norepinephrine, which are involved in satiety and appetite regulation.⁹ The dual action of boosting satiety hormones while suppressing hunger hormones helps your patients feel fuller for longer, leading to reduced calorie intake.^1-6

Protein and Energy Expenditure

High-protein diets increase energy expenditure in two ways: through diet-induced thermogenesis and by preserving resting energy expenditure (REE). Proteins require more energy for processing than fats and carbohydrates, with some estimates indicating 20–30% of total energy intake for protein versus 5–10% for carbohydrates and 0–3% for fats.^1,2,4,6 Protein has the ability to produce a significantly more thermogenic effect than other macronutrients. 

High-protein diets also help prevent the loss of lean muscle mass, commonly occurring during weight loss, especially on calorie-restricted diets. Lean mass preservation keeps REE stable, ensuring the body burns more calories even at rest. This combination of higher diet-induced thermogenesis and maintained muscle mass makes high-protein diets particularly effective for weight loss and maintenance.^1,3

Protein and Carbohydrates

Dietary protein intake also contributes to weight loss by stimulating gluconeogenesis, where excess amino acids are converted into glucose.^1,3 This process requires energy, which increases overall energy expenditure. The glucose produced can enhance feelings of satiety, further reducing food intake.^1,3,4 High-protein diets, especially with lower carbohydrate intake, increase levels of β-hydroxybutyrate, a ketone body produced during fat metabolism. Elevated levels promote satiety, potentially reducing dietary intake.^1,6 β-hydroxybutyrate promotes satiety by suppressing the hunger hormone ghrelin and stimulating CCK, which enhances feelings of fullness. It can also cross the blood-brain barrier, modulating hypothalamic neurons to reduce appetite-related neuropeptides like neuropeptide Y (NPY) and inhibiting AMP-activated protein kinase (AMPK) in the hypothalamus, signaling energy sufficiency and reducing food intake.¹⁰

The Type of Protein Matters

Studies also show that the type of protein may make a difference. Some data suggests that dietary branch-chain amino acids (BCAAs) stimulate satiety via the secretion of satiety hormones GLP-1, CCK, and PYY.^1,2,11,12 Whey protein, specifically, has been studied in relation to promoting more satiating effects due to its higher BCAA content, though research is mixed on this subject.^4,11

Plant-based proteins generally have slightly lower protein content and essential amino acid levels than animal-based proteins because many contain carbohydrates in addition to protein. Plant sources like wheat, hemp, and oats are lower in amino acids lysine and methionine, while animal proteins, particularly whey, have a more equal balance of amino acids. Some plant proteins, such as potato, pea, and brown rice, provide higher essential amino acid levels, making them more comparable to animal-based sources.¹² Active ‘protein combining’ doesn’t need to be a focus as the body can create what it needs, as long as a variety of plant proteins are consumed regularly. Plant-based dietary patterns have long been associated with lower body mass index (BMI), likely due to reduced energy intake, fat intake, and possibly through reduced inflammation and improvements in the gut microbiome.^13-15 While some studies show that animal proteins, particularly whey, may offer advantages in amino acid balance and satiety, evidence shows that plant-based dietary patterns and protein intake also support weight management. More research is needed to determine what type of proteins and dietary patterns, specifically, support weight loss the most.

Takeaways for Healthcare Providers

A high-protein diet can promote weight loss and improve body composition through multiple mechanisms: increased energy expenditure, satiety hormone regulation, gluconeogenesis, and ketogenesis. By enhancing feelings of fullness and promoting energy output and lean body mass maintenance, high-protein diets are a potentially powerful and effective tool for weight management. Educating patients that experimenting with a diet up to 1.6 g/kg BW/d may be a strategy for their health goals if weight loss is a focus. 

This brief is for informational purposes only and is not intended to be medical advice. The material presented in this brief, and displayed on the associated webpage(s), is not intended to be a substitute for professional medical advice, diagnosis, or treatment. You should seek the recommendation of a medical professional regarding a medical condition or treatment or before starting a new nutrition and/or health regimen.

Orgain, LLC is providing this brief on an “as is” basis and makes no representations or warranties of any kind with respect to this brief. Orgain, LLC nor any of its directors, employees or other representatives will be liable for damages arising out of or in connection with the use of this brief. This is a comprehensive limitation of liability that applies to all damages of any kind, including (without limitation) compensatory, direct, indirect or consequential damages, loss of data, income or profit, loss of or damage to property and claims of third parties.

References:

1. Moon J, Koh G. Clinical evidence and mechanisms of high-protein diet-induced weight loss. Journal of obesity & metabolic syndrome. 2020;29(3):166.
2. Braden ML, Gwin JA, Leidy HJ. Protein source influences acute appetite and satiety but not subsequent food intake in healthy adults. The Journal of Nutrition. 2023;153(6):1825-33.
3. de Carvalho KM, Pizato N, Botelho PB, Dutra ES, Gonçalves VS. Dietary protein and appetite sensations in individuals with overweight and obesity: a systematic review. European Journal of Nutrition. 2020;59:2317-32.
4. Lim JJ, Sequeira IR, Yip WC, et al. Postprandial glycine as a biomarker of satiety: A dose-rising randomised control trial of whey protein in overweight women. Appetite. 2022;169:105871.
5. Kondrashina A, Brodkorb A, Giblin L. Dairy-derived peptides for satiety. Journal of Functional Foods. 2020;66:103801.
6. Kim JY. Optimal diet strategies for weight loss and weight loss maintenance. Journal of obesity & metabolic syndrome. 2020;30(1):20.
7. U.S. Department of Agriculture and U.S. Department of Health and Human Services: Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. Available at DietaryGuidelines.gov
8. Wycherley TP, Moran LJ, Clifton PM, Noakes M, Brinkworth GD. Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012;96:1281–98.
9. Jahan-Mihan A, Luhovyy BL, El Khoury D, Anderson GH. Dietary proteins as determinants of metabolic and physiologic functions of the gastrointestinal tract. Nutrients. 2011;3(5):574-603.
10. Holm S, Husted AS, Skov LJ, Morville TH, Hagemann CA, Jorsal T, Dall M, Jakobsen A, Klein AB, Treebak JT, Knop FK. Beta-hydroxybutyrate suppresses hepatic production of the ghrelin receptor antagonist LEAP2. Endocrinology. 2022 Jun 1;163(6):bqac038.
11. Lueders B, Kanney BC, Krone MJ, Gannon NP, Vaughan RA. Effect of branched-chain amino acids on food intake and indicators of hunger and satiety-a narrative summary. Human Nutrition & Metabolism. 2022;30:200168.
12. Gorissen SHM, Crombag JJR, Senden JMG, et al. Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids. 2018;50(12):1685-1695.
13. Ewy MW, Patel A, Abdelmagid MG, et al. Plant-based diet: is it as good as an animal-based diet when it comes to protein?. Current nutrition reports. 2022 Jun;11(2):337-46.
14. Tran E, Dale HF, Jensen C, Lied GA. Effects of plant-based diets on weight status: a systematic review. Diabetes, Metabolic Syndrome and Obesity. 2020:3433-48.
15. Ivanova S, Delattre C, Karcheva-Bahchevanska D, et al. Plant-based diet as a strategy for weight control. Foods. 2021;10(12):3052.