Protein is a vital nutrient that has many critical roles in the body. The building blocks of proteins are amino acids. There are 22 amino acids used in the human body. Nine of these have to come from the food we eat and are called essential.
Functions of protein include repair and maintenance of body tissues, energy, the formation of some hormones, enzymes and antibodies, and the transportation and storage of molecules. Protein also increases thermogenesis and satiety, both of which are useful for weight loss.
Let’s look at what the research says about protein, appetite and weight loss. We’ll also find out if there is a difference between animal protein and plant protein.
Protein and Body Composition
Clinical trials have found that consuming more protein than the recommended dietary allowance not only reduces body weight, but also enhances body composition by decreasing fat mass, while preserving fat-free mass in both low-calorie and standard-calorie diets (1).
Protein and Weight Loss
Fairly long-term clinical trials of 6-12 months show that a high-protein diet provides weight-loss effects and can prevent weight regain after weight loss. High protein diets have not been reported to have adverse effects on bone density or renal function in healthy adults (1).
Protein and Appetite
High protein diets increase appetite reducing hormones while decreasing appetite enhancing hormones such as ghrelin, resulting in increased satiety and reduced food intake (1,2,3).
Research comparing the effects of fat, protein and carbohydrates on both lean and obese men found that a high protein meal suppressed hunger for longer in both lean and obese men. However, the obese men were less satiated by the high fat meal than the lean men (4).
Protein and Cardiovascular Disease
Short-term high protein weight loss diets have been shown to have beneficial effects on total cholesterol and triacylglycerol in overweight and obese subjects. The subjects also achieved greater weight loss on the high protein diet compared to the standard protein diet (5).
What Are the Effects of Protein?
The mechanisms by which high protein diets increase energy expenditure are two-fold:
- Protein leads to a higher diet induced thermogenesis than carbohydrates and fats.
- Protein intake prevents the loss of fat free mass, including muscle, which helps maintain resting energy expenditure despite weight loss.
In conclusion high protein diets are an effective and safe weight loss-inducing method that can prevent obesity and obesity-related diseases. However, long-term clinical trials spanning more than 12 months are needed (1).
Plant Protein vs Animal Protein
There are many studies showing the benefits of eating a plant based diet on many aspects of human health and environmental health. A review into the effects of protein from a range of plant sources found that plant proteins have beneficial effects on blood sugar levels, appetite, cardiovascular health and muscular health and are more sustainable than animal based diets (6).
In one study obese men were given either vegetarian or meat based meals comprising 30% protein, 30% fat, and 40% carbohydrate. Appetite control, weight loss and gut hormone profile were similar for both diets. This suggests that vegetarian diets can be as effective as meat-based diets for appetite control during weight loss (7).
- J Obes Metab Syndr. 2020 Jul 23. Clinical Evidence and Mechanisms of High-Protein Diet-Induced Weight Loss. Moon J et al.
- Physiol Behav 2020 Aug 5;113123. Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials. Kohanmoo A et al.
- Am J Clin Nutr 2013 May;97(5):980-9. Contribution of gastroenteropancreatic appetite hormones to protein-induced satiety. Belza A et al.
- Am J Physiol Gastrointest Liver Physiol. 2012 Jul;303(1):G129-40. Effects of fat, protein, and carbohydrate and protein load on appetite, plasma cholecystokinin, peptide YY, and ghrelin, and energy intake in lean and obese men. Brennan IM et al.