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Protein is one of the building blocks of any healthy diet - it’s what our organs, muscles, hair, and skin are made out of. Protein is necessary to form blood cells, and is an essential part of the immune response, cellular repair and growth/development.
Protein is found in a variety of animal food sources such as meat, eggs, milk and fish. Plant based food sources such as soy, legumes, beans, nut butters and grains like wheat germ and quinoa all contain protein.
Protein foods are broken down into parts called amino acids during digestion. The human body needs a number of amino acids in large enough amounts to maintain good health. Amino acids can be classified as either ‘essential’, meaning that we must obtain them from diet or ‘nonessential’, meaning that they can be synthesized from other amino acids. Conditional amino acids are ones that are needed in times of stress.
Vegetarian and vegan diets have historically been thought to lack complete protein sources. According to NHANES data, vegetarians had a higher prevalence of protein inadequacy than non vegetarians (1). As nutrition knowledge has evolved, it has become more apparent that a well-balanced, calorie-adequate vegetarian diet can be a very healthy source of protein, fat and carbohydrates.
Eating a variety of plant based protein sources is key. There is no need to consciously combine different plant proteins at each meal as long as a variety of foods are eaten from day to day, the human body maintains a pool of amino acids which can be used to complement dietary protein (2).
Older individuals on a vegetarian or vegan diet may require higher protein intake as the need for protein increases with advanced agen (1).
Nutritional adequacy of plant-based diets for weight management: observations from the NHANES
Farmer B. , Am J Clin Nutr, 2014
Protein and vegetarian diets.
Marsh KA, Munn EA, Baines SK., Med J Aust. 2013;199(S4):S7-S10., 2013
Muscle fibers are made of blocks of protein and adequate protein intake is required to maintain healthy muscle mass.
Protein needs can vary based on physical activity. For example, The International Society of Sports Nutrition (ISSN) recommends that endurance athletes consume 1.0g/kg to 1.6g/kg of protein per day. In order to build and maintain muscle mass, ISSN recommends an overall daily protein intake in the range of 1.4-2.0g/kg/day. There is evidence that suggests protein intakes greater than 3.0g/kg/day may have positive effects of body competition such as promoting loss of fat mass in resistance-trained individuals. Additionally, ISSN’s stand is that athletes consume protein from whey and casein sources due to superior digestibility and increased muscle protein accretion (1).
The European Food Safety Authority (EFSA) concluded that a cause and effect relationship has been established between the dietary intake of protein and the growth or maintenance of muscle mass (1).
International Society of Sports Nutrition position stand: protein and exercise
Campbell B, Kreider RB, Ziegenfuss T, et al., Journal of the International Society of Sports Nutrition, 2007
The effect of higher-protein diets on body weight management is thought to be partly due to modulations in energy metabolism, appetite, and energy intake.
Higher-protein diets that contain between 1.2-1.6g/kg/d protein provide improvements in appetite, body weight management, and cardiometabolic risk factors compared with lower-protein diets. In studies where participants increased protein consumption, they reported increased satiety, weight loss, fat mass loss, and the preservation of lean mass were also observed. It is touted that dietary protein may increase energy expenditure by eliciting a greater postprandial thermic effect of food (TEF) than carbohydrates or fats. Dietary protein requires 20-30% of its usable energy to be expended for metabolism and/or storage, whereas carbohydrates require 5-10% and dietary fats require 0-3%. Additionally, higher-protein diets have been found to prevent a decline in resting energy expenditure (REE) (1).
Research suggests that protein improves satiety through elevation of anorexigenic hormones, including glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK) and peptide tyrosine-tyrosine (PYY). Release of GLP-1, CCK, and PYY is stimulated by proteins that also stimulate the vagus nerve, thus reducing food intake (2)
The role of protein in weight loss and maintenance
Leidy H, Clifton P, Astrup A et al., Am J Clin Nutr, 2015
Clinical Evidence and Mechanisms of High-Protein Diet-Induced Weight Loss.
Moon J, Koh G. J, Obes Metab Syndr. 2020;29(3):166-173., 2020