What is protein?
Protein is one of the three major macronutrients along with fat and carbohydrates that are commonly found in foods. While usually considered in diets for its muscle building – also known as hypertrophy – properties, protein also has an important role in various bodily functions. Protein is comprised of molecules called amino acids that the body uses for biochemical reactions and are the basis of essential structures (1).
How much protein do I need to eat?
The amount of protein intake varies depending on one’s goals and activities but is generally recommended to be 0.8 grams per kg of body weight per day in accordance with the Dietary Reference Intake (2). For hypertrophy purposes, there is still much debate regarding the optimal protein intake. Although there is good evidence to suggest a target daily protein intake of 1.6 grams per kg of body weight to 2.2 grams per kg of body weight (3). Regardless of the controversies surrounding protein intake, the benefits of adequate protein consumption have been well established that can contribute to significantly improving one’s health. Specifically, protein can help with physiological functions, weight management, and muscle tissue. This article will examine these beneficial effects to emphasize the importance of protein.
What are the effects of protein on the body?
As previously mentioned, protein is integral for bodily functions and structures. This is because of the amino acids that make up protein and are used to provide the basis of body structures, like skin and hair; enzymes that are responsible for various biochemical reactions; and antibodies that help with our immune system (1). In very severe cases, insufficient protein intake can lead to a condition called hypoproteinemia and may severely compromise physiological function (4, 5).
As an example of its function in body structures, consuming protein in the form of collagen – a structural protein in the body – can be broken down in the body to provide the necessary amino acids to build keratin which is an essential protein for helping form hair and skin (6 -8).
Forms of protein malnutrition, such as kwashiorkor and marasmus, have been found to be associated with hair thinning and hair loss (9). Furthermore, protein is also known to produce enzymes that are necessary for normal functioning. A study of a low protein diet in pigs – which are considered an ideal animal model in human health research because of their similar anatomical and physiological profile with humans (10) – found it impaired digestive function because of its effects on reducing pepsin, which is an enzyme in the stomach that functions to digest proteins from foods (11, 12). Additionally, protein can help with the production of antibodies which is important for a strong immune system to protect the body from diseases.
Low protein intake can be particularly detrimental to the immune system and is known to increase the risk or severity of infections (13). Support for this has been demonstrated in a study using a supplementation of arginine – an amino acid found in protein thought to enhance immune system function (14) – which found it increased T-lymphocyte (antibodies) cell numbers in postoperative surgical patients (15). Taken together, the available evidence demonstrates the importance of protein in physiological functions.
Protein's effect on weight management, hunger, and metabolism.
Another benefit of protein is that it can be used to improve health through weight management. This can be in the form of weight loss or preventing excessive weight gain to maintain a healthy weight. Calculating one’s body mass index (BMI) is a common method for determining a healthy weight and can be done by dividing one’s weight in kilograms divided by the square of height in meters (16). It is important to note that BMI calculations may be inaccurate in populations with muscular builds or older persons (17) and should be considered a general estimate. A BMI over 25 is classified as overweight and is recognized to increase the risk for many diseases and conditions such as hypertension (high blood pressure); type 2 diabetes; coronary heart disease; decreased quality of life; mental illness; mortality (all-causes-of-death); and others (18). Given these risk factors, having a BMI above 25 is widely recognized to be indicative of an unhealthy weight.
Protein can be an effective tool to avoid an overweight BMI due to its high thermic effect (19). Simply put, protein consumption can increase metabolism as reflected by a greater expenditure of calories that may be utilized to facilitate a caloric deficit. For successful weight loss strategies, it is known that a caloric deficit must be present which is defined as consuming fewer calories than your body needs to maintain its current weight (20). Evidence for protein’s effects on metabolism has been shown in a study that found a 42% increase in metabolic rate with a high protein diet (21).
Protein may also contribute to reducing one’s appetite, but this remains unclear. An early study found that protein – as measured by amino acid concentrations in the blood – was related to lower levels of reported hunger (22).
Similarly, another finding demonstrated that men with obesity consuming 25% of calories from protein had increased feelings of fullness, decreased snacking behaviour by 50%, and a 60% reduction in obsessive thoughts of food (23). Contrary to these results, another study showed that those with a higher daily protein intake of 1.4 grams per kg of body weight had lower satiety relative to a lower protein intake of 1.0 grams per kg of body weight (24). Despite this finding, this does not mean that protein cannot elicit a feeling of fullness. Rather, its satiating effect may be dependent on daily protein intake and warrant further scientific investigation. Although the recommended daily protein intake is still under debate, it can still be an effective tool to combat an overweight BMI while avoiding negative health consequences.
How does protein aid muscle hypertrophy and preservation?
Finally, the most recognized beneficial effect of protein is related to hypertrophy and preservation of muscle. Muscle is particularly important to allow proper functioning of daily activities (25). This can range from household chores to playing sports. To emphasize this importance, a systematic review – which summarizes academic literature pertaining to a topic under investigation (26) – found low muscle mass was related to diminished performance in activities of daily living (27). It is well known that adequate protein intake is needed for building muscle (28). A meta-analysis study – a research process that statistically analyzes studies examining the same question (29) – demonstrated a relationship between higher protein intake and greater muscle mass (30).
Regarding the maintenance of muscle, a study showed that protein intake mitigated muscle loss during energy-reduced diets (31). A prevailing issue that is common during diets is muscle loss which usually accounts for 8–10% of total weight loss (32). Such losses in muscle when dieting may be attenuated with protein intake. Based on the evidence provided, protein can be advantageous for muscle tissue by inducing hypertrophy and preserving muscle. Having a healthy amount of muscle mass can allow one to properly perform daily activities, whether it is for excelling in sports or doing mundane chores.
Conclusion
In conclusion, protein is beneficial for physiological functions, weight management, and muscle tissue. These effects can significantly affect one’s health and quality of life. While it remains unclear regarding the recommended protein intake, much of the recommendations stated are available for individualized practices. Ultimately, the optimal protein intake is the one that you feel is healthy, easy to stick to, and can gain muscle.
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