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Protein: It’s more than just a macronutrient

Protein is a crucial component of a healthy and balanced diet and its role in the human body is essential for overall health and wellness. As a personal trainer, I understand the importance of protein in supporting muscle growth, regulating appetite, and increasing energy expenditure.

In this essay, I will dive into the various functions of protein in the body, including its impact on the thermic effect of food, regulation of the mTOR pathway, and role in hormone regulation with specific emphasis on insulin and leptin. Whether you're looking to build muscle, lose weight, or simply maintain a healthy diet, understanding the significance of protein is key. By incorporating a balanced and adequate amount of protein into your diet, you can achieve optimal health and wellness and reach your fitness goals.


Protein plays a crucial role in regulating appetite and therefore food intake. When we consume protein-rich foods, they stimulate the release of hormones in the gut that promote feelings of fullness and satiety. These hormones, such as glucagon-like peptide-1 (GLP-1), signal to the brain that we are full and should stop eating.

In addition, proteins have a slower rate of digestion compared to carbohydrates, which means that they take longer to empty from the stomach and provide a longer-lasting feeling of fullness. This can help to reduce the frequency of snacking and overeating, which are common factors contributing to weight gain.

Furthermore, consuming an adequate amount of protein has been shown to increase feelings of fullness and decrease hunger, making it easier to stick to a calorie-controlled diet and achieve weight loss goals. Thus, incorporating protein-rich foods into the diet can be an effective strategy for managing appetite and reducing the risk of overeating.

Thermic effect

Proteins have a higher thermic effect compared to carbohydrates and fats, meaning that the body burns more calories digesting protein than it does digesting the same amount of carbohydrates or fats. This phenomenon is known as the "thermic effect of food" (TEF), refers to the number of calories the body uses to digest, absorb, and process the nutrients from food.

The TEF of protein is so high that, depending on the individual, 10-20% of the calories in protein is burned during digestion. This means that consuming a diet high in protein can lead to an increased metabolic rate and a greater number of calories burned each day.

To understand the TEF of protein, it is helpful to consider two examples. Firstly, consider a diet that consists of 50% carbohydrates, 35% fat, and 15% protein. The TEF for this diet would be around 10% of total energy intake, meaning that 10% of the calories consumed would be used for digestion and processing. However, if we increase the proportion of protein in the diet to 25%, while keeping the same amounts of carbohydrates and fat, the TEF would increase to around 20%. This means that 20% of the calories consumed would be used for digestion and processing, resulting in a higher metabolic rate and greater number of calories burned each day.

Please note: The TEF of food will depend on a number of factors such as the type of foods consumed, the macronutrient composition of the diet, the individual's age, weight, and activity level, as well as other metabolic factors. The actual increase in calories burned due to the TEF of protein can vary greatly between individuals and should not be relied upon as an exact measure.


The mTOR (mammalian target of rapamycin) pathway is a complex signalling network that regulates a variety of cellular processes, including cell growth, protein synthesis, and metabolism. Protein plays a crucial role in the regulation of the mTOR pathway and the stimulation of protein synthesis.

When we consume protein-rich foods, amino acids are absorbed into the bloodstream and transported to the cells where they can be used for protein synthesis. This increase in amino acid availability stimulates the activation of the mTOR pathway, which then triggers the initiation of protein synthesis, which is the process by which the body builds new muscle tissue.

Resistance exercise is also one of the key stimuli for activating the mTOR pathway and stimulating muscle growth. When you perform resistance exercise, the mechanical stress placed on the muscle fibers leads to an increase in amino acid availability, which then stimulates the activation of the mTOR pathway and the initiation of protein synthesis. Thus, through this combination of a high protein diet and resistance training, new muscle can be built via the mTOR pathway.

Hormonal regulation

Protein plays a role in the regulation of hormones that are important for both fat loss and muscle building.

One key hormone involved in this regulation is insulin, which is an anabolic hormone that plays a role in both glucose and amino acid uptake by the cells. When we consume protein, insulin is released in response to the increase in amino acid availability. This insulin release stimulates the uptake of amino acids by the cells and also regulates the storage of glucose as glycogen in the muscles. Insulin also activates the mTOR pathway, which stimulates protein synthesis and contributes to muscle growth. This is one reason why bodybuilders use insulin to gain crazy amounts of muscle mass.

Leptin is another hormone that plays a role in the regulation of protein metabolism and body weight. Leptin is a hormone produced by the fat cells and is involved in regulating energy balance by suppressing appetite and increasing energy expenditure. High protein diets have been shown to increase leptin levels and improve insulin sensitivity, which can help to regulate body weight and promote fat loss.

In conclusion, it is very clear how important protein is in maintaining and improving ones physique or health. However, you would like more information on nutrition or are considering my guidance as a personal trainer/ online trainer, then please be in touch.

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