It is well-known that diet and exercise have interrelated effects on a body’s energy balance. Of course, exercise doesn’t only help “burn calories” - in fact, regular physical activity increases the body’s overall energy flux, meaning the rate at which energy is consumed, used, and stored. The higher this flow, the more active and metabolically “alive” the body remains. Energy flux should not be confused with energy balance: the latter reflects whether we consume more or less energy than we burn, while the former shows how quickly these processes occur. Exercise, therefore, not only affects the energy “balance”, it also affects the speed and manner in which the body handles energy.
Whatever type of workout you choose - whether it’s circuit training with resistance exercises (e.g., for back, chest, shoulders, and abs), Pilates, or any type of anaerobic or aerobic exercise - protein is the nutrient that is necessary to accompany your every effort. And not because it’s just a Fitness trend, but because protein is essential for muscle recovery, to strengthen your body and get the most out of your workout.
Exercise & Metabolism
What is the effect of exercise on metabolism and on the body’s primary metabolically active tissue - muscle? How does physical activity influence the body as a whole?
To answer these questions, we need to examine how human metabolism works behind every workout, repetition, or minute on the treadmill, as our body performs thousands of internal processes to provide energy and recover afterwards.
- The mobilization of metabolism during exercise serves to meet the energy demands resulting from muscle activity.
- During exercise, energy production relies on a mixture of various sources, mainly carbohydrates and fats, working together to support physical effort.
- Exercise not only affects the muscles actively involved but also causes metabolic changes in other organs and tissues, such as the liver, adipose tissue, and the heart.
- The body’s metabolic adaptations of the body to exercise are modulated according to the intensity, duration, and nature of the activity as well as the individual’s characteristics and environmental conditions.
- After the completion of exercise, the metabolism doesn’t immediately return to resting levels, since certain functional adaptations persist for a while and become particularly evident during the recovery period.
- Regular training can shape one’s metabolism functions, both at rest and during exercise, compared to someone who does not work out.
This is why exercise is considered the most powerful modulator of metabolism!
Therefore, one of the reasons we need to consume sufficient protein when we exercise is to support the metabolic adaptations that occur in muscle tissue. Let’s break this down further…
Protein & Exercise: Why do we need protein when we exercise?
Protein is one of the three macronutrients in food, along with carbohydrates and lipids. A macronutrient is an ingredient that the body needs in large quantities (g) —compared to vitamins, which are micronutrients— the body needs them in much smaller quantities (mg).
Each protein molecule is made up of simpler building blocks, called amino acids, which are joined together to form protein molecules (chains). Thus, each protein is the result of the binding of a different combination of the 22 amino acids involved in protein synthesis, of which 9 are considered essential amino acids (EAAs), as they cannot be synthesized by the human body and must be obtained through the diet.
During exercise, especially in anaerobic training (such as Weights, Pilates, HIIT, Crossfit), micro-injuries are induced in the muscles to cope with the needs of the training. The body breaks down muscle tissue (structural and contractile protein molecules) and then rebuilds it to repair and strengthen the muscles. The result of these processes determines our muscle mass —that is, whether our muscles grow or shrink. When protein synthesis is greater than protein breakdown, we have muscle growth, or hypertrophy.
In order to carry out the above process, it is necessary to supply the body with the required "blocks". Consequently protein is essential for the body, which it uses to "build" or "repair" muscle tissue.
As exercise can be aerobic or anaerobic, each type of exercise has a different effect on the muscles and the protein turnover. Aerobic exercise, such as walking, jogging or swimming, is characterized by lower intensity but longer duration, and relies on the consumption of oxygen for energy production. Although it does not cause as much muscle breakdown, it helps maintain muscle mass and improves cardiovascular health. Anaerobic, on the other hand, increases the demand for protein and amino acids and enhances muscle growth when combined with proper diet. However, it is important to remember that protein needs are influenced not only by the nature and intensity of exercise, but also by how trained one is, as well as other factors such as gender, age and the presence of disease. Take, for example, a marathon runner, 35 years old, who does semi-professional sports, with a gymnast, 22 years old, who is running in the Olympics.
Protein needs are adjusted, based on a total range of factors, from the nature of the exercise, the level and the physiological characteristics of the trainee!
Protein and daily consumption: How much and when?
The amount of protein considered adequate for the average adult is 0.8 grams per kilogram of body weight per day. However, for people who exercise regularly the need for protein increases significantly. According to relevant guidelines from scientific institutions, the daily intake ranges from 1.2 to 1.4 grams per kilogram for those doing aerobic exercise, and from 1.2 to 1.7 grams per kilogram for those engaged in anaerobic exercise and muscle strengthening.
At the same time, the European Food Safety Authority confirms that a protein intake twice the recommended intake for the general population is still considered safe under normal conditions.
However, it's not only important to meet your daily protein requirements, but also to pay attention to the timing of protein intake.
Protein after exercising
Consuming protein, 30 minutes after finishing exercise seems to play an important role in how the body responds, as the anabolic response is even stronger.
Tip: What to eat after a workout? Choose protein of high biological value, such as poultry, fish, milk, cheese, yoghurt and eggs.
Constant protein intake
It appears that protein needs remain elevated for up to two days after exercise, while the body has no mechanism for storing amino acids. Therefore, maintaining adequate protein intake throughout each day is essential to support muscle growth.
Caution! Without the muscle stimulus provided by physical activity, excess protein, in addition to energy balance, like excess carbohydrate, can be converted to fat and result in weight gain in the long term.
Extra tip: Your priority regarding protein intake should always be its total coverage throughout the day and then the time in which it’s consumed in. E.g. There’s no point in prioritizing post-exercise protein intake if I can’t even manage to meet my total daily requirement of 150g, which is the actual target I need to focus on first!
Whey Protein: The most popular and well-studied protein supplement
Often, we hear terms such as "whey protein", "lean protein" or "protein for gaining mass" that can be confusing, especially for those just starting out in nutrition and training. By consensus, the most popular protein supplement is whey protein. You have probably noticed when you open a can of strained yogurt—that clear liquid that has collected on the surface - that's whey, a liquid by-product of yogurt and cheese production.
Although there are many different products on the market with brand names and "special" purposes, in reality the basic types of Whey protein are two: Concentrate and Isolate, which are derived from the same raw material but differ in the degree of processing.
- Concentrated Whey protein
Concentrated protein powders are the Go-to choice. They are derived from filtering whey to remove part of the carbohydrates, lactose and fat and then spray-dried to produce the protein-rich powder. Concentrate's protein content ranges from 70-80 grams of protein per 100 grams of product making it an excellent choice in the start-up phase.
- Isolated Whey protein
Whey protein isolate practically involves an additional processing step from concentrate. This is none other than an additional filtering process that separates fat, cholesterol and lactose even more efficiently. The result of this is a lean, high purity protein powder, typically around 90 grams per 100 grams of product. It also exhibits higher digestibility, which is key for faster muscle recovery, as it facilitates absorption and increases the bioavailability of amino acids.
Both Isolate and Concentrate Whey have a similar amino acid profile because they come from the same source. However, Isolate contains a higher amount of essential amino acids (EAAs) per 100 grams of product due to its higher protein content. Among the EAAs, the amino acid leucine stands out for its ability to "signal" the body to start synthesizing muscle protein.
- Caution! Whey Concentrate is not suitable for people with milk allergy, as it may cause gastrointestinal symptoms in people with lactose intolerance, since only a part of the lactose is removed during the filtering process, keeping the majority of it in the final product. In contrast, Whey Isolate contains significantly less lactose due to the extra processing step. This makes it a more lactose-friendly option for people with a sensitive gastrointestinal system or mild lactose intolerance.
Disclaimer: Regardless of the form of protein - Concentrate or Isolate - as mentioned above, the decisive factor for muscle strengthening remains the adequate coverage of our daily protein needs. The minimum carbohydrate and fat content that characterizes Concentrate will not negatively affect the progress towards the goal, provided that our gastrointestinal system is healthy and the overall diet is balanced.
Conclusion
In summary, one of the most important goals to be set for muscle maintenance or growth, is adequate daily protein intake, especially during anaerobic exercise, which can be achieved perfectly through diet, without the need for supplements. However, in some cases, such as when needs are increased due to intense training, or when the pace of daily life makes it difficult to consume sufficient amounts of protein through food, a protein supplement can be a practical and easy solution. Both Whey Concentrate and Isolate are excellent sources of high biological value protein which makes them very popular. Whey Concentrate is a more affordable option, ideal for those without digestive issues, while Isolate excels in protein content and digestibility and has the lowest lactose content, making it more suitable for people with a sensitive gastrointestinal system or mild lactose intolerance.
Scientific References
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Watford, M., & Wu, G. (2018). Protein. Advances in nutrition, 9(5), σελ. 651–653. Available at: https://doi.org/10.1093/advances/nmy027
Campbell, B., Kreider, R. B., Ziegenfuss, T., La Bounty, P., Roberts, M., Burke, D., Landis, J., Lopez, H., & Antonio, J. (2007). International Society of Sports Nutrition position stand: protein and exercise. Journal of the International Society of Sports Nutrition, 4(8). Available at: https://doi.org/10.1186/1550-2783-4-8
EFSA NDA Panel (2012). Scientific Opinion on Dietary Reference Values for protein. EFSA Journal, 10(2):2557, page 66. Available at: https://www.efsa.europa.eu/en/efsajournal/pub/2557
Koopman, R., Crombach, N., Gijsen, A. P., Walrand, S., Fauquant, J., Kies, A. K., Lemosquet, S., Saris, W. H., Boirie, Y., & van Loon, L. J. (2009). Ingestion of a protein hydrolysate is accompanied by an accelerated in vivo digestion and absorption rate when compared with its intact protein. The American journal of clinical nutrition, 90(1), σελ. 106–115. Available at: https://doi.org/10.3945/ajcn.2009.27474
P.J. Luck, B. Vardhanabhuti, Y.H. Yong, T. Laundon, D.M. Barbano, E.A. Foegeding (2013). Comparison of functional properties of 34% and 80% whey protein and milk serum protein concentrates. Journal of Dairy Science, 96(9), page 5522-5531. Available at: https://doi.org/10.3168/jds.2013-6617
Dairy Processing Handbook (2025) Whey Processing, Available at: https://dairyprocessinghandbook.tetrapak.com/chapter/whey-processing, (Access date April 7, 2025)
Dietician - Nutritionist, BSc (Hons)
info@hollandandbarrett.gr
*Text editing: Maria Kirmanidou
