The Role of Protein in our Bodies

By: Amber Whittemore RD, BSN, MHSc(c)

If you have been following along you know we are in the middle of our nutrition series on the “big three” macronutrients: carbohydrates, protein, and fat!

Macronutrients are the components of our food that provide our bodies with calories and energy for optimal physical and mental functioning. Each macronutrient plays its own unique role in our body, from promoting muscle strength to ensuring our brain is functioning optimally.

The previous posts were dedicated to carbohydrates, and this week we are focussing on protein!

The Basics & Its Role in Our Health

Proteins are quite literally the building blocks of our muscles, organs, bones, skin and hair. Every cell in the human body contains protein, meaning we require protein for proper growth, maintenance, and functioning.

When our body digests protein it is broken down into its most simple components: amino acids. Unlike carbs, which are virtually all broken down into glucose, protein is broken down and separated into 20 different amino acids. Nine of these amino acids are considered essential, because our body cannot make them, so we need to obtain them from our food!

The essential amino acids include1:

  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Threonine
  • Tryptophan
  • Valine

These amino acids play many essential roles in our body to promote our overall health, including:

  1. Growth and maintenance: because protein is an integral part of most of our body’s structures (skin, hair, bones, muscles, organs, etc.) they are needed for proper growth, healing, and maintenance of our health!
  2. Enzymes and metabolism: protein is needed to promote enzymatic reactions, such as breaking down food in our gut, creating energy in the body, and maintaining a well-functioning metabolism.
  3. Hormones: majority of our body’s hormones are proteins, therefore if we are lacking in protein, we are unable to adequately create and circulate hormones through the body!
  4. Circulation: proteins are the vehicles that carry all substances around our body for delivery to different tissues and muscles, such as vitamins, minerals, oxygen, and lipids.
  5. Immunity: antibodies are made of protein; these are the substances that fight off viruses or foreign substances in our bodies – making up much of our immunity. Therefore, we need adequate protein to ensure our immune system is functioning optimally!
  6. Energy: although carbohydrates are our body’s preferred energy source, if we are ever deficient in carbs then proteins step up to provide this energy. Our bodies are able to convert amino acids to glucose to do this.

Where to Find It

There are two main sources of protein: animal-derived and plant-derived.

Animal-based proteins, such as meat, poultry, fish, dairy and eggs, are considered “complete proteins”. This means that, in general, they offer all 9 of the essential amino acids when eaten in adequate portions.

In contrast, some plant-based proteins, such as nuts, seeds, legumes, and grains, are coined “incomplete” since they are lacking one or more of the essential amino acids. Because of this, it is important to be mindful of pairing complementary proteins if you tend to eat more plant-based meals. We will look closer at how to pair complementary plant-based proteins in the section “tips for increasing your protein”!

Of note, soy protein, such as tofu, tempeh, and soy milks, are considered complete without pairing.

How Much Do We Need?

How much protein we need depends on a multitude of factors, such as our weight, age, activity level, and health status! The more active we are the more protein we need to grow, repair, and maintain our muscles and bones.

As a general rule of thumb, it is recommended that most healthy adults who are sedentary or lightly active need 0.8 grams of protein per kilogram (kg) of body weight. This equates to around 0.4 grams per pound (lb) of body weight, since 1kg is equivalent to 2.2lbs. This is the current Recommended Daily Allowance (RDA) for protein in Canada.

Children and adolescents require more protein since they are still growing. The current RDA2 for children is 1.5 g protein per kg of body weight daily, and for adolescents it is 1.0 g protein per kg per day.

While it is hard to pin down exact recommendations for adults above the RDA for protein, some research3 suggests the following:

  • Recreational athletes, such as those at the gym a few days a week, should aim for a daily protein intake closer to 1.1 to 1.4 grams per kilogram of body weight per day.
  • Endurance athletes, such as marathon runners, should be in the range of 1.2 to 2 grams per kilogram g of body weight daily
  • Strength athletes, such as weightlifters, should be in the range of 1.4 to 2 grams per kilogram of body weight on average per day.

Can We Get Too Much?

Yes! Despite many of the current diet trends promoting a high protein diet, there is ample evidence to support that fact that eating more protein than our body needs can actually be detrimental to our health. Some of the negative effects of a chronically high protein intake include harm to the bones, kidneys, and liver2. Of note, just like the consumptions of any macronutrient, overconsumption of protein will lead to the excess being stored as fat if it cannot be used in the body.
There is good evidence4 to suggest that at any given time (i.e., at a meal), our body can only properly utilize around 20-25 grams of protein for muscle and cell repair, growth, and maintenance, and that the protein ingested above this level will simply be used for other tasks or stored. Therefore, keeping your protein intake within the recommended ranges listed above, and aiming for ~20 grams of protein per meal is the best way to ensure you are getting the protein you need – as well as not over-consuming based on your body’s needs.

The Bottom Line

Protein is part of our cellular structure, we need it to grow, heal, and function as human beings! Therefore, ensuring you are getting enough in your day is an important part of planning a balanced and optimized diet.

Despite popular diet trends, we can consume too much protein – so be mindful of keeping your intake within the recommended level for your age and activity levels.

If you have any questions or would like help planning a balanced diet that is right for you, reach out to your HEC dietitians for support and guidance!

References

1Lopez, M. J. & Mohiuddin, S. S. (2021). Biochemistry, Essential Amino Acids. Received from: https://www.ncbi.nlm.nih.gov/books/NBK557845/

2Delimaris I. (2013). Adverse Effects Associated with Protein Intake above the Recommended Dietary Allowance for Adults. ISRN nutrition, 2013, 126929. https://doi.org/10.5402/2013/126929

3Today’s Dietitian. (2014). Athletes and Protein Intake. Vol 16, no. 6, pp 22. Received from: https://www.todaysdietitian.com/newarchives/060114p22.shtml

4Schoenfeld, B. J., & Aragon, A. A. (2018). How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. Journal of the International Society of Sports Nutrition, 15, 10. https://doi.org/10.1186/s12970-018-0215-1