Nutrition 101: Proteins
Most people would agree its pretty easy to identify meats, fish & poultry as proteins. So why is there so much confusion and debate around protein? Well, that seems to be coming from discussing non-animal protein sources, what are “healthy” protein sources, & how much protein we really need. So here's a guide to help you understand proteins better: what they are, what they do, & how they fit into our diets.
What are they?
Proteins are one of the 3 macronutrients in the diet – meaning they are one of the 3 main pieces of the diet along with carbohydrates and fats. All proteins are made up of a combination of carbon, hydrogen, oxygen, and nitrogen molecules. Proteins are made up of a series of amino acids held together by peptide bonds. The sequencing of these amino acids determines what the protein is & the protein’s specific role in the body. It’s all just chemistry. Proteins can be categorized a few different ways including by: food source, fat content, and amino acid content.
Food Source
Animal Protein
Plant-based Protein
Fat Content
Very high or high fat protein - fried meats, bacon, sausage, hot dogs, some cold cuts, organ meats, processed meats, spare ribs, full-fat dairy
Very lean or lean protein - lean cuts of red meats (loins), chicken, turkey, fresh seafood, low-fat dairy, legumes, nuts, seeds
Amino Acid Content
Complete protein or high-quality protein
Incomplete protein or low-quality protein
Why do I need them?
Proteins serve several functions in the body including:
Cellular growth and repair
Developing & maintaining muscles, tissues, organs, tendons, cartilage, & blood vessels
Maintaining healthy hair, skin & nails
Building & contracting muscle
Blood clotting
Supporting vision
Strengthening the immune system
Fluid balance
Producing hormones & enzymes
Transporting nutrients & oxygen efficiently through the body
The Science of Proteins
There are 20 common amino acids - 9 of which are essential amino acids, 3 being branched-chain amino acids (BCAAs), and 11 of which are nonessential amino acids. Essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine) cannot be made by the body; therefore, it is essential that we are getting these amino acids from foods. The 3 BCAAs (leucine, isoleucine and valine) are known for their ability to be readily available and rapidly absorbed by the body. This function has made BCAAs popular in the sports nutrition world. Nonessential amino acids (alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, tyrosine) are not essential for us to consume in our diets as they can be made in the body by using essential amino acids or by breaking down the body’s muscles and proteins.
The content of essential vs nonessential amino acids in a protein food determine if the food is a complete (high-quality) or incomplete (low-quality) protein. Complete proteins contain all essential amino acids in adequate amounts (i.e. an egg). Incomplete proteins are either missing one or more essential amino acids or contain inadequate amounts of essential amino acids (i.e. beans). An incomplete protein can be paired with another incomplete protein that compliments, or makes up for, its lacking amino acids to create a complete protein - this is called complementary proteins. Complementary proteins are especially useful in plant-based diets to ensure all animo acids are accounted for. A common example of complimentary proteins is beans and rice. Individually, they are each low-quality proteins but together they make a high-quality protein.
Dietary proteins are broken down into these absorbable amino acids by pepsin and hydrochloric acid during digestion. After breakdown, these amino acids can be used in the body as needed. Inadequate protein intake could lead to protein-energy malnutrition and vitamin and mineral deficiencies. Animal protein foods are rich sources of vitamins and minerals including B vitamins, choline, copper, iron, phosphorus, selenium, vitamin D, vitamin E, and zinc. It is often found that individuals who do not consume animal proteins have an increased risk of vitamin B6, B12, and vitamin D deficiencies. Following up with a dietitian to ensure proper supplementation can be helpful if you do not eat animal proteins.
What are the food sources?
Proteins are found in many more foods than you would anticipate. Even vegetables contain a small amount of protein.
Quality Animal Sources of Protein
Beef
Cold Cuts
Dairy products - cheese, milk, yogurt
Fish, shrimp & other seafood
Pork including bacon & sausage
Poultry - Chicken & Turkey
Quality Plant Sources of Protein
Beans & Legumes
Nuts & Seeds
Soy products including edamame, tofu & tempeh (plant-based cheese is often not a quality source of protein)
Whole Grains, specifically quinoa
How much do I need?
The USDA RDA recommends that the diet be made up of 15-35% protein foods. Protein needs vary based on your stage of life, gender, health, and lifestyle. Increased protein needs are common in stages of growth, athletics, pregnancy, lactation, illness, and recovery from wounds, burns, surgery, etc. Decreased protein needs are seen in circumstances such as kidney disease & protein metabolism errors. On average, most Americans meet their protein needs daily.
What is a serving?
It is estimated that most adults need around 6 oz protein equivalents daily. A 1 oz protein equivalent is roughly the size of 1 egg, 1 Tbsp or 2 fingers. There are many measurements you can use. A typical serving of protein is about 1 palmful or 3 oz - this is where the deck of cards image that most of us have heard to use comes into play. As stated above, protein needs vary by individual.
Dietitian Recommendation
For a well-balanced diet & and confidence that you are getting all essential amino acids, it’s best to eat a variety of protein sources. In general, Americans are lacking nutrition from dairy and seafood sources. It is recommended to have a seafood source such as salmon or tuna 2-3 times per week and a dairy source 2-3 times per day. My recommendation would be to focus there to begin with.
It’s important that any diet recommendations that you adhere to are given by a qualified professional. If you are committed to a highly individualized plan to meet your goals and needs, you want to consider working with a dietitian 1:1. I often see people seeking protein recommendations from unqualified individuals such as gyms, influencers, etc. Although well-intentioned, they likely are not qualified experts & are speaking solely from personal experience. Even physicians most often defer protein recommendations and education to dietitians because they recognize this is not their expertise.
Last food for thought - Whereas under consuming protein may result in forms of malnutrition and deficiency, over consuming protein may cause unnecessary strain on the kidneys with long-term effects. It’s also possible that replacing other food groups, such as carbohydrates, with proteins, as often recommended by fad diets, will result in deficiencies of nutrients found in the food group being replaced & disrupt normal nutrient metabolism in the body.
Resources:
1.Academy of Nutrition and Dietetics. Teaching Dietary Protein Basics. Eatrightpro.org. https://www.eatrightpro.org/practice/practice-resources/international-nutrition-pilot-project/teaching-dietary-protein-basics. Nd. Accessed April 10, 2020.
2. Gordon, B. How Much Protein Should I Eat? Eatright.org. https://www.eatright.org/food/nutrition/dietary-guidelines-and-myplate/how-much-protein-should-i-eat. Published May 28, 2019. Accessed April 10, 2020.
3. Holeček M. Branched-chain amino acids in health and disease: metabolism, alterations in blood plasma, and as supplements. Nutr Metab (Lond). 2018;15:33. Published 2018 May 3. doi:10.1186/s12986-018-0271-1.