We have discussed what proteins are, how they are made, how they are digested and absorbed, the many functions of proteins in the body, and the consequences of having too little or too much protein in the diet. This section will provide you with information on how to determine the recommended amount of protein for you, and your many choices in designing an optimal diet with high-quality protein sources.

How Much Protein Does a Person Need in Their Diet?

The recommendations for the Recommended Daily Allowance (RDA) and AMDR for protein for different age groups are listed in Table 6.2 “Dietary reference intakes for protein”. A Tolerable Upper Intake Limit for protein has not been set, but it is recommended that you do not exceed the upper end of the AMDR. The AMDR for protein in adults is 10-35%.

Protein Input = Protein Used by the Body + Protein Excreted

The appropriate amount of protein in a person’s diet is that which maintains a balance between what is taken in and what is used. The RDAs for protein were determined by assessing nitrogen balance. Nitrogen is one of the four basic elements contained in all amino acids. When proteins are broken down and amino acids are catabolized, nitrogen is released. Remember that when the liver breaks down amino acids, it produces ammonia, which is rapidly converted to nontoxic, nitrogen-containing, urea, which is then transported to the kidneys for excretion. Most nitrogen is lost as urea in the urine, but urea is also excreted in the feces. Proteins are also lost in sweat and as hair and nails grow. The RDA, therefore, is the amount of protein a person should consume to balance the amount of protein used up and lost from the body. For healthy adults, this amount of protein was determined to be 0.8 grams of protein per kilogram of body weight. You can calculate your exact recommended protein intake per day based on your weight by using the following equation:

(Weight in lbs. ÷ 2.2 lb/kg) × 0.8 g/kg

Note that if a person is overweight, the amount of dietary protein recommended can be overestimated.

To calculate the RDA for protein, we used data from multiple studies that determined nitrogen balance in people of different age groups. A person is said to be in nitrogen balance when the nitrogen input equals the amount of nitrogen used and excreted. A person is in a negative nitrogen balance when the amount of excreted nitrogen is greater than the amount consumed, meaning that the body is breaking down more protein to meet its demands. This state of imbalance can occur in people who have certain diseases, such as cancer or muscular dystrophy. Someone following a low-protein diet may also be in a negative nitrogen balance as they are taking in less protein than needed. Positive nitrogen balance occurs when a person excretes less nitrogen than what is taken in by the diet, such as during child growth or pregnancy. At these times, the body requires more protein to build new tissues, so more of what gets consumed gets used up and less nitrogen is excreted. A person healing from a severe wound may also be in positive nitrogen balance because protein is being used up to repair tissues.

Dietary Sources of Protein

The protein food group consists of foods made from meat, seafood, poultry, eggs, soy, dry beans, peas, and seeds. According to the Harvard School of Public Health, “animal protein and vegetable protein probably have the same effects on health. It’s the protein package that’s likely to make a difference.”^[2]

Simply put, different protein sources differ in their additional components, so it is necessary to pay attention to the whole nutrient “package.” Protein-rich animal-based foods commonly have high amounts of B vitamins, vitamin E, iron, magnesium, and zinc. Seafood often contains healthy fats, and plant sources of protein contain a high amount of fibre. Some animal-based protein-rich foods have an unhealthy amount of saturated fat and cholesterol. When choosing your dietary sources of protein, take note of the other nutrients and also the non-nutrients, such as cholesterol, dyes, and preservatives to make good selections that will benefit your health. For instance, a hamburger patty made from 80 percent lean meat contains 22 grams of protein, 5.7 grams of saturated fat, and 77 milligrams of cholesterol. A burger made from 95 percent lean meat also contains 22 grams of protein, but has 2.3 grams of saturated fat and 60 milligrams of cholesterol. A cup of boiled soybeans contains 29 grams of protein, 2.2 grams of saturated fat, and no cholesterol. For more comparisons of protein-rich foods, see Table 6.3 “Sources of dietary protein”.

To select protein-rich foods that benefit your health, opt for vegetable sources of proteins, and lean meats, such as round steaks, top sirloin, extra lean ground beef, pork loin, and skinless chicken. Additionally, consuming seafood every week can help ensure you are getting the healthy omega-3 fatty acids that have been linked to a lower risk for heart disease. Another tip is to choose to eat dry beans, peas, or soy products as a main dish. Some of the menu choices include chilli with kidney and pinto beans, hummus on pita bread, and black bean enchiladas. You could also enjoy nuts in a variety of ways. You can put them on a salad, in a stir-fry, or use them as a topping for steamed vegetables in place of meat or cheese. If you do not eat meat, you can get all the protein you need from a plant-based diet. When choosing the best protein-rich foods to eat, pay attention to the whole nutrient package and remember to select from a variety of protein sources to get all the other essential micronutrients.

Andrew George Jr. is a renowned Indigenous chef and pioneer in promoting Indigenous cooking in British Columbia and all across Canada. He is from the Wet’suwet’en community, specifically belonging to the Bear clan (Gitdumen) and Grizzly house (Cas yex). Chef Andrew’s passion for cooking stems from his upbringing, where he participated in traditional Indigenous practices such as fishing, hunting, and preparing food on open fires. As of late, Chef Andrew creates Indigenous menus for international restaurants and hotels and offers cooking lessons to Indigenous students. He is known for his two cookbooks, A Feast for All Seasons and Modern Native Feasts, which introduce Indigenous recipes, such as his Grilled Salmon Skewers and Fresh Dill Sauce, to households across the globe.^[3] The full recipe can be found online at Carrier Sekani Family Services. 

Protein Quality

While protein is contained in a wide variety of foods, it differs in quality. High-quality protein contains all the essential amino acids in the proportions needed by the human body. Therefore, the amino acid profile of different foods is one component of protein quality. Foods that contain some of the essential amino acids are called incomplete protein sources, and those that contain all nine essential amino acids are called complete protein sources, or high-quality protein sources. Complete protein sources include animal foods such as milk, cheese, eggs, fish, poultry, meat, and a few plant foods, such as soy and quinoa. The only animal-based protein that is not a complete source is gelatin, which is made of the protein collagen. Examples of incomplete protein sources include legumes and corn.

Most plant-based foods are deficient in at least one essential amino acid and therefore are incomplete protein sources. For example, grains are usually deficient in the amino acid lysine, and legumes are deficient in methionine or tryptophan. Because grains and legumes are not deficient in the same amino acids, they can complement each other in a diet. Incomplete protein foods are called complementary foods because when consumed in tandem, they contain all nine essential amino acids at adequate levels. Individuals from diverse ethnic backgrounds may have distinct dietary traditions that incorporate specific protein-rich foods. In certain Asian cuisines, tofu and tempeh are valued as plant-based complete protein sources, while in traditional Mexican cuisine, beans and corn tortillas are common complementary foods. Some examples of other complementary protein foods are provided in Table 6.4 “Complementing protein sources the vegan way.” Complementary protein sources do not have to be consumed at the same time—as long as they are consumed within the same day, you will meet your protein needs.

The second component of protein quality is digestibility, as not all protein sources are equally digested. In general, animal-based proteins are completely broken down during the process of digestion, whereas plant-based proteins are not. This is because some proteins are contained in the plant’s fibrous cell walls and these pass through the digestive tract unabsorbed by the body.

Protein Digestibility Corrected Amino Acid Score (PDCAAS)

The PDCAAS is a method to determine a food’s protein quality. It is calculated using a formula that incorporates the total amount of amino acids in the food and the amount of protein in the food that is actually digested by humans. The food’s protein quality is then ranked against the foods that have the highest protein quality. Milk protein, egg whites, whey, and soy all have a ranking of one, which is the highest ranking. Other foods’ ranks are listed in Table 6.5 “PDCAAS of various foods”.

Protein Considerations: Vegetarian/Vegan Diets, the Elderly and Athletes

Some groups may need to examine how to meet their protein needs more closely than others. We will take a closer look at the special protein considerations for vegetarians, the elderly, and athletes.

Vegetarian and Vegan Diets

People who follow variations of the vegetarian diet and consume eggs and/or dairy products can meet their protein requirements by consuming adequate amounts of these foods. People who follow vegetarian and vegan diets can also attain their recommended protein intakes if they give a little more attention to high-quality plant-based protein sources. However, when following a vegetarian diet, the amino acid, lysine, can be challenging to acquire. Grains, nuts, and seeds are lysine-poor foods, but tofu, soy, quinoa, and pistachios are all good sources of lysine. Following a vegetarian diet and getting the recommended protein intake is also a little more difficult because the digestibility of plant-based protein sources is lower than that of animal-based protein sources.

To begin planning a more plant-based diet, start by finding out which types of food you want to eat and in what amounts you should eat them to ensure you get the protein you need.

Here are some examples of the types of vegetarian diets:

1. Plant-based: Fifty percent of protein is obtained from plant foods.
2. Lacto-ovo vegetarian: All animal products except eggs and dairy are eliminated.
3. Vegan: All animal products are eliminated.

The Elderly

As we age, our muscle mass gradually declines. This is a process referred to as sarcopenia. A person is sarcopenic when their amount of muscle tissue is significantly lower than the average value for a healthy person of the same age. A significantly lower muscle mass is associated with weakness, movement disorders, and a generally poor quality of life. It is estimated that about half the population of men and women above the age of eighty are sarcopenic. A review published in the September 2010 issue of Clinical Intervention in Aging demonstrates that higher intakes (1.2 to 1.5 grams per kilogram of weight per day) of high-quality protein may prevent aging adults from becoming sarcopenic.^[9]

Currently, the RDA for protein for the elderly population is the same as that for the rest of the adult population. However, several ongoing clinical trials focused on determining the amount of protein in the diet that prevents the significant loss of muscle mass, specifically in older adults.

Athletes

Muscle tissue is rich in protein composition and has a very high turnover rate. During exercise, especially when it is performed for longer than two to three hours, muscle tissue is broken down and some of the amino acids are catabolized to fuel muscle contraction. To avert the excessive borrowing of amino acids from muscle tissue to synthesize energy during prolonged exercise, protein needs to be obtained from the diet. Intense exercise, such as strength training, stresses muscle tissue so that afterwards, the body adapts by building bigger, stronger, and healthier muscle tissue. The body requires protein post-exercise to accomplish this. Below are the current daily protein recommendations for athletes:^[10]

1. Endurance athlete: 1.2-1.6 g/kg of body weight per day. Some endurance athletes may need up to 2.1 g/kg of body weight per day
2. Strength athlete: 1.6-1.7 g/kg of body weight per day. Some strength athletes may need up to 2.2 g/kg of body weight per day
3. Game players: 1.2-1.4 g/kg of body weight per day.

There is general scientific agreement that endurance and strength athletes should consume protein from high-quality sources, such as dairy, eggs, lean meats, or soy; however, eating excessive amounts of protein at one time does not further stimulate muscle-protein synthesis. In fact, it is recommended that after a training session, athletes should consume 0.25-0.4 g/kg of body weight of protein in their post-exercise meal.^[11] Sports nutrition research also suggests that if strength athletes do not complete sessions that include exercise to failure, they should consume this protein within one hour after exercise to enhance muscle protein synthesis. However, if the athlete’s session includes exercise to failure, this window may extend up to 24 h. ^[12]

Protein Supplements

Branched-chain amino acid supplements containing leucine, isoleucine and valine have been touted as a way to build muscle tissue and enhance athletic performance. Despite these marketing claims, most studies that evaluated a variety of exercise types failed to show any performance-enhancing effects of taking branched-chain amino acids.^{[13] [14]} While it is recommended to consume protein in the post-exercise period that contains 3 g of leucine (leucine drives muscle protein synthesis) ^[15], because all BCAAs are absorbed using the same amino acid transporter, when you consume a high dose of BCAAs, isoleucine and valine may compete with leucine for absorption and therefore impact muscle protein synthesis.

There is some scientific evidence that suggests consuming high-quality dairy proteins, such as casein, whey, and soy proteins positively influences muscle protein synthesis. As a complete protein that is rapidly digestible and has a high leucine content, whey protein stimulates the most muscle protein synthesis, followed by soy and then casein. If you choose to buy a bucket of whey protein and use it to make a protein shake after an intense workout, there is no need to add more than what is required to obtain 0.25-0.4 g/kg of body weight, (approx. 20 to 25 grams of protein). As always, choosing high-quality protein foods will help you build muscle and not empty your wallet as much as buying some supplements. Moreover, relying on supplements for extra protein instead of food will not provide you with any of the other essential nutrients. The bottom line is that whether you are an endurance athlete, strength athlete, or just someone who takes Zumba classes, there is very little need to put your money into commercially sold protein and amino acid supplements. There is insufficient evidence to show that they are superior to regular food in enhancing exercise performance.

What about the numerous protein shakes and protein bars on the market? Are they a good source of dietary protein? Do they help you build muscle or lose weight as marketers claim? These are not such a bad idea for an endurance or strength athlete with little time to fix a nutritious exercise-recovery snack. However, before you ingest any supplement, do your homework. Read the label, be selective, and don’t use them to replace meals, but rather as exercise-recovery snacks now and then. Some protein bars have a high amount of carbohydrates from added sugars and are not the best source of protein, especially if you are not an athlete. Protein bars are nutritionally designed to restore carbohydrates and protein after endurance or strength training; therefore, they are not suitable meal replacements. If you want a low-cost alternative after an intense workout, make yourself a peanut butter sandwich on whole-grain bread and add some sliced banana for less than fifty cents.

Supermarket and health-food store shelves offer an extraordinary number of high-protein shake mixes. While the carbohydrate count is now lower in some of these products than it was a few years ago, they still contain added fats and sugars. They also cost, on average, more than two dollars per can. If you want more nutritional bang for your buck, make your own shakes from whole foods. Exploring low-cost alternatives that incorporate whole foods, such as fruits, vegetables, and legumes, can provide more affordable and accessible options for individuals from lower-income backgrounds. Use the AMDRs for macronutrients as a guide to fill up the blender. Your homemade shake can now replace some of the whole foods on your breakfast, lunch, or dinner plate. Unless you are an endurance or strength athlete and consume commercially sold protein bars and shakes only post-exercise, these products are not a good dietary source of protein.