- Calculate your Recommended Dietary Allowance for protein and know the A.M.D.R. for protein.
- Plan a one-day eating plan for one of the following: vegetarian, Lacto-Ovo vegetarian, and vegan. For each, calculate nutrient intake, then assess for adequacy, balance, and variety.
- Discuss protein supplements, their appropriate use, and overuse among the general population.
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 set by the I.O.M. for the Recommended Daily Allowance (R.D.A.) and A.M.D.R. for protein for different age groups are listed in Table 7.7.1. A Tolerable Upper Intake Limit for protein has not been set, but it is recommended that you not exceed the upper end of the A.M.D.R.
|Age Group||R.D.A.(g/day)||A.M.D.R.(% Calories)|
|Infants (0-6 months)||9.1*||Not Determined|
|Infants (7–12 months)||11.0||Not determined|
|Adult Males (19+)||56.0||10–35|
|Adult Females (19+)||46.0||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 R.D.A.s 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 R.D.A., therefore, is the amount of protein a person should consume in their diet 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:
Note that if a person is overweight, the amount of dietary protein recommended can be overestimated as this formula is based on having the correct proportion of lean body mass.
The I.O.M. used data from multiple studies that determined nitrogen balance in people of different age groups to calculate the R.D.A. for protein. 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 negative nitrogen balance when the amount of excreted nitrogen is greater than that 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 who has a low-protein diet may also be in negative nitrogen balance as they are taking in less protein than what they actually need. 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 burn or wound may also be in positive nitrogen balance because protein is being used to repair tissues.
Normal use of protein
- Nitrogen intake = nitrogen excreted
Higher use of protein
- Nitrogen intake is greater than nitrogen excreted (occurs during pregnancy or high growth periods)
Body in undersupplied with nitrogen
- Nitrogen intake is less than nitrogen excreted (occurs during fasting, certain diseases, injuries and wounds)
Dietary Sources of Protein
The protein food group consists of foods made from meat, seafood, poultry, eggs, soy, 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. Simply put, different protein sources differ in their additional components, so it is necessary to pay attention to the whole nutrient “package.” 1 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 fiber. 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, in order 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 7.7.2 . To find out the complete nutrient package of different foods, visit the US Department of Agriculture (USDA) website listed below.
1 “Harvard School of Public Health. “Protein: The Bottom Line.” The Nutrition Source. © 2012 The President and Fellows of Harvard University. http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/protein/. Accessed June 21, 2019.
|Food||Protein Content (g)||Saturated Fat (g)||Cholesterol (mg)||Calories|
|Hamburger patty 3 oz. (80% lean)||22.0||5.7||77||230|
|Hamburger patty 3 oz. (95% lean)||22.0||2.3||60||139|
|Top Sirloin 3 oz.||25.8||2.0||76||158|
|Beef chuck 3 oz. (lean, trimmed)||22.2||1.8||51||135|
|Pork loin 3 oz.||24.3||3.0||69||178|
|Pork ribs (country style, 1 piece)||56.4||22.2||222||790|
|Chicken breast (roasted, 1 c.)||43.4||1.4||119||231|
|Chicken thigh (roasted, 1 thigh)||13.5||1.6||49||109|
|Chicken leg (roasted, 1 leg)||29.6||4.2||105||264|
|Salmon 3 oz.||18.8||2.1||54||175|
|Tilapia 3 oz.||22.2||0.8||48||109|
|Halibut 3 oz.||22.7||0.4||35||119|
|Shrimp 3 oz.||17.8||0.2||166||84|
|Shrimp (breaded, fried, 6–8 pcs.)||18.9||5.4||200||454|
|Tuna 3 oz. (canned)||21.7||0.2||26||99|
|Soybeans 1 c. (boiled)||29.0||2.2||0||298|
|Lentils 1 c. (boiled)||17.9||0.1||0||226|
|Kidney beans 1 c. (canned)||13.5||0.2||0||215|
|Sunflower seeds 1 c.||9.6||2.0||0||269|
This interactive USDA tool allows you to enter the foods you eat (with serving size) and find out the whole nutrient package.
The USDA provides some tips for choosing your dietary protein sources. Their motto is, “Go Lean with Protein”. The overall suggestion is to eat a variety of protein-rich foods to benefit health. The USDA recommends lean meats, such as round steaks, top sirloin, extra-lean ground beef, pork loin, and skinless chicken. Additionally, a person should consume 8 ounces of cooked seafood every week (typically as two 4-ounce servings) to assure they are getting the healthy omega-3 fatty acids that have been linked to a lower risk for heart disease. Another tip is choosing to eat beans, peas, or soy products as a main dish. Some of the menu choices include chili 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, the USDA has much more information on how to 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.
The American Heart Association has a great infographic regarding portion sizes of protein. Click here to see it.
The USDA manages the website choosemyplate.gov. The site provides a lot of tips and information about protein-rich foods.
Tools for Change
Try some new, healthy, protein-rich food recipes by visiting the Harvard School of Public Health website. You will find recipes for protein foods and a quiz as well.
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. The amino acid profile of different foods is, therefore, one component of protein quality. Foods that contain some of the essential amino acids are called incomplete protein sources, while those that contain all nine essential amino acids in ratios that support growth are called complete protein sources, or high-quality protein sources. Foods that are complete protein sources include animal foods such as milk, cheese, eggs, fish, poultry, and meat, and a few plant foods, such as soy and quinoa (Figure 7.7.2). The only animal-based protein that is not complete is gelatin, which consists of the protein, collagen.
Most plant-based foods are low 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 do not contain methionine or tryptophan. Because grains and legumes are not low 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. Some examples of complementary protein foods are given in Table 7.7.3. Most vegetarians who consume sufficient energy and consume grains, legumes, and seeds do not need to consider complementing proteins. They will consume sufficient amino acids each day to meet their protein requirements.
Tools For Change
Explore some ethnic grocery markets to find new high-protein foods for your diet and/or experiment with the much cheaper plant-based protein sources. See Table 6.7.3 for complementing protein sources in a vegan way.
|Foods||Decreased Amino Acids||Complementary Food||Complementary Menu|
|Legumes||Methionine, tryptophan||Grains, nuts, and seeds||Hummus and whole-wheat pita|
|Grains||Lysine, isoleucine, threonine||Legumes||Cornbread and kidney bean chili|
|Nuts and Seeds||Lysine, isoleucine||Legumes||Stir-fried tofu with cashews|
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 (P.D.C.A.A.S.)
The P.D.C.A.A.S. is a method adopted by the US Food and Drug Administration (F.D.A.) 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 highest in protein quality. Milk protein, egg whites, whey, and soy all have a ranking of one, the highest-ranking. Other foods’ ranks are listed in Table 7.7.4
Protein Needs: Special Considerations
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.
Vegetarians and Vegans
People who follow variations of the vegetarian diet and consume eggs and/or dairy products can easily meet their protein requirements by consuming adequate amounts of these foods. Vegetarians and vegans 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 made a little more difficult because the digestibility of plant-based protein sources is lower than the digestibility of animal-based protein.
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 that you get the protein you need.
The D.G.A.C. states that people who choose to obtain proteins solely from plants should include foods fortified with vitamins B12, D, and calcium. Other nutrients of concern may be omega-3 fatty acids and choline. Two large observational studies with thousands of participants demonstrated that in comparison to regular meat-eaters, people who followed a vegetarian diet had a significantly decreased risk of dying from heart disease or cancer.2
2 Lindbloom, E. “Long-Term Benefits of a Vegetarian Diet.” Am Fam Physician.2009; 79 (7): 541–42. Accessed June 21, 2019.
Tools For Change
Make a sustainable choice to go meatless more than once a week. To get some ideas on how to expand your dietary choices, see this handout with links from the Vegetarian Resource Group.
As we age, 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 US population of men and women above the age of eighty are sarcopenic. Experts continue to debate whether higher levels of protein intake above the R.D.A. may slow or reverse sarcopenia. Baum et al. 1discussed these issues in the peer-reviewed journal, Nutrients. They suggest that by utilizing the A.M.D.R. range of 35% of total energy requirements, protein needs could be optimized. Currently, the R.D.A. for protein for elderly persons is the same as that for the rest of the adult population, but several clinical trials are ongoing and are focused on determining the amount of protein in the diet that prevents the significant loss of muscle mass specifically in older adults.
1 Baum JI, Kim IY, Wolfe RR. Protein Consumption and the Elderly: What Is the Optimal Level of Intake?. Nutrients. 2016;8(6):359. Published 2016 Jun 8. DOI:10.3390/nu8060359.
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 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 afterward, the body adapts by building bigger, stronger, and healthier muscle tissue. The body requires protein postexercise to accomplish this. The I.O.M. does not set different R.D.A.s for protein intakes for athletes, but the Academy of Nutrition and Dietetics, the American College of Sports Medicine, and Dietitians of Canada have the following position statement:
- Ingesting protein (approximately 20 to 30 g total protein, or approximately 10 g essential amino acids) during exercise or the recovery period(postexercise) led to increased whole-body and muscle protein synthesis as well as improved nitrogen balance.
- Current data suggest that dietary protein intake necessary to support metabolic adaptation, repair, remodeling, and for protein turnover generally ranges from 1.2 to 2.0 g/kg/day.
An endurance athlete who weighs 170 pounds should take in 93 to 108 grams of protein per day ((170 ÷ 2.2) × 1.2 and (170 ÷ 2.2) × 1.4). On a 3,000-kilocalorie diet, that amount is between 12 and 14 percent of total kilocalories and within the A.M.D.R.. 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 an excessive amount of protein at one time does not further stimulate muscle-protein synthesis. Nutrition experts also recommend that athletes consume some protein within one hour after exercise to enhance muscle tissue repair during the recovery phase, but some carbohydrates and water should be consumed as well.
|Foods||Protein (g)||Carbohydrates (g)||Calories|
|Whole-grain cereal with nonfat milk||14||53||260|
|Medium banana with nonfat milk||10||39||191|
In response to hard training, a person’s body also adapts by becoming more efficient in metabolizing nutrient fuels both for energy production and building macromolecules. However, this raises another question: if athletes are more efficient at using protein, is it necessary to take in more protein from dietary sources than the average person? There are two scientific schools of thought on this matter. One side believes athletes need more protein and the other thinks the protein requirements of athletes are the same as for non-athletes. There is scientific evidence to support both sides of this debate. The consensus of both sides is that few people exercise at the intensity that makes this debate relevant. It is good to remember that the increased protein intake recommended by the Academy of Nutrition and Dietetics, American College of Sports Medicine, and Dietitians of Canada still lies within the A.M.D.R. for protein.
Visit “Nutrition 101, Eating for Exercise and Sports.” This USDA site contains a wealth of nutritional information for active people.
Protein supplements include powders made from compounds such as whey or soy and amino acids that either come as a powder or in capsules. We have noted that the protein requirements for most people, even those that are active, is not high. Is taking protein supplements ever justified, then? Neither protein nor amino acid supplements have been scientifically proven to improve exercise performance or increase strength. In addition, the average American already consumes more protein than is required. Despite these facts, many highly physically active individuals use protein or amino acid supplements. According to the Academy of Nutrition and Dietetics, American College of Sports Medicine, and Dietitians of Canada 2016 Position Statement, “When whole-food protein sources are not convenient or available, then portable, third-party tested dietary supplements with high-quality ingredients may serve as a practical alternative to help athletes meet their protein needs.” Branched-chain amino acids, such as leucine, are a way to build muscle tissue and enhance athletic performance. Despite marketing claims, an 8 oz glass of low-fat milk contains adequate leucine and is easily and rapidly digested to help stimulate muscle growth and repair. In fact, high-quality protein foods are a better and cheaper source for branched-chain amino acids and a chicken breast (100 grams) contains the equivalent of seven times the amount of branched-chain amino acids as one supplement tablet. This means if you are interested in enhancing exercise performance or building muscle, you do not need to support the $20 billion supplement industry.
Although the evidence for protein and amino acid supplements impacting athletic performance is lacking, there is some scientific evidence that supports consuming high-quality dairy proteins, such as casein, whey, and soy proteins positively influencing muscle recovery in response to hard training. If you choose to buy a bucket of whey protein, do not add more than what is required to obtain 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 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 or 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. The evidence to show that they are superior to regular food in enhancing exercise performance is not sufficient.
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 who has 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 actually the best source for 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 good 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 lower now in some of these products than 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. Use the A.M.D.R.s for macronutrients as a guide to filling 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 postexercise, these products are not a good dietary source of protein.
Proteins in a Nutshell
Proteins are long chains of amino acids folded into precise structures that determine their functions, which are in the tens of thousands. They are the primary construction materials of the body serving as building blocks for bone, skin, hair, muscle, hormones, and antibodies. Without them we cannot breakdown or build macromolecules, grow, or heal from a wound. Eat proteins in moderation, at least 10 percent of the calories you take in and not more than 35 percent. Too little protein impairs bodily functions and too much can lead to chronic disease. Proteins are in a variety of foods. More complete sources are in animal-based foods, but choose those low in saturated fat and cholesterol. Some plant-based foods are also complete protein sources and don’t add much to your saturated fat or cholesterol intake. Incomplete protein sources can easily be combined in the daily diet and provide all of the essential amino acids at adequate levels. Growing children and the elderly need to ensure they get enough protein in their diet to help build and maintain muscle strength. Even if you’re a hardcore athlete, get your proteins from nutrient-dense foods as you need more than just protein to power up for an event.
Nuts are one nutrient-dense food with a whole lot of protein. One ounce of pistachios, which is about fifty nuts, has the same amount of protein as an egg and contains vitamins, minerals, healthy polyunsaturated fats, and antioxidants. Moreover, the F.D.A. says that eating one ounce of nuts per day can lower your risk for heart disease. Can you be a hardcore athlete and a vegetarian? Many Olympians are vegetarians: figure skater Charlene Wong, sprinter Leroy Burrell, hurdler Edwin Moses, and Carl Lewis, who won ten medals (nine of them gold) in track and field. The analysis of vegetarian diets by the D.G.A.C. did not find that they were inadequate in any nutrients, but did state that people who obtain proteins solely from plants should make sure they consume foods with vitamin B12, vitamin D, calcium, omega-3 fatty acids, and choline. Iron and zinc may also be of concern, especially for female athletes. Being a vegetarian athlete requires that you pay more attention to what you eat, however, this is also a true statement for all athletes.
Getting All the Nutrients You Need – The Plant-Based Way
Below are five ways to assure you are getting all the nutrients you need while working toward a more plant-based diet;
- Get your protein from foods such as soybeans, tofu, tempeh, lentils, and beans. Many of these foods are high in zinc too.
- Eat foods fortified with vitamins B12 and D and calcium. Some examples are soy milk and fortified cereals.
- Get enough iron in your diet by eating kidney beans, lentils, whole-grain cereals, and leafy green vegetables.
- To increase iron absorption, eat foods with vitamin C at the same time.
- Don’t forget that carbohydrates and fats are required in your diet too, especially if you are training. Eat whole-grain bread, cereals, and pasta. For fats, eat an avocado, add some olive oil to a salad or stir-fry, or spread some peanut or cashew butter on a bran muffin.
- The R.D.A. set for protein for adults is 0.8 grams per kilogram of body weight and represents the amount of protein in the diet required to balance the protein that is used up by the body and that is excreted.
- The protein food group consists of foods made from meat, seafood, poultry, eggs, soy, beans, peas, and seeds.
- By determining a food’s amino acid content and the amount of protein that is actually digested and absorbed we can determine that food’s protein quality.
- Most animal-based proteins are complete protein sources and most plant-based proteins are incomplete protein sources. The exceptions are soy, which is a plant-based complete protein source, and gelatin, which is an incomplete animal-based protein source.
- A vegan’s protein needs are slightly higher because of the lower digestibility of plant-based sources. The elderly may require more protein in their diets to prevent significant muscle wasting. There is some debate on whether and how much athletes protein should be included in an athlete’s diet.
- Protein and amino acid supplements do not enhance exercise performance and do not promote a gain in muscle mass any more so than protein from foods.
- Unless you are an endurance or strength athlete, commercially sold protein bars and shakes are not a good dietary source of protein.
- What is the consensus in your class on how easy it is to follow a more plant-based diet?
- Even though high-protein diets may not cause significant health problems in healthy people, are they a sustainable option for losing weight? What are the consequences to the environment of consuming more and not less animal-based sources of protein?