In this new series on different aspects of using food to Health Yourself, Victor Katch examines the conundrum of proteins; their different kinds, where they come from, how much you need, and the problem of eating meat as your major source of protein. As an alternative, he suggests a whole-food, plant-based approach to fulfilling protein needs.
In last month’s column on confined animal feeding operations (CAFOs) I brought up the many problems related to decreasing meat quality resulting from industrial farming. Many of the emails I received raised questions regarding the role of meat in our diet, specifically related to protein quality. How could someone get enough protein, regardless of where and how it was grown, if one did not eat meat?
In this month’s column I discuss the many aspects of protein and try to clear up some common misconceptions. In subsequent columns I will discuss fat and carbohydrate nutrients and address the roles these nutrients play in your personal health promotion.
Macro- and MicronutrientsThere are five major nutrients. Macronutrients consist of carbohydrates (sugars), lipids (from the Greek lipos, meaning “fat), and proteins (from Greek, meaning “of prime importance”). Macronutrients provide energy to maintain bodily functions during rest and physical activity. They serve to preserve the body’s structural and functional integrity.
Micronutrients consist of vitamins and minerals, found in the watery medium of the body, that play highly specific roles in facilitating energy transfer and tissue synthesis. Micronutrients contain no energy.
Combinations of linked amino acids form proteins. An average-sized adult contains between 22-26 pounds of protein, with skeletal muscle containing the largest quantity (13-18 pounds; 60- 75 percent of all the body’s protein). Additionally, approximately 7.4 oz. (210 grams) of amino acids exist in free form, largely as glutamine, a key amino acid that serves as fuel for immune system cells.
The typical adult generally ingests about 10-15 percent of their total calories as protein. During digestion, protein breaks down to amino acids for absorption by the small intestine. Amino acids not used to synthesize protein or other compounds (e.g., hormones), or not used for energy metabolism quickly convert to fat, and store in different fat pads around the body (think belly fat, thigh fat, and … ). That’s right, excess proteins convert to fat for storage!
Structurally, proteins resemble carbohydrates and fats because they contain carbon, oxygen, and hydrogen atoms. But they also contain about 16 percent nitrogen, along with sulfur and occasionally phosphorus, cobalt, and iron. A combination of more than 50 linked amino acids forms a protein. Approximately 50,000 different protein-containing compounds exist in the body. The biochemical functions and properties of each protein depend on the sequence of specific amino acids.
There are 20 different amino acids required by the body. The potential for combining these 20 amino acids produces an almost infinite number of possible proteins, depending on their amino acid combinations. For example, linking just three different amino acids could generate 203, or 8,000, different proteins!
Kinds of protein
The body cannot synthesize eight amino acids (nine in children and some older adults), so they must be consumed in foods that contain them. We call these essential (or indispensable) amino acids. You may have heard or read about these essential amino acids: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
With a few exceptions, the body manufactures the remaining nine nonessential amino acids. The term nonessential does not indicate a lack of importance; rather, they are synthesized from other compounds already in the body at a rate that meets the body’s needs for normal growth and tissue repair.
Animals and plants both manufacture proteins that contain essential amino acids.
Plants synthesize amino acids by incorporating nitrogen from the soil (along with carbon, oxygen, and hydrogen from air and water). In contrast, animals have no broad capability for amino acid synthesis. Instead, they consume most of their protein by eating plants (or other animals).
Complete proteins (sometimes referred to as higher-quality proteins) come from foods that contain all the essential amino acids in the quantity and correct ratio the body needs. An incomplete protein lacks one or more essential amino acid. A diet of incomplete protein can eventually lead to protein malnutrition, whether or not the food sources consumed contain an adequate amount of energy or protein.
How much protein do you need?
It is impossible to recommend precisely the exact amount of protein any one individual needs. It can depend on many factors including body size, level of physical activity, gender, etc. Through the years, however, beginning in 1943 and updated periodically, the Food and Nutrition Board of the National Research Council/National Academy of Science has generated nutritional guidelines based on “best” scientific evidence. Currently, the Recommended Dietary Allowance (RDA) for protein, expressed as a daily average, represents a liberal yet safe excess to prevent protein deficiencies in practically all healthy persons. The RDA represents a probability statement for adequate nutrition; as nutrient intake falls below the RDA, the statistical probability for “malnourishment” increases for that person and the probability progressively increases with lower intake.
The following table lists the protein RDAs for adolescents and adults. On average, 0.029 oz. of protein per 2.2 lbs body weight (0.8 g per kg) represents the RDA.
|Protein Recommended Dietary Allowance (RDA) for Adolescent and Adult Mean and Women|
|Grams protein perk kg body weight||
|Grams protein based on average body weight||
To put this in perspective by way of an example, I weigh 156 lbs (70.7 kg), so my protein requirement is 4.5 oz. (57 g) protein per day (0.8 g/kg x 70.7 kg).
Think about this for a moment. To get my protein requirement I could visit my local McDonald’s and consume one quarter pounder with bacon and cheese (37 g; 600 kcal); one large order of french fries (6 g; 500 kcal); and one (16 fl. oz.) chocolate McCafe shake (15 g; 700 kcal). At this single meal with only three items I’ve already consumed my RDA for protein and a whopping 1800 kcal, and I haven’t even counted my breakfast or what I would eat for dinner. At this rate, I could overdose on protein, increase my percent of body fat (remember, excess protein stores as fat), and consume way too many calories. WOW!
The protein RDA holds even for overweight persons; it includes a reserve of about 25 percent to account for individual differences in the protein requirement for about 97 percent of the population. Generally, the protein RDA (and the quantity of the required essential amino acids) decreases with age. Pregnant women should increase total daily protein intake by a little under 1 oz. per day, and nursing mothers should increase their intake by 0.35 oz. per day. Stress, disease, and injury usually increase daily protein requirements.
In my Nutrition, Exercise, and Weight Control class, I poll students every semester about why they eat meat. Believe me, I get some strange answers, but more than 98 percent of them say (incorrectly) you need to eat meat everyday to ensure adequate protein intake.
Sources of food that contain high-quality protein (rated on a scale from 0-100) are shown in the table below. Eggs provide the optimal mixture of essential amino acids among all foods; hence they earn a protein rating of 100.
|Examples of common sources of dietary protein rated for protein quality.|
With the exception of a few plant proteins like soy-isolate proteins (such as tofu and quinoa, which also provide all essential amino acids), most of the high-quality proteins in our diet come from animal sources. However, a major problem with relying on animal sources for the majority of dietary protein, as is the case in most major industrialized nations, is the relatively high cholesterol and saturated fatty acid intake that comes with them (more on this below).
While plant-based foods remain incomplete in one or more essential amino acids, eating a variety of grains, fruits, and other plant-based foods (vegetables) can easily supply all of the essential amino acids.
The problem of eating meat as your major source for protein
Undeniably, meat is a fine source of high-quality protein, but relying on meat as a major source of protein leads to unintended health consequences that are now coming to light.
The scientific research literature is growing (although admittedly inconsistent) showing a strong causal link between animal consumption (primarily red meat) and an increasing number of health-related problems. These studies stand up to strong scientific scrutiny and their increasing frequency in scientific journals cannot be dismissed as frivolous.
For example, red meat associates with development of type 2 diabetes and cardiovascular disease; increased weight and body fat; obesity-related inflammation and insulin resistance; a higher plasma concentration of C-reactive protein (a cardiovascular inflammatory biomarker); abnormal glucose metabolism; increased risk of stroke; high blood pressure; kidney disease; and decreased longevity.
The scientific weight of accumulated research suggests substituting servings of animal-based protein (in particular, red meat) with plant-based protein to improve health outcomes. Thus, meat eaters should consider at the minimum:
- reducing the amount of animal products consumed per day
- eliminate meat at least one day per week
- make meat a side dish rather than a main dish
- adopt a whole food, plant-based diet!
A whole-food, plant-based diet: The vegan approach
True vegetarians, or vegans, consume nutrients from only two sources—the plant kingdom and dietary supplements (although not necessary). Vegans constitute less than 4 percent of the U.S. population, yet between 5-7 percent of Americans consider themselves “almost” vegetarians. For vegans, nutritional diversity remains the key to obtain all of the essential amino acids. For example, a vegan diet contains all the essential amino acids if the recommended intake for protein contains 60 percent of protein from grain products, 35 percent from legumes, and 5 percent from green leafy vegetables.
An increasing number of competitive and champion athletes consume diets consisting predominantly of nutrients from varied plant sources, including some dairy and meat products with no degradation in performance. In contrast to diets that rely heavily on animal sources for protein, well-balanced vegan and vegetarian-type diets provide abundant good carbs so crucial for good health and not surprisingly intense, prolonged training. Such diets contain abundant fiber and little or no cholesterol. A plant-based diet also includes more than enough diverse phytochemicals and antioxidant vitamins.
A lactovegetarian diet provides milk and related products such as ice cream, cheese, and yogurt. The lactovegetarian approach minimizes the difficulty of consuming sufficient high-quality protein and increases the intake of calcium, phosphorus, and vitamin B12 (produced by bacteria in the digestive tract of animals). Adding an egg to the diet (ovolactovegetarian) ensures sufficient high-quality protein intake.
One of the most common myths about the vegan diet is that after ditching meat it becomes nearly impossible to get enough protein. The table below offers some examples of plant-based options to get your protein.
|Cooked kale||2 cups||5|
|Boiled peas||1 cup||9|
|Sweet potato||1 cup cooked||5|
|Refried beans||1 cup||15.5|
|Garbanzo beans (and hummus)||1 cup||14.5|
|Pinto, kidney, black beans||1 cup||13-15|
|Sesame seeds||1 oz.||6.5|
|Walnuts||1/4 cup (2 oz.)||5|
|Nut butters (peanut, almond, cashew)||2 tbsp.||8|
|Non-dairy milk (soy, almond, ancient grain)||1 cup||7-9|
|Grains: Quinoa (amaranth, bulgar, wheat germ, oat bran)||1 cup||9|
|Seitan or flavored wheat gluten||1 cup||52|
|Sprouted grain products (buns, tortillas)||1 slice||7-10|
- 1Anthelme Brillat-Savarin, Physiologie du Gout, ou Meditations de Gastronomie Transcendante, 1826.
- Azadbakht, L., Esmaillzadeh A., Red meat intake is associated with metabolic syndrome and the plasma C-reactive protein concentration in women. Journal of Nutrition 2009;139:335–9.
- Feskens, E.J. et al. Meat consumption, diabetes, and its complications. Curr Diab Rep 2013;13:298–306.
- Montonen, J. et al. Consumption of red meat and whole-grain bread in relation to biomarkers of obesity, inflammation, glucose metabolism and oxidative stress. Eur J Nutr 2013;52:337–45.
- Mursu, J. et al. Intake of fruit, berries and vegetables and risk of type 2 diabetes in Finnish men: the Kuopio Ischaemic Heart Disease Risk Factor Study. Am J Clin Nutr 2014;99:328–33.
- Pan, A. et al. Red meat consumption and risk of type 2 diabetes: 3 cohorts of US adults and an updated meta-analysis. American Journal of Clinical Nutrition 2011;94:1088–96.
- Sylvia, H.L. et al. Association between red meat intake and biomarkers of inflammation and glucose metabolism in women. American Journal of Clinical Nutrition 2014;99:352-60.
- The InterAct Consortium. Association between dietary meat consumption and incident type 2 diabetes: the EPIC-InterAct study. Diabetologia 2013;56:47–59.
- Vergnaud, A-C et al. Meat consumption and prospective weight change in participants of the EPIC-PANACEA study. Am J Clin Nutr 2010;92:398–407.