An oxymoron is a figure of speech in which contradictory terms appear in conjunction. One of my favorite oxymorons is ‘jumbo shrimp.’’ Some food and beverage manufacturers promote their products using terms such as ‘high-energy protein bar’ or ‘high-energy protein drink.’ These oxymorons will serve as the basis for our discussion below.
First, some background information: Protein is one of 6 essential nutrients needed by the body for survival (the other 5 are carbohydrate, fat, vitamins, minerals, and water). Amino acids serve as the building blocks of the large and complex protein molecules that we consume in our diet. In fact, dietary protein winds up as individual amino acids at the end of the digestion process. The amino acids are then transported across the intestinal wall and into the bloodstream.
You don’t have to look very far to find protein in the U.S. food supply. Animal and soy products, as well as quinoa (a type of grain) are complete proteins; which means that they contain all of the essential amino acids in the balance required by the body. Plant-based proteins such as nuts and seeds, green vegetables, whole grains, and legumes are also a significant source of dietary protein. However, these sources are incomplete proteins because each one is deficient in one of the essential amino acids. Vegans easily solve this potential problem by combining their incomplete proteins in certain ways. For example, consuming red beans and rice or a peanut butter sandwich yields a complete protein, with all of the essential amino acids. This is where the term ‘complementary proteins’ comes from. The essential amino acid lacking in the red beans is found in the rice, and vice-versa. Thus, the red beans and the rice are complementary proteins, much like the bread and the peanut butter.
Next, let’s discuss the many functions of dietary protein.
Amino acids play an important role in cell growth and cell repair; this of course includes muscle cells. Additionally, many important substances within the body are made from amino acids. These include hemoglobin, enzymes, some hormones, and the plasma proteins albumin and globulin. As we will see below, protein also serves as a very minor source of energy.
Now for the energy part of our discussion: All cells in the body require energy in order to function. This chemical energy, known as adenosine triphosphate or ATP, comes primarily from the breakdown of carbohydrate and fats inside our cells. In fact, the overwhelming majority of published studies have shown that for normal individuals, ~95% of the energy needed for cell function comes from carbohydrate and fat. The other ~5% comes from amino acids (protein). It is well accepted that in continuous athletic events lasting for more than a couple of hours, amino acids can provide up to 12-15% of the body’s energy needs. The branched-chain amino acids (leucine, isoleucine, and valine) are particularly important for this relatively small proportion of energy. For example, during the later portion of a 5-hour stage in the Tour de France, cyclists may obtain up to 15% of their energy from amino acids. So, even for the tiny percentage of the adult population who are training or competing for hours at a time, protein is not a major fuel source for energy. Thus, the notion of a ‘high-energy protein bar’ or ‘high-energy protein drink’ is a perfect example of an oxymoron! We are not saying that these bars or drinks are necessarily bad; it’s just that protein is not a major fuel source for energy unless you are in a starvation state to begin with.
So how much protein do people need? Great question! That depends on a number of factors such as age, sex, body size, how much exercise is performed, and what the goals are.
For the vast majority of the adult population who is either sedentary or engages in regular light physical activity, the current recommendation is 0.36 grams of dietary protein per pound of body weight per day. For example, a normal adult individual weighing 180 lbs. would need about 65 grams of protein per day. For individuals who are training vigorously on a daily or near-daily basis, the recommendation is 0.6 grams and 0.8 grams of protein per pound of body weight for endurance athletes and strength athletes, respectively. Despite what you might hear either from Billy Biceps in the gym or from the manufacturers of protein supplements, there’s really no evidence of a benefit from consuming amounts greater than this. Regardless of which of the physical activity categories you fall into, it should be fairly easy for you to obtain all of the protein you need from food. Therefore, you need not walk around with a bucket of protein powder all day, even if you are highly active.
Here are some examples of the protein content of various foods and beverages:
- 4 ounces of chicken, beef or fish contains about 30 grams of protein
- 8 ounces of cow or soy milk contains about 8 grams of protein (please note that rice milk and almond milk contain only about 1 gram of protein per 8 ounces).
- 1 cup of yogurt contains about 8 grams of protein
- 1 cup of Greek yogurt contains about 13 grams of protein
- 1 cup of beans contains about 12 grams of protein
- 1 large egg contains about 7 grams of protein
- 1 ounce of cheese contains about 6 grams of protein
- 1 cup of cooked pasta contains about 5 grams of protein
- 1 slice of bread contains 2 grams of protein
So the main takeaways from this discussion are that:
- While protein is an essential nutrient, it is not a major fuel source for energy.
- The average normal healthy adult requires about 0.36 grams of protein per pound of body weight per day.
- Additional protein is needed for the relatively small percentage of adults who are training vigorously on a daily basis.
- Protein is very easy to find in the U.S. food supply.