As mentioned in the previous post, Protein is a macronutrient and that means that we measure its consumption by the gram. Protein provides us with 4 kcal per gram. Usually when someone is speaking about protein they will say that it “has 4 Calories per gram.” Just remember that that is a capital ‘C’ on Calories.
Chemically, protein contains carbon, oxygen, and hydrogen, just like carbohydrates and fat. But it also contains nitrogen. Though protein is not the only source of dietary nitrogen, it is the most important source and proteins are 13-19% nitrogen by weight. In future posts we will address nitrogen more, but for now it is just an interesting distinction worth remembering.
Proteins are made up of chains of amino acids (AA). There are about 20 amino acids that humans use and 9 of these are essential. In the study of nutrition, essential has a very precise meaning: an essential nutrient is a nutrient that must be consumed in the diet because the body does not produce any or in amounts too low to meet metabolic needs; removing them from the diet will result in poor and deteriorating health.
Despite the fact that the body can use protein for energy, only some of that energy is actually used for the purpose of meeting our daily needs. This is because protein has so many more functions than just providing energy.
For example, protein is the primary structural component throughout our body. It is part of our muscles, bones, and other connective tissue. Proteins also make up our enzymes (catalysts for metabolic reactions), transport molecules and other parts of our blood, and antibodies. Proteins make up our organs, hair and nails and some hormones.
It is hard to overstate the importance of adequate protein consumption. Fortunately, most Americans eat more protein than is necessary to support these functions and the remainder is used to meet our energy needs.
The Recommended Daily Allowance (RDA) for protein is established at 56 grams per day for men and 46 grams per day for women. This is the average amount that a generally healthy person must consume each day to remain healthy. If you want to do the math, this amounts to 0.4 grams of protein per pound of body weight.
How easy is it to consume this much protein? If you eat an omnivorous diet, it is hard not to get this much. Six ounces of roasted chicken breast will provide you with 39 grams. Meat and animal products are the easiest way to meet your daily protein requirements, but they are far from the only way.
For the vegans out there, here are some examples of plant based sources of protein: steamed broccoli has 4 grams of protein per cup, brown rice has 5 grams of protein per cup, and black beans have 15g per cup. Though vegans and vegetarians are at an increased risk of consuming too little protein, even a moderately well-planned diet can provide more than enough.
But is enough actually enough?
Remember, the RDA is meant to be a guideline for most healthy people. How does physical activity change our needs for protein?
For those who are resistance training, the requirements jump to 0.5-0.9 grams per pound of body weight with the low end being for more recreational lifters and the higher end being for those who are lifting more intensely trying to gain muscle.
Even endurance trained athletes can benefit from a higher daily consumption of protein. Recommendations for them range between 0.6-0.7 grams per pound of body weight.
These recommendations are for both sexes. The above RDA is different for males and females because males are typically larger.
As an example, a relatively lean 150 pound person would require 60 grams of protein (150 pounds × 0.4 grams/pound) of protein if sedentary...
between 75 and 135 grams (150 × 0.5 to 150 ×0.9) if resistance training...
and between 90 and 105 grams (150 × 0.6 to 150 × 0.7) grams per day if engaging in endurance training.
It is worth noting that there is rarely harm in overshooting these targets if there are no underlying conditions.
In the next post we will take a look at carbohydrates.