Eating an ideal amount of high-quality protein is a cornerstone of optimal nutrition. Unfortunately, not all proteins are created equal.
Deriving a scoring system to rate the relative quality of proteins dates back to the early 1970s. The Food and Agriculture Organization of The World Health Organization (FAO/WHO) is the official body responsible for ranking the quality of dietary proteins. What we’ve discovered in the process is that essential amino acids (EAAs) play a primary role in protein nutrition and overall well-being.
When ranking protein quality, scientists must first consider the amount of essential amino acids (EAAs) relative to the amount of non- essential amino acids (NEAAs) in the protein. In addition, the profile of the EAAs—which is the amount of each EAA in relation to the others—is favorable in a high-quality protein. The optimal profile is defined as closely paralleling the requirements for the individual EAAs. Also, EAAs in the dietary protein must be able to be digested and absorbed into the body, and a high-quality protein is highly digestible.
All the qualities of a protein are put into an equation to calculate the Digestible Indispensable Amino Score (DIAAS). The DIAAS is expressed as a percent of the requirement for the most limiting individual EAA if you were to eat the estimated average requirement for dietary protein (0.66 g protein/kg/day) of the test protein.
For example, a score of 100 means that if you were to eat 0.66 g/kg/day of the test protein you would consume 100% of the essential amino acid that is the lowest content in the protein relative to its requirement. Subsequently, you would be consuming more than 100% of the requirements for all the other EAAs. Some representative DIAAS values are shown in the figure below. The higher the quality of the protein, the higher the value.
The highest quality proteins are “animal” based or derived from animals; these include meat, dairy, fish, poultry, and eggs. Lower quality proteins include many of the plant-based proteins such as those in wheat, beans, and rice. They are lower quality because they do not provide adequate amounts of all the EAAs and because of poorer digestibility and absorption.
Protein Food Sources
Take a look again at the values in the figure above. Excluding protein supplements, notice how you’re probably not eating many pure proteins. Rather, you are likely getting most of your proteins from food sources.
There are a number of things to consider when evaluating a protein food source. In addition to the protein quality, we should think about the non-protein components of the protein food source. For example, when you eat a steak you are consuming a lot of high-quality protein, but you are also eating about half of the calories in the form of saturated fat. When you eat kidney beans as a protein food source, you are also eating carbohydrate and fiber. These factors should be taken into account in dietary planning.
The protein density is high in a high-quality protein food source. Protein density refers to the amount of protein per total grams of food source. The significance of protein density can be appreciated by looking at the number of calories that must be consumed from a protein food source to meet all daily EAA requirements. Check out the figure below.
You may find some values surprising. For example, a hamburger is the poster-child for obesity in America, yet the number of calories you consume in the form of a beef patty to obtain your EAA requirements for the day is less than one-third the calories you need if you look to plant-based proteins to meet your EAA requirements. Furthermore, the fiber in plant-based food sources, while providing some health benefits, at the same time impede the digestion of EAAs in the protein component of the food, which in turn reduces the DIAAS.
Whether you look at the protein quality (DIAAS) or the protein density of protein food sources, it is evident why consumption of a variety of animal-based proteins simplifies the task of satisfying EAA requirements. It is possible to achieve adequate protein/EAA nutrition on a vegetarian or even a vegan diet, but much more careful planning is necessary. This planning is important because you will consume a much higher proportion of your caloric allotment for the day in conjunction with your protein food source, and this leaves less flexibility for the remainder of your diet.
Dietary EAA supplements can play a crucial role in enabling you to achieve optimal EAA nutrition. The DIAAS for a well-balanced EAA formulation is over 300, reflecting the complete absorption of free amino acids, the exclusion of NEAAs, and the ability to adapt the profile of the EAAs to match the metabolic requirements. In addition, protein density in a well-balanced EAA formulation is complete, as there is no non-protein component. EAA supplements can be beneficial in all circumstances and can be particularly useful in diets that are otherwise low in EAAs, which is the case with diets that limit the consumption of animal-based proteins.