Diet and Nutrition- Information regarding proteins and their importance in your diet

Function

The primary function of protein in your diet is to build and repair body tissues and structures. It is also involved in the synthesis of hormones, enzymes and other regulatory peptides. Additionally, protein can be used for energy if calories or carbohydrates are insufficient in the diet.

Proteins are made up of amino acids linked together by peptide bonds. The body uses approximately 20 amino acids to build its many different proteins.  These amino acids are like the letters of the alphabet—just as specific words are formed by certain sequences of letters, arranging the amino acids in different sequences will yield the body’s myriad of proteins, from a muscle protein like actin to proteins that make up the lens of the eye.  There are two general classes of amino acids: essential and non-essential.  Essential amino acids cannot be manufactured in the body or are manufactured in insufficient amounts; therefore, they must be obtained from your diet or some other exogenous source.

Due to their rate of synthesis within the body, arginine and histidine are considered semi-essential amino acids. It appears that these amino acids cannot be manufactured by the body at a rate that will support growth (especially in children).

Dietary protein is the delivery vehicle for amino acids. Meats, fruits, vegetables, grains, dairy products and even supplements supply us with the valuable building blocks of protein we need. If a type of food supplies all of the essential amino acids in appropriate ratios, it is called a complete protein. If a food source is low or lacking in one or more essential amino acid, it is called an incomplete protein. The essential amino acid that is missing or present in the smallest amount is called the limiting factor of that protein. Because the process of protein synthesis works on an all-or-none principle, all amino acids must be present at the site of protein manufacture or synthesis will be reduced to the point where the cell runs out of the limiting amino acid.

The ability of a protein to satisfy these essential amino-acid requirements can be quantified in several ways. Terms used to rate dietary protein include protein efficiency ratio (PER), net protein utilization (NPU) and biological value (BV). BV is a measure frequently used when discussing protein sources in popular media and by supplement manufacturers. Essentially, BV is a measure of protein quality, or how well it satisfies the body’s essential amino-acid needs. A protein source with a higher score provides an amino-acid profile that is more closely related to the needs of the human body. BV is a concept that is often misused, especially by marketers of protein supplements. One is led to believe that consuming specially prepared high-BV proteins will allow an individual already consuming adequate protein to build muscle to a greater degree or more quickly. Consuming protein above requirements will not force the body to unleash a previously untapped muscle-building capacity. However, if one exclusively consumes very high BV proteins, their amino acid requirements would be met with less protein. Conversely, if one chooses a diet composed of mostly lower BV protein sources, their total protein requirements will increase.

Exercise

Both anaerobic and aerobic exercise will affect your body’s protein requirements in different ways. Exercise increases the oxidation of amino acids as well as the rate of protein turnover in lean body mass during recovery. Because different types of exercise have specific effects, an individual participating in both types of exercise may have a need for protein greater than someone involved in only one.

Caloric Intake

Because protein can be used for tissue repair and synthesis as well as for energy, protein requirements will increase as total energy intake decreases.    As total caloric intake is reduced in your diet, energy needs may no longer be satisfied by carbohydrate and fat intake alone, necessitating that protein utilization to provide energy. The goal is to satisfy the majority of energy needs with carbohydrates and fat, saving protein for tissue repair and growth. This is why carbohydrates are often referred to as protein sparing. If your diet does not provide adequate amounts of carbohydrates and/or fat (as is often seen in low-calorie or low-carbohydrate diets or during physique-competition preparation), more protein will be used for energy by default.  Individuals interested in general fat loss or muscle hypertrophy have erroneously mimicked the acceptable use of a high-protein diet by a physique competitor. However, under the proper circumstances, these diets, when used temporarily, can be effective.

In addition to the above factors, protein intake may be adjusted to aid in satiety (feeling of fullness). Protein’s role in satiety is an important consideration. As with all macronutrients, protein activates specific satiety mechanisms and may be more satiating than fat and carbohydrates. Protein-induced suppression of food intake in animals and humans is greater than its energy content alone.  This suggests that the amount of protein in your diet has a direct effect on satiety.  In studies of rats and humans, a preload of protein suppressed their food intake for several hours and to a greater extent than a similar energy load of fat and carbohydrate.  Athletes seeking fat loss may benefit from the satiating properties of protein in order to feel full and energized throughout the day. This would assist athletes in program adherence.

Because of protein’s structure and function, protein supplementation may be the easiest to rationalize. However, in a healthy population, protein supplementation is difficult to defend, at least in its general use among athletes. The concept that “more is better” is the conventional thinking of many users of protein supplements, especially in the bodybuilding community.

 No evidence has shown a constant, linear increase in muscle mass or performance related to excessive levels of protein in your diet. Thus, there is a physiological threshold for incorporating dietary protein into fat-free mass (FFM), or for using protein as an immediate energy substrate.

One defensible reason to ingest supplemental protein is to quickly get amino acids into the blood following exercise. Research has shown that the use of protein and carbohydrate supplements before and after weight training can enhance anabolic hormones compared to a non-supplemented state.   Theoretically, this would enhance recovery, allowing the body to spend more time on building muscle rather than repair.