Proteins are always considered as a friendly food component by the layman as well as the nutritionists. Millions of words have been spoken and written about the bad effects of carbohydrates and fats, the other two bulk nutrients in foods we consume. While protein has a vital role in body building through tissue development and maintenance through replacement due to aging and normal attrition, carbohydrates and fats are sources of biological energy required to fuel the metabolism that drives life. By now it is very clear that over consumption of these two energy sources can lead to over weight and health disorders that are prevalent to day. How about proteins? Do they have any adverse effects on body if not properly balanced in the diet? If current trend of scientific investigations is taken at their face value, proteins can cause imbalances in body metabolism similar to fats under certain circumstances.
Twenty amino acids, contained in proteins, are the building blocks of all tissues and are involved in a variety of body functions vital for life sustenance. Out of these nine are considered essential as the human body does not have the capacity to make them and are to be supplied through the diet. Others are formed in the body through inter conversions by the mediation of a plethora of enzymes. There are three 'special' amino acids called Branched Chain Amino Acids (BCAA) Leucine. Isoleucine and Valine which are concentrated in muscle tissues and have very important role in muscle formation and physical activity. The two characteristic proteins actin and myosin contained in the muscles have BCAAs up to 35% and therefore they have critical role as raw materials for muscle tissue building. Strenuous exercise for lengthy periods causes break down of muscle tissues and consequently depletion of BCAAs which provides quick energy as other sources become insufficient. BCAAs can decrease up to 20% after intense physical activity in athletes and other heavy workers. BCAAs also help to suppress lactic acid produced during muscular activity which otherwise can lower the pH causing muscle fatigue.and adversely affect muscle contraction. This is one of the reasons why BCAA supplements are taken by athletes and sports persons whose need for these amino acids far exceeds that for a normal person.
BCAAs are components in most proteins and deficiency of these amino acids is not very common. If adequate recommended amount of proteins are not provided through the diet, there can be deficiency of BCAAs also. Most diets for normal persons provide 55-140 mg of BCAAs per kg body weight but for athletes undergoing intense training take supplements containing 5 gm leucine, 4 gm of valine and 2 gm of isoleucine per day to compensate for muscle loss and increased muscle mass, though benefits of such supplementation has not been conclusively proved so far. High intake of BCAAs is not considered harmful as they are converted to other amino acids or used as an energy source or converted to fat for storage. Liver has limited capacity to metabolize BCAAs which pass through it practically unchanged to be preferentially metabolized in muscle cells.
Chance observation that obese people have high BCAA level attracted attention of the nutritionists and any association between excess BCAA and over weight became focus of investigation by some groups of scientists working on obesity problem. High fat content in the diet is certainly a cause for worry because of the attendant consequences but high fat with high BCAA levels in the diet constitutes a much bigger threat in the form of faster development of insulin resistance leading to diabetes. Animal studies show that feeding high fat diets supplemented with BCAAs results in development of insulin resistance with much lesser amount of food consumed. Parallel rise in levels of BCAAs and insulin resistance in over weight individuals is an indicator for likely development of Type II diabetes in the not too distant future. BCAAs, in presence of high fat, seem to be working at the molecular level in the insulin pathway and cause a build up of acyl carnitine involved in fat transportation, at least in animals, that affects the glucose absorption at the cellular level. BCAAs may also be working by chronically activating mTOR, a signaling protein that regulates cell growth and survival and functions as a sensor of cellular nutrition and energy levels. Last word has not yet been said about ill effects of BCAAs as all the above studies were in rats, requiring validation by human studies. But caution is called for while consuming diets rich in fat as well as proteins because of the possibility of developing insulin resistance with even lesser amount of food consumed.