All about Macronutrients

Nutrients are substances needed for growth, metabolism, and for other body functions. Macronutrients are nutrients that provide calories or energy. There are three broad classes of macro-nutrients: carbohydrates, proteins and fats. The main function of macronutrients is to provide energy, counted as calories. Macronutrients also have specific roles in maintaining the body and contribute to the taste, texture and appearance of foods, which helps to make the diet more varied and enjoyable.
Carbohydrates and fats are the primary source of energy and provide calories. Carbohydrates in particular are the primary energy source for the brain and main source of calories to maintain body weight. They are also involved in the construction of the body organs and nerve cells. Dietary fiber, which is a carbohydrate, also helps keep the bowel functioning properly. Carbohydrates include starches, sugar and celluloses and are obtained through cereals, pulses, sugar, fruits and vegetables. Sugars are simple carbohydrates and are readily digested and absorbed. Starches being complex carbohydrates require certain enzymatic reactions for conversion to sugar before they are absorbed. According to the Dietary Reference Intakes (RDI) published by the Unites States Department of Agriculture (USDA), between 50 and 55% of calories should come from carbohydrates and 20-35 g dietary fiber per day should be taken by all those over two years of age.
Proteins are growth promoting and body building substances and are essential for every function of the cell. Dietary protein is required for growth especially by children, teenagers, and pregnant women, tissue repair, immune system function, hormone and enzyme production, and for lean muscle mass and tone maintenance. These are found in cereals, pulses, animal foods such as flesh, meats and milk. Animal foods are ready sources of good quality proteins. However, combinations of plant foods like cereals and pulses can provide protein of an equally good quality. According to the RDI, adults need to eat about 60 grams of protein per day (0.8 g per kg of weight). Adults who are physically very active or trying to build muscle need slightly more. In other words between 10 and 35% of calories should come from protein.
Fats are concentrated sources of energy and provide twice the energy than that of carbohydrates and proteins. Besides being a source of energy, fat stores protect the internal organs of the body. Some essential fats are also required for the formation of hormones. Fats are the slowest source of energy but the most energy-efficient form of food. They are stored by the body either in the abdomen (omental fat) or under the skin (subcutaneous fat) for use when the body needs more energy. According to RDI 20-35% calories should come from fats. Fats that are in foods are combinations of four main types:
Saturated Fats: Are solid at room temperature and are most often of animal origin. Examples are butter, cheese, coconut and palm oil. These fats provide a concentrated source of energy in the diet and are building blocks for cell membranes and a variety of hormones and hormone-like substances. An excess of these fats in the diet however, is believed to raise the cholesterol level in the bloodstream.
Monounsaturated Fats: Are liquid at room temperature. Examples are olive, peanut and canola oil. Nuts such as pistachio, almonds, hazelnuts, macadamia, cashew, pecan, peanuts, avocados, and their oils are also examples of monounsaturated fats. They appear to protect against heart disease, in that they reduce blood cholesterol levels.


Polyunsaturated Fats: Are also liquid at room temperature and can be further divided into the omega-6 and the omega-3 families. Polyunsaturated fats are thought to reduce the risk of coronary heart disease. The omega-3 forms are believed to have a positive impact on heart health and to play an important role in brain and eye function. Oily fish such as salmon, herring and mackerel are examples of omega-3s, and they are also found in walnuts and some oils like soybean and rapeseed. Sunflower seeds, wheat germ, sesame, walnuts, soybean, corn and their oils are good sources for omega-6s.
Trans-fatty acids: Are produced by the partial hydrogenation of vegetable oils and present in hardened vegetable oils, most margarine, commercial baked foods, fatty meat from beef and sheep and many fried foods. An excess of these fats in the diet is thought to increase the risk of heart disease.
An eating plan that is balanced in its macronutrient distribution can help reduce the risk of disease and foster lasting weight loss. Based on a 2000 calorie intake; for adults and children above four years of age the recommended daily allowance for macronutrients is listed below.


Source: USDA Recommended Daily Allowance


While each of these macronutrients provides calories, the amount of calories that each macronutrient provides varies.
Carbohydrate provides 4 calories per gram.
Protein provides 4 calories per gram.
Fat provides 9 calories per gram.
For example, if the Nutrition Facts label of a given food indicates 12 g of carbohydrate, 2 g of fat, and 0 g of protein per serving, then to calculate total calories that you will get per serving, you need to do following simple calculation.


Total Calorie = Grams of Carbohydrate * 4 + Grams of Protein * 4 +Grams of Fat * 9
In this case:
Total Calorie = 12* 4 + 0 * 4 +2 * 9
Total Calorie = 66 Calories per serving.


There is one more substance that provides calories - Alcohol. Alcohol provides seven calories per gram. It is however not a macro-nutrient and we don't need it for survival. In fact, if you are serious about your health then alcohol is one of those substances that you should avoid.
Using the above given calorie calculation equation you will be able to make much better choice of food as per your requirements. The food we eat and healthy dietary practices are the cornerstones of good health and vitality. Thus understanding the basics of macronutrients is important as a fundamental knowledge of what we eat everyday and adds to our ability of taking proper nutrition decision.
Originally Published in Valley India Times, May 2011
Sources:
Laberge M, "Macronutrients", Diet.com, Your Nutrition and Health Solution, 2000
National Institute of Nutrition, Hyderabad, India

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