THE MACRONUTRIENTS



The term macro means big. Macronutrients are molecules which we can obtain energy from and which are involved in the maintenance of health. Thus, macronutrients are molecules which not only provide us with energy and other important factors needed for good health but are also relatively bigger and consumed in greater quantities in the diet than other nutrients. There are three macronutrients: carbohydrates, fats and proteins.

Carbohydrate. The name carbohydrate is another name for sugar. Carbohydrates are called such because they all contain the elements carbon, oxygen and hydrogen.36 Examples of carbohydrates include bread, rice, potatoes, glucose (blood sugar), lactose (milk sugar), cakes, fructose (fruit sugar), and sucrose (table sugar). Most carbohydrates for the human diet are derived from plants.36 Carbohydrates can be subdivided into the following types of molecules: monosaccharides, disaccharides oligosaccharides and polysaccharides. Each name is related to the number of sugars that make up the molecule in question. For example, monosaccharides are single sugar molecules while disaccharides are composed of two sugar molecules linked together. Polysaccharides are composed of many (usually from ten to thousands) of sugar molecules linked together.

Polysaccharides

Polysaccharides are composed of between ten to literally thousands of sugar molecules chemically bonded together. Examples of polysaccharides include starch, glycogen and fiber, to name a few.

* Starch. Starch is the carbohydrate storage molecule of plants. Starch is found in foods such as spaghetti, rice, cereal and bread. Complex carbohydrates usually refer to starch.36
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* Glycogen. Glycogen forms the stored sugar reserves in animals and humans. Glycogen is found in both the muscle - where it serves as a direct energy source to the muscles during activity - and the liver, where it allows for an even distribution of blood sugar levels between meals. Glycogen is produced from the bonding together of many glucose molecules during the process called glucogenesis and broken down by the process called glycogenolysis 36. Glycogen breakdown, along with fats, serve as the major macronutrients used as fuel during aerobic exercise. Glycogen is the limiting factor such that when one runs out of glycogen, exercise stops (runners call this hitting the wall). The average person has between 1500 to 2000 calories of glycogen stored in his or her body enough energy to power a 20 mile run at high speed.36
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* Fiber. Fiber is a general term used to describe indigestible plant structures.26 Fiber is found only in plants. 37 Fiber gives bulk to food and helps people feel full. In terms of weight control, fiber may aid in reducing weight gain and obesity by reducing the number of calories consumed. While the typical American diet contains 12-15 grams of fiber per day, the recommended dietary allowance (RDA) for fiber is 20-35 grams per day.26 Fiber can be divided into both water-soluble fiber and water-insoluble fiber. Studies show that water-soluble fiber such as pectin and oats can modestly reduce blood cholesterol levels.26 Water- insoluble fiber does not show cholesterol lowering effects.36 In addition to evidence linking increased fiber intake to reduced obesity and cholesterol levels, fiber also contains other nutrients beneficial to good health. For example, fiber contains magnesium which may play a role in preventing diabetes.26 Examples of high fiber foods include Fiber One cereal, Raisin Bran cereal, whole wheat pasta, brown rice and oatmeal.
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Fiber and Health

Dietary fiber has received much attention as of late because of research showing that enhanced fiber intake is associated with reduced risk of various diseases. Studies of large numbers of people (epidemiological studies) have shown that people who consume the most fiber show reduced risk of diabetes, obesity, heart disease, high blood pressure (hypertension), and intestinal disorders.46, 47 Theories abound as to the protective effect of fiber and include (1) that added fiber may decrease the amount of time that harmful materials are in the body, (2) that fiber dilutes and/or binds harmful materials, reducing the chance that they cause problems in the body and (3) that fiber may result in a scraping or scrubbing action on the cells of the gastrointestinal tract, which in theory would dislodge harmful (and possibly cancer-causing molecules.36 It may be that fiber exerts all of these functions as well as others which have yet to be determined.

Throughout the world, carbohydrate serves as a major component of daily calorie intake. In the typical American diet, carbohydrates make up between 40-50% of daily calories.36 Some experts recommend that individuals who exercise should increase their carbohydrate intake to 60% of daily calories.36 These carbohydrate calories should come from nutrient-dense foods such as vegetables, fruits and grains and not from processed products such as candy, soda, cookies or cakes.






Lactose Intolerance



Some people lack the ability to digest milk sugar (lactose). Specifically, these individuals lack the enzyme lactase which breaks down lactose. In these individuals, consumption of milk or milk products which contain lactose may result in gastrointestinal distress. Over-the-counter products are available which can be of assistance to lactose intolerant individuals to help them digest lactose.





Carbohydrates and Exercise. Carbohydrates are essential to the exercising individual because they are a rate-limiting fuel. That is, once carbohydrates are depleted from the body, exercise performance decreases dramatically. Also, carbohydrates are utilized in greater amounts as exercise intensity increases.36 Another way of stating this is that carbohydrates are used mostly during activities that are of high intensity and short duration. The greater the need for quick energy, the greater demand is placed on carbohydrates (and thus anaerobic metabolism) for fuel. For example, running an eight minute mile uses a greater percentage of carbohydrates than running a ten minute mile.

Another important fact about carbohydrates is that they are essential to fat burning. The reason is that metabolic byproducts from carbohydrate metabolism are required to properly break down body fat. 36 Thus, reducing carbohydrate intake may result in incomplete fat breakdown. Related to the incomplete fat breakdown resulting from inadequate carbohydrate intake is the formation of ketones - acidic molecules which can cause havoc in the body. If left unchecked, elevated ketones (a syndrome called ketosis) could result in death. Good sources of carbohydrates include oatmeal, pancakes, cereals, breads and cakes.