Physical Education · Ch 5 — Sports and Nutrition
Carbohydrates
Carbohydrates
5.2.1 Carbohydrates
Carbohydrates are organic compounds made up of carbon, hydrogen and oxygen. They are a major source of energy, providing 4 kcal per gram, and are found in abundance in plant foods. There are three types of carbohydrates — monosaccharides, disaccharides and polysaccharides.
- Monosaccharides are simple, single units of sugar such as glucose, fructose and galactose.
- Disaccharides are formed when two monosaccharides join together: maltose (glucose + glucose), lactose (glucose + galactose) and sucrose (glucose + fructose). These simple sugars (mono- and disaccharides) occur in fruits (as sucrose, glucose and fructose), in milk (as lactose) and in commercially produced sweets added to foods to sweeten them, prevent spoilage or improve texture.
- Polysaccharides are many monosaccharide units joined together — the starches and fibre (cellulose). Also called complex sugars, they are found in whole-grain cereals, rice, oats, potatoes, bread, legumes, corn and flour.
All carbohydrates must be broken down to their smallest unit, glucose, before they can be absorbed and used by the body. However, cellulose and other large carbohydrate molecules cannot be digested in the human digestive tract; these are termed fibre, or non-available carbohydrates. Sugars and starches, which can be digested and used for the body's functions, are the available carbohydrates. Diets rich in complex carbohydrates are healthier than low-fibre diets based on refined and processed food.
Sources of carbohydrates include rice, cereal grains, breads, pasta, milk, fruit, root vegetables, sugar, sweetened products such as jams and jellies, honey and jaggery. Fibre is found in whole-grain cereals (whole-wheat atta), whole pulses, green leafy vegetables, peas, carrot, beans and other vegetables, and fruits such as guava, apple, orange and pineapple.
Do you know? — Carbohydrates prevent ketosis
Weight-loss diets often recommend avoiding carbohydrates, but the body needs at least 50–100 g of carbohydrate per day for the complete oxidation of fat and to avoid producing excess ketone bodies. Accordingly, the ICMR (2020) RDA for carbohydrate is 130 g/day for adults and children, based on the glucose used by carbohydrate-dependent tissues such as the brain and red blood cells. When carbohydrate supply is inadequate, the body breaks down its fat reserves for energy; this yields energy but also produces ketone bodies. A few ketone bodies are used by muscle and other tissues, but in excess they build up in the blood and cause ketosis (a disturbance of the normal acid-base balance) — a condition often seen in diabetics and a life-threatening one.
Summary — Macronutrients, their functions and sources
| Nutrient | Functions | Sources |
|---|---|---|
| Carbohydrates | • Provide the energy the body needs (1 g gives 4 kcal) • Main source of energy for the nervous system, brain and red blood cells • Spare proteins for their important functions (if enough carbohydrate is unavailable, protein is used for energy) • Enable proper use of fat by providing substrates for fat metabolism | Fruits, cereal grains, milk, sugar, rice, root vegetables, pasta, breads |