Food Sources of Calories
When we eat food, the nutrients present in it, are released by the process of digestion. Digestion starts in the mouth, where the food is broken into smaller bits, and mixed with saliva. The food is then sent to the stomach and the duodenum where it is further broken down by chemical action. The food is then sent to the small intestine where the process of absorption of nutrients begins.
The chemical reactions in our body cause the complex molecules present in food to be broken down into simple molecules. These simple molecules are absorbed by the walls of the small intestine. They then enter the bloodstream and are then transported to the various parts of the body. These simple molecules are then burnt by the cells to provide energy.
Food contains a number of basic elements such as carbohydrates, proteins, fats and alcohol. These elements all produce different quantities of energy when burnt. The amount of energy produced when one gram of any of these elements is burned is known as its calorific value.
The calorific value of each of these food elements is given below:
Carbohydrate = 4 Calories
Protein = 4 Calories
Fat = 9 Calories
Alcohol = 7 Calories
Carbohydrates are the main source of energy for the human body. When they are broken down they form glucose. Glucose is essential as a source of energy and is also important for maintaining tissue protein. The brain and central nervous system depend solely on glucose for their energy requirements.
Carbohydrates are obtained from foods such as whole-grain cereals and breads, pasta, corn, beans, peas, potatoes, fruit, vegetables, and milk products. These food groups together normally constitute more than 50 per cent of the calorie requirement of the human body. It is recommended that carbohydrates should contribute 60-70 per cent of the total calories in a day's diet.
The carbohydrates that are found in such foods are called complex carbohydrates. They are slowly broken down into glucose and absorbed by the body. This ensures that healthy levels of glucose are always maintained in the body.
Simple sugars are carbohydrates that are obtained by refining naturally occurring sugars. These simple sugars are found in processed foods. Simple sugars are readily absorbed by the body. The body’s glucose requirement is usually exceeded and the supply of glucose does not last over a period of time. Processed foods are also devoid of minerals and other nutrients that are required by the body. They are also deficient in dietary fibers that are required by the body to aid the process of digestion.
Soluble fibers are found in food such as oats, barley, beans, peas, apples, strawberries and citrus fruits. These fibers aid the body by slowing down the process of absorption of glucose, thereby lowering the cholesterol levels in the body. Insoluble fibers are found in vegetables, whole-grain products and bran. These fibers speed up the process of elimination of the feces and help prevent constipation.
Proteins are complex nitrogen-containing compounds that build and repair body tissue. They also form antibodies, hemoglobin, enzymes, and hormones. The protein that is absorbed through food is used to perform these vital functions, though it may also be used to provide energy to the body, in the absence of sufficient carbohydrates and fats.
Proteins are made up of amino acids. Most of these amino acids are not synthesized by the body, but must be obtained from food. These essential amino acids are obtained from eggs, milk, meat, fish and poultry. Plants, by themselves, do not provide all the essential amino acids, but they may do so in combination with other vegetarian sources of food. For example, when cereals are combined with pulses, they provide most of the essential amino acids. Vegetarians must take especial care to ensure that their body’s requirement of protein is sufficiently met by their diet.
The body’s daily requirement of protein is between ten to fifteen per cent of the daily calorie requirement. A deficiency in the intake of protein can retard growth and development and inhibit the body’s ability to fight infection. An excess of protein puts an additional burden on the kidneys to eliminate the excessive waste products, and should also be avoided.
The body’s protein requirement varies with factors such as age, physiology, and stress. Pregnancy greatly increases the protein requirement of the body, as does infection. These additional requirements are normally accomplished by the intake of protein supplements.
Fats are the most concentrated source of energy in our diet. They also impart flavor to the food, which is why low-fat foods are never as tasty as foods that are high in fat. Fat plays several important roles in diet. It is important for the absorption of fat-soluble vitamins such as Vitamin A, D, E and K. Fats also provide essential fatty acids, which are important for the structure and function of cells. Fat also cushions the vital organs and protects the body from extremes of cold and heat.
Food contains two types of fat: visible fats, and invisible fats. Visible fats are derived from coconut, groundnut, mustard, cottonseed, soybean, sesame, butter, and cod-liver oil. Invisible fats are derived from a variety of food sources such as Cereals, pulses, vegetables, spices, nuts, tubers, fruit, milk products, and meat.
Fats can also be classified as saturated, monounsaturated, and polyunsaturated fat. Saturated fat is obtained from eggs, dairy products, and meat. A high intake of these can be unhealthy. Monounsaturated and polyunsaturated fats are obtained from vegetable oils, nuts, olives, and avocados.
Saturated fats also contain cholesterol. Cholesterol is used to build cell membranes, protect nerve fibers, and produce vitamin D. Cholesterol is manufactured by the liver and small intestine to satisfy this requirement. Hence, the body does not require cholesterol from food sources. When we eat foods with saturated fats, we increase the level of a cholesterol carrying substance called lipoprotein in our blood stream. These low density lipoproteins (LDL) leave a coating of cholesterol in the artery walls and slowly clog the arteries. Due to the narrowing of the arteries, the heart has to pump harder, and parts of the body do not get a sufficient blood supply. This leads to various diseases including obesity, hypertension, cancer, and heart disease.
There is another type of lipoprotein that is good for the body. High density lipoproteins (HDL) remove cholesterol from the wall of the arteries and return it to the liver, where the cholesterol is excreted as bile. High density lipoproteins are found in monounsaturated and polyunsaturated fats.
The body requires approximately forty grams of fat in a day. Half of this requirement is met by invisible fats. Therefore, we need to consume only twenty grams of visible fat in a day. Vegetable oils which can help the body complete its fat requirement include soybean oil and mustard oil with groundnut or sesame oil. It may also be obtained by eating hundred to two hundred grams of fish twice a week.
Alcohol provides higher calories than carbohydrates and proteins. Unfortunately, these calories are devoid of the essential vitamins, minerals and proteins that enable the body to use these calories as energy. These calories instead, are converted into fat and stored by the body, contributing to obesity.
Alcohol in moderate amounts may be beneficial as it increases the level of high density lipoproteins in the body. However, excessive consumption of alcohol results in a variety of ailments such as cirrhosis of the liver, damage to the brain and peripheral nerves, and weakening of the heart muscle. It can also lead to nutritional deficiencies and an increased risk of cancer.