Nutrients-The food we eat provides us with different nutrients. Nutrients are substances that provide energy for growth, physical activity and basic body functions (breathing, thinking, temperature control, blood circulation and digestion), and materials for the growth and repair of the body, and for keeping the immune system healthy. Each type of nutrient serves a particular function in the body. Nutrients are divided into two classes, macronutrients and micronutrients.
Macronutrients are needed in large amounts. These are:
- Carbohydrates, in the form of sugars, starches and dietary fibre;
- Proteins; and
- Types of fat are saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), trans fatty acids and cholesterol.
Micronutrients are essential to the body, but are needed only in small amounts, and include:
- vitamins, such as vitamin A, the vitamin B complex (including folate), vitamins C, E and D; and
- minerals, such as iron, iodine, zinc, calcium and magnesium.
There are three types of carbohydrates: starches, sugars and dietary fibre. Carbohydrates are the major source of food energy for most of the world’s population. Dietary energy is measured in units called kilocalories (symbol: kcal). Each gram of carbohydrate provides 4 kcal of energy.
Food sources of carbohydrates (starches)
Foods rich in carbohydrates are cereals such as rice, maize and wheat; cereal products such as bread, macaroni, spaghetti; and root crops such as potatoes and sweet potatoes. Legumes such as peas and beans also provide smaller amounts of carbohydrates.
Fibre is an important part of a healthy diet. A diet high in fibre has many health benefits. It can help prevent heart disease, diabetes, weight gain and some cancers, and can also improve digestive health.
Dietary fibre comes from plant foods. Fibre is commonly classified as soluble (it dissolves in water) or insoluble (it doesn’t dissolve):
- Soluble fibre: This type of fibre can help lower blood cholesterol and blood sugar levels. It is found in oats, peas, beans, apples, citrus fruits and carrots.(Nutrients)
- Insoluble fibre: This type of fibre promotes the movement of material through your digestive system and increases stool bulk, so it can be of benefit to those who struggle with constipation or irregular stools. Whole-wheat flour, wheat bran, legumes (e.g. chickpeas and lentils), nuts, and vegetables (especially those where the skin is eaten, like tomatoes, green beans and potatoes) are good sources of insoluble fibre.
Sugar provides only energy, with no other nutritional benefits. A small amount of sugar can be added to foods like porridge and tea to improve their taste. In addition to sugar added to foods, chocolates, biscuits, puddings, sweetmeats, jams, etc., all contain sugar. Many of these sugary foods, especially commercially processed ones, also contain a lot of fat. Sweets and carbonated soft drinks may be taken occasionally but should never be eaten instead of meals. Frequent consumption of sugary foods and very sweet tea, especially between meals, can lead to tooth decay. Frequent consumption of sweetened carbonated drinks and fruit juice can lead to obesity. Obesity, especially severe obesity, is associated with a high risk of coronary heart disease, diabetes, hypertension, eclampsia during pregnancy, orthopaedic problems and other diseases. (Nutrients)
Cells and tissues in the body are mainly made from proteins that are made up of amino acids. There are about 20 amino acids that join together to make different proteins. There are nine essential amino acids that are required from food; the other amino acids can be made by the body. Proteins are needed for the growth and repair of the body. Proteins can also provide the body with energy. Like carbohydrates, 1 gram of protein provides 4 kcal of energy. However, as foods containing protein are generally eaten in smaller quantities than cereals, they contribute less to a person’s total energy intake.
Food sources of proteins
Good sources of protein are all types of meat, poultry, fish, milk cheese, yoghurt, eggs, beans, soybean, almonds, walnuts, pistachios, and seeds (pumpkin, sesame, sunflower, melon and watermelon seeds). Breast milk is also a good source of high quality protein.
Cereals such as rice and wheat also contain significant amounts of protein, and because these are staple foods and eaten in large quantities, they provide most of the protein for many people in Afghanistan.
Different foods have different combinations of amino acids. Except for soybean, the proteins from plant foods do not have all the essential amino acids in one food type. However, when different plant foods are eaten together, all the essential amino acids are provided. It is therefore important to eat combinations of foods in the same meal, for example, rice and beans or naan with lentils or with a little meat, fish, egg or dairy foods. Some common Afghan dishes contain a good mix of foods, such as rice, curd and mungbeans (kechery krut); pumpkin and chickpeas (qorma kadu); and eggplant with yoghurt (banjan krut). Eating in this manner will ensure that all the essential amino acids can be provided for healthy growth in children, and maintenance and repair of body tissue.
Fats and oils
Fats and oils are a concentrated source of energy, providing 9 kcal energy per 1 gram of fat, which is more than twice the energy yielded by carbohydrates and proteins. Fat can therefore add a lot of energy to the diet without increasing the volume or bulk of the diet. This is important for people doing heavy physical work. It is also important for infants and young children with small stomachs, who need a lot of energy and nutrients for physical growth and mental development relative to their body size. Some fatty or oily foods contain important vitamins, such as vitamins A and D, and fat makes it easier for the body to absorb these vitamins. Thus fats and oils, and specific types of fat, are essential to health. They also improve the taste of meals. (Nutrients)
Dietary fats and oils are made up of fatty acids. The fatty acids are divided into two main groups: saturated and unsaturated. All fats and oils eaten by humans are mixtures of saturated and unsaturated fatty acids.
Unsaturated fatty acids
This group includes both polyunsaturated and mono-unsaturated fatty acids. Unsaturated fatty acids contain groups called omega-3 and omega-6 fatty acids, which help to protect the body from heart disease. Some of the omega-3 and omega-6 fatty acids are ‘essential fatty acids’: they must be obtained from food because the body cannot make them. They are needed for building cells, especially the cells of the brain and nervous system.
Food sources of unsaturated fatty acids
Foods containing mainly unsaturated fatty acids are most vegetable oils, walnuts, almonds, pistachios, sunflower seeds, sesame seeds and other oilseeds and oily fish. Foods rich in omega-3 fatty acids are oily sea fish and some seeds and pulses, such as linseed and soybean. Foods rich in unsaturated fatty acids are good choices for healthy eating; eating too many foods with a lot of saturated fatty acids or trans-fatty acids can increase the risk of heart disease.
Saturated fatty acids
These fatty acids have important health implications because excess intake of saturated fats is one of the risk factors associated with arteriosclerosis (the hardening and narrowing of the arteries, which leads to stroke and heart attacks) and coronary heart diseases. Therefore these fats should be limited in the diet.
Food sources of saturated fatty acids
Fats from land animals (i.e. meat fat such as sheep fat and beef fat, butter and ghee (butter oil) contain more saturated fatty acids than do those of vegetable origin. (Nutrients)
When vegetable oils are processed to make them “harder” (e.g. for use in margarine and other solid fats), some of the unsaturated fatty acids are changed into trans-fatty acids, as the oils become partially hydrogenated. These trans-fatty acids are considered very harmful to health as they lower the ‘good’ cholesterol and increase the ‘bad’ cholesterol in the body (also see ‘cholesterol’ below).
Food sources of trans-fatty acids (partially-hydrogenated fatty acids)
Foods containing trans-fatty acids are margarine and lard (shortening); fried foods, such as chips (French fries) and other commercially fried foods, such as doughnuts; as well as processed and ready-made foods such as commercially baked goods, biscuits, cakes and ice cream. Processed foods containing trans-fatty acids should be avoided as they are very harmful to health. Nutrition labels on packaged foods can help identify foods containing trans-fats. (See box “Read food labels for healthier choices” under Guideline 4, later on in this document.)
Cholesterol is a lipid present in all human cells. Cholesterol is found only in animal foods, but the body can make it from other fat sources. We need some cholesterol for our bodies to grow and function properly.
There are two kinds of cholesterol in the blood: ‘good’ and ‘bad’.
High levels of ‘good’ cholesterol (high-density lipoprotein – HDL) can reduce the risk of heart disease. Eating foods containing mainly unsaturated fatty acids can increase the level of good cholesterol.
High levels of ‘bad’ cholesterol (low-density lipoprotein) can lead to an increased risk of heart disease. Eating a diet containing mainly saturated fats, i.e. animal fats rather than plant fats, as well as food containing trans fats, tends to increase the level of bad cholesterol, especially if the diet is also high in carbohydrates (in particular, sugary foods).