All the nutrients the body needs can easily be obtained from a vegetarian diet. In fact, research shows a vegetarian diet can be healthier that that of a typical meat eater. Nutrients are usually divided into five classes: carbohydrates, proteins, fats and oils, vitamins and minerals. We also need some dietary fibre and water. All are needed in varying quantities, from about 250 g of carbohydrate per day to less than two micrograms of vitamin B 12.
Most foods contain a mixture of nutrients, but it is convenient to classify them by the main nutrient they provide. Girls aged 15-18 years need around 45 g of protein a day (more, if very active or lactating) and boys aged 15-18 need about 55 g (more if very active). Too much protein may aggravate poor or failing kidney function. Vegetarians obtain protein from four main sources: - Nuts and Seeds - Peas, Beans and Pulses - Grains and Cereals - Dairy and Eggs The humble Soya bean is an excellent source of vegetarian protein and is found in veggie bacon, tofu, pot noodles, sausages and sauces! It can be made into milk and other dairy substitutes for vegans. It is also consumed widely by omnivores as soya is found (as a bulking agent) in 70% of processed foods.
It is maintained by some that it is necessary to 'combine' the proteins in a vegetarian diet to obtain an adequate supply of amino acids, eight of which are essential for adults and nine for children. Vegetarian proteins are usually deficient in one of the eight essential amino acids, so some people advise that we combine the proteins we eat in a meal or throughout the day to achieve a full complement. Any two of the protein groups in the diagram above can be combined to achieve a full complement of protein. Meals such as beans on toast, or cereal and milk are excellent examples of how proteins can be easily combined to create the full complement of amino acids. The latest research suggests that the body has a short term pool of amino acids and, because of this, we don't have to worry about complementing amino acids at every single meal, as long as our diet is varied and well-balanced. Even foods not considered to be very high in protein are adding some amino acids to this pool.
Carbohydrates give us energy. There are three main types of carbohydrates: simple sugars (monosaccharides), complex carbohydrates or starches (disaccharides), and dietary fibre (non-starch polysaccharides or NSP). Simple sugars are found in fruits (intrinsic sugars), milk (lactose) and ordinary table sugar. Refined sugars (non-milk extrinsic sugars) are best avoided, as they provide energy without any associated nutrients - they are empty calories - and are the main cause of dental decay. Complex carbohydrates are found in starchy foods such as bread, rice, pasta, oats, barley, potatoes and parsnips.
A high intake of complex carbohydrates is an important component of a healthy diet. Unrefined foods such as wholegrain breads and brown rice are best of all as these contain dietary fibre and B vitamins. Starchy foods are very filling relative to the number of calories they contain and so form an essential part of a slimming diet. Dietary fibre or NSP, refers to the indigestible parts of a carbohydrate food. Fibre is found in fresh and dried fruits, whole foods such as wholegrain cereals and wholemeal breads and vegetables.
Fibre in the diet protects against digestive disorders by keeping the system clean. We need about 11 g of fibre per day for a healthy digestive system. Too much fat - especially saturated fat - is very bad for us, but some fats and oils are necessary in the diet to keep our tissues in good repair, for the manufacture of hormones and to act as a carrier for some vitamins. Like proteins, fats are made from smaller units, called fatty acids.
The way in which the acids form compounds determines whether they are saturated, monounsaturated or polyunsaturated. Saturated fats come mainly from animal sources and include lard and butter and also a few plant sources such as palm oil. Vegetable fats tend to be unsaturated. Monounsaturated fats include oils such as olive oil and groundnut oil.
Polyunsaturated oils include sunflower oil. Linoleic and linolenic acids are the essential fatty acids and are found in cold-pressed oils such as maize (corn), soya and sunflower seed oils, nuts and avocados. Vitamins are micro-nutrients that cannot be synthesised by the body in sufficient amounts for health. Therefore we must ensure an adequate supply in the diet. Vitamins A, D, E and K are fat-soluble vitamins; Vitamin C and the B-complex are water soluble. Vitamins in food must be looked after carefully otherwise they will be lost.
You can eat as many over boiled and soggy carrots and sprouts as you like - but they won't do you much good! Vitamins A, C and E are often referred to as antioxidants. This means they help to protect the body from reactive oxygen species (free radicals) which are produced by the body's normal metabolic processes. If free radicals accumulate they can damage key DNA molecules and proteins.
This process may be responsible for some cancers. It has been shown that those consuming large amounts of vitamin rich orange and yellow fruits and dark green and orange vegetables seem to be less prone to some forms of cancer. It is recommended that we eat five portions of fruit and vegetables a day. Girls aged 15-18 need 600 micrograms of Vitamin A per day and boys aged 15-18 need 700 micrograms.
Betacarotene is the vegetarian form or precursor of Vitamin A and retinol is the form found in meat and animal products. Betacarotene is converted to retinol in the body. Vitamin A is essential for good night vision and prevents eye disorders such as night-blindness and severe eye-lesions. It is also needed for healthy skin tissues, especially those excreting mucus.
Red, orange and yellow vegetables such as carrots, peppers, mangoes, and sweet potatoes are excellent sources of betacarotene. Green leafy vegetables also provide a source. Animal foods such as cheese also contribute to our intake. The B-Vitamin Complex.
These help us to convert the carbohydrates in our food into energy, are needed for the metabolism of amino acids, for rapidly dividing cells and the metabolism of fat. Deficiencies can lead to beriberi (thiamin), pellagra (niacin) and megaloblastic anaemia (B 12). As the B vitamins act as co-factors in different enzyme-systems in the body, diets lacking in B vitamins may lead to multiple deficiency diseases within a few months. B Vitamins include B 1 (thiamin), B 2 (riboflavin), B 3 (niacin), B 6 (pyridoxine), B 12 (cyancobalmin), folate, pantothenic acid and biotin. The entire B-Vitamin complex except B 12 occurs in yeasts, wholegrain cereals (especially wheatgerm), nuts, pulses, seeds and green leafy vegetables. Vitamin B 12 may cause some difficulty, as it is usually not present in plant foods.
Only very tiny amounts are needed and vegetarians can usually obtain this from dairy produce and eggs. Vegans and vegetarians consuming few animal foods should include foods fortified with B 12 such as Marmite, soya milks, veggieburgers and some breakfast cereals. Girls and boys aged 15-18 both need 40 mg of Vitamin C per day. Vitamin C is plentifully and easily available in a vegetarian diet full of fresh fruit such as blackcurrants and strawberries, orange and other fruit juices, peppers, salad vegetables, leafy greens and potatoes. Vitamin C is necessary for healthy connective tissues. Deficiency can result in bleeding, slow wound healing and scurvy, a skin disease.
Vitamin D is needed for the absorption of calcium from the intestine and to deposit the calcium in the bone - mineralisation. Vitamin D is not found in plant foods but humans can make their own supplies in the skin when it is exposed to sunlight. Vitamin D is added to margarine's and is present in milk, cheese and butter. Deficiencies can occur in those confined indoors and to women whose religion requires their skin to be fully covered.
These may lead to rickets in children and osteomalacia (bone softening) in adults. Vitamin E's main use in the body is as an antioxidant. It is widely available in cold pressed oils, wholegrain cereals and eggs. Vitamin K is necessary for the normal clotting of blood. Supplements are often given to babies at birth. Vitamin K is produced via bacterial synthesis in the intestine, and dietary sources include fresh vegetables, cereals and grains.
Girls aged 15-18 years need 800 mg of calcium per day. Boys aged 15-18 need 1000 mg per day. Calcium, in partnership with magnesium, builds a healthy skeleton and strong teeth. Calcium is also needed for muscle contraction (including the heart muscle), nerve function, blood clotting and the activity of several enzymes. Sources of calcium include dairy produce, leafy green vegetables (particularly watercress), white bread, sesame seeds and dried figs. Vitamin D is essential for the absorption of calcium.
A diet high in saturated fats can lead to calcium leaching from the bones. Deficiencies of calcium in the diet are apparent around the time of the menopause, when heavy losses of calcium can lead to osteoporosis or brittle bone syndrome in women. Girls aged 15-18 need 15 mg of iron per day, and boys aged 15-18 need 11.3 mg. It is especially important for teenage girls to ensure an adequate intake of iron.
Iron is needed to maintain the supply of red pigment (haemoglobin) in the blood, which carries oxygen from the lungs to the tissues, and a deficiency will lead to anaemia. Vegetarian sources of iron include fortified breakfast cereals, wholemeal bread, plain chocolate, eggs, leafy greens, lentils and pulses. Vegetarian sources of iron are not as easily absorbed as animal sources, but the rate of absorption can be greatly increased by eating iron rich foods with Vitamin C rich foods. Eating a handful of dried apricots and brazil nuts with a glass of fruit juice can bolster a healthy varied diet with extra iron. Zinc is essential for wound healing and is also involved in enzyme activity. It is mainly present in the bones.
Girls aged 15-18 need 7.0 mg of zinc per day and boys aged 15-18 need 9.5 mg. Zinc plays a role in many enzyme reactions and in the health of the immune system. It is found in cheese, sesame and pumpkin seeds, lentils and wholegrain cereals.