What is a Healthy Diet
Healthy diet
A healthy diet that is healthy contains a balanced quantity of nutrients daily. Those required in the greatest amount are carbohydrates, protein and lipids. These molecules provide the main respiratory fuels which include glucose, fatty acids, ketones and amino acids. They are used in metabolic processes and produce water, carbon dioxide and urea. The energy released is stored for a short period of time in ATP (adenosine triphosphate) before being used by the body.
The body has an amazing ability to convert one dietary molecule into another. This means that if enough energy is obtained in the diet then it is not too important which of these main nutrients is eaten to provide it. A healthy diet can therefore vary a lot because fats, carbohydrates and protein can be converted from one to another. Other substances are essential and have to be obtained from the diet. These contain a benzene ring which is a hexagonal arrangement of six carbon atoms (C6H6) with alternating single and double bonds between them. It is a basic component of many organic molecules especially aromatic ones which are so called because many have a sweet smell.
Only micro-organisms and plants can make aromatic molecules and are therefore an important source of aromatic amino acids such as phenylalanine, tyrosine and tryptophan. They also provide certain vitamins such as folate (a water soluble vitamin B), vitamin K and coenzymeQ.
The role of amino acids in a healthy diet.
Amino acids are the basic building blocks of proteins and so all are required to make a new protein. Some are also made into neurotransmitters. Most of the 20 amino acids needed are obtained from the protein we eat. Those that cannot be made by the body are called essential amino acids and 8 are always needed in the diet:
Leucine Tryptophan
Isoleucine Phenylalanine (tyrosine)
Lysine Threonine
Valine Methionine (cysteine)
Children also need Ariginine and Histidine to grow properly.
Non essential amino acids can be made in the body from products of carbohydrate metabolism and are:
Glutamate Asparginine
Aspartate Glutamine
Glycine Serine
Alanine Proline
Not all proteins eaten provide all the amino acids. Casein found in milk provides all the amino acids but gelatin lacks tryptophan and vegetable proteins may be deficient in certain amino acids, for example, sweet corn has insufficient tryptophan and lysine. In a vegetarian healthy diet a mixture of plant proteins is therefore necessary. Legumes example peas, beans and lentils are high in amino acids protein and are low in starch and are therefore similar to animal proteins.
The role of fatty acids in a healthy diet.
The most common oils and fats in our diet are triglycerides and these can be made from carbohydrate or from fatty acids. We cannot make linoleic acid and linolenic acid and so they are essential fatty acids. They are made by plants and are essential for health. Polyunsaturated fatty acids are needed to make cell membranes and to make prostaglandins. These substances are involved with the regulation of vasodilatation, blood clotting and the immune response.
Fish oils such as herring, mackerel and sardine are rich in polyunsaturated fatty acids made from linolenic acid. They have beneficial effects on health because they have anti-inflammatory properties. They also reduce the risk of atherosclerosis. Eskimos who eat a high proportion of fish oil have a low incidence of coronary heart disease.
The role of vitamins in a healthy diet.
Vitamins are essential for normal growth and development. Only tiny amounts are needed and so it is possible to overdose on them if
too many additional supplements are taken. At high doses vitamins cause side effects such as nausea, diarrhoea and vomiting.
There are 14 vitamins important for health and they are grouped into fat soluble and fat insoluble.
Fat Soluble Fat Insoluble (Water soluble)
Vitamin A (retinol) Vitamin B1 (thiamin)
Vitamin D ( calciferol) Vitamin B2 (riboflavin)
Vitamin E (tocopherol) Vitamin B3 (nicotinic acid)
Vitamin K (phylloquinone) Vitamin B5 (pantothenic acid)
Vitamin B6 (pyroxidine)
Vitamin B7 (biotin)
Vitamin B9 (folic acid)
Vitamin B12 (cyanocobalamin)
Lipoic acid
Vitamin C (ascorbic acid)
A vitamin is an organic substance which cannot be made and so has to be provided in the diet. However, microorganisms in the gut called gut flora (shown in the image) can produce Vitamin K and biotin whilst one form of Vitamin D can be made in the skin when it is exposed to ultra violet radiation. Humans can make some vitamins from precursors that are eaten. Vitamin A can be made from beta carotene and niacin can be made from the amino acid tryptophan.
The role of fiber in a healthy diet.
Fiber is obtained from the cell walls of plants. The body cannot absorb it from the gut and so it is not a nutrient and does not supply
energy or vitamins. However it has several important functions which are
- It helps the digestive process and aids the absorption of nutrients. Fiber increases the speed at which food passes through the gut.
- It helps to lower blood cholesterol because fiber binds to cholesterol and bile acids preventing them from being absorbed into the body. This may protect against coronary heart disease and strokes.
- Fiber has an important role in the colon where there are many types of microorganism capable of carrying out anaerobic respiration of complex carbohydrates. Short chain fatty acids are produced that can be used as an energy source by the colon and the body tissues. Carbon dioxide, methane and hydrogen are also released. The chemicals produced in the gut can damage the lining and can increase the risk of diseases such as cancer of the colon. Fiber can also bind to these chemicals so that they are excreted from the body rather than being absorbed.
- It makes you feel full for a longer period of time and so reduces your appetite. Also by increasing the bulk of the faeces (stools) it helps defecation and so reduces the risk of constipation, haemorrhoids and varicose veins.
Fiber occurs as soluble fiber and insoluble fiber. Soluble fiber includes gums and pectin and can lower blood cholesterol and control blood sugar. It is found in fruit and vegetables particularly oats, barley, legumes, guar gum and strawberries.
Insoluble fiber contains cellulose, hemicellulose and lignin. It adds bulk to faeces and helps prevent constipation. It is found in wholemeal and wholegrain foods, pulses, bran, brown rice and fruits with edible seeds.
The body needs about 18g of fiber each day with a mix of both types.
The role of minerals in a healthy diet.
The main minerals are sodium, potassium, calcium, magnesium, iron, sulfur, chloride and phosphate. They are used in making the skeleton or as buffers in the body fluids. A buffer helps stabilize the pH.
Mineral deficiencies are unlikely for most people in a healthy diet but problems sometimes arise. For example, a heavy loss of blood can produce an iron deficiency. Women are susceptible because of menstrual loss (periods), pregnancy and lactation. Iron is mainly needed for the transport and storage of oxygen and so one symptom of a deficiency is tiredness. Selenium and manganese are used to make enzymes which remove reactive forms of oxygen (are antioxidants) and so protect cells against free radical damage.
