Food Groups in Human Nutrition

Introduction
Variety in food is very important for the maintenace of good health and prevention of disease. Fats, lipids, carbohydrates, minerals, trace elements, vitamins and water must all be present in moderate ammounts in the daily diet. Recommended daily allowances (RDA) represent a refence base for nutrition intake. RDA vary in different countries, and they do not indicate individual requirements or clinical needs.

A healthy diet should consist of varying amounts of the following food groups: cereals, legumes, vegetables, fruit, meat, fish and sea foods, eggs, milk and milk products, fats and oils, beverages.

Cereals
Cereals are the staple food of most diet, providing 2/3 of the energy intake in developed countries. The major cereal grains are wheat, rice and corn. Cereals are an important source of carbohydrates, protein, minerals, vitamins, and fiber. Other cereals include barley, sorghum, millet, oat, rye. Corser flours are much richer in vitamins and nutrients than more refined flours. Maize is low in niacin, which is the reason why poplulations relying mainly on maize have cases of pellagra. Maize is also low in tryiptophan which can be converted into niacin by the body. Rice has comparatively high level of essential amino acids among other cereals. Poputions relying primary on rice as a source of energy exhibit more frequent cases of Beri Beri (Vitamin B1 deficiency).

Legumes
Legumes include peas, lentils, beans, soy bean, ground nuts. Energy comes from 23% protein, 68% carbohydrate energy. Provide approximately 1500kJ/100g. Dietary fibre composes 10‐20% which interferes with bioavailability of minerals. Legumes are a good source of vit B1, B2 and niacin (not fatsoluble vitamins or Vit C)

Tubers
The main tuber in western culture is the potato. Potato is high in protein, thiamine, iron, and fibre. Vitamin C is lost during boiling. Fat is absorbed during frying of potatoes. Sweet potato and yam are other tubers. They are very high starch and vit c. They contain lower protein count and some carotene.

Root Crops
Root crops include turnips, carrots and parsnips. Properties include high water content, fibre and nutrients. They contain low protein content. Sugar beet is a root crop, which is processed to sucrose (table sugar).

Other Vegetables
Leafy vegetables are low in energy, high in carotenoids, vitamin C, folates, B vitamins, vitamin K, Mg, trace elements. Cooking in water leads to leaching and thermal loss of vit C. Freezing involves minor losses of labile vitamins, canning produces greater losses and drying produces total loss. Vegetables consumed as fruits incluide cucumber, courgette, marrow, pumpkins and squashes have high water, provide taste and texture but relatively low in nutritional value. Sweet peppers and tomato have high vitamin C content.

Fruits
Fruits are high in water which increases the bulk of food. They contain sucrose, glucose and fructose (in varying proportions), vit c, and caratenoids.

Meat
Not essential component of diet as societies who have adopted vegetarian diet do not show signs of malnutrition, provided total supply of food is adequate. It is a important source of protein, especially in growing children. Composition of all meats is dependent on the ratio of fat to lean. Meat is also an important source of fat. Meats are high in vitamin K, Mg, P and Fe (if not bled out), vitamin B12 ( and other b vitamins), and fat soluble vitamins.

Fish and Sea Food
Fish and sea foods are a good quality protein, w high proportion of long chain polysaturated FA. Some sea foods accumulate trace elements (oysters‐ Zn). Sea food can be a major source of iodine.

Eggs
Eggs are good sources of protein (similar amino acid composition as required for humans), lipids (phospholipids, high polyunsaturated fat, saturatedfat) and (cholesterol 280mg/egg). It contains a wide range of vitamins and minerals. Protein avidin, binds to biotin making it unavailable to man. Cooking denaturises avidin abolishing its effect.

Milk and dairy products
Milk and dairy products are ruch in protein (casein, lactalbumin, immunoglobulis). Proteins are high in lysine, so cereals and milk products complement each other. They are also a source of fat, Na, K, Ca, Mg, P and vitamins ( especailly vitamin B and C, but vitamin C is l ost on storage and heating).

Fats and Oils
Oils are fluid at ambient temp while fats are solid. Energy content is 36kJ/g, making fats the richest source of energy. Fats and oils are a source of essential fatty acids (for example linoleic acid). They contribute to absorption of fat soluble vitamins. They improve palatability of food which constrains compliance when giving nutritional advice to reduce total fat intake.

Beverages
Water is essential in hydration of tissue, composition of extra-cellular fluid, prevention of renal damage and nephrolithiasis. Soft drinks are very high in energy. Fruit juices provide vitamin C and improve availability of Fe in a meal. Tea, coffee, cocoa contain caffeine (stimulant). Alcohol may provide good source of available iron whose absorption is enhanced by alcohol, it is however a substance of abuse.