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 adequate amounts in the daily diet. Recommended daily allowances (RDA) represent a reference base for nutrition intake levels of the essential nutrients judged to be adequate for meeting the known nutritional needs of the healthy population groups. They do not indicate individual requirements, which are variable.

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.

Food definition: According the EU legislation (Regulation EC No. 178/2002) "food" (or "foodstuff") means any substance or product, whether processed, partially processed or unprocessed, intended to be, or reasonably expected to be ingested by humans. "Food" includes drink, chewing gum and any substance, including water, intentionally incorporated into the food during its manufacture, preparation or treatment.

Foods of vegetable origin

Cereals

Cereals are the staple food of most diet, they may provide up to 2/3 of the energy intake in developing countries and about 1/3 in developed countries . The major cereal grains are wheat, rice and corn. Other cereals include barley, sorghum, millet, oat, rye. All cereals have similar content of main nutrients: 7-14% of protein, up to 75% of carbohydrates, and 2-7% of fat. Starch is the principal constituent of the grain. Cereals, especially wholegrain are an important source of potassium, calcium, magnesium, iron, selenium (if the soil they grew upon contains it), most of B vitamins, and fiber. Wholegrain flours are much richer in micronutrients than refined flours.

Niacin in maize, is bound in a form that humans cannot utilize and there is only a little of tryptophan - the limiting essential amino acid in maize - from which humans can form niacin. For this reason pellagra may occur in populations relying mainly on maize. Pellagra today occurs only in very poor population groups or in emergency situations and refugees in Africa and Asia. It does not occur among the native people in America - its original home - due to the traditional treatment of maize with lime or wood ashes - mild alkali liberates the bound niacin .

Brown rice is rice from which only the hull has been removed. Milled rice, marketed as polished or white rice, is rice from which the hulls and most of the undelying layer (germ, pericarp, and aleurone) have been removed. Protein, fat, vitamins and minerals are present in greater quantities in the bran removed than in the remaining endosperm, which is composed mostly of starch. In populations relying primarily on polished rice vitamin B1 deficiency (beri beri) may occur. Beri beri, similarly as pellagra today occurs only in very poor population groups or in emergency situations and refugees .

Legumes

Legumes (pulses) include peas, lentils, beans, soy bean, ground nuts. Legume seeds are a good source of protein and energy. Approximately 23% of the energy comes from the protein and 68% from carbohydrates. Boiled legumes provide approximately 1300kJ of energy per 100g (except for soya beans: 1600kJ/100g). Dietary fibre composes 10‐20% of dry legumes which may interfere to some extent with bioavailability of minerals. Legumes are a good source of vit B1, B2 and niacin, folic acid and iron (although the bioavailability of iron is lower than from animal foods). The fat content, except for soya beans, is low. Legumes do not contain fat-soluble vitamins or vitamin 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.

Some foods commonly considered as vegetables are botanically fruits. Vegetables consumed as fruits include 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.

Foods of animal origin

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 rich 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.

Links

References

VLADIMIR, Bencko. Hygiene and Epidemiology : Selected Chapters. First edition. 2004. ISBN 978-80-246-0793-1.

KUMAR, Vinay. Pathological basis of disease. Eigth edition. 2010. ISBN 978-80-246-0793-1.