Dietary sources supplementation and fortification

Because our food is almost entirely made up of components that were once parts of living organisms and since there is a broad similarity between the nutritional requirements and cellular biochemistry of most forms of animal and plant life, it is to be expected that our needs for the mineral nutrients will be met by a conventional mixed diet (Coultate, 1985). It is usually only in exceptional situations, where, for example, there is a reliance on locally produced food in an area where

Table 4.3 Good food sources of minerals

Food

Mineral

cereal

vegetable

dairy

meat

Fish

other

Ca

*green

*

*

nuts

Mg

*

nuts

Fe

*fortified

*green

*

Zn

*

*

*

Cu

*

*

Se

*

*

*

nuts

I

*

*

iodised salt

Mn

*

*

*

tea

Mo

*

Cr

*

*

*

Brewer's yeast

the soil is deficient in a particular mineral, or where the diet is deliberately restricted to a limited number of food types, that problems of mineral deficiencies occur.

Some food sources are better than others as sources of minerals. Plant foods are generally poor in iron and zinc, with the exception of certain dark green vegetables such as spinach. Dairy products are generally an excellent source of calcium. Red meat and offal, such as liver, are the best dietary sources of easily absorbed iron. Many of the trace elements are found in relatively high concentrations in fish and other seafoods. Table 4.3 lists some of the best food sources of a number of the essential minerals. As is indicated in the table, there are some unusually good sources of a number of these minerals. Milk, for example, is often an excellent source of iodine because of the presence of residual iodine-containing compounds used to sterilise dairy equipment. Tea is a major source of manganese in the UK diet. An important source of chromium in the diet of some people is canned food which picks up the metal that is one of the ingredients of the alloy used to produce 'tin'cans (Reilly, 2002).

For many people supplements are an important source of minerals. It has been estimated that as many as 40% of the US population consume them, and up to 60% in the UK, either as 'over-the-counter' self-selected products or prescribed by a physician or other health advisor (Balluz et al, 2000).

Mineral supplements are available in a number of chemical forms, either as inorganic compounds, such as ferrous sulphate and calcium carbonate, or as organic preparations such as selenium yeast and zinc gluconate. The products vary in the amounts of the different elements they contain, in their absorbability and in other qualities and while undoubtedly their use can make a definite contribution in some cases to nutritional health, there can also be problems such as over-dosing and interactions with other components of the diet (Huffman et al, 1999).

The addition of minerals and other nutrients to foods to increase their nutritional value is widely practised. In the 1920s iodised salt was introduced in some countries to help combat endemic goitre. Iodised salt, as well as other iodised foods such as bread and monosodium glutamate, are today widely used in parts of the world where iodine deficiency diseases (IDD) are still endemic, such as India, and China, Papua New Guinea, Central Africa and the Andean region of South America.

Legislation was introduced in several countries during World War II which required the addition of iron and calcium, as well as of certain water-soluble vitamins, to bread and flour in order to combat nutritional deficiencies caused by food restrictions. The success of these measures in improving health led to the extension of the legislation into peacetime. Some countries, such as the UK, still require that bread and flour be fortified with calcium and iron (Statutory Instrument, 1984).

Bread and flour are the only foodstuffs required by law to be fortified with minerals in the UK. There is, in addition, legal provision for the voluntary addition by food processors of other minerals to other foodstuffs, with the exception of alcoholic drinks. This has given manufacturers the opportunity to produce a variety of foods enriched with other minerals. Most ready-to-eat (RTE) breakfast cereals are enriched with iron and zinc. Some varieties will also contain added iodine and other minerals. These are normally added at levels which are well below those which might cause toxic effects (Brady, 1996). Fortified RTE cereals have been shown to make a significant contribution towards meeting the nutritional requirements of consumers for iron, as well as for copper, manganese and zinc (Booth et al, 1996). Currently a considerable amount of research is being carried out on methods, such as fortification of a variety of commonly used foods with minerals and other nutrients, as a way of improving nutritional status in countries where deficiency problems regularly occur (Gibson and Ferguson, 1998).

In recent years there has been a growth in the production of foods, which have been deliberately selected or formulated to provide, according to their promotors, specific physiologic, health promoting and even disease-preventing benefits. They have been given a variety of names such as 'designer food', 'nutraceuti-cals', 'functional foods' and, officially in Japan, 'foods for specific health use' (FOSHU). Several of these products contain minerals such as selenium (Reilly, 1998).

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