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Vitamins are organic compounds required in very small amounts, and a distinct feature is that the human body is unable to synthesize them. Most vitamins regulate processes essential for normal metabolism, growth and development. Those vitamins involved in energy metabolism are like the spark plugs of an engine. They do not provide energy but are involved in the production of energy from fuel stores by acting as catalysts for metabolic reactions. More specifically, they are responsible for the storage and utilization of energy in the body.

Eat at least five different fruit and vegetables every day.

Vitamins are either classified as fat soluble (A, D, E and K) or water soluble (B complex and C). The fat-soluble vitamins are stored in body tissues, so consuming excessive amounts of these vitamins, especially vitamin A, can lead to toxicity and organ damage. Water-soluble vitamins, on the other hand, are not stored in the body and any intake in excess of daily requirements generally results in ‘expensive urine’.

MICRONUTRIENT	GOOD FOOD SOURCES
VITAMINS
Thiamin (vitamin B1)	Fortified breakfast cereals, whole-wheat breads, pork, liver, legumes, nuts, yeast (vegetable) extract and brewer’s yeast
Riboflavin (vitamin B2)	Dairy products, red meat, fish, poultry, eggs, fortified cereals
Niacin (vitamin B3)	Lean meat, chicken, fish, legumes, eggs, fortified cereals, nuts
Pyridoxine (vitamin B6)	Lean red meat, poultry, fish, eggs, wholewheat breads and cereals, nuts, bananas, yeast (vegetable) extract, soya beans
Pantothenic acid	Liver, yeast, egg yolk, red meat, dried fruit, nuts
Biotin	Liver, red meat, egg yolk, nuts, peanut butter
MINERALS
Magnesium	Wholegrain cereals, legumes, nuts, sesame seeds, dried figs, green vegetables
Iron	Organ meat, lean meat, egg yolk, dried fruit, fortified cereals, dark green leafy vegetables
Zinc	Oysters, red meat, dark meat of chicken, peanuts, sunflower seeds, wholegrain cereals, legumes
Copper	Organ meats, shellfish, nuts and seeds, mushrooms, cocoa
Chromium	Red meat, liver, egg yolk, seafood, wholegrain cereals, molasses

Vitamins and minerals needed for energy metabolism.

The role of B complex vitamins in energy metabolism.

Although these vitamins tend to be non-toxic, very large amounts have been found to impair the absorption and utilization of other nutrients. The most important vitamins and minerals needed for energy meta bolism and production are the B Complex group, magnesium, iron, zinc, copper and chromium (see p24). Vitamins of the B complex group are involved with muscle contraction, nerve function, and also act as co-factors of enzymes for energy metabolism as do iron, zinc, copper and chromium. Other functions of these nutrients include haemoglobin synthesis, immune and antioxidant function, tissue repair and protein synthesis.

Deficiencies in any of these vitamins will impair meta bolism, sports performance and, of course, health. Generally, athletes’ diets have been shown to supply adequate vitamins and minerals, provided the diet is well planned and varied to meet the athletes’ energy requirements. Those at risk are low-energy consumers, chronic carbohydrate loaders and athletes not able to meet over all nutritional needs (calcium and iron, for instance) through diet alone. Specific situations, such as exercising at altitude or in extreme environmental conditions or ath letes with chronic fatigue or with special medical problems, may also have increased requirements (see p89). It is widely accepted that vitamin deficiencies will impair performance, but there is no evidence to show that supplementing a diet already adequate in vitamins and minerals will enhance performance. Supplementation of vitamins is discussed in more detail in chapter 7.

Practical tips

1. Correcting dietary deficiencies through food should always be the first approach, before considering supplementation, because nutrients coexist in foods. The assistance of a registered dietitian is recommended.

2. Enjoy eating a wide variety of fruits and vegetables – the more colour and crunch the better. Aim for an intake of between 5–9 fruit and vegetables per day.

3. Where possible choose fresh produce, especially those in season. Frozen vegetables, if cooked correctly, are also nutritious.

4. Limit the storage time of vegetables. Shop regularly for fresh produce and, if buying market produce, ensure that the fruit and vegetables have not been standing in the sun for any length of time.

5. Avoid overcooking. Limit the amount of water used, keep the lid on the pot and limit cooking times.

6. Do not add bicarbonate of soda to colour green vegetables as this destroys the B vitamins.

7. Make use of fortified cereals.

8. To enhance iron absorption:

▪ When eating non-meat (eggs, whole grains and fortified cereals, lentils, soya, green leafy vegetables) sources of iron, add a food rich in vitamin C because vitamin C increases the absorption of iron. Foods rich in vitamin C include tomatoes, citrus fruit, guavas, strawberries, broccoli and green peppers.

▪ Avoid tea or coffee with your meal as caffeine and tannin decreases iron absorption.

▪ Remember that an iron supplement will not correct other nutritional inadequacies. If you are worried about your iron status, then have your iron and serum ferritin levels checked before resorting to a supplement.