There are many different antioxidants, and fruit and vegetables are the best dietary source. Antioxidants act in the body by helping to stop certain chemical reactions which produce substances called free radicals. These substances can cause damage to tissues in the body, which may lead to the development of certain cancers and heart disease.
The antioxidant vitamins are A, C and E. Vitamin A is most commonly found in carrots and dark green vegetables, vitamin C in citrus fruit, peppers and kiwi fruit, and vitamin E in cereals, grains, nuts and vegetables.
Tomatoes are a major source of lycopene, another effective antioxidant. An anomaly is that it appears to be more beneficial when foods rich in lycopene are processed. Tinned tomatoes and tomato puree, for example, are very good sources of lycopene.
In addition to being antioxidants, flavonoids are believed to protect against heart disease in other ways. There are many different flavonoids found in foods, having names such as caffeic, ellegic and ferulic acids. A higher intake of flavonoids has been associated with a reduced risk of cardiovascular disease. Flavonoids are predominantly found in fruit and vegetables, and also in red wine and in tea. A moderate amount of alcohol may protect against heart disease because of the flavonoids present, although this effect may also be due to the way in which alcohol works on certain types of cholesterol. However, excessive intakes of alcohol have the opposite effect, increasing the risk of heart disease.
Garlic and similar foods
Onion, garlic, leeks and chives are known as allium vegetables. These foods contain allyl sulphides that give them their characteristic smell. Research has shown that allyl sulphides may have antiseptic properties, cholesterol lowering effects and may protect against cancer, particularly of the stomach. Studies have shown that in areas where garlic and onion consumption are high, there are low rates of stomach cancer. However, much research is still needed, as it may be that some of the active ingredients are lost in processing garlic into garlic preparations.
Phytoestrogens are substances found naturally in plant foods, particularly pulses, and especially soya-beans. Oat-bran is another source. Research has shown that they may help some of the symptoms of the menopause such as hot flushes, and protect against osteoporosis, heart disease and some types of cancer.
Their action may lie in the way the body metabolises phytoestrogens to produce substances which mimic the hormone oestrogen. During the menopause, oestrogen levels in women start to fall and this can lead to symptoms such as hot flushes. Oestrogen protects bone tissue, which is why women after the menopause are more at risk of osteoporosis.
Research is also looking at the way in which foods rich in phytoestrogens may protect against cancers of the breast, prostate and lungs. There is still more research required to prove the beneficial effects of increasing intake of phytoestrogen foods. However, foods such as oat bran, pulses and soya protein contribute towards a healthy diet in any case.
In the US it has long been common practice to fortify certain foods with vitamins and minerals, such as vitamins in margarine and breakfast cereals. This is often to make up for nutrients which are lost during processing. However, the new range of functional foods are aimed at treating medical conditions. Guidelines now recommend that the new products emerging are backed by scientific evidence, and there are also regulations about the health claims made on products.
Such foods often have to be eaten daily in fixed quantities to achieve the desired results, just like taking a particular drug. For example, margarines which lower cholesterol are only effective if consumed in adequate amounts each day. The cholesterol lowering effect is lost if consumption ceases..
This concept has actually been around for many years and describes the effect a carbohydrate food has on blood glucose levels. Carbohydrates can be divided into two groups, namely sugars, including fruit and milk, and starchy foods. All carbohydrate foods are digested into glucose, which is absorbed into the blood stream. Research has shown that different carbohydrate foods are digested and absorbed at different rates.
Foods with a high glycaemic index produce a rapid rise in blood glucose levels after eating, whereas low glycaemic index foods produce a much more gradual rise in the blood glucose.
Starchy foods with a high glycaemic index include potatoes and some breakfast cereals. Foods with a low glycaemic index include pasta, oats and lentils. Further factors which can affect the glycaemic index of a food are the cooking method, the amount of processing the food has undergone, and the other foods eaten with it. For example, eating cheese with bread produces a lower glycaemic index than eating the bread on its own. Furthermore, the effects vary from individual to individual.
It is believed that moving towards a lower GI diet helps individuals with diabetes or related conditions, as one of the main aims of treatment is to prevent a large rise in blood glucose levels after eating. There has also been increasing media coverage suggesting that low glycaemic index foods may help with weight control and blood lipid levels (cholesterol). However, more scientific evidence is required before this is proven.
It is important that high GI foods are not viewed as unhealthy if eaten as part of a balanced diet. There are some foods such as potatoes and certain fruit and vegetables which, although having a high GI value, are healthier choices than some lower GI foods having a higher fat content, such as chocolate.