Antioxidants

Antioxidants

About oxidation

The process of oxidation in the human body damages cell membranes and other structures, including cellular proteins, lipids and DNA.

When oxygen is metabolised, it creates unstable molecules called ‘free radicals’, which steal electrons from other molecules, causing damage to DNA and other cells.

The body can cope with some free radicals and needs them to function effectively. However, the damage caused by an overload of free radicals over time may become irreversible and lead to certain diseases (including

heart

and

liver disease

) and some cancers (such as

oral

, oesophageal,

stomach

and

bowel

cancers).

Oxidation can be accelerated by:

stress

cigarette smoking

alcohol

sunlight

pollution

other factors.

Antioxidants and free radicals

Antioxidants are found in certain foods and may prevent some of the damage caused by free radicals by neutralising them. These include the nutrient antioxidants, vitamins A, C and E, and the minerals copper, zinc and selenium.

Other dietary food compounds, such as the phytochemicals in plants, are believed to have greater antioxidant effects than

vitamins or minerals

. These are called the non-nutrient antioxidants and include phytochemicals, (such as lycopenes in tomatoes and anthocyanins found in cranberries).

The effect of free radicals

Some conditions caused by free radicals include:

deterioration of the eye lens, which contributes to

vision loss

inflammation of the joints (

arthritis

)

damage to nerve cells in the brain, which contributes to conditions (such as

Parkinson’s

or

Alzheimer’s disease

)

acceleration of the

ageing

process

increased risk of

coronary heart disease

, since free radicals encourage low-density lipoprotein (LDL) cholesterol to stick to artery walls

certain cancers

triggered by damaged cell DNA.

Disease-fighting antioxidants

A diet high in antioxidants may reduce the risk of many diseases (including heart disease and certain cancers). Antioxidants scavenge free radicals from the body cells and prevent or reduce the damage caused by oxidation.

The protective effect of antioxidants continues to be studied around the world. For instance, men who eat plenty of the antioxidant lycopene (found in red fruits and vegetables such as tomatoes, apricots, pink grapefruit and watermelon) may be less likely than other men to develop

prostate cancer

. Lycopene has also been linked to reduced risk of developing

type 2 diabetes

.

Lutein, found in spinach and corn, has been linked to a lower incidence of eye lens degeneration and associated vision loss in the elderly. Research also suggests that dietary lutein may improve memory and prevent cognitive decline.

Studies show that flavonoid-rich foods prevent some diseases, including metabolic-related diseases and cancer. Apples, grapes, citrus fruits, berries, tea, onions, olive oil and red wine are the most common sources of flavonoids.

Sources of antioxidants

Plant foods are rich sources of antioxidants. They are most abundant in fruits and vegetables, as well as other foods including nuts, wholegrains and some meats, poultry and fish.

Good sources of specific antioxidants

include:

allium sulphur compounds

– leeks, onions and garlic

anthocyanins

– eggplant, grapes and berries

beta-carotene

– pumpkin, mangoes, apricots, carrots, spinach and parsley

catechins

– red wine and tea

copper

– seafood, lean meat, milk and nuts

cryptoxanthins

– red capsicum, pumpkin and mangoes

flavonoids

– tea, green tea, citrus fruits, red wine, onion and apples

indoles

– cruciferous vegetables such as broccoli, cabbage and cauliflower

isoflavonoids

– soybeans, tofu, lentils, peas and milk

lignans

– sesame seeds, bran, whole grains and vegetables

lutein

– green, leafy vegetables like spinach, and corn

lycopene

– tomatoes, apricots, pink grapefruit and watermelon

manganese

– seafood, lean meat, milk and nuts

polyphenols

– herbs

selenium

– seafood, offal, lean meat and whole grains

vitamin A

– liver, sweet potatoes, carrots, milk, and egg yolks

vitamin C

– oranges, blackcurrants, kiwifruit, mangoes, broccoli, spinach, capsicum and strawberries

vitamin E

– vegetable oils (such as wheatgerm oil), avocados, nuts, seeds and whole grains

zinc

– seafood, lean meat, milk and nuts

zoochemicals

– red meat, offal and fish. Also derived from the plants that animals eat.

Vitamin supplements and antioxidants

There is increasing evidence that antioxidants are more effective when obtained from whole foods, rather than isolated from a food and presented in tablet form.

Research shows that some

vitamin supplements

can increase our cancer risk. For example, vitamin A (beta-carotene) has been associated with a reduced risk of certain cancers, but an increase in others – such as

lung cancer

in smokers (if vitamin A is purified from foodstuffs).

A study examining the effects of vitamin E found that it did not offer the same benefits when taken as a supplement.

Also, antioxidant minerals or vitamins can act as pro-oxidants or damaging ‘oxidants’ if they are consumed at levels significantly above the recommended amounts for dietary intake.

A well-balanced diet, which includes consuming antioxidants from whole foods, is best. If you need to take a supplement, seek advice from your doctor or dietitian and choose supplements that contain all nutrients at the recommended levels.

Dietary recommendations for antioxidants

Research is divided over whether antioxidant supplements offer the same health benefits as antioxidants in foods.

To achieve a healthy and well-balanced diet

, it is recommended we eat a wide variety from the main 5 food groups every day:

vegetables

and legumes or beans

fruit

grain foods and cereals (mostly wholegrain)

lean meat, poultry

or alternatives such as

fish

, eggs,

tofu

, legumes and beans,

nuts and seeds

dairy and dairy alternatives

– mostly reduced fat (reduced fat milk is not recommended for children under 2 years).

To meet your nutritional needs, as a minimum try to consume a serve of fruit and vegetables daily. Although serving sizes vary depending on gender, age and stage of life, this is roughly a medium-sized piece of fruit or a half-cup of cooked vegetables.

The

Australian Dietary

Guidelines

External Link

has more information on recommended servings and portions for specific ages, life stage and gender.

It is also thought antioxidants and other protective constituents from vegetables, legumes and fruit need to be consumed regularly from early life to be effective.

See your doctor or dietitian for advice.

Where to get help

Your

GP (doctor)

Dietitians

Australia

External Link

Tel.

1800 812 942

Australian guide to healthy

eating

External Link