Food
Healthy foods
Introduction
Is the secret to a long and healthy life really a matter of what food we eat? Well, it just might be.
In this article, we discuss the healthy properties of some common foods, the truth behind claims of so-called "wonder foods" and the merits of putting the magic of those foods into pills.
Do wonder foods exist?
Every other week, there's another revelation about the health-giving properties of a common foodstuff. If only we'd known sooner, we think, and shovel in another mouthful of broccoli, olive oil or dark chocolate. Is it already too late to start?
"Super" foods come in pretty disparate incarnations. Blueberries, green tea, chocolate and fatty fish have all been touted as amazing sources of this, that or the other beneficial goodie.
The magic is usually identified as a single component that fights symptoms of ageing and the causes of degenerative diseases, such as heart disease and cancer. In recent years there has been publicity over:
- quercetin contained in red onions, apples, red wine and black tea
- flavonoids in chocolate
- antioxidants in blueberries and grapes
- lycopene in tomatoes and watermelon
- isothiocyanates in broccoli and brussels sprouts.
Concentrated supplements
The media reports that follow these scientific discoveries often declare the particular food has the highest levels of the new magic ingredient ever found. In the blink of an eye, that ingredient appears concentrated in a supplement with advertising claims promising all but immortality. The reality is rather less exciting.
Lab tests can identify each component in food and even get them reacting with human cells in a test tube, but the problem is linking those results to real life.
Most of the evidence so far has been gathered from observations of groups of people linking diet and lifestyle with health. Absolute proof of the links is difficult to establish. Scientists can't spend years feeding potentially harmful diets to people, just to see how it affects them.
And there are always complicating factors: how do you decide on the relevance of other lifestyle and environmental factors, as well as genetic influences?
How food helps
Antioxidants
Much of the focus on healthy foods concerns the way they combat harmful substances called "free radicals".
Free radicals are made in the body during normal metabolism and during exposure to infection, UV light, pollution, radiation and even exercise. The body has "antioxidant" enzymes and other defence mechanisms to neutralise the free radicals, but when more free radicals are produced than are neutralised, they can damage the cells of the body.
This is where food comes in. Many of the phytochemicals in fruit, vegetables and other plant foods have an antioxidant action and will mop up the free radicals so they are no longer harmful. Numerous studies have demonstrated an association between high intakes of antioxidants, especially from fruit and vegetables, and a lower risk of cancers and cardiovascular disease.
Get it in a pill?
But individual substances in foods don't always work on their own. Studies have shown when substances are isolated out of food and concentrated as supplements, they don't seem to confer the same benefits. Studies of beta-carotene and vitamin E, for example, have failed to produce anticipated benefits.
In fact, completely opposite negative effects have occurred, producing increased cancer and /or cardiovascular risk in some people.
Current advice, therefore, recommends avoiding high doses of antioxidant supplements.
"I'll have a beer and a chocolate fish, thanks"
Though poor diet has a big effect on poor health, science is struggling to pin down exactly which ingredients in a good diet make the biggest difference to health. Alcohol, fish and chocolate have all been found to have positive effects, but fruit and vegetables seem to be emerging as the biggest heroes.
It seems increasingly likely that regular, generous servings of fruit and vegetables offer the most protection against the ravages of degenerative disease. Their magic comes not only from the vitamins, minerals and fibre they contain but also from phytochemicals. Thousands of these chemicals, many present in only tiny amounts, are thought to have protective effects on our health.
More than diet
It's worth remembering that diet isn't everything. Failure to get enough exercise, being overweight, smoking and a genetic predisposition to certain diseases are also important.
Good food isn't a cure for or a guarantee against degenerative disease, but a good diet overall does reduce the risk. If your family medical history increases your chances of getting heart disease or cancer, a good diet may slow the process or take you from high to moderate or low risk.
Other dietary factors can also make a difference. Saturated (animal) fats contribute to heart disease and some cancers. Charred and smoked meats, and those preserved with nitrates (bacon and corned meats), are known to be carcinogenic if consumed in quantity. Nuts and grains contaminated with the mould that produces aflatoxin are also known to cause cancer.
Which foods?
Alcohol
Studies consistently show moderate drinkers (one to two drinks per day) have healthier hearts and live longer than either heavy drinkers or teetotallers.
The antioxidants in red wine were originally thought to make the difference, but it now seems a moderate amount of any alcohol will do the trick.
However, the benefits of alcohol come within a very narrow intake margin. A little too much can do more harm than good and the benefits do not apply to everyone. Small, regular amounts of alcohol seem to do some good for middle-aged and older men and postmenopausal women, but there are more risks than benefits for younger people.
Binge drinking at any age can do serious harm. Drinking during pregnancy is risky for the baby. It is also best to avoid alcohol while breastfeeding.
High alcohol intakes can cause cancers in the mouth, throat, oesophagus and liver. It has also been linked with breast and bowel cancers, though the evidence is not conclusive.
Beer contains B vitamins, especially folate. Links between low folate levels and heart disease are beginning to emerge. But a diet rich in folate, which seems to affect factors that reduce the likelihood of blood clotting, may help prevent heart attacks.
While foods like legumes, vegetables, nuts, cereals, fruit and fortified cereal products are richer and better sources of folate, there is no denying that beer can also add to your dose.
Chocolate
The prospect of chocolate being a health food might be the most exciting nutritional news ever. Cocoa beans contain flavonoids that seem to inhibit the effects of LDL - the bad cholesterol in the blood - and enhance the benefits of good cholesterol (HDL). The flavonoids may also have beneficial effects against cancer by stopping the oxidation of free radicals that can damage cells.
Dark chocolate has more of the flavonoids than milk chocolate, and white chocolate has none.
But chocolate also contains saturated fat and sugar. Small quantities as part of a good diet will do most people no harm, but there are better ways of getting antioxidants and flavonoids. Most fruit and vegetables contain rich quantities, without the disadvantages of saturated fat and so much sugar.
Tomatoes
Lycopene is a red beta-carotene present in tomatoes. Research suggests people who eat a lot of tomato-based foods have a reduced risk of cancer, especially prostate cancer. The association seems strongest with cooked and tinned tomatoes and tomato products. Lycopene has also been found in watermelon.
Soy
Soya beans contain protein and phytoestrogens called isoflavones that mimic oestrogen's effects on parts of the body and seem to lower blood cholesterol levels. It also seems that phytoestrogens may have a cancer-protective effect.
The effects come from soya beans, tofu, soy milk, yoghurt and flour, but not from soy sauce or soya oil.
The effects of soy are very controversial. Some research suggests the hormonal effects of soy are not always beneficial and there is increasing evidence it may affect the thyroid function in some people. Research into the benefits and risks of soy is ongoing. Until more is certain it is wise not to eat large quantities of soy-based foods.
Broccoli and sprouts
Brassicas include brussels sprouts, cabbage, broccoli, kale, cauliflower, bok choy and watercress. Research has shown people who eat a lot of brassicas appear to face lower risk of cancer, particularly lung, stomach, colon and rectal cancers.
Broccoli releases sulphoraphane, which seems to activate anti-cancer enzymes in the lung and colon. In lab tests, sinigrin released by brussels sprouts seems to makes colon cancer cells self-destruct.
Spinach
The antioxidant action of lutein and zeaxanthin, found in spinach, other dark green leafy vegetables and green beans, seems to reduce the risk of developing macular degeneration, a very common cause of blindness in older people. It is too early to recommend how much to eat but it seems the vegetables help.
Garlic
Sulphur compounds in garlic, onions, leeks and chives may inhibit blood clots, reduce blood cholesterol levels and blood pressure, and block the formation of some cancer-forming substances in the colon.
Observational studies of populations who eat a lot of onions and garlic show low rates of cancer and heart disease, but not enough large or long-term studies have been done to confirm any of these connections.
Fish
Omega 3 oils are found in fish such as salmon, tuna, warehou, dory, eel and sardines. They have possible protective roles in arthritis, hypertension, cancer and heart disease, and are thought to play a role in vision and brain development and function.
Observational studies have shown groups of people who regularly eat a lot of fatty fish have lower rates of cardiovascular disease and stroke. This is because omega 3 oils prevent blood platelets from sticking together and onto artery walls, and also boosts levels of HDL - the good cholesterol - in the blood. See our Omega-3 fish oil supplements report for more information.
Tea
Tea contains catechins. These are polyphenols which plants use to protect their cells from ultra-violet light.
Though all tea contains them, green tea has higher concentrations of catechins that are more readily available for the body to use than black tea. In Japan, where green tea is popular, many studies suggest tea drinking has a positive effect on the heart.
It is thought catechins may work by mopping up harmful free radicals. Another flavonoid present in tea, quercetin, is also found in red onions, apples and red wine and has been linked with an improvement in lung capacity. It may also help to protect lungs against atmospheric pollution.
Our advice
There is growing evidence that food plays a big part in both causing and preventing degenerative diseases such as heart disease and cancer, as well as some other of the problems of old age.
Specific compounds with strong protective effects have been identified in many fruits and vegetables, but the science is incomplete and lots more goodies remain undiscovered.
On present evidence it seems unlikely you will get the same benefit from supplements. It is best to have real fruit and vegetables.
The greater the variety of fruit and vegetables you include in your meals, the more likely you are to get the benefits. But there are other things you also need to consider.
- Choose five or more servings of a wide variety of fruit and vegetables each day. Have fruit or vegetables with every meal or as snacks during the day.
- If you're eating meat, choose small servings of lean cuts.
- Include nuts, legumes or soy products instead of meat several times a week.
- Use low-fat dairy foods.
- Use poly and monounsaturated oils like olive, canola, soy, sunflower, or other seed or nut oils instead of butter or other animal fats.
- Eat two servings of oily fish a week.
- Choose wholegrain breads and cereals. Aim for six or more servings a day.
- Limit alcohol to one or two drinks a day and do not binge-drink. Have alcohol-free days on a regular basis.
- Avoid regularly eating charred, smoked and preserved meats.
- Keep fit by doing regular physical exercise.
- Be careful not to gain too much weight.
- Don't smoke.