New scientific evidence has identified pigments as holding the key to the healing potentials of fruits and vegetables. BEN UKWUOMA and CHUKWUMA MUANYA, report on how they could counter obesity , elevated blood sugar in addition to fighting inflammation and heart diseases.

HAS colour anything to do with the healing potential of fruits and vegetables? Recent studies suggest it does! With growing recognition of the health-promoting biological activity of plant pigments, many researchers are advocating that consumers expand the palette of colours on their dinner plates.

Medical Director, Elikaf Health Services, Ogba-Ijaiye, Lagos, Dr. Godwin Ihesie, told The Guardian that fruits and vegetables are a terrific source of antioxidants. Antioxidants are a group of naturally occurring compounds known to neutralise notoriously destructive cellular by-products known as free radicals.

Antioxidants are believed to counteract the negative effects of free radicals by binding to them, transforming them into non-damaging compounds or repairing the damage they have caused.

According to Ihesie, the highest concentrations of antioxidants are found in the most deeply or brightly coloured fruits and vegetables, such as spinach, carrots, red bell peppers and tomatoes. He said antioxidants come in a variety of forms and include Vitamin C, Vitamin E, beta-carotene, and selenium.

Ihesie said vitamin C can be found in citrus fruits, green peppers, broccoli, green leafy vegetables, strawberries, raw cabbage and potatoes.

"Vitamin E - wheat germ, nuts, seeds, whole grains, green leafy vegetables, vegetable oil and fish-liver oil. Beta-carotene - carrots, squash, broccoli, sweet potatoes, tomatoes, kale, collards, cantaloupe, peaches and apricots. Selenium - fish, shellfish, red meat, grains, eggs, chicken and garlic," he said.

Indeed, touted as everything from an antidote to ageing to a cure for cancer, antioxidant supplements can now be found on the shelves of local supermarket, pharmacy or health food store. But nutritionists insist that fresh deep-coloured fruit and vegetables are the best source.

A nutritionist at Nigerian Institute of Medical Research (NIMR) Yaba, Lagos, Dr. Rosemary Anyanwu, told The Guardian that depending on supplements to get one's antioxidants may end up short-changing one on their benefits in the long run, since they do not contain the variety of nutrients and phytochemicals found in whole fruits and vegetables, some of which are thought to work in tandem with other nutrients to maintain cell health.

There is also some evidence that high doses of single nutrients may be harmful. For example, study results suggest that large doses of beta-carotene supplements increase the risk for lung cancer among male smokers. Recent data also indicate that high doses of vitamin E may increase the risk of death from any cause.

So, at least for now, forget supplementation, suggests Anyanwu. "Eating a good diet with lots of whole grains, highly-coloured vegetables and fresh fruits and limiting meats and fat is the best way to ensure that you maximise your own genetic potential to avoid or delay chronic diseases," she stated.

Many studies have linked anticancer benefits and protection against heart disease with diets rich in produce, especially carotenoid-rich green, leafy vegetables.

The most recent of these reports, in the Journal of the National Cancer Institute, analysed dietary and health data for almost 72,000 female nurses and 38,000 male health professionals. The study found significantly less risk of chronic illness, especially heart disease, in study participants eating the most fruits and vegetables. Of all foods analysed, green leafy vegetables appeared most protective. In fact, for each daily serving of spinach or other greens consumed, an individual's risk of developing cardiovascular disease fell by 11 per cent.

In 2003, Tiina H. Rissanen of the University of Kuopio in Finland and her colleagues reported that the more servings of vegetables and fruits that middle-aged men consumed, the lower their risk of dying from heart disease. The data pointed to berries, in particular, as being protective.

These findings were consistent with others published that year by an Australian team. For six weeks, nutrition scientists gave 32 men fruit extracts every morning and vegetable extracts every evening. Several potential heart-disease indicators, such as blood concentrations of homocysteine and susceptibility of cholesterol to oxidation, were far lower in men taking the supplements than in volunteers who had eaten the same diet minus the supplements.

To probe what compounds might account for such benefits, researchers have been isolating and testing the effects of various constituents of fruits and vegetables, including purified flavonoids.

Flavonoids according to Anyanwu include beta-carotene and related carotenoids, which are responsible for many of the yellows, oranges, reds, and greens in produce. Other reds and most of the blues, purples, and blackish tints - especially in berries and potatoes, trace to flavonoids called anthocyanins.

These chemicals, the nutritionist suggests, are considered antioxidants because they quash free radicals, naturally forming molecular fragments that have several damaging effects. "Free radicals can kill cells, transform some of the blood's cholesterol-toting lipoproteins into agents of atherosclerosis," she says.

Indeed, James A. Joseph of USDA's Human Nutrition Research Centre on Ageing at Tufts University in Boston says that this basic effect may contribute to flavonoids' broad range of activities.

Joseph acknowledges that colour offers, at best, an imperfect measure of potentially beneficial antioxidant flavonoids. However, by choosing foods exhibiting a range of deep colours, he says, a person can be reasonably sure of getting a broad mix of beneficial flavonoids.

Scientists around the world have began developing new lines of crops explicitly for their intense antioxidant pigments. Some early lines of red and purple potatoes are now on the market, and other colourful crops are heading that way.

Probably the most famous example is known as golden rice. It is enriched with beta-carotene, a yellow chemical from which the body fashions most of its vitamin A. Swiss and German researchers used biotechnology to design this cereal in the late 1990s to improve vitamin-poor diets in developing countries. The golden grain is still being fine-tuned for eventual commercialisation.

Philipp Simon and his colleagues at a USDA laboratory in Madison, Wisconsin, United States, have been developing carotenoid-enhanced, yellow-orange cucumbers and red and anthocyanin-rich, dark-purple carrots. This team bred some of the carrots now on the market, which retain the traditional orange colour but produce 75 per cent more beta-carotene than carrots did 25 years ago. In another example of pigment boosting, researchers at Cornell University are breeding wheat with extra flavonoids.

John D. Folts' team at the University of Wisconsin, Madison has shown that grape skins and seeds contain flavonoids that limit blood platelet clumping. That clumping is a critical step in blood clotting, but it also contributes to the formation of clots underlying heart attacks and strokes. Although the flavonoids in either skins or in seeds have proved beneficial, the best results occurred when Folts' group added extracts of both to the diets of dogs and people.

Folts suggests that extracts of grape seeds and skins could provide all the heart-health benefits that have been linked to wine and grape juice. His group recently began studies of one commercial extract of grape seeds and skins. Such a food supplement might prove beneficial to people who'd prefer to avoid the alcohol in wine or the sugar in juice.

Pomegranates are even richer in antioxidant flavonoids, especially anthocyanins, than purple grapes are, according to research led by Michael Aviram of Rambam Medical Centre in Haifa, Israel. Over the past 5 years, his team has shown that the flavonoids in pomegranate inhibit cholesterol oxidation in human blood and slow the development of atherosclerotic disease in mice.

In one recent study, Aviram's team followed volunteers who had atherosclerosis, characterised by symptoms including a narrowing of their carotid arteries. Ten of the participants drank 50 millilitres of pomegranate juice daily for 1 to 3 years. Nine others took a flavonoid-free placebo drink. Throughout the trial, all continued to receive the heart medications that their doctors prescribed.

By the end of the study, the people drinking the pomegranate juice had experienced a 20 per cent drop in systolic blood pressure, while the placebo group showed no decline. Similarly, only the pomegranate group experienced a beneficial reduction in the thickness of their carotid artery walls and a dramatic drop in the oxidation-susceptibility of their low-density-lipoprotein cholesterol, the team reported in the June 2004 edition of Clinical Nutrition.

Related heart benefits emerged in Chinese studies of animals treated with black-rice pigments. Black rice contains flavonoids, especially pigmented relatives of anthocyanins, also found in fruits and vegetables, explains Wenhua Ling of Sun Yet-sen University of Medical Sciences in Guangzhou.

He and his colleagues fed mice and rabbits cholesterol-rich diets intended to promote heart disease. The scientists supplemented the animals' food with powdered rice bran. Half the animals got black-rice bran, the rest got equivalent amounts of pigment-free white-rice bran. The animals ingesting black-rice supplements developed far lower concentrations of oxidation by-products in their blood and in the tissues of their arteries and experienced less artery-clogging plaque, Ling's team reported in 2002 and 2003.

Ling says he was surprised by the potency of the pigments. He and his colleagues are now conducting research in which they give black rice pigments to people with atherosclerosis.

Plant flavonoids also show promise in other health areas. For instance, studies indicate that lycopene - the red carotenoid in tomatoes and watermelons, can prevent prostate cancer in animals and shrink prostate tumours in men. Anthocyanins in tart red cherries seem to provide a natural inflammation-fighting alternative to aspirin.

However, some of the most dramatic effects attributed to anthocyanins have emerged in studies of blue and purple foods. For instance, when Japanese scientists gave mice high-fat diets augmented with an anthocyanin-pigmented extract from purple corn, the animals maintained normal weights. Mice on the same diet but without the extract became obese. Moreover, only the latter group of animals developed excessive sugar and insulin concentrations in their blood, Takanori Tsuda of Doshisha University in Kyoto and his colleagues reported in 2003.

Last year, Tsuda's team showed that the purple-corn extract increased the activity of a gene that regulates the function of fat cells. It's the first food component to do so, the scientists reported in the March 26, 2004 edition of Biochemical and Biophysical Research Communications. They also recommended that anthocyanins be explored as nutritional supplements for "preventing obesity and diabetes." Tsuda says. "We need to perform a human study as soon as possible," he added.

Joseph, who is a neuroscientist, has been working with blueberries, which are rich in flavonoids. Five years ago, his team reported that adding blueberries to the diets of ageing rats not only prevented further declines in memory and mental agility but also reversed those trends in the animals.

In 2003, his team published a follow-up study in which they examined a strain of mice that normally develops Alzheimer's disease symptoms, including brain plaques and memory loss. Beginning when the mice were young, the researchers fed them 20 grams of blueberries per kilogram of food. The animals still eventually developed Alzheimer's-like brain plaques, but no memory loss. The researchers concluded that their data "indicate for the first time that it may be possible to overcome genetic pre-dispositions to Alzheimer's disease through diet."

Some of the benefit to memory appears to trace to enhanced brain-cell signalling in animals eating the blue fruit, Joseph says. Old neurons and those in individuals with Alzheimer's disease "are like old married couples: They do not talk to each other," he says. Blueberry's flavonoids "make them (communicate) like young lovers again."

Joseph speculates that, by fostering communication between neurons, the anthocyanins or related chemicals in blueberries affect learning and memory and also spur the growth of new nerve cells, a process called neurogenesis.

His group's latest studies indicate that in blueberry-fed animals, both anthocyanin concentrations and the rates of neurogenesis correlate with performance on memory tests.

Most flavonoid researchers argue that people should get healthy doses of these chemicals from colourful foods, not dietary supplements. Indeed, several studies have shown that megadoses of a flavonoid can trigger harmful effects, probably by boosting oxidation.

That is what biochemist Homer S. Black of Baylor College of Medicine in Houston Texas, United States, witnessed in studies of mice. His group showed that a diet overly enriched with beta-carotene increased skin cancer resulting from ultraviolet light's oxidative damage rather than protecting against it. Black is therefore "leery of supplementing with single antioxidants," but he heartily recommends consuming a broad mix of them every day in whole foods.

Another reason for consuming antioxidants in foods rather than as supplements is that the chemistry of these agents can be influenced by what is eaten along with them. For instance, the carotenoids tinting most vegetables preferentially dissolve in lipids. Unless these pigments are eaten along with fat - such as the oil in salad dressing, the body absorbs only a small fraction of them, notes Steven J. Schwartz of Ohio State University in Columbus.

He recently showed that avocado, a high-fat fruit, facilitates carotenoid uptake by the body. In tests with 11 men and women, his team showed that adding about half an avocado to an undressed salad dramatically increased carotenoid absorption. For instance, lutein absorption more than quadrupled, and beta-carotene absorption rose 12-fold. Schwartz now recommends mashed avocado as a salad dressing.

Anthocyanins, in contrast to carotenoids, are extremely water soluble, so they do not need fat to be absorbed, reports chemist Ronald L. Prior of the USDA lab at the Arkansas Children's Nutrition Centre in Little Rock.

However, adds Joseph, because these flavonoids appear to be useful to the brain and "something has to be (fat) soluble to get across the blood-brain barrier," even anthocyanins may benefit from a fat chaser. Toward that end, he suggested that the California Avocado Commission consider teaming its favourite fruit with his.