Thursday, September 9, 2010
Variety really is the spice of life
No longer content with exhorting us simply to eat five portions of fruits and vegetables a day, scientists now say that consuming a broad and varied range of produce is where it’s at.
So let’s not restrict our vegetable and fruit intake to iceberg lettuce, peas, carrots and bananas (bland foods that many people favor). Instead, why not add more assertively flavored foods to your meal plan, such as leeks, beets, cauliflower, radicchio, parsnips, onions, chard, broccoli, garlic, kale, mushrooms, eggplant, spinach, peppers or red and blue berries? Only by consuming the broadest-possible range of vegetables and fruits can we obtain the widest-possible spread of nutrients.
When you think about it, this is hardly surprising: Humans did not evolve on a mono-diet comprising only a handful of foods. They survived on whatever the terrain and prevailing seasons had to offer, and this would have translated into a wide variety of foods. By some estimates, our hunter-gatherer ancestors ate more than 800 different types of wild plant foods. These days many of us in the industrialized west are lucky if we get more than 20 different fruits and vegetables into our bodies on a regular basis. (Or five portions a day, for that matter.) No wonder our collective health is flagging.
While it is generally accepted that we need to eat a certain amount of greens each day – at least five portions, or about 200 grams each of vegetables and fruits – to maintain health, quantity is not enough. Diversity – eating five portions or 400 grams of different vegetables and fruits a day, and varying these constantly – is increasingly seen as a key to good health.
Talk of dietary diversity in cancer prevention received fresh fuel a few days ago when the medical journal Cancer Epidemiology, Biomarkers & Prevention published a study that found smokers who eat a wide variety of vegetables have a statistically significantly lower risk of developing lung cancer than those whose diet includes little vegetal variety.
The study is drawn from the ongoing, multi-centered European Prospective Investigation into Cancer and Nutrition (EPIC) study, a large-scale investigation involving nearly half a million participants in 10 countries. Scientists sorted the subjects into four groups depending upon how many of 14 fruits and 26 vegetables they had eaten over a two-week period. Those in the top quartile ate between 23 and 40 different fruits and vegetables; those in the lowest quartile ate less than 10 different types.
After tracking participants on average for almost nine years, researchers found that – regardless of the amount eaten – increased diversity of vegetables was linked with reduced risk of lung cancer, especially for smokers. Smokers who ate the greatest variety of vegetables had a 23% lower risk of lung cancer than those consuming the lowest variety. And smokers who ate the greatest variety of fruits and vegetables were 27% less likely to get squamous cell lung cancer, which accounts for 25-30% of all lung cancers.
Of course, this doesn’t mean that you can smoke and still remain healthy as long as you eat your greens. “By far the best way to reduce one’s risk of lung cancer is to stop smoking altogether,” says H. Bas Bueno-de-Mesquita, one of the study’s lead authors and project director of cancer epidemiology at the National Institute for Public Health and the Environment in The Netherlands. However, for the billion smokers worldwide who are addicted to nicotine and find it impossible to quit, eating a variety of vegetables and fruits may represent at least a small risk reduction, he said in an interview.
After years of searching for the Holy Grail of anti-cancer foods – Broccoli sprouts? Green tea? Tomato paste? Turmeric? – scientists increasingly believe that the very combination and interaction of these foods – and many others – may afford the best protection against cancer.
Several studies have suggested that eating a wide diversity of healthy foods may reduce the risk of various cancers, notably those of the digestive tract (see this study, this and this) and breast cancer – even in women with a genetically heightened risk of developing breast cancer. The health effect of a varied diet is most noticeable with vegetables and fruits; varying different types of meat or cereal grains does not appear to have noticeable benefits. (Needless to say, a wide variety of junk foods has no positive health effect at all.)
What this boils down to is that we should embrace dietary variety, consuming many different whole, fresh foods every day. Eating seasonal produce (locally produced for optimum freshness) is an easy way to vary your nutrient intake; as the seasons change, so does the food on your plate. Alas, many people aren’t keen on eating vegetables and fruits; indeed, among the population investigated in the EPIC study, only 23.8% fell into the highest-variety quartile.
Vegetable-phobes may be tempted to substitute a wide diversity of fresh vegetables and fruits with food supplements. However, “a nutritional supplement can never replace the complex matrix of a whole food,” says Dr Bas Bueno-de-Mesquita. As he explains it, each fruit or vegetable contains many different bioactive compounds, none of which can be solely responsible for reducing cancer risk. “A rich mix of vegetables and fruits will expose you to a rich mix of bioactive compounds which may interact and reinforce each other” to help reduce cancer risk, he says.
It may be too early for governments to issue formal recommendations based on these initial findings, but I for one will continue piling my plate high with vegetables and fruits of all sorts. Like everyone, I have good and bad days on the diversity front. Today was good: I ate peppers and onions (breakfast frittata), a nectarine and three plums (snacks), onions, tomatoes, carrots, celery, garlic and dried mushrooms (Bolognese sauce), leeks, broccoli, spring onions and more carrots (vegetable soup). Can I do it again tomorrow?
For more information on increasing the variety of healthy foods in your diet: Zest for Life, The Mediterranean Anti-Cancer Diet (http://www.zestforlifediet.com)