The turn of the year means the majority of adults will be feeling fat and fed up.
By the second week of the month, new year’s diets will have been abandoned by around 80 per cent of those who swore that this would be the year to slough off the extra weight and get healthy. This, despite the overwhelming evidence showing how important diet is for good health.
It’s hard to avoid newspaper headlines announcing the latest cancer-preventing, dementia-delaying, stroke-reducing miracle fruit or vegetable. But with huge numbers of new studies being reported each month, what is the truth about what fruit and vegetables can do for our bodies? And can they actually preventserious diseases?
It is largely agreed among scientists that fruit and vegetables are important for health because they contain fibre which aids digestion, are low in calories so are good for controlling weight, and are rich in vitamins and minerals which help the body run smoothly.
Vitamin A is important for eyesight and the immune system, vitamin B is good for hair, skin and nails, and vitamin C helps keep cells and tissues healthy. There is also evidence fruit and vegetables can help prevent some serious diseases, with numerous studies linking particular vitamins, acids, nutrients and antioxidants found in fruit and veg to a reduced risk of heart disease, certain types of cancers, obesity, and type 2 diabetes.
There are a huge number of studies relating to cancer. For example, vitamin C has been found to help prevent the formation of cancer-causing nitrogen compounds. Cruciferous vegetables such as broccoli, cauliflower, and cabbage contain phytonutrients known as glucosinolates, which some studies have shown may help inhibit the metabolism of some carcinogens. And pomegranates contain high levels of ellagic acid which in lab studies have been shown to inhibit cancer cell growth.
This research often leads to bold headlines, such as ‘Broccoli and cabbage among vegetables that cut cancer risk’ and ‘Blueberries protect against colon cancer’, both in the Daily Mail, and ‘Mediterranean diet rich in fruit and vegetables could cut the risk of dementia’ in the Daily Express.
Inevitably, such health claims bring scrutiny and scepticism. Last year, for example, scientists at Tuft’s University in Boston reviewed the link between fruit and vegetables and dementia and claimed there was little evidence.
“Studies find inconsistent relationships between fruit and vegetables and their components and cognitive decline and dementia,” said the authors. “Inconsistencies throughout the research on fruit and vegetables and their components do not allow for strong conclusions to be made at this time regarding their influence on cognitive function.”
You should always treat big claims with caution, says Professor Martin Wickman, head of nutrition at Leatherhead Food Research. “There are a lot of things people believe could be magic bullets but it is very speculative at the moment, there is not a huge amount of solid evidence and it is a tricky area to get definitive answers.”
While it may not be proven that a particular fruit could ease a particular ailment, Alison Tedstone, director of diet and nutrition at Public Health England, says that people who eat a variety of fruit and vegetables, no less than five portions or 400g a day, tend to have a lower risk of coronary heart disease and some cancers.
“It is not clear which precise components of fruit and vegetables are responsible for the beneficial effect,” she says. “Some studies suggest that the effect of fruit and vegetable consumption is greater than the impact of the individual nutrients when they are consumed as supplements,” she explains – ie the whole fruit does something the individual ingredients do not.
To avoid any doubt, the best policy is to “eat a variety of fruit and veg in order to achieve the balance of nutrients,” says Tedstone.“It is thought the combination of these properties, rather than one particular component, may have a protective effect against disease.”
Superfoods: do they really exist?
It is a seductive term, often applied to berries, pomegranates, dark green vegetables, citrus fruit and sweet potatoes, but the label ‘superfood’ or ‘superfruit’ is simply a marketing term with no agreed scientific definition, according to Tedstone.
While it is true these fruits and vegetables are high in antioxidants, such as vitamins C and E, beta-carotene and flavonoids, consumers should treat claims about disease prevention with caution, says Eleftheria Stavridou, plant molecular nutritionist and research leader at East Malling Research.
“For example, berries have been reported to contain high levels of antioxidants, whichare associated with the prevention of cardiovascular disease and cancer.
“Although there may be scientific evidence to support that certain antioxidants help to reduce the risk of these diseases, many of these claims have not been validated by human models or through human trials,” she says. “The evidence supporting the claims may also involve unrealistic doses, ie exposure to an antioxidant at a level which would not naturally occur when eating the fruit, or the antioxidants are applied in an artificial way in a lab which may not be realistic to what would happen in the body.”
The Fresh vs Processed debate
Think of a healthy plate, and images of fresh fruit and vegetables spring to mind. But it’s not necessarily the case that fresh is always better for your health than frozen or canned produce, says Wickham. In fact, processed can even be the healthiest choice in certain situations.
“If you look at the nutrients we take in from a fresh carrot or tomatoes, so beta-carotene in fresh carrots or lycopene in tomatoes, we find out that we as humans only take in a very small amount, around five per cent of what is available. However if we heat it and put it in a can, it breaks down the structure of the food, so the beta-carotene or the lycopene suddenly become very available to us so we absorb a lot more,” he says.
“We’ve always been told that processing is bad for vegetables, and it may be the case that it is for some because some vitamins and minerals are destroyed by heat, but for others it is the reverse.”
One example of a processed product that may not be the best choice, however, is fruit juice. While juices contain vitamin C, Wickham says research has shown that in the case of oranges for example, “there are components in an orange that are needed to help the uptake of vitamin C, so you get a lot more vitamin C from eating an orange than a glass of juice.”
In addition, “juice is very high in sugar, and there is none of the original plant tissue in there so there is no fibre,” Wickham points out. “So we are much better off eating an orange than drinking the juice.”
What is indisputable is that fruit and vegetables – fresh, frozen or processed – are good for you. Scientists will always argue about the details, but that shouldn’t stop the industry proudly shouting its credentials from the rooftops.
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