Shutterstock Conversation Geoff Webb

Only a quarter of UK adults manage to eat the officially recommended five portions of fruit and vegetables a day. In fact, almost half eat less than three a day. It seems unlikely, then, that most people would be able to reach the ten a day suggested by several pieces of research published in the last few years. The Conversation

Most recently, a paper in the International Journal of Epidemiology laid out evidence that upping your intake of fruit and veg to ten portions (800g) a day would further reduce your risk of cancer, cardiovascular disease and premature death. But how strong is this evidence, and how practical is this advice for most individuals or society as a whole? A closer look suggests we need to be cautious about turning this complex research into simple and useful recommendations.

The five-a-day mantra goes back to recommendations from the World Health Organisation in 1990 and numerous developed countries have adopted it as official advice. Since then, further research has shown that each of the first five 80g portions of fruit and veg a person eats every day is associated with about a 5 per cent decrease in overall and cardiovascular deaths. But the link between vegetables and disease prevention isn’t always that clear. For example, in 2010 the massive European Prospective Investigation into Cancer and Nutrition (EPIC) found only a small decrease in cancer risk associated with eating fruit and veg.

Then came two studies that have put forward the case for eating even more than five a day. The first, in 2014, linked lifestyle information on 65,000 English adults from the Health Survey for England to mortality records. It reported that the more fruit and veg people ate, the less likely they were to die from cardiovascular disease or cancer. The death rate among those who ate on average under one portion a day was twice that among those who ate more than seven a day.

But fruit and veg intake wasn’t the only thing related to the death rate. The one-a-day group were also more likely to be very elderly, male, less well educated, smokers, physically inactive and heavy drinkers. So the researchers analysed the data in a way that took account of these other factors, although they couldn’t do this for unrecorded things such as saturated fat intake.

After this correction, the data showed that those who ate three to five portions of fruit and veg were still 25per cent less likely to die than those in the one-a-day category. Those who ate five to seven portions a day were a further 6per cent less likely to die and those who ate more than seven a day saw another 3 per cent drop. This meant the biggest benefit was from increasing fruit and veg consumption to up to five a day.

The more recent study brought together the results from 95 cohort studies that each tracked a large group of people over a time. It found a strong association between eating up to ten portions of fruit and veg a day and reduced death – overall, and from cardiovascular disease in particular. But again, the study showed these benefits were biggest as consumption increased up to five a day and were markedly smaller after that. There was also a decline in cancer deaths as people ate more fruit and veg but it was smaller and flattened out earlier.

These studies confirm that increased fruit and veg consumption is associated with fewer deaths, less cardiovascular disease and maybe some decrease in cancer risk. The benefits are particularly seen as people increase their fruit and veg intake up to five portions a day. But the benefits related to eating more than this are much smaller and less certain.

We also don’t know for sure whether eating fruit and veg actually causes these apparent benefits. It’s possible that they are due to other linked factors or confounding variables, such as eating less saturated fat. Most researchers try to adjust their data to take this into account but there is no statistical magic wand that can do this faultlessly. Some factors are hard to gauge accurately and others might be missed altogether.

However, the association between eating more fruit and veg and living longer is strong, consistent, graded according to how much is eaten and remains strong even after many other factors are taken into account. This means eating more fruit and veg probably does cause the associated health benefits. But we can’t say this for eating more than five portions a day. Further studies probably won’t change this and nor can they prove cause and effect.

Weak evidence

The recent studies provide only weak evidence of a small extra benefit of eating more than five portions of fruit and veg a day. We then have to ask whether making this an official recommendation would be worthwhile. For one thing, almost all studies have used middle-aged or elderly adults. So we don’t know if ten-a-day would be appropriate for other groups such as rapidly growing children and adolescents.

What’s more, while getting people who eat very little fruit and veg to eat more will likely produce big benefits, raising the official target to ten-a-day might actually discourage some people. Most people would struggle to eat this much, so failing to hit the target would become expected, and then accepted and excusable.

To get most people in the UK to ten-a-day would mean the country would have to eat four times as much fruit and veg as it currently does. The environmental, economic and ecological impact of such a massive increase in demand for these bulky products would be enormous and probably unsustainable. Fruit and veg are already expensive in terms of calories per penny and increased demand might make them completely unaffordable for many people. And they couldn’t just eat less of other foods because fruit and veg contain relatively low numbers of calories.

Ultimately, these concerns are theoretical because no one expects the bulk of the population to get anywhere near ten-a-day. But we have to question whether it is responsible to make such recommendations – and on weak evidence – just because you know hardly anyone will implement them.

This article was originally published on The Conversation. Read the original article.