“Fruit and vegetable intake: five a day may not be enough, scientists say” is one of the headlines in the Guardian to-day 1st April 2014(1). In the article it is stated that:

“The clear finding was that eating more fresh fruit and vegetables, including salads, was linked to living a longer life generally and in particular, to a lower chance of death from heart disease, stroke and cancer.”

This is based on the results of research conducted at University College London in which data collected for the Health Survey of England (HSE) have been analysed. The report of the work has just been published in the Journal of Epidemiology and Community Health and is freely available to all (2).

The big problem with any research of this type is that although it can be demonstrated that those who consume plenty of fruit and vegetables, on average, live longer than those who consume a small amount, this is not proof that if you eat plenty of fruit and vegetables then this in itself will increase your life span. It may well be that a high intake of fruit and vegetables is simply an indicator of a generally healthy lifestyle. If this is the case then the impact of increasing consumption of fruit and vegetables on its own will be relatively small.

As it happens the research paper actually provides comprehensive information on the characteristics of those involved in the HSE. Table 1 shows how these vary with the consumption of fruit and vegetables.

Table 1. Variation in personal characteristics with consumption of fruit and vegetables

Portions per day, F&V 0-1 1-3 3-5 5-7 7+
Fruit 0.2 1.2 2.5 3.8 6.1
Vegetables 0.3 1.1 1.6 2.2 3.1
Male,% 49.5 46.1 42.6 41.4 41.3
Non-manual,% 33.5 43.9 51.2 56.3 60.8
Degree or equivalent,% 7.4 12.1 16.9 22.0 28.5
Current smoker,% 39.0 24.3 15.4 11.1 10.4
Inactive,% 6.1 4.7 3.7 2.5 1.4
Vigorous activity,% 5.9 7.1 9.0 11.4 13.8
Alcohol, over double daily recommendation,% 18.7 14.6 11.1 10.1 9.6
BMI, 27.7 27.7 27.7 27.6 27.6
Deaths,% 8.2 7.9 6.4 5.3 4.1

 

The picture which emerges from these data is somewhat different from that presented in the media to the public. While it is evident that over the time of the investigation, those who consumed over 7 portions of fruit and vegetables had a death rate which was only 50% of those who consumed very little, there were also very big differences with respect to other factors. Those with the highest death rate were also much heavier smokers, took less exercise and were much more likely to be manual workers who did not have a degree qualification. They were also more likely to abuse alcohol. The fact that women, who have a life expectancy which is about 5 years greater than men, are more strongly represented in the low death rate group is not in the least surprising.

An interesting finding which seems to have been ignored so far is that the BMI for all the groups is virtually the same. So here we have a big difference in death rate despite the fact that there is no change in BMI, which seems to fly in the face of all the hype about obesity.

Although there is no information on incomes shown it is almost certain that there is a relationship between death rates and income levels, which may well be n important contributory factor. Nevertheless it is clear that the cohort of people who consume lots of fruit and vegetables is very different from those who consume hardly any. It is not in the least surprising that those smoke the most cigarettes, exercise least, abuse alcohol the most as well as having a low consumption of fruit and vegetables have a reduced life expectancy. This is not exactly rocket science. In fact it is only what is to be expected. We know that there are big differences in life expectancy between different parts of the country and even between different areas within cities.

Unfortunately the authors of the paper fall into the trap of reading too much into their results. They claim that:

With increasing evidence of their health benefits, policy-makers may need to consider broader initiatives to promote fruit and vegetable consumption, particularly vegetables and salad”

The press release which accompanied publication states that:

Eating at least 7 daily portions (of fruit and vegetables) was linked to a 42% lower risk of death from all causes and from cancer and heart disease/stroke of 25% and 31% respectively    They conclude that the current dietary guidelines…..might need to be revised

The press release concludes that:

The study findings imply that even those who do get their recommended quota, need to eat more, they say. “Is it perhaps time to update the ‘5-a-day’ message to ‘10-a-day’?they ask”.

It may well be that increasing consumption will result in some improvement in general health and possibly a small increase in life expectancy. But the message that is being presented is very different. There is a very clear implication that there will be very substantial benefits. This is quite misleading. If people increase their fruit and vegetable consumption from the lowest to the highest in this study there is absolutely no possibility they will halve their death rate, unless they also make other fundamental changes to their lifestyle. This means increasing exercise, reducing smoking and avoiding excessive alcohol consumption.

The harsh reality is that many people simply do not have the opportunity or the inclination to make the changes because they are restricted by their income, where they live and their general background.

My fundamental criticism is not with the research but with the way in which the results have been portrayed and the response from journalists, who have accepted the line presented to them. This is particularly regrettable as in this case the original research paper is freely available and it would have been very easy for any individual to do what I have done here.

REFERENCES

  1. http://www.theguardian.com/uk-news/2014/apr/01/fruit-and-vegetables-seven-portions-ucl-study
  2. http://jech.bmj.com/content/early/2014/03/03/jech-2013-203500.full.pdf+html