Seven Portions of Fruit and Veg?

Dr Geoff recently went on ITV News to voice his opinion on this study. He would like to clarify his views and review the study properly in the report below:

Seven Portions of Fruit and Veg?

Overview

The paper that caused such a media frenzy (1/04/2014) was an epidemiological study which confirmed that people who eat more fruit and vegetables tend to live longer and to be less likely to die of cancer or heart disease within the study period than those who eat less. Most nutritionists, including myself, accept that part of this is due to a direct beneficial effect of eating a diet rich in fruit and vegetables. I agree with the authors’ recommendations that we should all be encouraged to eat more fruit and vegetables.

The study

The group, based at University College London, used data on around 65,000 people collected as part of an official programme (The Health Survey for England) to monitor the health and well-being of the English population including, since 2002, limited aspects of their diet. I consider this to be a good paper of its type; the authors did as good a job as they could with the data that was available to them. The data did have many flaws and limitations as is almost always the case with this sort of epidemiological study using data not specifically collected for the purpose of the project. The method for assessing diet was very limited and crude as were some of the methods used to assess the other characteristics of the subjects. It is all but impossible to get a detailed and accurate picture of what a large group of people normally eat. Many important dietary and other characteristics of the subjects were simply not measured. They used the data that had been collected to relate estimates of fruit and vegetable intake to risk of dying from any cause and specifically from cancer or heart disease.

The main findings

They found that the risk of dying from any cause or specifically from cancer or heart disease decreased progressively with increasing fruit and vegetable consumption. Their highest grouping was people who said that they ate more than 7 portions per day and this group had the lowest death rate. What their analysis also shows is that people who ate the most fruit and vegetables were:

• Less likely to be male
• Less likely to smoke or to have ever smoked
• Less likely to drink excessively i.e. more than twice the recommended level
• Less likely to be in manual occupations
• More likely to have a higher level of education
• Likely to be more active (although activity data was not available for over 60% of the sample).

The people in the 7-a-day category are therefore very different from the people in the less than 1-a-day category. The authors did try to allow for this but the process of correction is imperfect and becomes more imperfect if the population can only be divided up into broad, crude groupings for most measures. What the authors cannot correct for is the many other differences in diet and lifestyle of the groups who ate the most and the least fruit and vegetables because these were simply not recorded. They cannot properly allow for differences in the working and living environment of the groups and the other likely major differences in the diets of the groups. I would confidently predict (educated guess) that compared to the lowest grouping, the group who ate the most fruit and vegetables:

• Ate less cheap processed meats like sausages and pies and ate less economy range ready meals and biscuits
• Ate eat less fat, saturated fat and salt
• Were generally more health conscious and more proactive in their attempts to live and eat healthily
• Were more likely to have access to private health care and take more advantage of screening programmes
• Were less likely to be exposed to all sorts of pollutants at home and at work
• To live in nicer or larger homes in more desirable areas and to have a more pleasant workplace environment
• And so on.

The interpretation

All sorts of nutrition pundits and experts, including myself, have contributed sound-bites and quotations for the media about this study. Some have suggested that the current recommendations of at least 5 portions per day should be raised to 7 or even 10-a-day

Should we go for 7-a-day or more?

It seems extremely premature to start suggesting changes in policy on the basis of one epidemiological study of this type.
Less than 10% of the sample ate more than 7-a-day and only 25% reached the current recommended 5 portions per day. A shocking 14% ate less than one portion per day and nearly 30% ate less than 3-a-day. The improvement in mortality was biggest when one went from the lowest category up through the categories to our current recommendation of 5-a-day. The additional benefit of going beyond 7-a-day was relatively small even if one takes the data at face value and ignores the unavoidable flaws with it. We should be focusing upon the bulk of the population who are falling short, often very short, of the current 5-a-day target rather than small and highly speculative benefits for those already meeting these guidelines. If successful, campaigns aimed at achieving increases in the intakes of those in the lowest categories offer hope of the greatest benefit for the greatest number.
The authors went on to try and assess the benefits of 9 different categories of foods within the broad category of fruit and vegetables. Much has been made in the media of the suggestion that those consuming lots of tinned or frozen fruit had slightly higher overall mortality. I would be reluctant to draw any firm conclusions using this analysis and would certainly not want to make any practical recommendations on the basis of this observation. It is probable that those who chose to or had to eat canned and frozen fruit were very different as a group from those who eat mainly fresh produce.

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One thought on “Seven Portions of Fruit and Veg?

  1. Pingback: Fruits and vegetable: should it be 5,7, or even 10-a-day? | Dr Geoff

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