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Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies

BMJ 2014; 349 doi: https://doi.org/10.1136/bmj.g4490 (Published 29 July 2014) Cite this as: BMJ 2014;349:g4490

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The authors state that “there was a threshold around five servings of fruit and vegetables a day, after which the risk of all cause mortality did not reduce further”. While they also conclude that “this meta-analysis provides further evidence that a higher consumption of fruit and vegetables is associated with a lower risk of all cause mortality, particularly cardiovascular mortality”, within 24 hours this study has been translated in the mainstream media to “Eating more than five fruit and veg a day may be waste of time” (1).

This story falls hot on the heels of recent suggestions that there may be further health benefits to be obtained from increasing consumption to seven portions a day (2). A backlash was always to be expected, as many still struggle to achieve five (3). For the majority, health benefit up to 5-a-day remains a positive message, but where does this leave those minorities who routinely consume much more (some vegetarians and vegans, and most raw foodists)? The manner in which this controversial conclusion has been arrived at deserves unpicking…

In this study, fruit and vegetable consumption was divided into six categories:

1. One portion per day
2. Two portions per day
3. Three portions per day
4. Four portions per day
5. Five portions per day
6. Six or more portions per day

For each category a pooled hazard ratio was calculated. These express the risk of death from all causes for each level of consumption in comparison to no consumption.

Here are the hazard ratios:

1. One portion per day HR = 0.92
2. Two portions per day HR = 0.85
3. Three portions per day HR = 0.79
4. Four portions per day HR = 0.76
5. Five portions per day HR = 0.74
6. Six or more portions per day HR = 0.74

Taken by themselves, it does look as if each sequential portion added reduces your risk of dying by less than the last one (a curvilinear association). If true, this doesn’t seem unreasonable: your first portion of the day does you the most good, and the second does you good but not quite as much, and so on.

The authors also report 95% confidence intervals for these figures. These give the range within which we can be 95% confident that the true value lies.

Here are the confidence intervals:

1. One portion per day HR = 0.92 CI = 0.90-0.95
2. Two portions per day HR = 0.85 CI = 0.81-0.90
3. Three portions per day HR = 0.79 CI = 0.73-0.86
4. Four portions per day HR = 0.76 CI = 0.69-0.83
5. Five portions per day HR = 0.74 CI = 0.66-0.82
6. Six or more portions per day HR = 0.74 CI = 0.65-0.82

If the confidence intervals for any two groups being compared do not overlap, then it is likely that a difference truly exists, as for the difference between one and three portions per day for example. However, if we compare eating three with eating six or more portions, there is significant overlap, so we cannot say that there is a real difference. This may in part be because the confidence intervals become wider with each subsequent portion of fruit and vegetables.

Here, in brackets, are the widths of the confidence intervals:

1. One portion per day HR = 0.92 CI = 0.90-0.95 (0.05)
2. Two portions per day HR = 0.85 CI = 0.81-0.90 (0.09)
3. Three portions per day HR = 0.79 CI = 0.73-0.86 (0.13)
4. Four portions per day HR = 0.76 CI = 0.69-0.83 (0.14)
5. Five portions per day HR = 0.74 CI = 0.66-0.82 (0.16)
6. Six or more portions per day HR = 0.74 CI = 0.65-0.82 (0.17)

The width for six or more portions is more than three times the width for one portion. Most likely this is because in the seven studies assessed for all-cause mortality, there were fewer and fewer subjects in each subsequent category, and the smaller the sample size the wider the confidence intervals.

This data is not provided in the original article, but they do provide Table 2 that gives categories of consumption for each of the studies included in the meta-analysis.

For the two studies that reported consumption in terms of servings per day (as opposed to grams per day) the maximum consumption categories were 5.9 servings per day of fruit and 5.2 servings of vegetables for one study, and 5+ servings for the other. The two studies reporting consumption in times per week gave maximum consumption categories (for fruits and vegetables separately) of 4 to 7 and 6 to 7 times per week, indicating relatively low consumption levels in their study populations.

The study that reported a maximum of 5.9 servings of fruit and 5.2 servings of vegetables was the JACC study (4), conducted in Japan where they advocate seventeen portions of fruits and vegetables per day (5). Unfortunately the JACC study alone does not give sufficient power to this meta-analysis to draw firm conclusions as to the benefits of increasing fruit and vegetable consumption at higher levels of intake.

Rather than state as fact the existence of a threshold for health benefit from fruit and vegetable consumption, the authors should have acknowledged that they were unable to comment conclusively on health benefits at levels of consumption higher than five portions per day, due to insufficient data. A prospective matched cohort study of vegetarians, vegans, raw foodists and others in a Western setting consuming ten or more portions per day, or 80-100% of their total calories from fruits and vegetables, would be illuminating.

References:

1. Eating more than five fruit and veg a day may be waste of time. Muiris Houston. Irish Times, 30th July 2014: http://www.irishtimes.com/news/health/eating-more-than-five-fruit-and-ve...
2. Oyebode O, Gordon-Dseagu V, Walker A, Mindell JS. Fruit and vegetable consumption and all-cause, cancer and CVD mortality: analysis of Health Survey for England data. Journal of Epidemiology and Community Health. 2014.
3. Trend in the consumption of fruit and vegetables in men, women and children in England to 2011. Food Statistics Pocketbook 2013, p.51. Department for Environment, Food and Rural Affairs: https://www.gov.uk/government/uploads/system/uploads/attachment_data/fil... Accessed on 30th July 2014.
4. Nagura J, Iso H, Watanabe Y, Maruyama K, Date C, Toyoshima H, et al. Fruit, vegetable and bean intake and mortality from cardiovascular disease among Japanese men and Women: the JACC Study. Br J Nutr 2009;102:285-92.
5. Is five a day enough? Luke Waterson. The Guardian, 25th May 2006: http://www.theguardian.com/lifeandstyle/2006/may/25/healthandwellbeing.h... Accessed on 30th July 2014.

Competing interests: Dr Ellen Storm is a graduate from the eCornell University certificate course in Plant-based Nutrition, and currently consumes a high raw vegan diet.

30 July 2014
Ellen M Storm
Paediatric Trainee
Liverpool