The Journal wisely encourages the use of the “Number Needed to Treat” instead of “Relative Risk Reduction”.(1) Wang et al only provided hazard ratios when estimating risk for all cause, cardiovascular, and cancer mortality by levels of fruit and vegetable consumption.(2)
From the data provided by ref 42 one can calculate that the number needed to treat to avoid one death from ischemic heart disease during 8.4 years is 500 (6.7 deaths per 1000 persons consuming 3 portions of fruits and vegetables per day vs 4.7 deaths per 1000 persons consuming 8 portions per day).
Using the population attributable fraction (PAF) would have been even more appropriate to illustrate the true burden of poor diets. PAF is the proportional reduction in population disease or mortality that would occur if exposure to a risk factor were reduced to an alternative ideal exposure scenario.
Despite a weak association applied to the population may still be meaningful for public health, shifting to an herbivore or chimp diets is unlikely to be both enforceable and acceptable. Last, poor diet is simply a marker of more serious unhealthy behaviours and poor social determinants that influence cancer risk (alcohol, tobacco, lack of physical activity, obesity …).
1 Moore A, McQuay H. Numbers needed to treat derived from meta analysis. NNT is a tool, to be used appropriately. BMJ. 1999 Oct 30;319(7218):1200.
2 Wang X, Ouyang Y, Liu J et al. 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:g4490.
Competing interests: No competing interests