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Apparently damning with faint praise!
- Kit Byatt (6 September 2009)
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Re: Apparently damning with faint praise!
- Jim Mann (16 September 2009)
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Kit Byatt, consultant physician & geriatrician The County Hospital, Hereford
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I would like to thank Jim Mann for his very nearly excellent leading article. It is extremely informative, positive and encouraging in places. However, having read it several times, I am still trying to work out what his message actually is here! In paragraphs 2 to 5 (of 10) Mann carefully spells out the statistically significant massive health benefits of a 'vegetarian diet' (incidentally, without defining what he means by this term). He points out that, for the population included in the substantial trials he quotes, the overall all-cause SMR is 50% (although he doesn't explicitly specify which of the trials yield this finding), and the cancer SMR is about 70% (whether meat-eating or not) - in other words this is an extremely healthy trial group overall, whether 'vegetarian' or meat-eating. Despite this very much above average survival for both groups, he shows that within the study population there is still a distinct survival benefit from having a vegetarian diet (including a reduced IHD mortality of ~24%, a relative risk of 0.39 for type 2 diabetes and =<0.45 for hypertension; additionally a World Cancer Research Fund/American Institute for Cancer Research report suggested meat as 'the only "convincing" dietary association with colon cancer'). In paragraph 7 he sets out the possible health risks of a opting for a 'vegetarian diet' and in paragraph 8 acknowledges that 'vegetarianism covers a wide spectrum' of sub-groups with consequently differing potential risk types and magnitudes. In paragraph 9 Mann states that 'vegetarians who participate in long term prospective studies have appreciably lower mortality than the general population' (omitting to mention that meat eaters do, too [as shown in para 6], albeit less so), but there is little evidence to show it is the 'meat avoidance' per se that achieves this. He also implies that much of the benefit is because vegetarians tend to be non-smokers. In his summary in paragraph 10, Mann states that vegetarianism is therefore overall an 'acceptable' dietary practice, but not better than 'Mediterranean, Asian or "modified conventional Western" dietary patterns.' - not defining any of these terms (especially the latter, which means nothing to me, and a Google search for "modified conventional Western diet" returns 0 hits). His conclusion from all this expertly summarized mass of heavyweight data is that "Claims for unique benefits from a vegetarian lifestyle may be more appropriately made on ecological grounds." I don't argue with this assertion, but I have four concerns: 1. Mann implies that vegetarians' (non-)smoking habits might account for their lower mortality ratios. If that aspect of the work was done in the original trials, then please summarize it explicitly. If not, how can the study be regarded as meaningful? Surely it would be unethical not to control for smoking in any study purporting to examine aspects of cardiovascular epidemiology (did none of the quoted studies of diet on IHD outcomes consider this factor?). 2. The Department of Health states on its website that the 'target on obesity is the Government's first, high level response to the major public health problem posed by the continuing rise in obesity.'[1] Mann's analysis mentions 'the low rates of obesity.. among vegetarians' although not quantifying this. Why not investigate a possibly useful prevention approach as suggested by these data, rather than suggesting an alternative reason for its 'unique benefits?' 3. Why pick only the ecological argument for considering vegetarianism to have an unique benefit? Animal welfare may be considered as compelling a reason to consider vegetarianism (or veganism) as a lifestyle choice[2]. Why ignore this alternative consideration? 4. The tenor of the discussion in the last two paragraphs is almost dismissive. I can accept the science shows that we do not yet know for certain which aspect of being a 'vegetarian' confers the benefit. However, as an analogy, NICE report that UKPDS showed an overall benefit of metformin of 0.68 on all-cause mortality in overweight participants[3]. Do we know exactly which of metformin's biochemical actions achieves this effect? We still use it, though. I am left feeling that Mann might be being patronising about vegetarianism and thus tacitly inviting his audience to condescend to those who choose (for whatever reason) this lifestyle. Whether he does this unintentionally or not is impossible to discern. The unqualified use of the word 'acceptable' in his concluding paragraph can be taken to imply 'tolerable' or 'just good enough', although the same word can also be used to mean 'absolutely fine'. This potentially confusing quasi-homonymy is perhaps analogous to the current use of the word 'competent' in medical education. It can be taken as meaning 'skilled' or 'expert' on the one hand, or 'barely achieving an acceptable level' on the other, depending on how it is said or qualified. This causes much unease amongst assessors and trainees alike as to what was actually meant when it was deployed! I realize that the constraints of a word-limited editorial result in much qualifying text having to be redacted, but I hope in his response Jim Mann will answer the numbered points above and also confirm which usage for the word 'acceptable' he intended. On the positive side, however, there are some very encouraging data summarised here suggesting that at least some of the lifestyle choices of vegetarians are evidence based! References 1. http://www.dh.gov.uk/en/Publicationsandstatistics/Publications/PublicationsPolicyAndGuidance/Browsable/DH_5721976 (accessed 5 September 2009) 2. Humane Slaughter in British Abattoirs a 'Sham' http://animalaid.org.uk/h/n/AA/HOME/ (accessed 5 September 2009) 3. http://guidance.nice.org.uk/CG66/Guidance/pdf/English (accessed 5 September 2009) Competing interests: I am a vegetarian for health, ecological and animal welfare reasons |
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Jim Mann, Professor of Human Nutrition & Medicine University of Otago
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The word limit for editorials may account for some of Dr Byatt’s concerns. It was certainly not my intention to be dismissive, patronising or condescending about a vegetarian diet. The vegetarian dietary pattern has been associated with several positive health outcomes including reduced rates of obesity and the fact that relatively few vegetarians are smokers must contribute to the overall lower rates of smoking related diseases amongst those who choose this dietary pattern. However, there is ample evidence that dietary practices independently of smoking can indeed influence important indicators including blood pressure, measures of body fatness and cholesterol levels. The fact that we cannot disentangle which component of the vegetarian dietary pattern confers health benefits does not in any way detract from its positive attributes. I am very happy to acknowledge animal welfare as an additional justification for considering vegetarianism. I was not implying any particularly novel dietary pattern when referring to a “modified conventional western dietary pattern”. Many diets consumed in western countries are relatively high in saturated fat, sugars and energy dense foods rich in these nutrients. I was merely attempting to indicate that when the totality of evidence is considered, it appears that by modifying what is typically eaten in such countries, one may be able to achieve the health outcomes which have been attributed to traditional Asian, Mediterranean, African and vegetarian diets. Competing interests: None declared |
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