Background:

• Dr. Hirayama examined the effects of a small amount of food groups in relation to a large amount of mortality end points in a Japanese cohort of very large size. An extended review of his work was published as a book in 1990 (Hirayama T [5]). Data about this cohort is seldom included in current systematic reviews about the relations mentioned. Dr. Hirayama published a lot of articles stating that vegetables and meats were related to several disease end points, adjusted for age and sex. However, the book included one page showing effects after multivariate analysis including cigarette smoking, meat, green-yellow vegetables, and alcohol. And this analysis showed that a large amount of previously published effects completely changed when these variables were taken into account.
  Since a) Dr. Hirayama himself only published sex, and age-adjusted results in the English language, while results following multivariate analysis were completely different b) the results were published as a book and not in a peer-reviewed journal, and c) Dr. Hirayama was the only researcher examining this cohort, results from his cohort are debatable. Results will be presented including effects from his work, but his work will not be included in the evidence for a possible effect.
• In 1999, Key TJ published a collaborative analysis of combined data from 4 prospective studies, including primarily vegetarian subjects, and including 2,264 IHD deaths. However, when vegans, fish eaters and occasional meat eaters were filtered out of the results, the final analysis included 1,433 deaths for the association between meat eaters vs vegetarians. Findings about 3 of these cohorts were published following this publication, including a longer follow-up period. Cohort-specific results were chosen to be included in the systematic review, instead of results from the collaborative analysis, because this allowed for a larger amount of cases to be included in the analysis.
• In 2002, Appleby PN published results about "The Oxford Vegetarian Study". Results were published for a) vegetarians vs nonvegetarians, and b) meat eaters vs non-meat eaters. Though it seems obvious to include the results from the meat eaters vs non-meat eaters, the non-meat eating group in this analysis included both low consumers of meats, and fish eaters. Therefore, results for vegetarians vs nonvegetarians were included.

CHD risk: Data was provided about 3 cohorts, including 1,303 cases. In one cohort, a significantly increased risk was found among women, but not men (Buckland G [16]); while in another cohort, a significantly increased risk was found among men, but not women (Fraser GE [1]). No other associations were found. The average RR = 1.25.
Effect modification: No data was found.
CHD mortality: Data was provided about 8 cohorts, including 2,928 cases. Significantly increased risks were found in 2 cohorts, including 1,659 cases (57% of all cases). No other associations were found, but all RR's for meat consumption were > 1. The average RR for meat consumption = 1.47 (excluding incomplete data from Knekt P [7], Kinjo Y [5], and Tanaka H [3]).
Effect modification: No effect modification was found by gender (Key TJ [11 + 16]), or a history of CVD/diabetes (Key TJ [11]). An analysis of 4 cohorts showed that vegetarianism was protective among subjects being a vegetarian for > 5 years, and who died before age 80 only (Key TJ [11]).

Conclusion: Inconsistent findings were done among both men and women, relating meat consumption to CHD risk. Inconclusive evidence was found for an association between total meat consumption and CHD risk.
Significantly increased risks of meat consumption were found in 2 cohorts, one of which was of very small size. Suggestive evidence was found that total meat consumption increases CHD mortality (+ 47%). This effect may be restricted to subjects being a vegetarian for > 5 years, and who died before age 80.
Limitations: Most significant effects were found among cohorts consisting of primarily vegetarian subjects, and few results were adjusted for other dietary variables. But RR's for meat consumption were consistently > 1.