Animal products, including meat, cheese, and eggs contain carnitine and choline, metabolites that are converted by gut bacteria into TMA, which is then converted by the liver into TMAO. Plasma levels of TMAO are associated with an increased risk of disease and death, so should we limit intake of these animal products? Separately, fish contains relatively high levels of TMAO, and blood levels of TMAO spike after fish consumption, but there is a decreased all-cause mortality risk for fish consumers. To explain these disparate findings, other factors may be involved in the TMAO-health and disease story. In the video, I discuss the impact of kidney function on plasma levels of TMAO, disease and mortality risk.
To answer the question proposed in the title, today I’ll look at the results of the Oxford Vegetarian study, in which risk for all-cause mortality, ischemic heart disease and malignant neoplasms was determined (Appelby et al. 1999). 6000 vegetarians and 5000 non-vegetarians were recruited, and, all participants were further divided into 4 groups: vegans, defined as those who never ate animal products; vegetarians, who never ate meat or fish but did eat dairy products, eggs, or both; fish eaters, who ate fish but no meat; and meat eaters (who ate meat more than once per week).
All groups consumed the same amount of total calories. However, when comparing individual macronutrients, vegans had the lowest protein (3.3% of total calories less than meat eaters) and fat intake (4.6 % less), but they made up for this difference by having a higher carbohydrate intake (9.5%), relative to all other groups. A similar dietary pattern was found in vegetarians, when compared with both fish and meat eaters.
A decreased total cholesterol/HDL ratio (TC/HDL) was found in vegans, when compared with vegetarians, fish and meat eaters The TC/HDL ratio has been shown to be a strong independent predictor for the development of peripheral arterial disease (PAD, Ridker et al. 2001), a disease in which plaque builds up in the arteries that carry blood to the head, organs, and limbs. In vegans, TC/HDL = 2.88; in vegetarians, 3.25; fish eaters, 3.21; meat eaters 3.56. Based on these results, the incidence of ischemic heart disease was predicted to be 57% lower in lifelong vegans and 24% in lifelong vegetarians than in meat eaters.
When considered as a whole group (11,000 subjects), significant associations between individual dietary components and mortality risk for ischemic heart disease were determined. For example, eating up to 5 eggs per week did not significantly increase mortality risk, but eating 6+ eggs per week increased risk by 270%. Eating cheese (excluding cottage) up to 4 times per week did not increase mortality risk, but eating cheese more than 5 times per week increased mortality risk by 247%. Relative to the lowest intake of animal and saturated fat, mortality risk was increased by 329% and 277%, in the highest intake, respectively. Similarly, those that ate the most cholesterol had a 353% increased mortality risk, relative to the lowest intake. In other words, high amounts of eggs cheese, animal and saturated fat were found to be associated with increased risk for ischemic heart disease.
Death rates, risk of ischemic heart disease and the risk of malignant cancer were 20%, 28% and 39% reduced in in non-meat-eaters when compared with meat eaters.Cumulatively, these results provide yet another reason to reduce meat consumption! (Also see http://atomic-temporary-71218033.wpcomstaging.com/2014/07/25/methionine-restriction-extends-lifespan-another-reason-to-reduce-meatprotein-intake/).
If you’re interested, please have a look at my book!
Appleby PN, Thorogood M, Mann JI, Key TJ. The Oxford Vegetarian Study: an overview. Am J Clin Nutr. 1999 Sep;70(3 Suppl):525S-531S.
Ridker PM, Stampfer MJ, Rifai N. Novel risk factors for systemic atherosclerosis: a comparison of C-reactive protein, fibrinogen, homocysteine, lipoprotein(a), and standard cholesterol screening as predictors of peripheral arterial disease. JAMA. 2001 May 16;285(19):2481-5