Montag, 29. April 2013

Cliffnotes on Vegetarianism and Diet in general: The Big Picture

I know how unbelievably hard it is not just to parse research, since there is so much of it, but also to understand its implications. Over time I have gotten better at this, but it does take practice. Here, I will try to put current research into context and given how popular paleo-style diets are, I will also address this issue. I think a pattern is emerging:

Ramsden et al. 2013 (2) extended their older meta-analysis that found n6 polyunsaturated fats (PUFA) to be at best health-neutral and possibly harmful. Yes, this seems to be a "win" for the paleo-diet in a sense, but better scientific arguments against excessive n6 PUFA intakes existed for a long time. For instance, a simple argument based on oxidative stress.

Notably, the next few studies are inconsistent with the "paleo-hypothesis":

The huge PREDIMED trial (3) showed that the addition of two plant foods: tree nuts and even more so virgin olive oil (EVOO) is beneficial in primary prevention; laying the foundation for Mediterranean-style moderate-to-high-fat vegetarianism. Consistent with Ramsden et al. EVOO performed slightly better!

(As a side note: There is still no good research linking moderate fructose intakes to bad health outcomes. )

Huang et al. 2012 (1) re-confirmed an older meta-analysis that found modestly reduced mortality in vegetarians.

Another research group  found a novel mechanism which may explain how and why meat is harmful to health. (4) This year the group extended their research on trimethylamines (TMA or TMAO) that gut microbiota could produce from meat constituents.

The only reasonable conclusion
Three very high impact papers (1-3) have produced concordant results. If we combine the data we are able to confirm that Mediterranean-style (3) vegetarianism (1) that emphasizes MUFA from olive oil, and to some extent "balanced" n3 and n6 from nuts over saturated fats and n6 PUFA (2), produces the best health outcomes.

This dietary recommendation rests on a sound foundation of basic (e.g. ref. 4) and translational research when compared with the classical low-fat food pyramids. Evidently, some questions need to be answered but this should not affect the above recommendation.

Just to be clear: I do endorse flexible vegetarianism. In the end it is all about your average long term intake.

(1) Ann Nutr Metab. 2012;60(4):233-40. doi: 10.1159/000337301. Epub 2012 Jun 1.
Cardiovascular disease mortality and cancer incidence in vegetarians: a meta-analysis and systematic review.
Huang T, Yang B, Zheng J, Li G, Wahlqvist ML, Li D.

*(2) BMJ. 2013 Feb 4;346:e8707. doi: 10.1136/bmj.e8707.
Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis.
Ramsden CE, Zamora D, Leelarthaepin B, Majchrzak-Hong SF, Faurot KR, Suchindran CM, Ringel A, Davis JM, Hibbeln JR.

(3)  Estruch R, Ros E, Salas-Salvadó J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med 2013; DOI: 10.1056/NEJMoa200303.

*(4) Nat Med. 2013 Apr 7. doi: 10.1038/nm.3145. [Epub ahead of print]
Intestinal microbiota metabolism of l-carnitine, a nutrient in red meat, promotes atherosclerosis.
Koeth RA, Wang Z, Levison BS, Buffa JA, Org E, Sheehy BT, Britt EB, Fu X, Wu Y, Li L, Smith JD, Didonato JA, Chen J, Li H, Wu GD, Lewis JD, Warrier M, Brown JM, Krauss RM, Tang WH, Bushman FD, Lusis AJ, Hazen SL.

*papers I have not yet read in full, although, I am familiar with earlier work. Hope I can blog on this in the future

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