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Vegetarian – Yes or No?

It is widely believed that vegetarians are healthier than omnivores, but the evidence to support this is unclear. That’s not surprising. There are many different vegetarian diets and many different omnivore diets. This means that one is not comparing two but multiple options, and those options may be very different in different countries. To complicate matters further, there are many other life-style variables that impact on health and life expectancy; and to kick up a final cloud of dust, the longer-term studies generally rely on food diaries or recollections, both of which are notoriously unreliable.

One influential early study suggested a plant-based diet was linked to a longer life expectancy (1), but the data was complicated by the fact that the communities studied (such as 7th Day Adventists) had a range of behaviours which were likely important co-variables.

A subsequent cross-sectional study (derived from the Austrian Health Interview Survey AT-HIS 2006/07) found that while a vegetarian diet is related to a lower BMI it is also associated with poorer health (higher incidences of cancer, allergies, and mental health disorders), a higher need for health care, and poorer quality of life (2).


A larger and more recent Australian study involving nearly 300,000 subjects found no significant difference in mortality risk between vegetarians vs non-vegetarians, or between pesco-vegetarians, semi-vegetarians and meat eaters (3). The authors of this study stated that there was ‘no evidence that following a vegetarian diet, semi-vegetarian diet or a pesco-vegetarian diet has an independent protective effect on all-cause mortality.’


While vegetarians may be dying at the same rate, the data suggests that they are dying in slightly different ways. In a large meta-analysis comparing vegetarians and vegans to omnivores, the vegetarians had significantly reduced body mass index, total cholesterol, LDL-cholesterol, and glucose levels (4). They also had slightly less mortality from ischaemic heart disease, but were no different from omnivores in terms of total cardiovascular and cerebrovascular diseases, all-cause mortality and mortality from cancer. A second and almost equally large (but differently framed) meta-analysis produced similar results (5).


There are a number of biomarker studies which offer a different perspective. Telomere shortening is reckoned to denote reduced life span, and there is some evidence that those who eat a plant-based diet have slightly longer telomers than omnivores of the same age (6). This fits in with other studies which find that higher consumption of fruits and vegetables (which contain compounds linked to longer telomers) reduce all-cause mortality (7).


Set against that, there is an absolutely enormous global meta-analysis that linked increased meat consumption with increased life expectancy (8); and, for the sake of completeness, another very large meta-analysis that found vegetarians had a slightly longer health expectancy (9).


So, the data are a mess. We have to think in a more granular way about meat, and about plant foods.

Some meats are now thought to be healthier than others. Processed (generally cured) meats seem to be more likely to increase the risk of various diseases including CV and various cancers (10, 11).


Conversely, it is well known that cooking meat at lower temperatures produces less cooked meat carcinogens (HCA’s and PAH’s).


So an omnivore who mostly eats cuts of meat cooked in a sous vide is not the same as an omnivore who regularly eats bacon.

Similarly, some plant foods are healthier than others. I mentioned fruits and vegetables above, which provide generally protective phytonutrients, but plant foods also provide carbohydrates. Here the data is another mess.


In one of the largest studies to date (12), researchers estimated that from age 50, people eating a moderate-carb diet would live another 33 years, four years longer than those with very low carb consumption, and one year longer than those with high carb consumption. This suggests a sweet spot intake, but on close inspection the data appear to be unreliable because they do not distinguish between digestible and fermentable carbs.

Not all carbs are fibers, but all dietary fibers are carbs; and higher fiber intake seems to be very health-protective indeed (13).

So there are healthier and unhealthier ways to be an omnivore, and healthier and unhealthier ways to be a vegetarian also.  This last point is highlighted in a study which was presented at the Nutrition 2022 Live Online conference, and not yet in print. The researchers found that in those who ate a ‘healthy’ (ie unprocessed) diet were significantly protected against breast cancer, while those who consumed an ‘unhealthy’ (ie ultra-processed) diet had an increased risk.

In the final analysis, this field of research is over-shadowed by intractable problems including the untrustworthiness of much of the data, and the definition of both ‘omnivore’ and ‘vegetarian’. If we are going to promote vegetarianism, for example on ethical or environmental grounds, we have to keep this in mind.


To recap, there are many different ways of being vegetarian, and some of these ways are probably healthier than others. Vegetarian A, for example, who is physically active and eats large amounts of unprocessed fruits and vegetables is a very different animal from vegetarian B who lives a sedentary lifestyle and consumes smaller amounts of vegetarian foods, most of which are ultra-processed. Veggie A is likely to be much healthier than Veggie B. He or she is less likely to be suffering from dysnutrition, and less likely also to be suffering from chronic inflammation; and so Veggie A can expect, on average, a longer and a healthier life.


Even Veggie A, however, must be careful to balance his/her intake of grains and pulses, ensuring adequate amino acid intake; pay attention to trace elements (because levels of these depend on the soils in which the plant foods were grown); and focus on individual nutrients such as B12, Fe and the long chain omega 3’s.

The take-home message. Higher levels of fruit and vegetable consumption can be safely recommended, with the highest level of health protection kicking in at around 7 plus portions of fruit and vegetables per day. A moderate intake of carbs is health-positive, providing these are mostly fermentable carbs i.e. from pulses and legumes, rather than the refined carbs present in ultra-processed foods. Specific nutritional issues involving i.e. B12, iron and omega 3 HUFA’s can and should be dealt with individually.


In summary, the evidence indicates that we have to be granular when talking about or recommending diets; an approach that all MB coaches are already familiar with.

REFERENCES

  1. Singh PN, Sabaté J, Fraser GE. Does low meat consumption increase life expectancy in humans? Am J Clin Nutr. 2003 Sep;78(3 Suppl):526S-532S.

  2. Burkert NTMuckenhuber JGroßschädl FRásky EFreidl W. Nutrition and health – the association between eating behavior and various health parameters: a matched sample study. PLoS One. 2014 Feb 7;9(2):e88278.

  3. Mihrshahi S, Ding D, Gale J, Allman-Farinelli M, Banks E, Bauman AE. Vegetarian diet and all-cause mortality: Evidence from a large population-based Australian cohort – the 45 and Up Study. Prev Med. 2017 Apr;97:1-7

  4. Dinu M, Abbate R, Gensini GF, Casini A, Sofi F. Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies. Crit Rev Food Sci Nutr. 2017 Nov 22;57(17):3640-3649.

  5. Kwok CSUmar SMyint PKMamas MALoke YK. Vegetarian diet, Seventh Day Adventists and risk of cardiovascular mortality: a systematic review and meta-analysis. Int J Cardiol. 2014 Oct 20;176(3):680-6.

  6. Crous-Bou M, Molinuevo JL, Sala-Vila A. Plant-Rich Dietary Patterns, Plant Foods and Nutrients, and Telomere Length. Adv Nutr. 2019 Nov 1;10(Suppl_4):S296-S303.

  7. Nguyen B, Bauman A, Gale J, Banks E, Kritharides L, Ding D. Fruit and vegetable consumption and all-cause mortality: evidence from a large Australian cohort study. Int J Behav Nutr Phys Act. 2016 Jan 25;13:9.

  8. You W, Henneberg R, Saniotis A, Ge Y, Henneberg M. Total Meat Intake is Associated with Life Expectancy: A Cross-Sectional Data Analysis of 175 Contemporary Populations. Int J Gen Med. 2022 Feb 22;15:1833-1851.

  9. Appleby PN, Key TJ. The long-term health of vegetarians and vegans. Proc Nutr Soc. 2016 Aug;75(3):287-93.

  10. Choi Y, Larson N, Steffen LM, Schreiner PJ, Gallaher DD, Duprez DA, Shikany JM, Rana JS, Jacobs DR Jr. Plant-Centered Diet and Risk of Incident Cardiovascular Disease During Young to Middle Adulthood. J Am Heart Assoc. 2021 Aug 4:e020718.

  11. Papier K, Knuppel A, Syam N, Jebb SA, Key TJ. Meat consumption and risk of ischemic heart disease: A systematic review and meta-analysis. Crit Rev Food Sci Nutr. 2021 Jul 20:1-12.

  12. Seidelmann SB, Claggett B, Cheng S, Henglin M, Shah A, Steffen LM, Folsom AR, Rimm EB, Willett WC, Solomon SD. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. Lancet Public Health. 2018 Sep;3(9):e419-e428.

  13. Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. 2019 Feb 2;393(10170):434-445.

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