Red meat: another inconvenient truth
BMJ 2017; 357 doi: https://doi.org/10.1136/bmj.j2278 (Published 11 May 2017) Cite this as: BMJ 2017;357:j2278
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Dear Dr Godlee,
I have already mentioned, in responses to other iterations of this paper, that its conclusions are unsafe due to evidence of residual confounding and healthy-user bias in the NIH-AARP population, best shown In the earlier paper by Sinha et al, where similar associations were found, yet the associations between unprocessed red meat and accidental death in men, HR 1.26 (1.04-1.54), were as great as the associations for cancer mortality, HR 1.22 (1.16-1.29) or CVD mortality, HR 1.27 (1.20-1.35).[1] Sinha was second author on the present paper, and it is a mystery to me why she did not ensure that this important outcome was included.
Mechanisms related to heme iron effect on peroxidation may cancel themselves out in health-conscious populations because heme iron is also an essential component of catalase antioxidant enzymes and the CYP450 enzymes needed to detoxify carcinogenic chemicals, and meat is also a important source of zinc and other antioxidants; the story is thus not as one-sided as presented by Etemadi et al. This may help to explain why vegetarians have somewhat higher rates of cancer and cancer mortality than meat eaters when equally matched populations have been studied, which was not the case in Etemadi et al.[2,3]
Potter made the claim that meat-rich diets were the cause of early sexual development, however his reference found that, though such a difference did exist statistically, the difference between mean animal protein intakes in the early and late menarche groups was a matter of mere grams (41 vs 42.4, table 2).[4] Polyunsaturated fat, which is found in vegetable oils and white meat, was also associated with early menarche in that study. Diets rich in soy in infancy have also been associated with early menarche, and soy protein is regularly added to processed meat, as it is indeed added to every processed food for some unknown reason.[5] It has also been found that meat-eating and good nutrition is associated with a later menopause. Early menopause is naturally associated with a lower risk of reproductive cancers, but also with a higher risk of cardiovascular disease and all-cause mortality.[6] It is not surprising that poor nutrition would delay the onset and reduce the duration of the reproductive years but it is unclear what public health advice should follow from this.
Potter's claim that 110,000 L of water are required to raise 1 KG of meat protein (perhaps 6Kg of lean meat) can be refuted by looking out of my window and watching sheep be raised on pasture with only rainwater for irrigation and little in the way of fertilizer, added feeds, or pesticides, let alone antibiotics. Ironically chicken, a white meat favoured by the analysis of Etemadi et al, is raised in factory conditions eating grains and other crops which, unlike grass, could be eaten by humans, and regularly given antibiotics.
My suggestions would be, firstly, do not assume that everyone you see eats too much meat; many do not eat enough.
Do not assume that chicken or fish or even plants will be better for the planet than ruminants - this will not be true in every case (fishing and crop monoculture do a great deal of harm that is out of sight, out of mind). At the moment we are dealing with environmental modelling mainly generated by vegetarian and animal rights lobbyists, and we should wait to hear what others have to say.
Do encourage the reduction of waste and better nutrition by nose-to-tail eating and the proper use of fat, which is most of the energy produced by raising a ruminant (calculations involving protein alone give a false accounting).
And remember that a mixed diet of various types of animal and plant foods, as close to nature as is consistent with good hygiene, good digestion, and good eating, will always be the default option for good nutrition, which, in case we have forgotten, is the basis of good health.
[1] Sinha R, Cross AJ, Graubard BI, Leitzmann MF, Schatzkin A. Meat intake and mortality: a prospective study of over half a million people. Archives of internal medicine. 2009;169(6):562-571. doi:10.1001/archinternmed.2009.6.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2803089/
[2] Burkert NT, Muckenhuber J, Großschädl F, Rásky E, Freidl W. Nutrition and Health – The Association between Eating Behavior and Various Health Parameters: A Matched Sample Study.
PlosOne: February 7, 2014 https://doi.org/10.1371/journal.pone.0088278
[3] Key TJ, Appleby PN, Spencer EA et al. Cancer incidence in vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford). Am J Clin Nutr. 2009 May;89(5):1620S-1626S. doi: 10.3945/ajcn.2009.26736M.
http://ajcn.nutrition.org/content/89/5/1620S.full
[4] Rogers IS, Northstone K, Dunger DB, Cooper AR, Ness AR, Emmett PM. Diet throughout
childhood and age at menarche in a contemporary cohort of British girls. Public Health
Nutr 2010;357:2052-63. doi:10.1017/S1368980010001461 pmid:20529402.
[5] Adgent M, Daniels J, Rogan W, et al. Early life soy exposure and age at menarche. Paediatric and perinatal epidemiology. 2012;26(2):163-175. doi:10.1111/j.1365-3016.2011.01244.x.
[6] Gold EB. The Timing of the Age at Which Natural Menopause Occurs. Obstet Gynecol Clin North Am. 2011 September ; 38(3): 425–440. doi:10.1016/j.ogc.2011.05.002.
Competing interests: No competing interests
I am surprised that Drs Godlee, Potter and Etamadi et al have each missed an important issue.
Red meat contains N-Glycolylneuraminic acid (Neu5Gc). Neu5Gc occurs in virtually all red mammalian meat – with the exception of humans. In humans, the gene encoding CMP-N-acetylneuraminic acid hydroxylase mutated to an inactive form some three million years ago. It is thought that this conferred protection against an archaic form of malaria1.
When we eat red meat, Neu5Gc is absorbed and gives rise to an innate immune response. In the long term, this creates a chronic a low-grade inflammatory milieu. This will happen even if we eat fresh uncooked raw red meat2.
Such a milieu will promote cancers, insulin-resistance, hyperinsulinaemia and obesity, amongst other diseases.
I would speculate that Neu5Gc will be proven to be a major driving force of ill health.
01. Chou, H-H, Takematsu, H, Diaz, S et al A mutation in human CMP-sialic acid hydroxylase occurred after the Homo-Pan divergence. Proceedings of the National Academy of Sciences, 1998;95:11751–6. doi:10.1001/archinternmed.2011.2287 pmid:22412075.
02. Samraj, AN, Pearce, OM, Läubli et al A red meat-derived glycan promotes inflammation and cancer progression. Proceedings of the National Academy of Sciences. 2015;112:542–7. doi:10.1073/pnas.1417508112.
Competing interests: No competing interests
There were innumerable studies showing cooked meat eating is not good for health. Most of them were rubbished as lacking in research vigour! The meat industry must be at it. Nothing survives in this wonderful world that does not support the money bags. Even the most irrelevant studies are hailed as well done if they support a big industry. This can easily be done as most medical research is statistical and, therefore, without sense. (Steven Milloy-Statistics, science without sense).
Let us learn science from nature as I deem it as the best science. Natural meat eating animals like the tiger, cat and dog have a totally different anatomy and physiology compared to us. Two vegetarian animals--man and elephant--have straight legs vis-à-vis the meat eaters who have bent legs enabling them to outrun their prey for food. Man and elephant are vegetarians and their food does not run away for them to chase them. Meat eaters do not eat cooked meat. We and our domesticated animals eat cooked meat and drink another species’ milk also almost halving our life spans. Meat eaters have elongated face with prominent canine teeth to dig deep into their prey’s flesh. We have flat face and prominent molar teeth to grind vegetable fibre. Vegetarians have a long gut while meat eating animals, however big they are, have a comparatively very short gut length to throw away meat products out of the system as soon as possible.
“When the muscles of mammals, fish, or birds are cooked at high temperatures carcinogenic chemicals called heterocyclic amines are created that may increase the risk of breast, colon, lung, pancreatic, and prostate cancer”, writes Michael Greger. Eating boiled meat is probably the safest. Studies show if you eat meat that never goes above 212 degrees Fahrenheit, both your urine and faeces damage DNA significantly less than if you eat meat dry cooked at higher temperatures. In nature meat eaters never cook their meat!
With these in mind this week’s BMJ editorial makes lots of sense supported by the study published in the same issue (doi:10.1136/bmj.j1957 BMJ 12th May 2017). Dr. Potter’s comments in the same issue add support to my thesis. “Overconsumption of meat is bad for health and for the health of our planet,” he says. The study suggests that haem iron in red meat and nitrate/nitrite in processed meat are among the culprits. But Potter says that the ill effects are likely to be caused in many different ways, including carcinogens caused by cooking, contaminants in animal feed, and reduced intake of plant based foods.” (doi:10.1136/bmj.j2190 BMJ12th May 2017)
We probably became meat eaters during our hunter-gather days but our meat consumption then was very small. The modern western diet contains lots of meat and our energy seems to come mainly from meat. This not only depletes human health but also the overall health of our planet. Let us wake up before it is too late. Those of us who think that meat protein is essential for health should try to beat an elephant which does not get meat protein at all. Two plus two need not always be four in human health and science in general where uncertainty rules the roost. Let us learn science from nature instead of using science to teach nature a lesson or two!
Yours ever,
Bmhegde
Competing interests: No competing interests
Red meat: another inconvenient truth
There are several odd findings in this study
1) to quote:
“Meat consumption has been on the rise in the US and Europe in the past 40 years.22 An increased risk of premature death associated with red meat intake, and evidence for greater longevity among adults with very low meat intake, have been seen in previous studies from Europe and the US.”
Yet in both Europe and the US death from cardiac events is falling.
2) It is suggested that oxidative stress could be involved. To quote:
Oxidative stress may be the underlying common mechanism for many of these findings. Oxidative stress is a plausible part of the aging process, and systematic markers of oxidative stress are associated with increased risk of chronic disease multimorbidity and all cause mortality in the older population. Oxidative stress has also been linked to many components of the metabolic syndrome and insulin resistance.
This is indeed a valid point and indeed I suspect that a low level of anti-oxidants may well be involved in many chronic conditions of the aged due to an excessive intake of pro-oxidants/reduced intake of anti-oxidants. However this aspect of the study and the observed results have been totally ignored in the failure to measure this factor.
3) From Table 1 it is stated that between low meat to high meat death rate doubles to quote:
Meat intake category 1 2 3 4 5
Diabetes (n=3717) 504 576 687 845 1105
yet more meat intake would probably mean a reduced carb intake or a increased total food intake with maintained high carb intake. High carb intake is well known for causing hyperinsulinaemia (the first early stage of diabetes - Kraft, R. “Diabetes Epidemic and you” (The very earliest diagnosis of diabetes is neither by fasting blood sugars nor by glycated hemoglobin but only by insulin assays with normal glucose - Kindle Locations 165-166)
(Note:I might add that this comment is based on 14,000+ actual insulin/glucose tolerance tests)
This result to me suggests that total food intake has been ignored and the level of anti-oxidant intake from say fruit and veg has also been ignored.
4) The information has been obtained by query of the participants, a notoriously difficult way of assessing food quality and quantity of a long term diet
5) Another interesting item from Table 1 relates to Never-smokers, to quote:
Meat intake category(%) 1 2 3 4 5
Never smoker 43458 (40.5) 39887 (37.1) 37413 (34.8) 35135 (32.7) 31579 (29.4)
I assume that the numbers here relate to the number and percentage of each intake category. This lead me to search for how this was handled. To quote:
In general, the increased mortality associated with red meat, heme iron, and nitrate/nitrite were stronger in never/former smokers,
This raises the question about the known effects of smoking in a variety of conditions.
I am afraid that this study and its relatively small differences and its data source will not affect my view of this “inconvenient truth”.
Competing interests: No competing interests
Perhaps an inconvenient truth, but largely in America.
There, animal protein largely comprises 'lot fed' beef and pork, laced with antibiotics and fed largely on soy protein and other concentrates with restriction of movement for most of the life cycle of the animal. And, as you point out a large proportion is barbecued and/or smoked to produce considerable toxins from charring and overheating.
This is not comparable with UK and many Continental sources (yet) which also have higher fat, proportionate to protein as well as being wholly or partly grass fed or 'grass finished'. So the differences are pronounced and do not reflect the diet of those of us (me included) who eat meat in reasonable amounts interspersed with fish and white meat; low carbohydrate vegetables; fermented dairy (cheese) and eggs.
Our ancestors ate many things in the move from the equatorial plains into northern climes over thousands of years and yet even when we commenced down the agricultural route we were largely herders of animals, which still persists today in the far north and parts of Africa and yet according to Weston Price these peoples displayed stellar health on diets largely comprising animals; birds; fish and dairy, and fell extremely ill when introduced to western diets of rice; flour and sugar.
Our largest problem is the industrialisation of agriculture and the production of meat through inappropriate breed choices, favouring high yield milk cattle and meat animals that add weight rapidly in confined spaces on diets that could in no way resemble what one could term 'natural'. When hardy slow growing sheep and cattle can be raised on poor land not conducive to crops, we instead raise heather and game birds as well as that Highland 'pest' breed, the Red Deer. We forget that we could ameliorate our carbon footprint by replanting the trees we removed and at the same time reduce the flooding synonymous with bare hill sides.
This use of diets that do not mimic any previous grazing habitat input produces meats that are much higher in polyunsaturated fats that are mainly n-6, rather than fully saturated and monounsaturated, which in essence makes this meat much more unhealthy and more conducive to producing toxins in cooking because of the fragility of the n-6 molecules.
This is the diet of the study cohort along with the higher content of processed meat products that form a large elements of the American diet. These also have a proportion of preservatives, much higher than one would expect to see in European products especially those termed as 'artisan'. In addition, the US always list hamburger meat (an American staple) as being 'unprocessed' when it clearly is nothing of the sort being often laced with sodium or potassium nitrite (@0.6%). This undoubtedly distorts the study conclusions.
These nitrites form nitrosamines when cooked and even when introduced to stomach acid. It is however, a legal requirement to add these to prevent botulism. Nitrosamines are carcinogenic so a healthy addition of Ascorbic Acid is needed to combat this propensity but it will only ameliorate it.
So, let's all eat vegetables and save the planet some may say but the very nitrites used in meat preservation are very high in natural root and green leafy vegetables, the very things the vegetarian lobby exhorts us to eat. Well, I simply cannot accept that. We ate mammals; birds and fish for millennia with no ill effects, such that our colons shrank to a small proportion of that of our primate ancestors. So we are now adapted to eating meat however distasteful this is to the squeamish, because we are a predator species ourselves, no matter how much we sanitise our method of hunting it.
Competing interests: No competing interests
Re: Red meat: another inconvenient truth
You ask what doctors can do, and suggest lobbying for better research to support evidence based dietary guidelines.
Would this be the same profession that espouses and promotes the wholly arbitrary "5 a day"?
Competing interests: No competing interests