Re: Mortality from different causes associated with meat, heme iron, nitrates, and nitrites in the NIH-AARP Diet and Health Study: population based cohort study
The study by Etemadi and colleagues , the comment by John Potter  and the editorial by Fiona Godlee  all add to the negative publicity heaped on the red meat industry in recent years. This has already forced thousands of traditional livestock producers out of business in the UK , to be replaced, ironically, by more intensive ones who cut costs through increased scale and medication, and less natural diets. If the associations the authors find are robust then the criticism is fully justified, but they show signs of siloed thinking, appear to be unaware of differences between feeding systems and could be accused of throwing out the grass-fed ruminant baby with the bath water of intensive, grain-fed, beef. As such, they may inadvertently give yet another twist to the spiral of agricultural intensification.
At first glance, cutting meat consumption, or switching from beef to chicken, look like ways to reduce both greenhouse gas emissions (GHGs) and diet-related diseases. Potter tells us unequivocally that “Overconsumption of meat is bad for health and for the health of our planet”. Few people would deny that overconsumption of anything is bad, yet Etamadi’s study finds increased mortality at every stage from very low to excessively high red meat consumption. Are these perfectly graded associations credible for all nine diseases they cover?
It may be relevant that Etemadi’s study was undertaken in the US where most beef is finished in feedlots on diets based on corn and soya – not natural feeds for ruminants. While a proportion of beef cattle are fed grain-based diets in most parts of the world, many of these receive only modest amounts of grain and others are exclusively fed on grass. But cattle fed some grain are far better able than poultry to utilise arable crop residues, Brewers’ and Distillers’ grains, sugar beet pulp, Miller’s offal and most oilseed bi-products  all of which we cannot eat - the exception being soyabean meal, widely included in poultry feed.
There are two key reasons why this could make a difference to the health impact of the meat. First, studies in the UK  , US  and Australia  have found that meat from grass-fed cattle has an omega-6 to omega-3 ratio of well under 2:1, while grain-fed beef typically has a ratio of between 8:1 and 11:1 and was found to be 20:1 in one trial. Grass-fed beef was also higher in conjugated linoleic acid and lower in trans fats. Omega-6 breaks down into arachidonic acid which has pro-inflammatory effects which can be counteracted by the long chain omega-3 fatty acids . The consumption of oily fish is recommended for this reason, but there are no longer enough fish in the sea for everyone and for the significant proportion of the population who do not eat oily fish, grass-fed beef or lamb provides an important, if modest, contribution to omega-3 intake in a healthy balance with omega-6.
Second, several studies have noted a pro-oxidant effect from haem iron, which Etemadi and colleagues identify as the key source of higher mortality in red meat consumers. However, some studies  have also found higher levels of antioxidants including vitamin E and beta-carotene in grass-fed beef. Zinc is another important antioxidant. While beef is a good source of zinc, liver is much higher still in zinc. There has been a dramatic reduction in ox liver consumption in recent decades. This could mean that some red meat consumers who eat only grain-fed beef and no ox liver do not take in enough antioxidants to counteract the pro-oxidant effect of the haem iron in beef. This would apply particularly to those with below average fruit and vegetable intake, something which characterised the higher red meat consumers in Etemadi and colleagues’ study.
The UN report  Potter cites on the environmental side told us that livestock are responsible for 18 per cent of GHS. Almost half (48 per cent) of this related to rainforest clearance for cattle and soya. However, the team only analysed such trends in South America. They did not include regions where grazing land was being converted to forest, or where rainforest was being cleared for palm oil.
In 2013, some of the same authors published a further report  with the revised figure of 14.5 per cent. Yet in a third and even less well-known accompanying report  they acknowledged that even this was a significant over-estimate, because they based their analysis on rainforest destruction in 2005, which by 2013 had declined significantly.
Grass is the only major crop that restores degraded soil while producing food for humans, albeit indirectly. One major European study  has found that up to 1.2 adults cattle grazing per hectare can be carbon neutral – the carbon sequestered and stored by the grass compensates for all their GHGs. Such high levels of sequestration will not continue indefinitely but the importance of not ploughing the grassland to keep this carbon in the ground cannot be over-emphasised.
Grass covers 70 per cent of global farmland, mostly for sound agronomic or environmental reasons. Plough this land for continuous cropping to feed chicken, intensive beef cattle or humans and over a decade or so you release GHGs typically equivalent to 250 tonnes of CO2 per hectare , making the land more vulnerable to droughts, floods and soil erosion. Chicken is promoted by many people because the birds convert grain to protein much faster than cattle, but cattle are the most efficient converters of non-human edible feeds to protein.
The evidence suggests to me that the only sustainable way to get human edible food from existing grassland is to graze it with livestock, and where appropriate, grow arable crops in rotation with grass, not in continuous monocultures.
Perhaps the next team of researchers to address the red meat issue could consider the relative impacts of beef and lamb from different production systems?
 Etemadi A, Sinha R, Ward MH, Graubard BI, Inoue-Choi M, Dawsey SM, Abnet CC. Mortality from different causes associated with meat, heme iron, nitrates, and nitrites in the NIH-AARP Diet and Health Study: population based cohort study. BMJ 2017; 357.
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Competing interests: In addition to my work for the Sustainable Food Trust, which is a registered charity, I am also a partner in a family organic beef cattle and sheep farm which has its own retail butchers shop.