select search filters
briefings
roundups & rapid reactions
before the headlines
Fiona fox's blog
Feeding into the debate and uncertainty over whether the use of organic production standards affects food quality, researchers have published two meta-analyses in the journal British Journal of Nutrition which report the differences in nutrient content of organic and conventional bovine milk and meat. A Before the Headlines analysis accompanied these comments.
Prof. Ian Givens, Professor of food chain nutrition at the University of Reading, said:
“These papers clearly represent a substantial amount of work evaluating differences in key nutrients in conventional versus organic milk and meat. However, the study uses percentage increase measurements that can imply a greater change than is nutritionally relevant.
“Much emphasis is placed on the 56% higher n-3 fatty acid content of the organic milk; but this increase is in the milk fat, not in the whole milk. The effect also needs to be assessed in the whole diet. On average we consume about 2.2 g of n-3 fatty acids per day. Switching from conventional to organic milk would increase n-3 intake by about 33 mg per day – an increase of only 1.5% in our total diet. Such small changes are unlikely to represent any nutritional or health benefit.
“Organic produce isn’t more nutrient-packed in every regard, either. The lower iodine and selenium content of organic milk has been recognised before, and since milk is the greatest single source of dietary iodine, the lower value in organic milk needs to be recognised. This is especially true for pregnant women, for whom iodine is a critical nutrient to ensure the healthy development of their baby.
“Differences in content such as fatty acids or iodine occur primarily because organic animals are fed more of a forage-based diet, such as grass, than their non-organic counterparts. You get the same kind of changes in food composition if non-organic animals are fed forage-rich diets too. It’s the choice of feed, not the organic farming method, which makes the difference.
“Overall, this is very detailed and valuable work, but the differences between organic and conventionally farmed produce should be evaluated as part of the whole human diet. When they are, most differences are very small indeed.”
Prof. Margaret Rayman, Professor of Nutritional Medicine at the University of Surrey, said:
“This meta-analysis on the nutritional qualities of organic and non-organic milk has highlighted the higher concentration of omega-3 PUFAs and the lower concentration of the essential mineral, iodine, in organic milk.
“Using the figures in the paper, we have calculated that while a glass of full-fat organic milk (200 ml) will give 2% more of the daily requirement for long-chain omega-3 PUFAs (6.4% vs. 4.4%), it will provide 14% less of the adult daily iodine requirement (21.2% vs. 35.2%). This may have implications for public health as milk and dairy products are the main source of iodine in the UK diet and we have shown that iodine deficiency in pregnant women is linked to lower IQ in their children. As a considerable proportion of UK pregnant women are iodine deficient, a switch to organic milk may exacerbate this deficiency unless consumers include other iodine sources in their diet.”
“Further information can be found in our BDA Iodine Food Fact Sheet (https://www.bda.uk.com/foodfacts/Iodine.pdf).”
Prof. Tom Sanders, Professor emeritus of Nutrition and Dietetics at King’s College London, said:
“These two papers compare organically produced milk and meat compared to conventionally produced products focusing mainly on fatty acid content. The review found milk yield was 23% lower for organic milk and there were some minor differences in fatty acid composition which are more related to the production systems rather than whether they were organic or not.
“Generally, cows that eat grass produced milk and meat that contained up to 50% more omega-3 fatty acids than those fed on grains. In the countries where there is a lot of rain such as UK, Ireland, Brittany and New Zealand most milk and cheese comes from cows fed on grass and you can tell this from the bright yellow colour derived from the carotene present in grass.
“Both papers make claims for a higher polyunsaturated fatty acid content of organic milk and meat. However, bovine milk fat and fat from ruminants (cows, sheep, goats both organic or conventional) are poor sources of polyunsaturated fatty acid and but contain large amounts of potentially harmful saturated and trans fats. The blood cholesterol (especially low density lipoprotein cholesterol) raising effects of butter fat are well established and mainly attributed to its high saturated fatty acid content, but its trans fatty acid content also contributes. Recent research1 has shown that trans vaccenic acid, the trans isomer naturally found in butterfat, raises blood cholesterol as much as industrially produced trans fatty acids. There is no evidence to show that organically produced butter has a more favourable effect on blood cholesterol.
“Both papers place much emphasis on 50% greater omega-3 polyunsaturated fatty acid content of organic milk and meat. The omega-3s are mainly present as alpha-linolenic acid (from grass) whereas there are only trace amounts of the long-chain omega-3 fatty acids. Nuts and vegetable oils, such as soybean and rapeseed oil, are much richer sources of alpha-linolenic acid and oily fish and eggs are more important sources of the long-chain omega-3 fatty acids in the UK diet [2,3,4].
“Claims are also made for the higher vitamin E in organic products. However, milk and meat are poor sources of vitamin E and the best source of vitamin E (tocopherols) is vegetable oil. The studies claim slightly highly amounts of iron in organic milk and meat. Milk is a poor source of iron whereas as red meat is a good source. While iron from meat is well absorbed and helps prevent anaemia, it is present mainly as haem iron which has been linked to a higher risk of colorectal cancer5. Indeed risk of colorectal cancer is not any different in those who choose to eat organic food compared to those who do not6.
“In my opinion, the press release contains headline-grabbing speculative health claims that stretch credibility to the limit.”
‘Composition differences between organic and conventional meat: a systematic literature review and meta-analysis’ and ‘Higher PUFA and n-3 PUFA, CLA, α-tocopherol and iron, but lower iodine and selenium concentrations in organic milk: a systematic literature review and meta- and redundancy analyses’ by Srednicka-Tober et al. published in the British Journal of Nutrition on Tuesday 16 February 2016.
All our previous output on a related subject can be seen at these weblinks:
http://www.sciencemediacentre.org/nutritional-content-of-organic-and-conventional-foods/
Declared interests
Prof. Ian Givens has worked on studies into iodine levels in milk. He is employed by the University of Reading and has had grant funding from BBSRC, MRC, AHDB Dairy, a charity and commercial sources.
Prof. Rayman: no interests to declare.
Prof. Sanders: no interests to declare.