Is Organic More Nutritious? Part 2

A couple years ago I blogged about a study that found organic crops to be higher in 'antioxidants' and what that meant from a health perspective. Now, the same group of researchers have published data, in two separate papers (1,2), on the differences in nutritional profiles between organic vs conventional meats and dairy, mostly focusing on the fatty acid compositions. Naturally, the media has taken to promoting the hell out of this message:

Should you be buying organic meat and dairy for the nutritional value? For my TL;DR folks, the on-average changes instilled by the organic systems produce low impact differences in the nutrient profiles, requiring excessive intakes of meat/dairy fats to get to meaningful doses known to impart a physiological effect. Furthermore, when you consider these differences in the context of the whole diet, changes in nutrients like short and long chain omega 3 fats still don't make organic meats and dairy competitive against other cost-effective nutrient dense foods like flax seeds and fish. Without intervention trials comparing organic vs conventional meats/dairy, it's hard to make any strong sort of health claims; in the end, they will still have to be balanced against the negative impacts of the saturated fatty acid components of these foods on lipoproteins (note: the saturated fatty acids in organic vs conventional didn't meaningfully change much). 

For those who want to read further, let's delve into the analyses:

Meat: This publication was a meta-analysis that looked at 67 studies comparing the fatty acid composition of conventional vs organic meat; evidence to make comparisons for other nutrient differences (e.g. vitamins and minerals) was too weak. The primary outcome of the meta-analysis was the total polyunsaturated and omega 3 polyunsaturated fatty acid (PUFA) differences between organic and conventional, with a number of secondary and exploratory outcomes looking at specific fatty acids and how these differ between different animal species. The analysis found higher levels of total PUFAs (n-6 and n-3) in organic, with lower amounts of monounsaturated fats and similar amounts of saturated fats relative to conventional meats. When we get into specific fatty acids, the results depend on whether the model was weighted (uses only studies with reported N, mean and SD/SE) or unweighted (uses studies that report means without standard errors). In the weighted analyses, no significant differences were found for CLA, EPA, DPA, DHA and several other specific fatty acids - we can see these non-significant p-values in table 2. However, in the unweighted meta- analysis, allowing for inclusion of a greater number of studies that didn't report measures of variance, significant differences between organic and conventional are found, trending towards lower total fat and oleic acid (MUFA) and higher total long chain n-3s (EPA,DPA,DHA) in the organic meats group.  

What do we make of these differences? In my opinion, they do not mean a whole lot. The fatty acid concentrations from the individual studies are all converted to a common metric of 'g/100g fatty acid esters'. Let's consider the magnitude of the effect sizes here - a standardized mean difference of .22 for DHA between organic and conventional in the weight meta-analysis - means that for every 100g (~900 calories) of fat you consume, if you chose organic, you could get about 220mg more DHA; ignoring the fact that this amount of fat/animal fat consumption would put you outside of any nutrition organization's recommendations for a healthy diet, the differences are even more meaningless when you compare these to someone who consumes fatty fish, a concentrated source of omega 3s (3.5oz of farmed atlantic salmon gets you about 1.5g of DHA, and clocks in at about 200 calories); we could say the same about the alpha-linolenic acid changes relative to the amount in flax/chia/walnuts. To get a somewhat realistic viewpoint of these differences, the authors of this meta-analysis model the effects of eating organic vs conventional (using typical European consumption data and the unweighted meta analysis data): if you were eating 12-20g/d of beef fat (108-180 calories), by choosing organic, you could get an extra 200mg of total omega 3's (calculations for individual fatty acids aren't shown), while consuming the same amount of saturated fats (~6g) and about 300mg less monounsaturated fats. Since we might be concerned about red meat intake for reasons besides the solid fat content, those preferring white meats would need to eat 16-28g/d (144-252 kcals) of chicken fat to get an extra 100mg of total n-3's, followed by a ~1 gram reduction in MUFAs. 

Other comments that might be of interest to readers:

• While most of the analyses remain unchanged, the increase in EPA and DHA (arguably the more nutritionally relevant changes) for organics disappears in the 5th sensitivity analysis that excludes lower quality non-GC based fatty acid quantification methodologies.
• in their primary weighted meta analysis, the authors use the GRADE assessment and find that, for nearly all of the fatty acid parameters observed, there is a medium to strong risk of publication bias and low overall reliability. 
• The heterogeneity scores for the weighted meta-analysis were all very high, ranging from 75-98 percent; while statistical heterogeneity is inevitable, we usually want this to be lower than 50 percent. The authors identify a major reason for this heterogeneity to be the range of practices considered under the umbrellas of 'organic' and 'conventional' across the many different countries included in this analysis- if you remember back to my first post on organics, I mentioned that variability was a theme. This holds true for meat.
• the authors regularly calculate the n6:n3 ratio, which tells us relatively little about the health characteristics of the food. 
• the authors did not analyze publications that used conventional systems that were described as 'intensive' or 'free range', and chose to compare only organics to the 'standard conventional system'.
• the authors suggest that the feeding regimen (e.g. grazing time, use of concentrated feedings during finishing) explain some of the nutritional differences between organic and conventional; this would suggest that, if conventional farmers wanted to, they could alter feed composition/practices to attain the same (minimal) changes found in organic systems. One could also argue for supplementation of the concentrates with different fatty acids, as opposed to a change in feeding practices.

Dairy: the other meta analysis, performed by the same group, looks at 170 studies comparing conventional to organic bovine milk, performing a number of weight and unweighted analyses with different sensitivity models included (they also look at other milk species but this is a very small data set). This analysis is a bit thicker but you'll be having some deja vu. The authors report fatty acid composition changes in organic vs conventional - organic has similar MUFA and SFA to conventional, but higher PUFA, namely for n-3 PUFAs, ALA, EPA, and DHA (no significant differences were observed for n-6's/linoleic acid). Additionally, organic milk had higher concentrations of conjugated linoleic acid, iron and alpha tocopherol (vitamin E). Conventional milk, however, had higher yields, iodine and selenium contents. 

Again, we must consider the magnitude of these effects and their context in a typical diet: a mean percent difference of 56 percent between organic and conventional for alpha linolenic acid concentrations might sound significant, but consider that a a cup of full fat milk (150 calories), in the US, contains 180mg of ALA; 56 percent higher puts us at about 280mg of ALA. It's not an entirely insignificant difference, but when compared to an ounce of walnuts (180 cals), which has 2.3g of ALA, it doesn't really rouse the interests of too many nutritional scientists. That same ounce of walnuts will also get you .25mg of alpha tocopherol, whereas our cup of conventional milk gets of .17mg, and our organic cup of full-fat milk gets us 13 percent more, or .19mg. As you can see, having a greater increase in these nutrients still doesn't make them very nutritionally relevant. We could say the same thing for iron, as milk is not a good source of to begin with.  Milk is also not a great source of long chain n-3's (the USDA nutrient database lists the content of EPA and DHA in full fat milk as 0); however, the authors of the analysis suggest that a cup of full fat milk contains about 12mg of long chain n-3's, and a cup of the organic version contains about 20mg. Different health organizations worldwide recommend different levels of these fatty acids; the evidence generally points towards about 500mg/d for primary prevention of CVD (5). It's hard to claim that we should get too excited about the extra 8mg from organics... Lastly, the analysis of the CLA changes are difficult to evaluate, given the rejected health claims by the EFSA.

Other comments:

• similar to the meta analysis on meats, heterogeneity was very high, likely for similar reasons mentioned above; the overall reliability of the evidence was only high for milk yield, iron, and selenium. The PUFA outcomes tended to be of moderate reliability, with the rest of the outcomes varying from low to very low. Publication bias was seen as being moderate for nearly all of the outcomes, slightly less high than the meat meta analysis.
• the redundancy analyses performed by the authors find that the higher grazing/conserved forage intakes in organic systems were the main reason for milk composition differences. My thoughts are the same as above.
• the number of parameters reaching statistical significance in the weighted vs unweighted models was quite similar for the primary outcomes. The large number of sensitivity analyses performed didn't change the magnitude or statistical significance of the effect size nearly as much as it did for the meat analyses, showing that the effects of the amount of data available, experimental years, and production system weren't major contributors to the outcomes (whereas, for meat, it was a bigger contributor). The dairy dataset, overall, seems more robust.
• Changes in iodine concentrations are interesting, given that milk contributes about half of iodine intake for adults and about 70 percent for children (3). The decrease in iodine found in organic milk, however, doesn't appear to pose too large of a threat, and again, one could focus on consuming less sodium from pre-packaged foods (which is rarely fortified with iodine) and using iodized salt, or consuming good sources of iodine like seaweed and fish (the latter being a variable source). There are, however, populations with insufficient iodine intake, such as women of childbearing age/pregnant women (4) - health professionals may want to consider these differences between organic and conventional when assessing total dietary intake.
• For individuals who do consume large amounts of dairy fats, ignoring recommendations to reduce saturated fat intakes (e.g. some low-carb/paleo folks), these changes might amount to more meaningful levels.

For those of us still in the camp to reduce consumption of solid fats, the fatty acid changes reported in these two meta analyses are of little impact. For those who consume higher than the recommended intakes of saturated fats, these changes are probably still not reason enough to consume organics. Fish oil and multivitamins are quite cheap, and other dietary sources can give you a much better bang for your buck, while providing a number of other nutrients.

1. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10181405&fulltextType=RA&fileId=S0007114515005073
2. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10181431&fulltextType=RA&fileId=S0007114516000349
3. http://www.nature.com/jes/journal/v18/n6/full/7500648a.html
4. http://pediatrics.aappublications.org/content/134/4/e1282.1
5. http://ajcn.nutrition.org/content/83/6/S1526.full