The study, published in Food Science and Nutrition, examined fatty acid profiles in milk from cows managed under three systems in the United States: grass milk, organic milk and conventional milk.
Consistent with previous research, the study found that feeding a grass and legume (‘forage-based’) diet to cows produced milk with a far healthier ratio of omega-6/ omega-3 PUFAs, compared with cattle fed conventional diets containing around 47% grains.
The omega-6/ omega-3 (n-6/n-3) ratio in ‘grass milk’ was found to be around 1:1, compared with 2.3:1 in organic milk, and 5.8:1 in conventional non-organic milk, found the international multi-centre research team.
A high ratio of omega-6 to omega-3, which characterises the Western-style diet, is widely considered pro-inflammatory and is recognised as being associated with increased risk of cardiovascular and metabolic diseases. These ratios can exceed 10:1 in Americans, whereas the ideal ratio is around 1:1, the researchers explained.
"The near-perfect balance of omega-6 and omega-3 fatty acids in grass milk dairy products will help consumers looking for simple, lifestyle options to reduce the risk of cardiovascular and other metabolic diseases,” said study co-author Charles Benbrook, from the Bloomberg School of Public Health at Johns Hopkins University.
Grains excluded
Grains are almost totally excluded from the diets of cattle that produce grass milk. The exceptions are barley, oats and brown mid rib corn, which are permitted prior to boot stage, as their fatty acid profile is similar to that of grass.
Any non-grazing items in the feed must be sourced from “conserved, organic, forage-based feeds, including dried or fermented forages (alfalfa, clover, grass hay, etc.),” the researchers explained.
Shifting omega ratios
Switching from conventional milk to grass milk could have a big impact on the n-6/n-3 ratio of the overall diet, suggests Benbrook.
In previous research, Benbrook et al estimated that baseline n-6/ n-3 ratio (measured by linoleic acid (LA): alpha-linolenic acid (ALA) intake), might be as high as 11.3:1 in the total diet. For those consuming a typical level of non-dairy based LA, the ratio could be cut to 8.6 by switching to grass milk. This ratio could be reduced further to 5.9 if dairy intake were increased, Benbrook suggested.
Although the effect would need quantifying in further research, such a reduction is attainable, and likely to have a positive impact on cardiovascular and metabolic disease risk, suggested Benbrook.
Reducing n-6/ n-3 ratio may also assist the conversion of ALA to long-chain n-3 PUFAs (eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), though reduced competition for elongation enzymes, the researchers suggested.
“Impaired conversion of ALA to EPA and DHA is of considerable concern in the United States, because most Americans do not consume adequate fish to meet the recommended average intake of 250 mg/day of EPA + DHA,” highlighted Benbrook.
The study was partially funded by CROPP, the Wisconsin-based cooperative and a major supplier of organic milk in the U.S.
Source: Food Science and Nutrition
Published online 28 February 2018, doi: 10.1002/fsn3.610
“Enhancing the fatty acid profile of milk through forage-based rations, with nutrition modeling of diet outcomes”
Authors: Charles M. Benbrook et al