Study affirms the nutritional advantages of grass-fed milk, especially when it comes to fat profiles 03/12/2018
Milk is a somewhat controversial food.
That’s due in part to many people’s inability to comfortably digest lactose (milk sugar).
And for decades, some have claimed that milk can promote autoimmune problems or cause your body to produce too much mucus.
There’s no good evidence that cow’s milk promotes type I diabetes or other autoimmune conditions — in fact, milk may help prevent type II diabetes: see Full-Fat Dairy – Especially Yogurt – May Deter Diabetes.
The claim about mucus dates to the 12th century scholar Moses Maimonides, and that persistent medieval myth has been disproven in clinical studies.
Some trial participants reported that milk produced a “coating” sensation on their tongue and the back of their throat — but soy milk produced the same sensation.
Interestingly, the scientific literature doesn’t show that milk is particularly good for bolstering bone strength — despite milk’s high calcium content and modest amount of added vitamin D: see Bone Health: Busting Milky Myths.
Whatever your attitude toward cow's milk, there are real differences among types, based on what the cattle eat.
The results of a new study affirm prior signs that so-called “grass milk” from cows fed on pasture is healthier than conventional milk — and they show that grass milk even beats the milk from typical organic dairy farms.
Fatty acid profile of milk: a pressing concern
The diets of cows on conventional dairy farms are about half grain and half "forage" — a term that encompasses pasture, hay, and silage (fermented hay).
In contrast, the cows on most organic dairy farms get more grass and forage and less grain — which is why their milk typically offers a healthier fat profile and more antioxidants: see Organic Produce and Milk Offer More Antioxidants and Omega-3s, Organic Milk Found Richer in Omega-3s, and Is Organic Food Really More Nutritious?.
But the cows on most organic dairy farms still get about 20 percent of their diet from grain, so the nutritional profile of milk from cows raised almost entirely on pasture — organic or not — has looked superior in prior studies (see Grass-Fed Cows' Milk Seen as Healthier).
Before we delve into the details of the new study, let’s recall the critical difference between types of omega-3 fatty acids, which have distinctly different value to health:
- Short-chain (polyunsaturated) omega-3 ALA from plant foods.
- Long-chain (highly unsaturated) omega-3s (EPA and DHA) from seafood and fish oil.
The body only uses EPA and DHA for essential functions, and can only make very small amounts of these from plant-source omega-3 ALA, most of which gets burned as fuel.
Of the three omega-3s, DHA is by far the most important one to consume, because it’s essential to basic brain, immune, and eye functions, and to child development.
Omega-6 and omega-3 fatty acids are essential nutrients — but there’s growing evidence that the average American’s excessive intake of omega-6 fats (from cheap vegetable oils and prepared/packaged foods) and shortage of omega-3 fats can raise the risk of obesity, diabetes, dementia, and autoimmune disorders — even the risk of cardiovascular disease.
Today, Americans consume 10 to 15 grams of omega-6 fats for every gram of omega-3 fats, versus the estimated 3 to 1 ratio that predominated throughout most of human history — and still prevails in today's few remaining hunter-gatherer societies: see Amazonians' Breast Milk Beat Americans'.
For more on this topic, see our Omega-3/6 Balance: Hidden Health Risk page, and the “Out of Balance” video posted there.
International study affirms the superiority of milk from grass-fed cows
The research team behind the new study included scientists from the University of Minnesota, Johns Hopkins University, Britain’s Newcastle University, Australia’s Southern Cross University, and Denmark’s Aarhus University Hospital (Benbrook CM et al. 2018).
Previous studies have shown that consuming organic beef or organic dairy products lowers omega-6 fat intakes, while raising intakes of omega-3 and CLA (conjugated linoleic acid) fats, which are linked to better heart and metabolic health.
The authors wanted to compare the fatty acid profiles of milk from cows raised under three cattle husbandry systems in the United States:
- Grass-milk cows receive an essentially 100% forage-based diet consisting of pasture (grass and legumes) and dried or fermented grasses (i.e., hay and silage).
- Organic cows receive, on average, about 80% of their daily diet from forage-based feeds and 20% from grain and concentrates.
- Conventional cows get 53% of their daily diet from forage-based foods, with the other 47% coming from grains and concentrates. (Conventional milk accounts for more than 90% of the milk consumed by Americans.)
Using an independent laboratory, the international team commissioned analyses of 1,163 samples of whole “grass milk” from on-farm bulk tanks, prior to any processing, over a three-year period.
All the samples came from members of the farmer-owned CROPP Cooperative, whose milk is sold under the Organic Valley label.
In short, the researchers found that milk from cows fed entirely on pasture, hay and silage — i.e., grass milk — had significantly higher levels of omega-3 fatty acids and CLA.
In addition, grass milk also showed a healthier balance between omega-6 and omega-3 fatty acids.
Grass milk provided twice as much omega-3 fat versus conventional milk, 52% less omega-6 fat than conventional milk, and 36% less omega-6 fat than organic milk.
These were the team’s detailed findings:
- The average omega-6 to omega-3 ratio was much lower in grass milk — 0.95 (almost 1 to 1) versus 2.28 to 1 in organic milk and 5.7 to 1 in conventional milk.
- Average omega-3 levels were substantially higher in grass milk — 0.049 grams per 100 grams, versus 0.032 in organic milk and 0.020 in conventional milk.
- Average CLA levels were substantially higher in grass milk — 0.043 grams per 100 grams, versus 0.023 in organic milk and 0.019 in conventional milk.
- Average omega-3 EPA levels were modestly higher in grass milk — 0.0036 grams per 100 grams, versus 0.0033 in organic milk and 0.0025 in conventional milk. (Only the grass milk contained tiny amounts of omega-3 DHA.)
- Saturated fat levels were about the same in conventional, organic, and grass milk.
Co-author Charles Benbrook of Johns Hopkins University stressed the importance of these distinctions: “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.”
Hefty implications for public health
Daily consumption of grass milk dairy products could potentially improve Americans' health.
In addition to the well-established metabolic and cardiovascular benefits of omega-3 fatty acids and CLA, there are additional benefits for pregnant and lactating women, infants, and children.
Omega-3 DHA plays critical roles in the development of eyes, the brain, and the nervous system. Adequate omega-3 intakes can also slow the loss of cognitive function among the elderly.
Grass milk doesn’t contain significant amounts of DHA, but the human body can make significant amounts of DHA from the sole plant-source omega-3 fat (AHA), which is the dominant omega-3 in grass milk.
As the study authors wrote, “Because of often high per-capita dairy consumption relative to most other sources of omega-3 fatty acids and conjugated linoleic acid, these differences in grass milk can help restore a historical balance of fatty acids and potentially reduce the risk of cardiovascular and other metabolic diseases.”
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- Benbrook CM et al. Enhancing the fatty acid profile of milk through forage-based rations, with nutrition modeling of diet outcomes. Food Science & Nutrition (2018). DOI: 10.1002/fsn3.610
- Benbrook CM, Butler G, Latif MA, Leifert C, Davis DR. Organic production enhances milk nutritional quality by shifting fatty acid composition: a United States-wide, 18-month study. PLoS One. 2013 Dec 9;8(12):e82429. doi: 10.1371/journal.pone.0082429. eCollection 2013.
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