Organic milk is the healthiest on the market, research suggests, and it is all down to the grass the cows graze on.
When scientists compared the fat content of 400 brands of milk, the organic bottles and cartons consistently came out on top.
They found that the levels of polyunsaturated fatty acids – the ‘healthy fats’ good for the heart – were far higher in organic milks.
The difference was made by organic cows’ diet.
They went out to pasture and also ate forage-based feeds, instead of being given the corn and grains relied on by non-organic farms, the American researchers said.
Dr Charles Benbrook, who led the research team at Washington State University, said: ‘We were surprised by the magnitude of the nutritional quality differences.’
While total fat contents were consistent across the milks, the ratio between ‘healthy’ and ‘unhealthy’ fat varied hugely.
The study – the largest of its kind ever conducted – found that organic milks had more than twice as much healthy fat on average than the normal types.
One type of fatty acid, omega-3, is credited with improving the health of the heart.
But another, omega-6, is a risk factor for cardiovascular disease, cancer, inflammation and auto-immune disease.
The study – published in journal PLOS ONE – found that organic milks were proportionally twice as much higher in healthy fat and lower in unhealthy fat.
The organic milks had an average omega-6 to omega-3 ratio of 2.3-to-1. Normal milk had a ratio of 5.8-to-1.
Western diets typically have a ratio of up to 15-to-1, while a ratio of 2.3-to-1 is thought best for heart health.
The researchers estimate that by switching to organic milk, the average American or European could make 40 per cent of the change required to meet the guidelines.
Dr Benbrook said: ‘Surprisingly simple food choices can lead to much better levels of the healthier fats we see in organic milk.’
The researchers also compared the fatty acids in dairy products to those in fish.
Donald Davis, who co-authored the research paper, said: ‘We were surprised to find that recommended intakes of full-fat milk products supply far more of the major omega-3 fatty acid than recommended servings of fish.’
The researchers said more and more dairy farms are now feeding their cows with the kind of grass that would improve the milk.
The paper said: ‘The increasing reliance on pasture and forage-based feeds on dairy farms has considerable potential to improve the fatty-acid profile of milk and dairy products.
‘Improvements in the nutritional quality of milk and dairy products should improve long-term health status and outcomes, especially for pregnant women, infants, children and those with elevated cardio-vascular disease risk.’
Whole milk contains the most beneficial fatty acids. Skimmed and semi-skimmed organic milks will still contain healthy fats but in smaller amounts.
Previous studies have credited organic milk with higher levels of health-boosting anti-oxidants and vitamins, including vitamin E, and beta-carotene, a building block of vitamin A.