Yet another food study claims to show that something you thought was good for you is in fact bad. This time the controversy is around milk.
Women who drink a lot of cow’s milk have a slightly higher risk of heart disease, according to the research, and that applies whether it is full-fat, semi-skimmed or skimmed. There was no such link seen for men.
This finding contradicts UK diet guidelines that we should aim to have about three portions of low-fat dairy products a day, which would equate to three glasses of skimmed or semi-skimmed milk.
The healthiness, or otherwise, of milk and other dairy products is one of the most contentious areas of nutrition science. And advice differs from country to country.
So, what do and don’t we know about milk – and why can’t scientists agree on whether it is good or bad for us?
Milk hasn’t always been this controversial. For decades it was seen as an unalloyed health food, because of its vitamins, minerals and protein content. Some countries still have government-funded advertising campaigns, and subsidise its provision to schoolchildren.
But in the 70s, concerns rose over the fact that the fat in milk is a type known as saturated fat, which is thought to promote plaque formation inside our blood vessels, leading to heart attacks.
This led to the widespread advice that we should avoid having too much red meat and other sources of saturated fat, including eggs and dairy products.
Some people ditch dairy products completely, either for health or ethical reasons. But plant-based milks usually have lower levels of vitamins, minerals and protein.
If people are happy to consume cow’s milk, the mainstream medical view is that adults should use skimmed or semi-skimmed milk and other low-fat dairy products, for the sake of their hearts.
But there’s a hitch with that mainstream view. In the past decade, multiple studies have found that people who consume more of the specific kinds of saturated fat found in milk and other dairy products are, in fact, less likely to get heart disease and diabetes. This suggests that full-fat milk is better – which some would regard as medical heresy.
These studies drew attention, because they used a more reliable way to assess food intake than the usual kinds of dietary research. They measured levels of different kinds of fat in the blood, which could directly quantify how much dairy people consumed because of the fats’ unique chemical signature. Most previous dietary studies just asked people to fill in food diaries, which is less reliable.
The explanation is unclear. Perhaps the milk fats’ downsides are outweighed by other beneficial compounds in dairy produce. More controversially, there could be something unique about milk saturated fats that means they break the rule about saturated fat being bad. The latter possibility has led some scientists to wonder if guidelines should no longer advise people to cut out full-fat milk.
Now, the new research, published this week in the journal BMC Medicine, seems to have made things even more confusing.
This looked at people in Sweden, who are among the highest dairy product consumers in the world. It found that women who have four glasses of milk a day or more have about a 20 per cent higher risk of heart disease.
There was no effect seen in men, or in people who had equivalent amounts of fermented milk products, such as yogurt, or a similar substance called “filmjölk” a type of sourmilk that is popular in Scandinavia.
Professor Karl Michaëlsson at Uppsala University, who led the research, thinks this could be because fermented milk has lower levels of a milk sugar called galactose, which animal studies have suggested causes harmful inflammation, especially in females. “It would be better to consume fermented milk than non-fermented milk,” he said.
Partly because of previous similar work by Professor Michaëlsson and others, the Swedish Food Agency recommends people have fermented milk products in place of ordinary milk (all low-fat versions). In Sweden it is more common for people to have breakfast cereals with filmjölk, says Professor Michaëlsson.
In a different approach, the Australian Heart Foundation moved away from completely shunning whole milk in 2019. Its guidelines now say that while people with heart disease or high cholesterol should use skimmed milk, for everyone else, there is not enough evidence to say whether skimmed or whole milk is better. Either can be part of a heart-healthy diet, and milk, yogurt and cheese are good snack options, it says.
The British Heart Foundation, on the other hand, still recommends lower-fat milk and dairy products for the general adult population, in line with NHS guidelines.
If the range of research results and opinions seems confusing, it is worth bearing in mind that “observational studies”, such as the new Swedish one, can only find correlations between certain foods and health outcomes, and cannot prove that any one food has a specific effect, said Dr Kathryn Dalrymple, a nutrition lecturer at King’s College London. “It can’t prove causality.”
Only randomised trials can do that, and the type of large, long-term trials that would be necessary to demonstrate the hypothesised fairly small effects from most dietary changes are almost impossible to do.
With observational studies, the food element being measured might be a marker for differences in people’s broad diet pattern rather than being inherently dangerous, said Dr Dalrymple.
On average, dairy products only contribute a quarter of our total saturated fat intake, according to the British Heart Foundation. “I wouldn’t want to demonise an individual food product,” said Dr Dalrymple. “We need to think about our overall diets.”
This post was originally published on here
