Sugar is bad news for health — on this most would agree. But when it comes to fat, there has been real and sometimes acrimonious debate.
For decades we have been warned that eating too much dairy such as milk, butter and cheese could raise our risk of serious conditions such as heart disease and strokes — only for more recent studies to suggest they might actually protect us from these by lowering our risk of developing high blood pressure or type 2 diabetes.
So where does the truth lie — and why can’t the scientists agree?
The key reason dairy products are considered bad for us is their high saturated fat content.
Although our bodies need fats for energy, growth and to absorb fat-soluble nutrients such as vitamins A, D and E, eating too much saturated fat, in particular, can raise levels of so-called ‘bad’ cholesterol in our blood.
This can clog arteries, which in turn leads to health problems such as high blood pressure, heart disease and strokes.
For decades we have been warned that eating too much dairy such as milk, butter and cheese could raise our risk of serious conditions such as heart disease and strokes — only for more recent studies to suggest they might actually protect us from these
Unlike unsaturated fats (found in plants, nuts and fish), saturated fats (which mainly come from animal products, such as dairy and meat) are denser and harder for our bodies to digest.
The NHS recommends men consume no more than 30 g of saturated fat per day, while women are advised to stick to a limit of 20 g. But a 200 ml glass of whole milk contains 7.4 g of fat, of which 4.8 g is saturated — a quarter of a woman’s daily saturated fat allowance.
Butter contains around 80 per cent fat in total and 50 per cent saturated fat, equivalent to 5.2 g of saturated fat for every 10 g portion.
While the total fat content in cheese varies from 4 per cent in cottage cheese up to 35 per cent in Stilton and 44 per cent in mascarpone, a 30 g portion of Cheddar contains roughly 6.6 g of saturated fat.
‘Consuming saturated fats like those in dairy raises our blood cholesterol levels,’ says Dr Giles Yeo, principal research associate at the MRC Metabolic Diseases Unit at Cambridge University and honorary president of the British Dietetic Association. ‘We need cholesterol as it gives our cells structure — it’s what stops us from being a puddle on the floor — but too much of it causes arteries to harden, which leads to cardiovascular problems.’
Increased saturated fat consumption is the principal reason why scientists say people from cultures that consume a lot of dairy, such as the UK, U.S. and northern Europe, are at a slightly increased risk of premature death, particularly from heart attacks and strokes.
In the case of dairy, it’s certainly true that several studies observing large groups of people have failed to find a clear association between higher levels of dairy consumption and increased heart health risks
But the relationship between saturated fat and heart problems is far from clear. While scientists generally agree that eating saturated fats raises the level of fats in your bloodstream and may increase other risk factors for heart disease, such as inflammation, it is not clear that it directly leads to heart or cardiovascular problems.
Some researchers say saturated fat has been unfairly demonised. Arne Astrup, a professor in the department of nutrition, exercise and sports at Copenhagen University, argues that focusing on saturated fat alone ‘does not make sense’ as there are different types of saturated fatty acids which all have different effects on the body.
‘The effect is dependent on the food source it exists in — the effect of saturated fat is modified by all the other nutrients in the food,’ he wrote in 2019.
Could eating dairy be protective?
In the case of dairy, it’s certainly true that several studies observing large groups of people have failed to find a clear association between higher levels of dairy consumption and increased heart health risks.
There is a theory that this is because the other elements in dairy, such as calcium and certain fatty acids, work together in what is known as the ‘dairy matrix’ to protect our cardiovascular health.
Scientists have not yet been able to establish how this might work. But a 2018 study of more than 135,000 people in 21 different countries, who were monitored for nine years by researchers from McMaster University in Canada, found lower rates of death and cardiovascular disease in people who ate dairy than those who didn’t, with those who ate the highest amounts — two or more servings per day — the most protected.
A study published in September in the journal PLoS Medicine looked at 4,000 60-year-olds in Sweden (where diets are typically high in dairy) and found those who ate high levels were less likely to experience heart attacks, stroke or other cardiovascular problems — and were not any more likely to die than those who ate low levels.
‘A number of published studies suggest that, despite their saturated fat content, some dairy foods such as milk, cheese and yoghurt have a neutral or even positive effect on a person’s risk of heart and circulatory disease,’ says Victoria Taylor, a dietitian with the British Heart Foundation.
‘Studies have suggested that consuming dairy products is linked to a lower risk of type 2 diabetes and high blood pressure, both of which are factors that increase the chances of a heart attack or stroke.’
Under current recommendations adults and older children are advised to eat dairy in moderation, choose low-fat options where possible and avoid excessive consumption of butter or cheese
Calcium may stop fat absorption
It is thought that some of these positive effects may be caused by the combination of beneficial nutrients in dairy foods.
Milk contains protein and amino acids, which our bodies need for growth and repair, calcium and vitamin B12, vital for bone and blood health, as well as potassium, phosphorus and iodine, which we need to make thyroid hormones and regulate our metabolism. Some researchers believe these nutrients work to counteract potential damage from their high fat content.
‘There are several convincing studies to show that dairy foods are protective of our heart health,’ says Sophie Medlin, a dietitian with City Dietitians. ‘We think this may be due to the minerals in milk preventing full absorption of the saturated fats.’
High levels of calcium in cheese are thought to bind with fat in the gut, preventing some from being absorbed, so helping prevent it from raising ‘bad’ cholesterol levels.
One study, published in the European Journal of Nutrition in 2017, found that people who ate 40 g of cheese per day had a 14 per cent lower risk of heart disease and 10 per cent lower risk of stroke than those who never ate it.
Its authors attributed this to the probiotics — the ‘good bacteria’ —in cheese which they believe reduce the inflammation that can trigger heart disease. They also suggest that one of its fatty acids may boost levels of ‘good’ HDL cholesterol (which protects heart health) in the bloodstream and lower levels of ‘bad’ LDL cholesterol.
If this is true, it may mean cheese might not contribute to furring up arteries as once feared and may help stop fatty plaques forming on blood vessel walls. Other research has suggested that antioxidants which develop in cheese in the fermentation process could protect against some of the damage from its typically high salt content.
While scientists are unsure exactly how this works, for one study by Penn State University in the U.S., published in the Journal of Nutrition in 2019, 11 people were asked to follow different high-salt diets in rotation and found that when participants were on a diet where their salt intake came from four daily servings of cheese, their signs of blood vessel damage were much lower than when salt came from other sources.
Question marks over cheese
But other experts are unconvinced. ‘This [theory that cheese could be beneficial for our health] speaks to the broader point that we eat a food rather than individual macronutrients, and the complexity of food means that there are good bits and bad bits, and how they interact also changes how good or bad they are,’ says Dr Yeo.
‘So this may be possible but the short answer is: we don’t know yet. There is still no evidence that having higher levels of saturated fat in your diet is a good idea.’
The main reason debate about dairy has raged for so long is that almost all of the studies carried out into dairy consumption are observational, where researchers look at the diets of groups of people and record what happens to their health over a number of years. This type of study can’t prove cause and effect or explain why there might be an association between eating certain foods and developing certain illnesses.
Dr Yeo points out that the most reliable studies in science are randomised and double-blinded, where participants are allocated either a treatment or placebo at random and neither they nor the researchers know which one they are taking.
But this is very difficult with studies into diets because participants usually know what they are eating. ‘This means studies are open to bias,’ he says.This is why, despite a growing number of studies throwing doubt over the link between dairy and health problems, the NHS, the British Heart Foundation and the Government’s Scientific Advisory Committee on Nutrition say their advice on dairy is not changing.
Under current recommendations adults and older children are advised to eat dairy in moderation, choose low-fat options where possible and avoid excessive consumption of butter or cheese.
That means no more than two to three portions of dairy a day, with each portion equivalent to a third of a pint of milk, a small matchbox-sized piece of cheese or a small pot of yoghurt. The advice is different for children, who are recommended to drink 350 ml of milk a day, as research shows it helps young children’s growth.
Concern about sugar and salt
Dr Elijah Behr, a consultant cardiologist at Mayo Clinic Healthcare in London, agrees it’s too early to change dietary recommendations, particularly as we generally eat too much saturated fat already — the diet of the average Briton contains 12.6 per cent saturated fat, above the recommended maximum of 11 per cent — so it’s important we try to limit our consumption of fatty foods, such as fatty cuts of meat, sausages or biscuits.
He adds: ‘Recent research has suggested that it is not clear that dairy products will cause heart disease. However, these studies have limitations and, despite there being less consensus in the research community about whether dairy products are overall harmful or beneficial, we should be cautious before changing recommendations.’
Another flaw of many of the studies is they look at people’s overall consumption of ‘dairy’, ‘yoghurt’ or ‘cheese’ but do not differentiate between the specific types eaten.
Some researchers believe the ingredients added to some processed dairy products, such as salt and sugar, could be more harmful than the fat.
A plain full-fat yoghurt may be a healthier choice than a low-fat flavoured yoghurt, which can contain as much as 12 per cent sugar. Excess sugar consumption is linked with obesity and tooth decay.
Dairy contains the naturally occurring sugar lactose but this is not considered bad for our health as it is a complex sugar which releases energy more slowly and has a lower glycaemic index than most added sugars.
But added salt in dairy products such as cheese and butter can help raise blood pressure and increase the risk of heart attacks and strokes.
The NHS says we should have no more than one teaspoon (6 g) of salt a day.
But there is more salt in one matchbox-sized portion of Cheddar than in a packet of crisps, for example — around 0.5 g in the cheese compared to 0.4 g in a pack of salt and vinegar crisps.
‘Hard cheeses such as Cheddar are one of the biggest sources of salt in our diet and the sugar that is added to dairy products such as yoghurts, both whole milk and low-fat varieties, milkshakes and ice cream make dairy products a top source of free sugars in the UK diet,’ says Victoria Taylor.
But if we opt for foods without added salt or sugar, could the benefits of dairy nutrients outweigh the harm from fats? Sadly, we still can’t say for sure.
The results of one Harvard University-led study, published in 2016 in the American Journal of Clinical Nutrition, perfectly sum up the confusion around dairy: after following the diet and health of more than 222,000 Americans, researchers found no significant association between eating dairy and a higher risk of heart disease or stroke. But they did find that people who replaced dairy with vegetable fats or polyunsaturated fats — such as those found in fish and nut oils — saw their risk of developing these health problems drop by 10 per cent and 24 per cent, respectively.
So, eating dairy might not harm your health, but eating less of it might still be better for you.
…And links to breast cancer are being challenged too
Should women curb their consumption of dairy to reduce the risk of breast cancer? This is a question long mired in controversy.
The weight of evidence has been that it might raise the risk, including a study published in the International Journal of Epidemiology last year that suggested as little as one cup of dairy milk a day may increase the risk of breast cancer by 50 per cent.
There are several theories why dairy foods should be avoided, but the most popular is that they contain significant levels of oestrogen, fats and growth hormones thought to increase the risk of breast cancer. But now a major new study suggests that some dairy products can actually protect against breast cancer.
Indeed, the ‘comprehensive’ and ‘meaningful’ conclusions of the study, published last month in the journal BMC Cancer mean women should be encouraged to eat some types of dairy products, say the researchers from Zhejiang Chinese Medical University in China.
The research merged data from 36 studies from between 1986 and 2020, including information from more than a million women followed up for between 18 months and 22 years.It found that dairy can reduce the risk of breast cancer, particularly for oestrogen-receptor positive (ER-positive) and progesterone-receptor positive (P-positive) breast cancers, although this protection was not ‘statistically significant’ — meaning the protective effects identified may be just down to chance.
However, the extent of this protection varied widely. For example, fermented dairy such as yoghurt and cheese can reduce breast cancer risk after the menopause but not before it.
And, contrary to the study last year, non-fermented dairy foods such as milk and butter, had no effect on breast cancer risk.
The fat content of dairy products also made a difference.
Low-fat dairy products (with a fat content of 1.0 to 1.5 per cent) offer protection against breast cancer in women before the menopause, while high-fat dairy products (3 to 5 per cent fat), are ‘harmful to [all] women’, increasing their risk of breast cancer, the study concluded. While more studies are needed, the researchers advise ‘low-fat dairy products for pre-menopausal women and fermented dairy products for post-menopausal women’.
They also recommend ‘minimising the intake of high-fat dairy products’ for all women.
One suggestion is that the calcium, vitamin D and conjugated linoleic acid (a type of omega-6 fatty acid) in dairy affect cell growth and can inhibit tumour development.
Dairy may be particularly beneficial for protecting against hormone receptor-positive forms of breast cancer because its ingredients can ‘down-regulate’ oestrogen receptor activity, say the researchers.
With fermented dairy, the benefits may derive from probiotics or good bacteria it contains, which have been shown to protect against cancer by balancing bacteria in the gut (in turn affecting the body’s immune response, helping protect it from disease).
Levels of probiotics naturally decline with age, which may be why fermented products seem particularly beneficial for women after the menopause, say the researchers.
High-fat dairy, however, may raise the breast cancer risk by boosting cell growth and increasing the risk of obesity and type 2 diabetes (both linked to the disease). The researchers say the ‘association between dairy intake and breast cancer risk is stronger in premenopausal women’, possibly owing to ‘more robust interactions’ between the different components in dairy in younger women.
Commenting on the study, Professor Kefah Mokbel, a breast surgeon at the private Princess Grace Hospital in London, said: ‘The assumption that dairy products contain significant amounts of oestrogens and growth hormones has led to the widespread belief that dairy products increase the risk of hormone-sensitive breast cancer.
‘But scientific evidence reveals that the theoretical increases in oestrogen concentrations following consumption of dairy are minuscule relative to circulating concentrations in humans.
‘Almost all epidemiological studies show that women consuming low-fat dairy products have a lower risk of breast cancer than those who don’t consume dairy, and fermented low-fat dairy products confer additional protection.’