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expert reaction to study looking at dairy modified to be lower in saturated fat (from cows fed a special diet), and cholesterol levels and heart health

Research, published in the American Journal of Clinical Nutrition, reports that diary modified to be lower in saturated fats is beneficial to cholesterol levels and heart health.


Dr Duane Mellor, Registered Dietitian and Senior Teaching Fellow, Aston Medical School, Aston University, said:

“This is an interesting proof of concept trial which has shown you can change the makeup of dairy products based on what you feed the cow.  Then when you give that to people it can affect some markers in their body.

“However, it should be noted that while the press release says conventional dairy products increased cholesterol by 5.5% and the lower saturated fat ones did not, that is actually LDL (or bad) cholesterol, rather than total cholesterol.  It is also important to consider although difference in the LDL between the two groups was mathematically or statistically significant, it is perhaps not clinically that important.  Dietary changes can lower it by over 25% and drugs much more.  Although the study showed estimated LDL cholesterol changed using an equation, it was unclear how it actually changed as the different types of cholesterol particles based on size did not change.

“The study was designed to have enough people to be able to show a change in total cholesterol level, but surprisingly it did not show that – it only showed that the dairy produce with less saturated fat increased LDL cholesterol by a smaller amount than the normal variety did, which is actually not what the study was originally designed to do.

“So, this study is interesting in that it suggests that there could be benefits from changing the types of fat in dairy foods, but it did not really provide enough data to back this up this claim.  There has been debate recently about what the role is of dairy and saturated fat in heart disease development – in fact, the same researchers had previously published research that suggested some forms of dairy and saturated fats may actually reduce risk of heart disease.

“So, what might this new research mean?  It’s good that we may be able to change how we raise cattle to improve the nutritional qualities of dairy, and also in this case reduce the methane those cows emit, reducing greenhouse gas emissions linked to dairy.  It may not have a massively clinically significant impact on heart disease risk on its own, especially as dairy itself may not be the problem.”


Prof Paul Evans, Professor of Cardiovascular Science, University of Sheffield, said:

“These researchers have proposed an interesting strategy to lower cardiovascular risk by altering the composition of milk, butter and cheese.  They tested this by feeding cows with sunflower oil causing their milk to have reduced disease-associated saturated fats and higher levels of protective monounsaturated fats.  Individuals at risk of cardiovascular disease had improved arterial health when they consumed the modified dairy products.

“A limitation of the study, however, is that it is based on participants consuming higher-than-average levels of dairy products over a short period of time, and further work is therefore needed to know if modified milk can benefit individuals with normal intake of butter and cheese over a longer period.  Further studies are also required to know if modified butter and cheese can benefit patients with pre-existing cardiovascular diseases including those recovering from a heart attack or stroke.  Although modified dairy products could be helpful in the future, we can all reduce our cardiovascular risk by healthy eating including 5-a-day fruit and vegetables, regular exercise and stopping smoking.”


Dr Elizabeth Lund, Independent Consultant in Nutrition and Gastrointestinal Health, said:

“This very thoroughly conducted study shows that changing the fat composition of dairy products (milk, butter and cheese) can change some risk markers for cardiovascular disease.  The authors have previously demonstrated that feeding cows a diet high in a special type of sunflower oil enriched in mono-unsaturated fatty acids similar to those found in olive oil produced milk with less saturated fat and more unsaturated fat.

“It should be noted this is not about a low fat diet but about a change in fat composition.

“The present study involved feeding people (54 men and women aged between 25-70 at a moderate risk of cardiovascular disease) dairy products from these cows or from normally fed cows for 12 weeks.  Neither trial participants nor the researchers knew which type of dairy products they were being asked to eat and everyone got to eat both types of diet at some point, making for a very strong study design (double-blind randomised controlled crossover design).

“The trial was principally designed to look for changes in cholesterol levels and was able to show statistically important differences in LDL-cholesterol, the so called ‘bad’ cholesterol and the ratio between LDL and HDL (good) cholesterol such that the modified milk was beneficial in this respect.  After people had eaten the lower saturated fatty acid dairy products for 12 weeks their blood vessels were also more elastic than after eating the normal dairy products, which is a good thing but not the main aim of the study so should be treated more cautiously.

“The diets used were designed to have a similar total fat content to each other (38% of energy) but were slightly higher in fat than participants reported in their normal diet (36% of energy) and higher than the UK average diet (33%) which may explain the increase in cholesterol, albeit smaller, even with the modified dairy products.  Despite this caveat the ratio of LDL:HDL cholesterol still went down during the 12 weeks on the modified dairy diet.  The conclusion that this modified diet would reduce the chance of succumbing to cardiovascular disease related problems is encouraging especially as other researchers have shown that adding seed oils to cattle feed may also reduce methane production.”


Prof Graham Burdge, Professor of Nutritional Biochemistry, University of Southampton, said:

“This study clearly demonstrates the feasibility of using modified foods to produce specific changes in nutrient intakes which is of relevance to improving the nation’s health.  Unfortunately, the effects of this dietary modification on markers of cardiovascular health were modest and the authors do not indicate whether their approach alone would be sufficient to bring about meaningful changes in the health of the general population.  Overall, this study is a commendable first step in a long programme of research.”


Prof Paul Leeson, Professor of Cardiovascular Medicine, University of Oxford, said:

“The RESET study is an interesting experimental study that explores whether feeding cows differently can make our food healthier.  During the experiment one group of people ate traditional dairy products and the other group ate products from cows who had been fed with alternative plant-based fat sources.  Everyone ate the same amount of fat but those eating the altered dairy products did not have as big a rise in cholesterol and their blood vessels were ‘healthier’.

“This is a small study in people at risk of heart disease.  Those who took part also had to eat an unusually large amount of dairy products.  As a result, not everyone was able to finish the study and it is difficult to know whether these benefits would be seen in everyone, especially if they are already eating recommended amounts of these types of foods.  However, it does suggest that what we feed cows on farms may be relevant to our own health.”


Victoria Taylor, Senior Dietitian at the British Heart Foundation (BHF), said:

“It’s promising to see how natural changes to the fat content of some of our favourite dairy products could help to lower our cholesterol and risk of heart and circulatory diseases.

“Switching from foods high in saturated fat – such as biscuits, cakes and fatty meats – to foods with more unsaturated fat – such as oily fish, nuts and seeds – can also reduce cholesterol levels.

“This is a double-blind, randomised controlled trial where participants at an increased risk of heart and circulatory diseases replaced standard dairy products with modified versions.  The alternative dairy products provided a similar total fat content, but were lower in saturated fat and higher in monounsaturated fat.

“The trial was only tested on 54 people, so more research is needed to confirm these findings on a larger and more varied group of people and to understand what is behind the different effects.

“Whether the individual dairy products have a greater or lesser effect also needs to be explored further.  In this study participants were provided with milk, cheese and butter.  Milk and cheese have been shown to either have no effect on risk of heart and circulatory disease or a beneficial effect, but not butter.  This could be due to other nutrients found in these foods.  Therefore trials without butter could show an even greater effect.”


Mr Hugo Pedder, Senior Research Associate in Statistical Modelling at the Bristol Medical School, University of Bristol and Statistical Ambassador to the Royal Statistical Society, said:

“Although this a proof-of-concept trial in a small number of participants, it shows promising results that suggest changing the type of dairy we consume, rather than just the quantity, could have an impact on our health.  It also presents an interesting way of impacting human diet, not just by changing the dairy we consume but by changing what the cows that produce our dairy consume.

“As the first trial of its kind to investigate the impact of a modified dairy diet it is well-conducted, and the researchers have taken a number of steps to minimise bias and address potential limitations.  For example, the study participants weren’t aware of which type of dairy they were consuming, since the taste and appearance were found to be the same.  This meant that their expectations could not have influenced the results.

“However, there were some important limitations regarding how applicable these results would be to the real world.  The trial was relatively short, and only investigated blood markers to measure the impact of the modified diet on cardiovascular disease.  We aren’t yet sure if this would have meaningful beneficial impacts on cardiovascular health in the long run.

“It also only included participants with a higher cardiovascular risk and gave them a much higher dairy and fat content diet than most people would consume, meaning that the benefits might not be the same for the average person.”


Dr Riyaz Patel, Associate Professor and Consultant Cardiologist, and Clinical lead for Cardiovascular Prevention, Barts Health NHS Trust, said:

“This is an interesting proof of concept study that shows how naturally modifying the food of animals can lead to dairy products with less harmful (saturated) fats, compared to usual dairy products, which could in turn impact human health.

“This is a notoriously complex field with many conflicting previous results on the impact of dairy foods on heart health.

“This trial though, was well conducted, and patients were given one type of dairy first and then switched to the other.  Researchers and participants were both unaware of which type of dairy was being eaten at any time, making results more reliable.

“Nonetheless, the study is small and not easily generalizable to the wider population.  The benefits seen in the one measure of artery health is interesting but would need a bigger study to confirm.

“In other words, the study showed that eating lots of ‘normal’ fat dairy raises bad cholesterol and may harm artery health, while eating similarly high amounts of this new type of dairy won’t cause the same change in cholesterol and may be a little better for artery health.

“It is important to remember that the comparison group was people eating quite high levels of dairy fat – not a low fat or other diet.  As such, the study should not be taken to mean that eating high levels of dairy fat is good, rather that the modified dairy products may be a better option and could be a useful substitution to help in the battle against heart disease – especially as it seems to taste the same and may be good for the environment too.”


‘Reformulation initiative for partial replacement of saturated with unsaturated fats in dairy foods attenuates the increase in LDL cholesterol and improves flow-mediated dilatation compared with conventional dairy: the randomized, controlled REplacement of SaturatEd fat in dairy on Total cholesterol (RESET) study’ by Dafni Vasilopoulou author et al. was published in American Journal of Clinical Nutrition at 00:01 UK time on Wednesday 5 February 2020.

DOI: 10.1093/ajcn/nqz344


Declared interests

Dr Duane Mellor: “I have nothing to declare.”

Prof Paul Evans: “No conflicts.”

Dr Elizabeth Lund: “I have no conflicts of interest.”

Prof Graham Burdge: “I have no conflicts of interest with this article.”

Prof Paul Leeson: “No conflicts of interest related to this study.”

Mr Hugo Pedder: “No conflicts.”

Dr Riyaz Patel: “No COI or financial relationship with the food or dairy industry.  I have received honoraria and consulted for companies producing cholesterol lowering drugs.  I am funded by the British Heart Foundation.”

None others received.

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