3 April 1998

Work aims at heart

of the matter

One way to survive falling

milk prices is to increase

output by adding value to the

milk produced. Research at

ADAS Bridgets is examining

how to improve the health

characteristics of milk to

provide new and better

quality milk products.

Sue Rider reports

MILK enriched with essential fatty acids to protect against heart disease could be on supermarket shelves in five years.

Thats if work now underway at ADAS Bridgets Research Centre reaches commercial fruition. Its an ambitious target, says dairy director Bridget Drew. Milk contains few of the long chain poly-unsaturated fatty acids desired by nutritionists; indeed, 75% of fat in milk is the less desirable saturated type.

But Dr Drew is enthusiastic about the opportunities to make milk healthier still – bringing it more in line with the recommendations of the health of the nation white paper produced by the Committee on Medical Aspects of Health (COMA).

This requires that our energy intakes from saturated fats, currently at 16% of the total, are reduced to 10%. And with 40% of our daily intake of saturated fats coming from milk, dairy products and fat spreads (see Table 1), it is hardly surprising that nutritionists are keen to target milk, says ADAS researcher Rosemary Mansbridge, who is heading up the new project.

Substantial government backing for the work – £650,000 from MAFF which is matched by industry funding – demonstrates a commitment to improving the nations health by making food healthier still by altering the composition of animal diets.

As Ms Mansbridge explains, MAFF is not only keen to reduce levels of harmful saturated fat, particularly C14 and C16, in our diet (see Table 2). It also wants to increase levels of those fats believed to be beneficial – the monounsaturated fatty acids (MUFAs) such as C18:1 and long chain poly-unsaturated fatty acids (PUFAs). These occur mainly as linoleic acid (C18:2), part of the n-6 family and linolenic acid (18:3), part of the n-3 family and found in grass. Also valuable are the n-3s docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) – found in oily fish.

These are, therefore, present in high levels in the blood of Eskimos and Japanese – and whats significant is that both these populations suffer a very low incidence of heart disease, explains Ms Mansbridge.

Linseed is the only other significant source of the n-3 PUFAs, with the n-6 family of PUFAs found in soya and rape oils and more readily available in our diet. In fact, MAFF is concerned that there is too much n-6 in the diet compared with n-3 types, and seeks to redress the balance.

One way to do this is to improve the health characteristics of food we eat or drink every day. One such functional food is milk.

"Milk is one of the most naturally produced ingredients of a balanced diet," says Ms Mansbridge. "But despite liquid milk being 96% fat-free, fat content is high when expressed as a proportion of dry matter, and the fat in it is predominantly saturated."

These saturated fatty acids account for 75% of total fatty acids, with 21% occurring as MUFAs and only 4% as the PUFAs, which include the valuable n-3 fatty acid linolenic (LNA).

For patients with high blood pressure, high cholesterol or otherwise at risk from coronary heart disease, the ideal milk would be low in saturated fats, and high in MUFAs and n-3 PUFAs.

"Our research will try to increase levels of n-3 in milk, for example, without increasing n-6 levels and if we can reduce n-6s at the same time, thats even better," explains Ms Mansbridge.

Good news

The good news is that the fatty acids which we want in our diet – most of the MUFAs and all the PUFAs – come from the cows diet, not her own synthesis, she says.

"We must identify the dietary sources of the fatty acids we want in milk and, because the cow is a ruminant, find ways of protecting these in the rumen, so more ends up in milk."

Grass is a case in point. It contains high levels of the n-3 linolenic acid and is a safe and natural route to increase delivery of n-3s into the human food chain. But at present all LNA taken in by the grazing cow becomes saturated in the rumen. The route to healthier milk is to find out how to protect it. And because it is increasingly clear that cows – or humans – can synthesis EPA and DHA from LNA – milk could contain more of these n-3s too.

While scientists at the Institute of Environmental Research are trying to increase LNA in grass, and find out what can be done to protect it, ADAS Bridgets will examine the affect of feeding linseed – an alternative source of LNA – to dairy cows. The linseed is protected to prevent it from being saturated in the rumen.

If this proves to be a successful route to increasing LNA in the diet, then it would follow that the cow could make her own DHA and EPA – and so produce more in milk.

But work at ADAS Bridgets is also trying to increase levels of these two n-3s by feeding cows marine plants – again these are protected to stop them becoming saturated in the rumen.

Unsaturated fatty acids such as EPA and DHA are, however, more unstable than saturated fats, and prone to oxidation and as their concentration increases, so shelf life may be reduced.

For this reason, ADAS is also increasing the level of the anti-oxidants selenium and vitamin E in the cows diet to try to extend shelf-life at the same time as increasing PUFAs.

Cows at ADASBridgets fed linseed and marine plants should produce milk that contains more valuable fatty acids, linked with reduced heart disease.

Bridget Drew – enthusiastic about the opportun

-ities to make milk even healthier.

Table 1. Contribution of food groups to daily intakes of fat and fatty acids by adults (Adapted from British Nutrition Foundation, 1992)


Average daily intake (% of total intake)

Fatty acids

PUFA

Food group Total fat Saturated Trans MUFA n-6 n-3

Milk and milk products 15 23 10 12 2 6

Fat spreads 16 17 30 11 20 15

Meat and meat products 24 23 18 31 17 19

Fish and fish dishes 3 2 1 3 4 14

Cereal products 19 18 27 18 22 17

Vegetables* 11 6 6 12 24 22

MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids.

* Includes roasted and fried.

Table 2:MAFFs priority areas for future research on modifying the composition of milk


Action Health benefit

1. Reduce levels of saturated fats Lowers risk of coronary heart disease

2. Increase levels of unsaturated fats Lowers risk of coronary heart

disease

3. Increase levels of anti-oxidants To increase product shelf-life

Anti-oxidants could also act to

reduce heart disease

Rosemary Mansbridge – our research will try to increase n-3 in milk.