5 December 1997

OUTING UNHEALTHY FATS

Reducing saturated fat in

meat and milk is the aim of

current Nottingham

University research.

Jessica Buss reports

HEALTHIER lamb, beef and milk that would boost consumption could soon be possible through diet or genetic manipulation.

According to Nottingham University nutritional biochemist Andy Salter, recent research has identified the gene for the enzyme which is responsible for converting saturated fat to unsaturated fat.

It is believed a perceived high level of saturated fat in red meat has been a factor in reducing consumption. Sheepmeat is normally 2% saturated and 1.7% unsaturated fat. Beef fat is lower in fat at 1.5% of each. But the ratio of saturated to unsaturated fats could be altered to satisfy the health experts.

Ratio changes

In non-ruminants, the ratio can be changed through diet, but the cost of feeds high in unsaturated fats can be uneconomic. In ruminants, however, the composition of body fat is not influenced by diet; most fat is synthesised in fat tissue.

"The first synthesised is a saturated fat called palmitic acid, one of the fatty acids which increases blood cholesterol.

"But the animal can convert unhealthy fatty acids to form oleic acid – an unsaturated fat found in olive oil. Up to a third of the animals fat, in beef and sheep, can naturally be in this form," says Dr Salter.

In non-ruminant animals the enzyme desaturase is responsible for controlling oleic acid production, and his study has proven the enzyme also regulates oleic acid production in sheep. This unsaturated fatty acid was also found to be under hormonal control. When insulin was added to culture samples in the lab it doubled the unsaturated fat content of cells, he adds.

"These normal physiological controls could in theory be manipulated through diet. Getting the enzyme working faster would increase unsaturated fat production. Although this could be achieved fairly quickly, we dont know the scale of the effect on fatty acid composition in the animal," says Dr Salter. Rumen function may restrict fatty acid composition manipulation through diet.

He suggests that increasing unsaturated fat production by increasing the number of enzyme-producing genes could be more successful than diet manipulation in ruminants.

The single gene responsible for desaturase production was isolated at the Hannah Research Institute, Ayr, Scotland, and putting these genes into cell culture in the lab produced more unsaturated fat, points out Dr Salter.

There are two possible progressions in this work. The first is to use the gene identified and find animals or breeds that naturally produce more desaturase enzyme, and have a preferred fat composition, and breed from them.

Gene manipulation

The second is to use gene manipulation, if these practices become ethically and morally acceptable. Introducing more copies of the gene into an animal which only possesses one naturally would increase desaturase enzyme production and, therefore, unsaturated fat content. Producing the sheep with more genes would be expensive. But after developing a small breeding flock numbers could then be increased by breeding.

There is no reason for any detrimental effects on animals or any changes to management, adds Dr Salter.

"Increasing the proportion of unsaturated fat by 20% and as a result decreasing saturated fat would have major marketing benefits and health benefits for consumers, but the meat would initially be more expensive because of the high cost of stock."

Dr Salter believes these principles could also apply to milk where fat comes from adipose tissue, or is produced in the mammary glad, if the ratio of unsaturated to saturated fat produced can be altered.

* Sponsored by BBSRC and MAFF.

Reducing saturated fat levels in beef would have major marketing benefits and help benefits for consumers.

BOOST UNSATURATED FAT

&#8226 Controlled by specific enzyme.

&#8226 Increase enzyme-producing genes.

&#8226 By diet or genetic manipulation.