A low-fat diet supplemented with monounsaturated fat results in less HDL-C lowering than a very-low-fat diet

S A Morgan, K O'Dea, A J Sinclair

Journal of the American Dietetic Association, 1997, Vol 97, No 2, 151-156

Dietary manipulation to lower blood lipid levels has varying degrees of success. It has been found that low-fat, high-carbohydrate diets not only lower low density lipoprotein cholesterol (LDL-C), but also cause concomitant decreases in high density lipoprotein cholesterol (HDL-C). The latter effect is generally thought to be undesirable because HDL-C is regarded as a protective factor in the development of atherosclerosis.

Australian study

The authors of this paper set out to compare the effects of a very-low fat diet and a low-fat diet supplemented with monounsaturated oil on plasma lipid levels in hypercholesterolaemic subjects. After a 2 week baseline period, 24 free-living Australians (14 men and 10 women), with a mean age of 46 years and plasma cholesterol levels exceeding 6.00 mmol/litre, were randomly assigned to either the very-low-fat diet (10% of energy from fat), or the low fat diet (26% of energy from fat), supplemented with olive oil and an olive oil based margarine imported from Greece, for a 3 week period, after which the diets were reversed for another 3 weeks . Blood samples were drawn at baseline, two days before and at the end of each dietary treatment period to be analyzed for serum lipids. Subjects were asked not to increase their energy expenditure during the study and body weight was carefully monitored.

Two aspects of the dietary treatment are of particular interest. The researchers found that when the subjects were on the very-low-fat diet, they found it difficult to maintain their normal weight because of the low energy density of this diet. A carbohydrate supplement had to be added to the very-low-fat diet to provide 15% of dietary energy. Secondly, all the subjects ate 300 g (raw weight) lean beef, from which all additional fat had been trimmed, every day.

The following results were obtained:

Serum lipoprotein concentrations

Significant difference from baseline:* = P<0.05; *** P<0.001

(According to Morgan et al, 1997, p. 154)

These results show that both dietary treatments lowered serum cholesterol and LDL-C, but that the low-fat diets supplemented with monounsaturated fat, did not lower the HDL-C, as much as the very-low-fat diet. This is regarded as a positive finding in favour of the use of a diet that is less restricted in terms of fat content (26% of energy from fat), and is supplemented with monounsaturated fat to control and/or lower blood lipid levels in hypercholesterolaemic subjects. The study also confirmed previous findings that very lean beef and other red meats can be used in cholesterol-lowering diets.

Editor's Note

This Australian study has a very positive message for persons who have to control or lower their LDL-C levels. It is possible to lower "harmful" LDL-C levels in the blood, without lowering "protective" HDL-C levels, by using a low-fat diet which is a great deal more realistic in composition than the very-low-fat diet, provided the diet is supplemented with monounsaturated fat. Olive oil and products, such as margarine made from olive oil, can be a useful adjunct to cholesterol-lowering diets. In Thailand, olive oil is readily NOT available, AND tends to be rather expensive, while I have personally not come across margarines made from olive oil.

For the meat-eating population of Thailand, the news that lean red meat (beef) can be used successfully in cholesterol-lowering diets, will come as additional good news. This does not mean that hypercholesterolaemics should go overboard and eat vast quantities of red meat, but it does mean that they can include very lean red meat at the level of 300 g per day in their diets.