Multi-country Study- Effect of Dietary Fats on Fat Deposition

There is existing evidence to show that vegetable oils having unsaturated fatty acids in the sn-2 position with predominantly palmitic acid (C16:0) or stearic acid (C18:0) in the sn-1 and sn-3 positions of fat molecules do not raise serum cholesterol levels. These observations have come to be known as or explained by the "sn-2 hypothesis". New evidence have also emerged to show that saturated fatty acids (C16:0, C18:0) in the sn-1 and -3 positions reduces fat deposition in a rat model. Therefore, further studies in humans are warranted to confirm these earlier findings.

Fats and oils are made up of >90% triacylglycerol (TAG)- fat molecules which consist of a glycerol backbone to which 3 esterified fatty acids are attached. The positions of fatty acid attachment are referred to by stereospecific numbers, sn -1, -2 and -3. Early evidence shown that the unique stereospecificity of fatty acid distribution on the palm fat molecule conferred health benefits in that it inhibited experimental atherosclerosis in the rabbit model.

In vegetable oils, oleic acid [a monounsaturated fatty acid (MUFA)] is predominantly situated at the sn-2 position, while in animals fats it is predominantly palmitic acid or stearic acid (C16:0 or C18:0-saturated fat) that is situated there. Even though palm olein and lard have similar proportions of saturated fatty acid (SFA), MUFA and polyunsatuared fatty acid (PUFA), they differ significantly in their positional distribution on the TAG molecule. Palm olein TAG contains only 7-11 % palmitic acid at the sn-2 position while about 87% is unsaturated fatty acids (oleic acid and linoleic acid). Lard has the highest amount of palmitic acid in the sn-2 position at 70%. On the other hand, in human milk, palmitic acid is predominantly in sn-2 (53-57 %) while cow milk fat contains less palmitic acid (38 %) there. It is now believed that the distribution of fatty acids in the TAG is more important than the fatty acid composition alone in conferring the oils' 'saturated' or 'unsaturated' properties.

In this proposed study, the effects on the outcome measures investigated of different fatty acids (palmitic acid, oleic acid, linoleic acid) at the sn-1, sn-2 and sn-3 positions of the TAG molecule in three different test fats will be investigated.