Fatty acid chain length and degree of unsaturation alter cellularity of adipose tissue

Abstract

The effect of dietary fatty acid chain length and degree of unsaturation on adipose tissue cellularity was investigated in young growing pigs. Weanling pigs were assigned to one of six groups and each group received a diet differing in the main fatty acid. The dietary fats contained approximately 35% myristoleic and palmitoleic acids combined (14:1/16:1), 62% palmitic acid (16:0), 65% stearic acid (18:0), 52% oleic acid (18:1), or 41% linoleic acid (18:2). All diets except the control diet contained 33% myristic acid (14:0). Diets contained 10% starch (control diet) or 10% added fat and were fed for 35 days. Subcutaneous adipose tissue samples were collected from the area overlying the first cranial vertebra, and adipocytes were osmium fixed and urea liberated. Adipocyte number (cells/g adipose tissue) and volume (μm3) were measured on a Coulter Counter and Channelizer. Mean adipocyte volumes for pigs fed the control, 14:1/16:1, 16:0, 18:0, 18:1 and 18:2 diets were 167ab, 201a, 157b, 177a, 184a and 142b, respectively. Means with similar superscripts are not different (P > 0.05). Mean number of adipocytes/g adipose tissue (× 106) for pigs fed the control, 14:1/16:1, 16:0, 18:0, 18:1 and 18:2 diets were 3.54ab, 2.86bc, 4.46a, 3.81ab, 2.34c, and 2.98bc, respectively. These data suggest that the 18:2 diet reduced both adipocyte volume and cells/g. However, adipocyte diameter distributions indicated a substantial loss of larger adipocytes in tissues from pigs fed the 18:2 diet. These observations indicate that the 18:2 diet increased the fragility of the adipocytes (resulting in loss during sample preparation). Instead, diets high in the monounsaturates (14:1/16:1 and 18:1) significantly reduced the number of adipocytes per g tissue, which was consistent with their effects on adipocyte volume. The data suggest that fatty acid chain length and unsaturation are determinants of the effects of dietary fat on adipocyte number and volume in young growing animals.