Sensitivity of serum apolipoprotein A-IV levels to changes in dietary fat content

The distinctive biological properties of apolipoprotein A-IV suggest that its concentration in serum should be specifically regulated by dietary triglyceride. To test this hypothesis, serum lipids, lipoprotein cholesterol, and apolipoprotein levels were measured in 10 normolipidemic male subjects whose dietary fat intake was isocalorically modified over a range of 10%-50% of total calories. Serum apolipoprotein A-IV levels changed significantly from baseline in response to each dietary modification. Apolipoprotein A-IV levels decreased by 21% during the first week of the low-fat (10%) diet, increased to 12% over baseline during the first week of the moderate-fat (25%) diet, and increased further to 35% over baseline during the first week of the high-fat (50%) diet. Unexpectedly, during the second week of each dietary period, apolipoprotein A-IV levels demonstrated statistically significant trends back toward baseline, which were opposite in direction and proportional in magnitude to the changes during the first week. Nonetheless, serum apolipoprotein A-IV levels, but not apolipoprotein A-I or apolipoprotein B levels, were significantly and positively correlated with the percent of total daily caloric intake ingested as dietary fat. It was concluded that serum apolipoprotein A-IV levels are extremely sensitive to acute changes in dietary fat content and over the range of fat intake examined in this study are significantly correlated with the percent of total calories consumed as dietary triglyceride. Furthermore, the results also suggest that apolipoprotein A-IV may be subject to a rapidly acting autoregulatory mechanism.