The Dietary Total-Fat Content Affects the In Vivo Circulating C15:0 and C17:0 Fatty Acid Levels Independently

Abstract

Pentadecanoic acid (C15:0) and heptadecanoic acid (C17:0) have been described as dietary biomarkers of dairy-fat consumption, with varying degrees of reliability between studies. It remains unclear how the total amount of dietary fat, representing one of the main confounding factors in these biomarker investigations, affects C15:0 and C17:0 circulating concentrations independent of their relative intake. Additionally, it is not clear how changes in the dietary total-fat affects other fatty acids in circulation. Through two dietary studies with different total-fat levels but maintaining identical fatty acid compositions, we were able to see how the dietary total-fat affects the fatty acids in circulation. We saw that there was a statistically significant, proportionate, and robust decrease in the endogenous C15:0 levels with an increase in dietary total-fat. However, there was no significant change in the circulating C17:0 concentrations as the total-fat increased. To conclude, the dietary total-fat content and fat-type have a very complex influence on the relative compositions of circulating fatty acids, which are independent of the actual dietary fatty acid composition. Knowing how to manipulate circulating C15:0 and C17:0 concentrations is far-reaching in nutritional/pathological research as they highlight a dietary route to attenuate the development of metabolic disease (both by reducing risk and improving prognosis).

Keywords: 15:0; 17:0; biomarkers; dietary total-fat; heptadecanoic acid; odd chain fatty acids; pentadecanoic acid.

Figure 1

The effect of changing the amount of total-fat within the diet from 5% to 35% to 70% (% energy) on the serum fatty acid concentration (µmol) whilst maintaining identical dietary fatty acid compositions across the three diets (n = 6–7 per group). This is to see if the amount of total-fat within the diet influences the serum fatty acid concentration independent of the actual dietary fatty acid composition. The serum samples were analysed by gas chromatography separation with mass spectrometry detection. The significance of the difference between each group is shown by the p-value star system, where p ≤ 0.05 was considered statistically significant (p < 0.05 = *, p < 0.01 = **, p < 0.001 = ***). Error bars represent ± standard error of the mean.

Figure 2

The effect of changing the amount of total-fat within the diet (% energy) from 11% to 51% on the plasma fatty acid concentration (µmol) across three different formulations of dietary fat (Basal, Lard, and Fish oil) (n = 6–8 per group). This is to see if the amount of total-fat within the diet influences the plasma fatty acid concentration independent of the dietary fatty acid composition. The plasma samples were analysed by gas chromatography separation with mass spectrometry detection. The significance of the difference between each group is shown by the p-value star system, where p ≤ 0.05 was considered significant (p < 0.05 = *, p < 0.01 = **, p < 0.001 = ***). Error bars represent ± standard error of the mean.