Fatty acid carbon isotope ratios in humans on controlled diets

Abstract

Carbon stable isotope ratios for six serum fatty acids (FA) are reported for human subjects on controlled fat diets to determine the range of natural isotope abundance and to demonstrate the leveling effect of a well-controlled diet. Twenty-nine subjects were randomly assigned to one of three controlled diets containing high, medium, or low fat. Diets were consumed for 8 wk. Serum samples were collected at baseline (0), 5, 6, 7, and 8 wk. FA were extracted and methylated. Isotope ratios were analyzed by high-precision gas chromatography combustion-isotope ratio mass spectrometry. At baseline, mean delta 13C for 16:0b, 16:1a, 18:0a, 18:1c,18:2n-6d and 20:4n-6bc were -24.1, -21.7, -21.6, -25.6, -29.6, and -25.0/1000, respectively, with an average standard deviation of 1.9/1000. Most delta 13C decreased during the diet period and appeared to have stabilized by week 5 at -25.3, -21.9, -22.3, -26.5, -30.1, and -24.5/1000, respectively. Between-subjected variability decreased from 1.74 to 1.20/1000 on the controlled diets. Measurement variability was 0.53/1000. The within-subject variability during weeks 5-8 was 0.57/1000 (range of 0.32-0.84/1000), showing a minimum biological fluctuation on controlled diets. There was no diet group effect on delta 13C of serum FA. Except for 18:2, the delta 13C of experimental diets was lower than that of serum FA, consistent with observations in animals. These data show that carbon isotope ratios stabilize in response to controlled diets within 5 wk, reflecting the isotope ratio of their dietary source, and establish isotope ratio fluctuations for endogenous compounds for future studies.

Stable Isotope Composition of Fatty Acids in Organisms of Different Trophic Levels in the Yenisei River

“…Shrimps from Hong Kong streams, Caridina cantonensis , fed on phytoperiphyton, had significantly more depleted essential α-linolenic acid (18:3n-3, ALA), than that of the periphyton [33]. Rhee et al [34] when studied a controlled humans diet, found that the 13 C content of essential linoleic acid (18:2n-6) in serum was about 2‰ lower, than that of the diet, in contrast to non-essential saturated and monounsaturated acids. Bec et al [6] found that in laboratory experiment FA in Daphnia lipids were generally 13 C-depleted compared with their counterpart in the corresponding diet, including essential HUFA.…”

Expression of the dietary isotope signal in the compound‐specific δ13C values of pig bone lipids and amino acids

“…Interestingly, an identical pattern of δ 13 C values for these five fatty acids has previously been identified in redhead duck adipose fatty acids (Hammer et al, 1998) and for C 16 : 0 , C 18 : 0 and C 18 : 1 in the bones of pigs raised on controlled diets . The factors controlling the relationship between the δ 13 C values of fatty acids within a particular tissue are unknown, but they may involve isotopic fractionation during fatty acid desaturation or elongation (Rhee et al, 1997).…”

“…The development of compound-specific stable isotope analysis of individual lipids has stimulated research using both natural abundance and enriched tracers (Guo et al, 1993;Binnert et al, 1995) in a wide range of applications from studies of ancient and modern foodwebs (Pond et al, 1995;Stott et al, 1999), lipid metabolism (Rhee et al, 1997), and food authentication (Woodbury et al, 1995). Stott et al (1997) determined the δ 13 C values of fatty acids and cholesterol to investigate the routing and biosynthesis of lipids in pigs reared on controlled diets.…”

Natural abundance stable carbon isotope evidence for the routing and de novo synthesis of bone FA and cholesterol

“…Stott et al (16) also demonstrated that bone linoleic acid δ 13 C values, as expected, were highly consistent with dietary values. However, Rhee et al (30) observed a 3‰ depletion in serum linoleic acid δ 13 C values with respect to dietary values.…”