Effects of conjugated linoleic acid plus n-3 polyunsaturated fatty acids on insulin secretion and estimated insulin sensitivity in men

Abstract

Background/Objectives: Dietary addition of either conjugated linoleic acid (CLA) or n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs) has been shown to alter adiposity and circulating lipids, risk markers of cardiovascular diseases. However, CLA may decrease insulin sensitivity, an effect that may be reversed by n-3 LC-PUFA. Thus, the potential of CLA plus n-3 LC-PUFA to affect insulin secretion and sensitivity in non-diabetic young and old, lean and obese subjects was tested. Subjects/Methods: CLA (3 g daily) plus n-3 LC-PUFA (3 g daily) or control oil (6 g daily) was given to lean (n ¼ 12; BMI 20-26 kg/m 2 ) or obese (n ¼ 10; BMI 29-35 kg/m 2 ) young (20-37 years old) or lean (n ¼ 16) or obese (n ¼ 11) older men (50-65 years) for 12 weeks. The study had a double-blind, placebo-controlled randomized crossover design, and primary end points were insulin secretion and sensitivity during a standardized meal test, evaluated by modeling glucose, insulin and C-peptide data. Results: The combination was well tolerated. There was no significant difference in fasting levels of glucose, insulin or C-peptide after CLA/n-3 LC-PUFA treatment compared with control oil. Neither insulin secretion nor estimated sensitivity was affected by CLA/n-3 LC-PUFA in lean or obese young subjects or in older lean subjects. However, in older obese subjects, estimated insulin sensitivity was reduced with CLA/n-3 LC-PUFA compared with control (P ¼ 0.024). Conclusions:The results do not support beneficial effects of CLA/n-3 LC-PUFA for b-cell dysfunction or insulin resistance in humans but suggest that insulin sensitivity in older obese subjects is reduced.

10E,12Z-conjugated linoleic acid impairs adipocyte triglyceride storage by enhancing fatty acid oxidation, lipolysis, and mitochondrial reactive oxygen species

“…However, in our study, we have shown that 7 days of 10E,12Z-CLA treatment does not induce measurable Considerable research has been done examining the delipidating effects of 10E,12Z-CLA, but with confl icting results. While a few human supplementation studies suggest that 10E,12Z-CLA induces insulin resistance ( 17,43 ), many others do not fi nd such a correlation ( 34,(44)(45)(46). Similarly, published in vitro studies present contradicting results, with some suggesting that 10E,12Z-CLA reduces glucose uptake ( 11,47 ) and others suggesting that it enhances it ( 48 ), while some suggest that 10E,12Z-CLA induces lipolysis and/or fatty acid oxidation ( 48 ), and others that it suppresses these responses ( 25,(49)(50)(51).…”

Human health effects of conjugated linoleic acid from milk and supplements

“…In contrast, a negative effect on insulin resistance was reported in type 2 diabetic patients; however, this may have been due to the bias in the glucose tolerance between the supplementation and placebo groups and may not have been due to CLA supplementation (144) . A recent study also found increased insulin resistance in older obese subjects, but no effects of combined CLA-n-3 supplementation in lean or obese younger subjects or older lean subjects (153) . Supplementation with the individual isomers, c9,t11-CLA or t10,c12-CLA increased insulin resistance (þ15%) in obese men with the metabolic syndrome (60,78) , whereas a CLA isomer mixture did not affect insulin resistance (60) .…”

“…clamp (107,153) or the oral glucose tolerance test (50,56,58,65 -67,106,154,155) . Indeed the majority of results on the anti-diabetic properties of CLA relate to studies where only fasting plasma or serum glucose or insulin have been measured, are not the main focus of the study and typically have small sample sizes.…”

Conjugated Linoleic Acids Mediate Insulin Release through Islet G Protein-coupled Receptor FFA1/GPR40

“…Although a series of studies indicates that CLAs attenuate the development of impaired glucose tolerance and hyperinsulinemia (6,10,11), an at least equal number of studies support the notion that CLA intake is associated with serious adverse effects such as impaired insulin sensitivity, and ultimately, insulin resistance (8,12,13). Importantly, the molecular mechanisms underlying the effects of CLAs on glucose homeostasis are not completely understood.…”