Association of Serum Very-Long-Chain Saturated Fatty Acids With Changes in Insulin Sensitivity and ß-Cell Function: The Prospective Metabolism and Islet Cell Evaluation (PROMISE) Cohort.

A unique group of circulating very-long-chain saturated fatty acids (VLCSFAs), including arachidic acid (20:0), behenic acid (22:0), and lignoceric acid (24:0), have been associated with a lower risk of type 2 diabetes, although associations with early metabolic risk phenotypes preceding type 2 diabetes have received limited study. We aimed to examine the associations of VLCSFAs with longitudinal changes in insulin sensitivity and ß-cell function in a cohort at risk for type 2 diabetes. VLCSFAs in the four main serum pools (phospholipid, triacylglycerol, cholesteryl ester, and nonesterified fatty acid) were extracted from fasting baseline samples (n = 467). Generalized estimating equations were used to determine the associations between VLCSFAs and changes over 9 years in validated indices of insulin sensitivity (HOMA2-%S [insulin sensitivity as percentage of normal population and ISI) and ß-cell function (insulinogenic index [IGI], IGI divided by HOMA-insulin resistance [IGI/IR], and insulin secretion sensitivity index 2 [ISSI-2]). Associations of VLCSFAs with outcomes were strongest in the triacylglycerol lipid pool: 20:0 was positively associated with both insulin sensitivity and ß-cell function (5.01% increase in HOMA2-%S and 4.01-6.28% increase in IGI/IR and ISSI-2 per SD increase in 20:0); 22:0 was positively associated with insulin sensitivity, with a 6.55% increase in HOMA2-%S and a 5.80% increase in ISI per SD increase in 22:0. Lastly, 24:0 was positively associated with insulin sensitivity and ß-cell function (7.94-8.45% increase in HOMA2-%S and ISI, and a 4.61-6.93% increase in IGI/IR and ISSI-2 per SD increase in 24:0). Fewer significant associations were observed in the cholesteryl ester and nonesterified pools. Overall, our results indicate positive longitudinal associations of VLCSFAs with insulin sensitivity and ß-cell function, especially within the triacylglycerol pool.

Association of circulating branched chain fatty acids with insulin sensitivity and beta cell function in the PROMISE cohort.

Branched chain fatty acids (BCFAs) are mainly saturated fatty acids with a methyl branch on the penultimate or antepenultimate carbon atom. While BCFAs are endogenously produced via the catabolism of branched chain amino acids, the primary exogenous source of BCFAs in the human body is via the diet, including dairy products. Recently, BCFAs have been identified as having a potentially protective role in the etiology of cardiometabolic disorders although current literature is limited. We aimed to investigate the longitudinal associations of circulating BCFAs across four serum pools with insulin sensitivity, beta cell function, and glucose concentrations in the PROMISE Cohort. Estimates of insulin sensitivity were assessed using Matsuda's insulin sensitivity index (ISI) and the homeostasis model assessment of insulin sensitivity (HOMA2). Estimates of beta cell function were determined using the insulinogenic index divided by HOMA insulin resistance and the insulin secretion-sensitivity index-2 (ISSI-2). Baseline serum samples were analyzed for BCFAs using gas-chromatography flame ionization detection. Longitudinal associations were determined using generalized estimating equations. In the free fatty acid (FFA) pool, iso15:0 and anteiso15:0 were positively associated with logHOMA2 (iso15:0 logHOMA2-%S: ß = 6.86, 95% CI: [1.64, 12.36], p < 0.05, anteiso15:0 logHOMA2-%S: ß = 6.36, 95% CI: [0.63, 12.42], p < 0.05) while anteiso14:0 was inversely associated with measures of insulin sensitivity (iso14:0 logHOMA2-%S: ß = -2.35, 95% CI: [-4.26, -0.40], p < 0.05, logISI: ß = -2.30, 95% CI: [-4.32, -0.23], p < 0.05, anteiso14:0 logHOMA2-%S: ß = -4.72, 95% CI: [-7.81, -1.52], p < 0.05, logISI: ß = -6.13, 95% CI: [-9.49, -2.66], p < 0.01). Associations in other pools were less consistent. We identified the potential importance of specific BCFAs, specifically iso14:0, anteiso14:0, iso15:0, anteiso15:0, in cardiometabolic phenotypes underlying type 2 diabetes.

Lifestyle Factors Associated with Circulating Very Long-Chain Saturated Fatty Acids in Humans: A Systematic Review of Observational Studies.

Recent observational studies have documented inverse associations of circulating very long-chain saturated fatty acids (VLCSFAs), namely arachidic acid (20:0), behenic acid (22:0), and lignoceric acid (24:0), with cardiometabolic outcomes. In addition to their endogenous production, it has been suggested that dietary intake or an overall healthier lifestyle may influence VLCSFA concentrations; however, a systematic review of the modifiable lifestyle contributors to circulating VLCSFAs is lacking. Therefore, this review aimed to systematically assess the effects of diet, physical activity, and smoking on circulating VLCSFAs. Following registration on PROSPERO (International Prospective Register of Systematic Reviews) (ID: CRD42021233550), a systematic search of observational studies was conducted in MEDLINE, EMBASE, and The Cochrane databases up to February 2022. A total of 12 studies consisting of mostly cross-sectional analyses were included in this review. The majority of the studies documented the associations of dietary intake with total plasma or red blood cell VLCSFAs, in which a range of macronutrients and food groups were examined. Two cross-sectional analyses showed a consistent positive association between total fat and peanut intake with 22:0 and 24:0 and an inverse association between alcohol intake and 20:0 and 22:0. Furthermore, a moderate positive association between physical activity and 22:0 and 24:0 was observed. Lastly, there were conflicting results on the effects of smoking on VLCSFA. Although most studies had a low risk of bias; the findings of this review are limited by the bi-variate analyses presented in the majority of the included studies, therefore, the impact of confounding is unclear. In conclusion, although the current observational literature examining lifestyle determinants of VLCSFAs is limited, existing evidence suggests that circulating 22:0 and 24:0 may be influenced by higher total and saturated fat consumption and nut intake.

Association of branched chain fatty acids with cardiometabolic disorders in humans: a systematic review.

CONTEXT: Despite advances in treatments for cardiometabolic disorders such as type 2 diabetes mellitus and obesity, the increasing frequency of these conditions is of major clinical and public health concern. Therefore, primary prevention including diet and lifestyle approaches continues to play a key role in risk reduction. Meta-analyses of prospective cohort studies have documented inverse associations of dairy consumption with the incidence of different cardiometabolic disorders. Dairy is the largest dietary contributor of branched chain fatty acids (BCFAs), which have been suggested to not only serve as biomarkers of dairy consumption but may also have bioactive properties contributing to reducing the risk of cardiometabolic outcomes. To date, however, the literature on this topic has not been systematically reviewed. OBJECTIVE: The aim here was to report the results of a systematic review of the association of BCFAs with cardiometabolic disorders in humans. DATA SOURCES: Search terms were developed and run through the Ovid MEDLINE, Ovid Embase, and the Cochrane Library databases. DATA EXTRACTION: Articles were selected on the basis of prespecified inclusion criteria and assessed for risk of bias by independent reviewers. RESULTS: Four studies (n = 2 cross sectional; n = 1 randomized feeding trial and n = 1 pre-post study) were identified. Two studies reported significant inverse associations between serum BCFAs and insulin resistance, triglycerides and/or body mass index. One study identified an inverse association between adipose tissue monomethyl BCFAs and skeletal muscle insulin resistance. In contrast, the randomized feeding trial reported no significant differences to stool BCFA concentrations or body mass index in obese participants following assignment to fruit-vegetable or whole-grain diet groups compared with a refined-grain control group. CONCLUSIONS: Current evidence suggests beneficial associations of circulating BCFAs with cardiometabolic risk phenotypes, although data in human participants are limited, indicating that additional research is required. PROSPERO REGISTRATION NO: CRD42021224975.

Changes in adiposity mediate the associations of diet quality with insulin sensitivity and beta-cell function.

BACKGROUND AND AIMS: To examine the mediating role of adiposity on the associations of diet quality with longitudinal changes in insulin sensitivity and beta-cell function. METHODS AND RESULTS: Adults at-risk for type 2 diabetes (T2D) in the PROMISE cohort had 4 assessments over 9 years (n = 442). Alternate Healthy Eating Index (AHEI) scores were used to assess diet quality. Generalized Estimating Equations (GEE) evaluated the associations between the AHEI and longitudinal changes in insulin sensitivity (HOMA2-%S and ISI) and beta-cell function (IGI/HOMA-IR and ISSI-2). The proportion of the mediating effect of waist circumference changes was estimated using the difference method. In the primary longitudinal analysis, AHEI was positively associated with insulin sensitivity and beta-cell function over time (% difference per standard deviation increase of AHEI for HOMA2-%S (ß = 11.0, 95%CI 5.43-17.0), ISI (ß = 10.4, 95%CI 4.35-16.8), IGI/HOMA-IR (ß = 7.12, 95%CI 0.98-13.6) and ISSI-2 (ß = 4.38, 95%CI 1.05-7.80), all p < 0.05). There was no significant association between AHEI and dysglycemia incidence (OR = 0.95, 95%CI 0.77-1.17). Adjustments for longitudinal changes in waist circumference substantially attenuated all associations of AHEI with insulin sensitivity and beta-cell function. Mediation analysis indicated that waist circumference mediated 73%, 70%, 83% and 81% of the association between AHEI and HOMA2-%S, ISI, IGI/HOMA-IR, and ISSI-2, respectively (all p < 0.01). CONCLUSION: In a Canadian population at-risk for T2D, AHEI score was positively associated with changes in insulin sensitivity and beta-cell function. These associations were substantially mediated by waist circumference, suggesting that changes in adiposity may represent an important pathway linking diet quality with risk phenotypes for T2D.