Effect of changing the amount and type of fat and carbohydrate on insulin sensitivity and cardiovascular risk: the RISCK (Reading, Imperial, Surrey, Cambridge, and Kings) trial.

BACKGROUND: Insulin sensitivity (Si) is improved by weight loss and exercise, but the effects of the replacement of saturated fatty acids (SFAs) with monounsaturated fatty acids (MUFAs) or carbohydrates of high glycemic index (HGI) or low glycemic index (LGI) are uncertain. OBJECTIVE: We conducted a dietary intervention trial to study these effects in participants at risk of developing metabolic syndrome. DESIGN: We conducted a 5-center, parallel design, randomized controlled trial [RISCK (Reading, Imperial, Surrey, Cambridge, and Kings)]. The primary and secondary outcomes were changes in Si (measured by using an intravenous glucose tolerance test) and cardiovascular risk factors. Measurements were made after 4 wk of a high-SFA and HGI (HS/HGI) diet and after a 24-wk intervention with HS/HGI (reference), high-MUFA and HGI (HM/HGI), HM and LGI (HM/LGI), low-fat and HGI (LF/HGI), and LF and LGI (LF/LGI) diets. RESULTS: We analyzed data for 548 of 720 participants who were randomly assigned to treatment. The median Si was 2.7 × 10(-4) mL · µU(-1) · min(-1) (interquartile range: 2.0, 4.2 × 10(-4) mL · µU(-1) · min(-1)), and unadjusted mean percentage changes (95% CIs) after 24 wk treatment (P = 0.13) were as follows: for the HS/HGI group, -4% (-12.7%, 5.3%); for the HM/HGI group, 2.1% (-5.8%, 10.7%); for the HM/LGI group, -3.5% (-10.6%, 4.3%); for the LF/HGI group, -8.6% (-15.4%, -1.1%); and for the LF/LGI group, 9.9% (2.4%, 18.0%). Total cholesterol (TC), LDL cholesterol, and apolipoprotein B concentrations decreased with SFA reduction. Decreases in TC and LDL-cholesterol concentrations were greater with LGI. Fat reduction lowered HDL cholesterol and apolipoprotein A1 and B concentrations. CONCLUSIONS: This study did not support the hypothesis that isoenergetic replacement of SFAs with MUFAs or carbohydrates has a favorable effect on Si. Lowering GI enhanced reductions in TC and LDL-cholesterol concentrations in subjects, with tentative evidence of improvements in Si in the LF-treatment group. This trial was registered at clinicaltrials.gov as ISRCTN29111298.

No difference in the 24-hour interstitial fluid glucose profile with modulations to the glycemic index of the diet.

OBJECTIVE: Reducing the glycemic index (GI) of the diet may decrease metabolic risk, primarily through reduction and stabilization of blood glucose. The objective of this research was to investigate whether incorporation of lower or higher GI foods into mixed meals had different effects on daylong glucose profiles, measured in interstitial fluid by a continuous glucose-monitoring system. METHODS: The study was a randomized, balanced, two-way crossover intervention of 2 x 1-wk periods of lower and higher GI diets. Participants were 12 overweight healthy adult women (mean body mass index +/- standard deviation 27.5+/-2.3 kg/m(2)). Changes in GI were achieved through substitution of key staple carbohydrate-rich foods. After a 4-d run-in on each dietary regimen, participants wore the continuous glucose-monitoring system over 2 d of identical controlled feeding in the laboratory, separated by 1 d of ad libitum consumption at home. RESULTS: On controlled days, diets differed in GI by 15 U and provided equal energy, macronutrients, and fiber. On ad libitum days, diet diaries revealed a difference in GI of 14+/-1 U (mean +/- standard error), with no detectable difference in energy, macronutrient, or fiber intake. No differences were observed in glucose profiles between higher and lower GI interventions in the controlled or ad libitum setting. There was significant agreement in area under the glucose curve on repeated controlled feeding days (intraclass correlation 0.75). CONCLUSION: This study indicates that a difference in dietary GI of 14-15 U is insufficient to alter daylong glycemia as measured in interstitial fluid by the continuous glucose-monitoring system.

UK Food Standards Agency Workshop Report: the effects of the dietary n-6:n-3 fatty acid ratio on cardiovascular health.

This report summarises a workshop convened by the UK Food Standards Agency (FSA) on 11 September 2006 to review the results of three FSA-funded studies and other recent research on effects of the dietary n-6:n-3 fatty acid ratio on cardiovascular health. The objective of this workshop was to reach a clear conclusion on whether or not it was worth funding any further research in this area. On the basis of this review of the experimental evidence and on theoretical grounds, it was concluded that the n-6:n-3 fatty acid ratio is not a useful concept and that it distracts attention away from increasing absolute intakes of long-chain n-3 fatty acids which have been shown to have beneficial effects on cardiovascular health. Other markers of fatty acid intake, that more closely relate to physiological function, may be more useful.

Oily fish reduces plasma triacylglycerols: a primary prevention study in overweight men and women.

OBJECTIVE: Previous studies have demonstrated benefits of high-dose long-chain omega-3 polyunsaturated fatty acid (LC omega-3 PUFA) supplements on metabolic risk. Effects of increased dietary omega-3 PUFA, via oily fish and/or plant-derived omega-3 PUFAs, are less clear and may be modulated by the omega-6:omega-3 PUFA of the habitual diet. This study examined the effect on cardiovascular disease risk markers of reducing dietary omega-6:omega-3 PUFA by changes in linoleic acid:alpha-linolenic acid (LA:LNA) and/or increasing LC omega-3 PUFA. It tested whether decreases in LA:LNA modulate effects of LC omega-3 PUFA. METHODS: One hundred forty-two subjects, recruited to a 24-wk randomized study, were assigned to a control group or one of four interventions. Intervention groups received two portions of oily fish (4.5 g eicosapentaenoic acid + docosahexanoic acid) or white fish (0.7 g eicosapentaenoic acid + docosahexanoic acid) per week, and replaced habitual household fats with ones high in sunflower (high LA:LNA) or rapeseed (low LA:LNA) oil. RESULTS: Modest dietary manipulations of omega-6 and omega-3 PUFAs resulted in significant group x time interactions for serum triacylglycerols (TAGs; P = 0.05); at 24 wk the control and two oily fish groups showed lower TAG than did the white fish/sunflower group (P = 0.05). Reductions in TAG, associated with increased oily fish intakes, were maximized when combined with lower dietary LA:LNA. There were no significant changes in several other cardiovascular disease risk markers. CONCLUSIONS: Two portions of oily fish per week led to significant reductions in TAG relative to consumption of two portions of white fish per week. Changes in TAG were maximized when combined with lower LA:LNA.