Erik Díaz

Effect of the dietary fat quality on insulin sensitivity.

Recent evidence shows that specific fatty acids affect cell metabolism, modifying the balance between fatty acid oxidation and lipogenesis. These effects may have important implications in addressing the present epidemic of nutrition-related chronic disease. Intake of dietary saturated and n-6 PUFA have increased while n-3 fatty acid intake has decreased. Obesity, type 2 diabetes and insulin resistance are highly prevalent, and both are strongly related to disorders of lipid metabolism characterized by an increased plasma and intracellular fatty acid availability. Thus, it has been hypothesized that change in the quality of dietary fat supply is able to modify the degree of insulin sensitivity. Animal studies provide support for this notion. However, there is limited human data either from normal or diabetic subjects. This review aims to analyse human studies that address this question. To this purpose, the experimental design, dietary compliance, insulin-sensitivity method used and confounding variables are discussed in order to identify the role of dietary fat quality as a risk factor for insulin resistance. Most studies (twelve of fifteen) found no effect relating to fat quality on insulin sensitivity. However, multiple study design flaws limit the validity of this conclusion. In contrast, one of the better designed studies found that consumption of a high-saturated-fat diet decreased insulin sensitivity in comparison to a high-monounsaturated-fat diet. We conclude that the role of dietary fat quality on insulin sensitivity in human subjects should be further studied, using experimental designs that address the limitations of existing data sets.

Acute effect of meal glycemic index and glycemic load on blood glucose and insulin responses in humans

ObjectiveFoods with contrasting glycemic index when incorporated into a meal, are able to differentially modify glycemia and insulinemia. However, little is known about whether this is dependent on the size of the meal. The purposes of this study were: i) to determine if the differential impact on blood glucose and insulin responses induced by contrasting GI foods is similar when provided in meals of different sizes, and; ii) to determine the relationship between the total meal glycemic load and the observed serum glucose and insulin responses.MethodsTwelve obese women (BMI 33.7 ± 2.4 kg/m2) were recruited. Subjects received 4 different meals in random order. Two meals had a low glycemic index (40–43%) and two had a high-glycemic index (86–91%). Both meal types were given as two meal sizes with energy supply corresponding to 23% and 49% of predicted basal metabolic rate. Thus, meals with three different glycemic loads (95, 45–48 and 22 g) were administered. Blood samples were taken before and after each meal to determine glucose, free-fatty acids, insulin and glucagon concentrations over a 5-h period.ResultsAn almost 2-fold higher serum glucose and insulin incremental area under the curve (AUC) over 2 h for the high- versus low-glycemic index same sized meals was observed (p < 0.05), however, for the serum glucose response in small meals this was not significant (p = 0.38). Calculated meal glycemic load was associated with 2 and 5 h serum glucose (r = 0.58, p < 0.01) and insulin (r = 0.54, p < 0.01) incremental and total AUC. In fact, when comparing the two meals with similar glycemic load but differing carbohydrate amount and type, very similar serum glucose and insulin responses were found. No differences were observed for serum free-fatty acids and glucagon profile in response to meal glycemic index.ConclusionThis study showed that foods of contrasting glycemic index induced a proportionally comparable difference in serum insulin response when provided in both small and large meals. The same was true for the serum glucose response but only in large meals. Glycemic load was useful in predicting the acute impact on blood glucose and insulin responses within the context of mixed meals.

Pilot study: alterations of intestinal microbiota in obese humans are not associated with colonic inflammation or disturbances of barrier function

Aliment Pharmacol Ther 2010; 32: 1307–1314

Glycaemic index effects on fuel partitioning in humans.

The purpose of this review was to examine the role of glycaemic index in fuel partitioning and body composition with emphasis on fat oxidation/storage in humans. This relationship is based on the hypothesis postulating that a higher serum glucose and insulin response induced by high‐glycaemic carbohydrates promotes lower fat oxidation and higher fat storage in comparison with low‐glycaemic carbohydrates. Thus, high‐glycaemic index meals could contribute to the maintenance of excess weight in obese individuals and/or predispose obesity‐prone subjects to weight gain. Several studies comparing the effects of meals with contrasting glycaemic carbohydrates for hours, days or weeks have failed to demonstrate any differential effect on fuel partitioning when either substrate oxidation or body composition measurements were performed. Apparently, the glycaemic index‐induced serum insulin differences are not sufficient in magnitude and/or duration to modify fuel oxidation.

Consequences of food energy excess and positive energy balance

This paper discusses possible consequences of energy excess throughout the life cycle. Firstly we consider the effects of foods on hunger, satiety and satiation. Also, the changes in food availability and consumption in relation to changes in social and economic determinants of energy excess. The relationship between physical activity and energy intake (EI) is also considered. Secondly we explore the definition of energy excess and the metabolic effects of macronutrients (mainly in relation to fuel partitioning oxidation/storage) on energy balance. The cellular and molecular regulation determined by specific genes involved in lipogenesis, fuel partitioning and/or in energy dissipation are explored. Thirdly, we examine the main consequences induced by energy excess and positive energy balance, starting with the alterations in glucose utilisation (insulin resistance) leading to type 2 diabetes and the linkage of energy excess with other non-communicable diseases (NCDs). Biological, social and psychological consequences during perinatal, childhood and adolescence periods are specifically analysed. Fourthly, the transition from energy deficit to excess, under the optic of a developing country is analysed with country examples drawn from Latin America. The possible role of supplementary food programmes in determining positive energy balance is discussed especially in relation to pre-school and school feeding programmes. Fifthly, we deal with the economic costs of energy excess and obesity related diseases. Finally, some areas where further research is needed are described; biological and genetic determinants of individual and population energy requirements, foods and food preparations as actually consumed, consumer education and research needs on social determinants of energy imbalances.

Effect of glycemic index on whole-body substrate oxidation in obese women

BACKGROUND:Glycemic index is hypothesized to determine fuel partitioning through serum plasma insulin modifications induced by dietary carbohydrates, thereby modulating fat accretion or oxidation.OBJECTIVE:To assess the glycemic effects on postprandial fuel oxidation and blood response.DESIGN:In all, 12 obese women were fed on a randomized crossover design with two test meals (breakfast+lunch). High- or low-glycemic meals were provided on separate days. Energy intake on high-glycemic meal was 7758±148 kJ and for low-glycemic meal was 7806±179 kJ. Carbohydrates supplied were 273±5 and 275±6 g, respectively. Macronutrient distribution was 55% carbohydrates, 30% fat and 15% protein. Fuel oxidation was measured continuously in a respiratory chamber for 10 h. Serum glucose, free fatty acids (FFA), insulin and glucagon samples were taken for 5 h after breakfast.RESULTS:Glucose AUC changed significantly in response to different glycemic breakfast. Low- vs high-glycemic breakfast was 211±84 and 379±164 mmol/l (P<0.05). Similarly, insulin changed from 94±37 and 170±87 nmol/l (P<0.05), respectively. The rate of increment for serum glucose and insulin reached by the high- vs low-glycemic meal was 1.8 times more with the high-glycemic breakfast. Serum FFA were similarly suppressed by both meal types by 3 h after meal intake, but then raised significantly more with the low-glycemic meal by the fourth and fifth hour (P<0.05). Plasma glucagon did not show a significant variation with glycemic index. Carbohydrate and fat oxidation was not modified by glycemic meal characteristics, being virtually the same for low- vs high-glycemic comparisons in the 5 h following breakfast and lunch (P=NS).CONCLUSION:This study demonstrates that dietary glycemic characteristics were unable to modify fuel partitioning in sedentary obese women.

Relationship of Adiposity and Insulin Resistance Mediated by Inflammation in a Group of Overweight and Obese Chilean Adolescents

The mild chronic inflammatory state associated with obesity may be an important link between adiposity and insulin resistance (IR). In a sample of 137 overweight and obese Chilean adolescents, we assessed associations between high-sensitivity C-reactive protein (hs-CRP), IR and adiposity; explored sex differences; and evaluated whether hs-CRP mediated the relationship between adiposity and IR. Positive relationships between hs-CRP, IR and 2 measures of adiposity were found. Hs-CRP was associated with waist circumference (WC) in boys and fat mass index (FMI) in girls. Using path analysis, we found that hs-CRP mediated the relationship between adiposity (WC and FMI) and the homeostatic model assessment of insulin resistance (HOMA-IR) (p < 0.05) in both sexes. Our novel finding is that inflammation statistically mediated the well described link between increased adiposity and IR.

Efecto residual del ejercicio de fuerza muscular en la prevención secundaria de la obesidad infantil

INTRODUCTION The high prevalence of the obesity in Chilean students (23,1%), necessitates the application of interventions that incorporate muscle strength exercise, as this shows great efficacy in obese children. OBJECTIVE To evaluate the residual effect of muscle strength exercise on body fat, metabolic syndrome and physical fitness in obese schoolchildren. METHODS The sample included 111 obese schoolchildren, between 8 and 13 years, of 3 schools in the city of Santiago. Early intervention (n = 60) participated in parallel intervention that included muscle strength exercise, nutrition education and psychological support for 3 months. The late intervention (n = 51) incorporated the first 3 months, only the educational intervention and psychological support, and exercise was added between 3 and 6 months. At 9 months post intervention, we evaluated the residual effect of exercise. Body fat was determined by anthropometric equations. The metabolic syndrome was diagnosed by the criteria of Cook. Physical fitness was assessed by the distance walked in six minutes test. RESULTS The body fat percentage decreased at the end of the intervention and post intervention increased with the exception of the men of early intervention. The distance traveled increased at the end of the intervention but declined in the post intervention. Metabolic syndrome, decreased at the end of the intervention increased post intervention (p < 0,05). CONCLUSION The sustainability of the exercise is essential to maintain the changes, which is checked to determine the residual effect of exercise on body fat, metabolic syndrome and physical condition.

Effect of the melanocortin-3 receptor Thr6Lys and Val81Ile genetic variants on body composition and substrate oxidation in Chilean obese children

Mice genetically deficient in the melanocortin-3 receptor gene are characterized by normal body weight, increased body fat, mild hypophagia, reduced locomotor activity, and increased respiratory quotient compared with wild-type mice. In humans, the 6Lys–81Ile haplotype of melanocortin-3 receptor (MC3R) gene has been associated with childhood obesity, higher body fat percentage, and reduced fat oxidation compared to non-carriers. The aim of this study was to evaluate the association between MC3R 6Lys–81Ile haplotype with body composition and substrate oxidation in response to moderate exercise in obese children. Eight Chilean obese children (aged 8–12) carriers of MC3R 6Lys–81Ile haplotype were compared with eight age–gender-matched obese non-carriers. Children were identified through a previous cross-sectional study on genetic determinants of childhood obesity (n = 229). Genotypes for MC3R Thr6Lys and Val81Ile were determined by polymerase chain reaction–restriction fragment length polymorphism. Body composition was assessed by the four-compartment model (dual-energy X-ray absorptiometry, total body water by the deuterium dilution technique, and total fat mass by air-displacement plethysmography). Substrate oxidation was assessed by indirect calorimetry in response to moderate exercise (60% VO2 max). Wilcoxon matched-pairs test was used to compare quantitative variables. No significant differences among carriers and non-carriers were found in anthropometrical and body composition measurements. The Carriers of the 6Lys–81Ile haplotype showed higher respiratory quotient (p = 0.06) and a significantly higher glucose oxidation (p = 0.01) compared with non-carriers after standardization for fat-free mass. Our results are consistent with a possible participation of MC3R 6Lys–81Ile variants in glucose oxidation in response to moderate exercise.

Plasma Arachidonic Acid Influences Insulin-Stimulated Glucose Uptake in Healthy Adult Women

Background: Fatty acids can modulate lipid metabolism, this is related to insulin resistance (IR). This study evaluated the relationship of plasma fatty acid profile with IR, fuel oxidative metabolism and plasma lipid concentration in ‘healthy’ women. Methods: Sixteen ‘healthy’, sedentary and non-obese women were evaluated under fasting conditions for fuel oxidation, plasma fatty acid profile, free fatty acids, triglycerides, glucose and insulin concentrations. IR, fuel oxidation and plasma lipids were measured under insulin-stimulated conditions. Using the Spearman test the correlation between relevant variables was assessed. Stepwise multiple regression analysis was done to identify the main clinical/metabolic and fatty acid determinants of IR. Results: Plasma arachidonic acid content (%) determined IR, and in combination with insulin-stimulated plasma triglyceride concentration explained 45% of the IR variance. IR was inversely related to physical fitness (rs = –0.48, p = 0.01). The latter was inversely associated to plasma saturated fatty acid content (%) (rs = –0.48, p < 0.01), but directly associated to plasma docosahexaenoic acid content (%) (rs = 0.40, p = 0.04). Conclusions: Support for the hypothesis that specific fatty acids influence IR is provided. Plasma arachidonic acid was associated to IR, independent on clinical/metabolic study variables. Docosahexaenoic and saturated fatty acids could potentially affect insulin action through modulating mitochondrial oxidative function.