Limited predictive value of the IDF definition of metabolic syndrome for the diagnosis of insulin resistance measured with the oral minimal model.

AIM: To assess the agreement of the NCEP ATP-III and the IDF definitions of metabolic syndrome and to determine their predictive values for the diagnosis of insulin resistance. METHODS: For this purpose, we recruited 150 subjects (94 women and 56 men) and determined the presence of metabolic syndrome using the NCEP-ATP III and IDF definitions. We evaluated their insulin sensitivity S(I) using Caumo's oral minimal model after a standardized hyperglucidic breakfast test. Subjects whose S(I) was in the lowest quartile were considered as insulin resistant. We then calculated sensitivity, specificity, positive and negative predictive values of both definitions for the diagnosis of insulin resistance. RESULTS: The prevalence of metabolic syndrome was 37.4% (NCEP-ATP III) and 40% (IDF). Agreement between the two definitions was 96%. Using NCEP-ATP III and IDF criteria for the identification of insulin resistant subjects, sensitivity was 55.3% and 63%, specificity was 68.8% and 67.8%, positive predictive value was 37.5% and 40%, negative predictive value was 81.9% and 84.5%, respectively. Positive predictive value increased with the number of criteria for both definitions. CONCLUSION: Whatever the definition, the scoring of metabolic syndrome is not a reliable tool for the individual diagnosis of insulin resistance, and is more useful for excluding this diagnosis.

Training-induced improvement in lipid oxidation in type 2 diabetes mellitus is related to alterations in muscle mitochondrial activity. Effect of endurance training in type 2 diabetes.

AIM: We investigated whether or not, in type 2 diabetic (T2D) patients, an individualized training effect on whole-body lipid oxidation would be associated with changes in muscle oxidative capacity. METHODS: Eleven T2D patients participated in the study. Whole-body lipid oxidation during exercise was assessed by indirect calorimetry during graded exercise. Blood samples for measuring blood glucose and free fatty acids during exercise, and muscle oxidative capacity measured from skeletal muscle biopsy (mitochondrial respiration and citrate synthase activity), were investigated in the patients before and after a 10-week individualized training program targeted at LIPOXmax, corresponding to the power at which the highest rate of lipids is oxidized (lipid oxidation at LIPOXmax). RESULTS: Training induced both a shift to a higher-power intensity of LIPOXmax (+9.1+/-4.2W; P<0.05) and an improvement of lipid oxidation at LIPOXmax (+51.27+/-17.93 mg min(-1); P<0.05). The improvement in lipid oxidation was correlated with training-induced improvement in mitochondrial respiration (r=0.78; P<0.01) and citrate synthase activity (r=0.63; P<0.05). CONCLUSION: This study shows that a moderate training protocol targeted at the LIPOXmax in T2D patients improves their ability to oxidize lipids during exercise, and that this improvement is associated with enhanced muscle oxidative capacity.

Metabolic training: new paradigms of exercise training for metabolic diseases with exercise calorimetry targeting individuals.

For patients with metabolic diseases, as with other diseases, exercise training is a fully recognized therapy. Such training helps obese patients stabilize weight after slimming. For patients with type 2 diabetics, it is both a prevention and a glucose-lowering treatment and reduces health care costs. We propose a targeted training for individuals at the level of maximal lipid oxidation (LIPOXmax) with a protocol of exercise calorimetry (four 6-min workloads) based on Brooks and Mercier's crossover concept. Calorimetric interpretation of gas exchange at the fifth and sixth minutes of each stage shows a bell-shaped curve for lipid oxidation that peaks at LIPOXmax, a point that varies considerably among individuals. As well, glucose oxidation is a linear function of power (carbohydrate cost of the watt). Such a calculation predicts fairly actual lipid oxidation over 45 min at the same level. Other protocols, with 3-min workloads used in sports medicine, are not reliable for patients with metabolic diseases. For obese adults and teenagers, as well as those with type 2 diabetes, 2 months' training at the LIPOXmax (three sessions at 45 min per week) results in a net loss of fat mass, with preserved fat-free mass, and increased ability to oxidize lipids. At the end of this period, training can be "re-targeted" to be more effective and, possibly, associated with other strategies with stronger exercise intensities. Therefore, metabolic training is a viable option for patients with metabolic diseases, but the full concept is still evolving. However, the major challenge remains to transform inactive individuals into active ones.

Substrate oxidation during exercise: type 2 diabetes is associated with a decrease in lipid oxidation and an earlier shift towards carbohydrate utilization.

OBJECTIVES: Exercise is a recommended treatment for type 2 diabetes but the actual pattern of metabolic adaptation to exercise in this disease is poorly known and not taken in account in the protocols used. Metabolic defects involved in the pathways of substrate oxidation were described in type 2 diabetes. We hypothesized that type 2 diabetes, regardless of age, gender, training status and weight, could influence by its own the balance of substrates at exercise. METHODS: 30 sedentary type 2 diabetic subjects and 38 sedentary matched control subjects were recruited. We used exercise calorimetry to determine lipid and carbohydrate oxidation rates. We calculated two parameters quantifying the balance of substrates induced by increasing exercise intensity: the maximal lipid oxidation point (PLipoxMax) and the Crossover point (COP), intensity from which the part of carbohydrate utilization providing energy becomes predominant on lipid oxidation. RESULTS: Lipid oxidation was lower in the diabetic group, independent of exercise intensity. PLipoxMax and COP were lower in the diabetic group [PLipoxMax=25.3+/-1.4% vs. 36.6+/-1.7% %Wmax (P<0.0001)] - COP =24.2+/-2.2% vs. 38.8+/-1.9% %Wmax (P<0.0001). CONCLUSIONS: Type 2 diabetes is associated with a decrease in lipid oxidation at exercise and a shift towards a predominance of carbohydrate oxidation for exercise intensities lower than in control subjects. Taking into account these alterations could provide a basis for personalizing training intensity.