Marco Mensink

Protein supplementation improves physical performance in frail elderly people: a randomized, double-blind, placebo-controlled trial.

OBJECTIVES Protein supplementation has been proposed as an effective dietary strategy to increase skeletal muscle mass and improve physical performance in frail elderly people. Our objective was to assess the impact of 24 weeks of dietary protein supplementation on muscle mass, strength, and physical performance in frail elderly people. DESIGN/SETTING/PARTICIPANTS A total of 65 frail elderly subjects were included and randomly allocated to either daily protein or placebo supplementation (15 g protein at breakfast and lunch). MEASUREMENTS Skeletal muscle mass (DXA), muscle fiber size (muscle biopsy), strength (1-RM), and physical performance (SPPB) were assessed at baseline, and after 12 and 24 weeks of dietary intervention. RESULTS Skeletal muscle mass did not change in the protein- (from 45.8 ± 1.7 to 45.8 ± 1.7 kg) or placebo-supplemented group (from 46.7 ± 1.7 to 46.6 ± 1.7 kg) following 24 weeks of intervention (P > .05). In accordance, type I and II muscle fiber size did not change over time (P > .05). Muscle strength increased significantly in both groups (P < .01), with leg extension strength tending to increase to a greater extent in the protein (57 ± 5 to 68 ± 5 kg) compared with the placebo group (57 ± 5 to 63 ± 5 kg) (treatment × time interaction effect: P = .059). Physical performance improved significantly from 8.9 ± 0.6 to 10.0 ± 0.6 points in the protein group and did not change in the placebo group (from 7.8 ± 0.6 to 7.9 ± 0.6 points) (treatment × time interaction effect: P = .02). CONCLUSION Dietary protein supplementation improves physical performance, but does not increase skeletal muscle mass in frail elderly people.

Lower intrinsic ADP-stimulated mitochondrial respiration underlies in vivo mitochondrial dysfunction in muscle of male type 2 diabetic patients

OBJECTIVE—A lower in vivo mitochondrial function has been reported in both type 2 diabetic patients and first-degree relatives of type 2 diabetic patients. The nature of this reduction is unknown. Here, we tested the hypothesis that a lower intrinsic mitochondrial respiratory capacity may underlie lower in vivo mitochondrial function observed in diabetic patients. RESEARCH DESIGN AND METHODS—Ten overweight diabetic patients, 12 first-degree relatives, and 16 control subjects, all men, matched for age and BMI, participated in this study. Insulin sensitivity was measured with a hyperinsulinemic-euglycemic clamp. Ex vivo intrinsic mitochondrial respiratory capacity was determined in permeabilized skinned muscle fibers using high-resolution respirometry and normalized for mitochondrial content. In vivo mitochondrial function was determined by measuring phosphocreatine recovery half-time after exercise using 31P-magnetic resonance spectroscopy. RESULTS—Insulin-stimulated glucose disposal was lower in diabetic patients compared with control subjects (11.2 ± 2.8 vs. 28.9 ± 3.7 μmol · kg−1 fat-free mass · min−1, respectively; P = 0.003), with intermediate values for first-degree relatives (22.1 ± 3.4 μmol · kg−1 fat-free mass · min−1). In vivo mitochondrial function was 25% lower in diabetic patients (P = 0.034) and 23% lower in first-degree relatives, but the latter did not reach statistical significance (P = 0.08). Interestingly, ADP-stimulated basal respiration was 35% lower in diabetic patients (P = 0.031), and fluoro-carbonyl cyanide phenylhydrazone–driven maximal mitochondrial respiratory capacity was 31% lower in diabetic patients (P = 0.05) compared with control subjects with intermediate values for first-degree relatives. CONCLUSIONS—A reduced basal ADP-stimulated and maximal mitochondrial respiratory capacity underlies the reduction in in vivo mitochondrial function, independent of mitochondrial content. A reduced capacity at both the level of the electron transport chain and phosphorylation system underlies this impaired mitochondrial capacity.

Restoration of muscle mitochondrial function and metabolic flexibility in type 2 diabetes by exercise training is paralleled by increased myocellular fat storage and improved insulin sensitivity.

OBJECTIVE Mitochondrial dysfunction and fat accumulation in skeletal muscle (increased intramyocellular lipid [IMCL]) have been linked to development of type 2 diabetes. We examined whether exercise training could restore mitochondrial function and insulin sensitivity in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS Eighteen male type 2 diabetic and 20 healthy male control subjects of comparable body weight, BMI, age, and Vo2max participated in a 12-week combined progressive training program (three times per week and 45 min per session). In vivo mitochondrial function (assessed via magnetic resonance spectroscopy), insulin sensitivity (clamp), metabolic flexibility (indirect calorimetry), and IMCL content (histochemically) were measured before and after training. RESULTS Mitochondrial function was lower in type 2 diabetic compared with control subjects (P = 0.03), improved by training in control subjects (28% increase; P = 0.02), and restored to control values in type 2 diabetic subjects (48% increase; P < 0.01). Insulin sensitivity tended to improve in control subjects (delta Rd 8% increase; P = 0.08) and improved significantly in type 2 diabetic subjects (delta Rd 63% increase; P < 0.01). Suppression of insulin-stimulated endogenous glucose production improved in both groups (−64%; P < 0.01 in control subjects and −52% in diabetic subjects; P < 0.01). After training, metabolic flexibility in type 2 diabetic subjects was restored (delta respiratory exchange ratio 63% increase; P = 0.01) but was unchanged in control subjects (delta respiratory exchange ratio 7% increase; P = 0.22). Starting with comparable pretraining IMCL levels, training tended to increase IMCL content in type 2 diabetic subjects (27% increase; P = 0.10), especially in type 2 muscle fibers. CONCLUSIONS Exercise training restored in vivo mitochondrial function in type 2 diabetic subjects. Insulin-mediated glucose disposal and metabolic flexibility improved in type 2 diabetic subjects in the face of near–significantly increased IMCL content. This indicates that increased capacity to store IMCL and restoration of improved mitochondrial function contribute to improved muscle insulin sensitivity.

Improved skeletal muscle oxidative enzyme activity and restoration of PGC-1α and PPARβ/δ gene expression upon rosiglitazone treatment in obese patients with type 2 diabetes mellitus

Objective:To examine whether rosiglitazone alters gene expression of some key genes involved in mitochondrial biogenesis and oxidative capacity in skeletal muscle of type 2 diabetic patients, and whether this is associated with alterations in skeletal muscle oxidative capacity and lipid content.Design:Skeletal muscle gene expression, mitochondrial protein content, oxidative capacity and lipid accumulation were measured in muscle biopsies obtained from diabetic patients, before and after 8 weeks of rosiglitazone treatment, and matched controls. Furthermore, whole-body insulin sensitivity and substrate utilization were assessed.Subjects:Ten obese type 2 diabetic patients and 10 obese normoglycemic controls matched for age and BMI.Methods:Gene expression and mitochondrial protein content of complexes I–V of the respiratory chain were measured by quantitative polymerase chain reaction and Western blotting, respectively. Histochemical staining was used to quantify lipid accumulation and complex II succinate dehydrogenase (SDH) activity. Insulin sensitivity and substrate utilization were measured during a hyperinsulinemic–euglycemic clamp with indirect calorimetry.Results:Skeletal-muscle mRNA of PGC-1α and PPARβ/δ – but not of other genes involved in glucose, fat and oxidative metabolism – was significantly lower in diabetic patients (P<0.01). Rosiglitazone significantly increased PGC-1α (∼2.2-fold, P<0.01) and PPARβ/δ (∼2.6-fold, P<0.01), in parallel with an increase in insulin sensitivity, SDH activity and metabolic flexibility (P<0.01). Surprisingly, none of the measured mitochondrial proteins was reduced in type 2 diabetic patients, nor affected by rosiglitazone treatment. No alterations were seen in muscular fat accumulation upon treatment.Conclusion:These results suggest that the insulin-sensitizing effect of rosiglitazone may involve an effect on muscular oxidative capacity, via PGC-1α and PPARβ/δ, independent of mitochondrial protein content and/or changes in intramyocellular lipid.

Study on Lifestyle Intervention and Impaired Glucose Tolerance Maastricht (SLIM): preliminary results after one year

AIMS: Important risk factors for the progression from impaired glucose tolerance to type II diabetes mellitus are obesity, diet and physical inactivity. The aim of this study is to evaluate the effect of a lifestyle-intervention programme on glucose tolerance in Dutch subjects with impaired glucose tolerance (IGT).METHODS: A total of 102 subjects were studied, randomised into two groups. Subjects in the intervention group received regular dietary advice, and were stimulated to lose weight and to increase their physical activity. The control group received only brief information about the beneficial effects of a healthy diet and increased physical activity. Before and after the first year, glucose tolerance was measured and several other measurements were done.RESULTS: Body weight loss after 1 y was higher in the intervention group. The 2-h blood glucose concentration decreased 0.8±0.3 mmol/l in the intervention group and increased 0.2±0.3 mmol/l in the control group (P<0.05). Body weight loss and increased physical fitness were the most important determinants of improved glucose tolerance and insulin sensitivity.CONCLUSION: A lifestyle-intervention programme according to general recommendations is effective and induces beneficial changes in lifestyle, which improve glucose tolerance in subjects with IGT. Body weight loss and increased physical fitness were the most important determinants of improved glucose tolerance and insulin sensitivity.

Impact of 3-year lifestyle intervention on postprandial glucose metabolism: the SLIM study

Objective  To determine the effect of a 3‐year diet and exercise lifestyle intervention, based on general public health recommendations, on glucose tolerance, insulin resistance and metabolic cardiovascular risk factors in Dutch subjects with impaired glucose tolerance (IGT).

Type 2 Diabetes Mellitus and Skeletal Muscle Metabolic Function

Type 2 diabetic patients are characterized by a decreased fat oxidative capacity and high levels of circulating free fatty acids (FFAs). The latter is known to cause insulin resistance, in particularly in skeletal muscle, by reducing insulin stimulated glucose uptake, most likely via accumulation of lipid inside the muscle cell. A reduced skeletal muscle oxidative capacity can exaggerate this. Furthermore, type 2 diabetes is associated with impaired metabolic flexibility, i.e. an impaired switching from fatty acid to glucose oxidation in response to insulin. Thus, a reduced fat oxidative capacity and metabolic inflexibility are important components of skeletal muscle insulin resistance. The cause of these derangements in skeletal muscle of type 2 diabetic patients remains to be elucidated. An impaired mitochondrial function is a likely candidate. Evidence from both in vivo and ex vivo studies supports the idea that an impaired skeletal muscle mitochondrial function is related to the development of insulin resistance and type 2 diabetes mellitus. A decreased mitochondrial oxidative capacity in skeletal muscle was revealed in diabetic patients, using in vivo 31-Phosphorus Magnetic Resonance Spectroscopy (31P-MRS). However, quantification of mitochondrial function using ex vivo high-resolution respirometry revealed opposite results. Future (human) studies should challenge this concept of impaired mitochondrial function underlying metabolic defects and prove if mitochondria are truly functional impaired in insulin resistance, or low in number, and whether it represents the primary starting point of pathogenesis of insulin resistance, or is just an other feature of the insulin resistant state.

Prolonged Fasting Identifies Skeletal Muscle Mitochondrial Dysfunction as Consequence Rather Than Cause of Human Insulin Resistance

OBJECTIVE Type 2 diabetes and insulin resistance have been associated with mitochondrial dysfunction, but it is debated whether this is a primary factor in the pathogenesis of the disease. To test the concept that mitochondrial dysfunction is secondary to the development of insulin resistance, we employed the unique model of prolonged fasting in humans. Prolonged fasting is a physiologic condition in which muscular insulin resistance develops in the presence of increased free fatty acid (FFA) levels, increased fat oxidation and low glucose and insulin levels. It is therefore anticipated that skeletal muscle mitochondrial function is maintained to accommodate increased fat oxidation unless factors secondary to insulin resistance exert negative effects on mitochondrial function. RESEARCH DESIGN AND METHODS While in a respiration chamber, twelve healthy males were subjected to a 60 h fast and a 60 h normal fed condition in a randomized crossover design. Afterward, insulin sensitivity was assessed using a hyperinsulinemic-euglycemic clamp, and mitochondrial function was quantified ex vivo in permeabilized muscle fibers using high-resolution respirometry. RESULTS Indeed, FFA levels were increased approximately ninefold after 60 h of fasting in healthy male subjects, leading to elevated intramuscular lipid levels and decreased muscular insulin sensitivity. Despite an increase in whole-body fat oxidation, we observed an overall reduction in both coupled state 3 respiration and maximally uncoupled respiration in permeabilized skeletal muscle fibers, which could not be explained by changes in mitochondrial density. CONCLUSIONS These findings confirm that the insulin-resistant state has secondary negative effects on mitochondrial function. Given the low insulin and glucose levels after prolonged fasting, hyperglycemia and insulin action per se can be excluded as underlying mechanisms, pointing toward elevated plasma FFA and/or intramuscular fat accumulation as possible causes for the observed reduction in mitochondrial capacity.

Phenotyping the effect of diet on non-alcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD) is associated with the growing incidence of metabolic syndrome. Diet is an important contributor to the pathogenesis of NAFLD. In this review, we focused on recent publications reporting on the effect of macro- and micronutrients on development and progression of NAFLD. In general, saturated fat and fructose seem to stimulate hepatic lipid accumulation and progression into NASH, whereas unsaturated fat, choline, antioxidants, and high-protein diets rich in isoflavones seem to have a more preventive effect. Knowledge of the underlying mechanisms by which diet affects NAFLD is expanding, not in the least due to innovative techniques, such as genomics tools that provide detailed comprehensive information on a large high-throughput scale. Although most nutrients seem to interfere with the balance between hepatic de novo lipogenesis (endogenous synthesis of fatty acids) and lipid oxidation (burning fat for energy), there are also indications that diet can trigger or prevent hepatic lipid accumulation by influencing the interaction between liver, gut, and adipose tissue. This review now gives a current detailed overview of diet-mediated mechanisms underlying NAFLD development and progression and summarizes recent results of genomics (transcriptomics, proteomics and metabolomics) studies that contribute to improved staging, monitoring and understanding of NAFLD pathophysiology.

Impaired Skeletal Muscle Substrate Oxidation in Glucose-intolerant Men Improves After Weight Loss

Objective: An impaired fatty acid handling in skeletal muscle may be involved in the development of insulin resistance and diabetes mellitus type 2 (DM2). We investigated muscle fatty acid metabolism in glucose‐intolerant men (impaired glucose tolerance (IGT)), a prediabetic state, relative to BMI‐matched control men (normal glucose tolerance (NGT)) during fasting and after a meal, because most people in the western society are in the fed state most of the day.