Elevated intramyocellular lipid concentration in obese subjects is not reduced after diet and exercise training

To determine the effects of weight loss on intramyocellular energy substrates, vastus lateralis muscle biopsies were taken from six obese subjects (body mass index 34 +/- 5 kg/m(2)) before, after 15 wk of energy restriction (ER; -700 kcal/day), and after a further average 20.7 +/- 1.6 wk of endurance training plus low-fat diet (ET-LFD). Body weight fell from 100 +/- 6 to 89 +/- 6 kg during ER and to 84 +/- 4 kg after ET-LFD. Lipids and glycogen were histochemically measured in type I, IIA, and IIB fibers. Total muscle glycogen content (MGC; per 100 fibers) decreased after ER [from 72 +/- 13 to 55 +/- 8 arbitrary units (AU)]. A similar but not significant decrease was seen in total muscle lipid content (MLC; 14 +/- 5 to 9 +/- 1 AU). After ET-LFD, MGC returned to initial values (74 +/- 8 AU), and MLC approached near-initial values (12 +/- 3 AU). Individual fiber lipid concentration did not change throughout the protocol in all fiber types, whereas glycogen concentration increased after ET-LFD. The training effects of ET-LFD were measured as increasing activities of key mitochondrial enzymes. Although total muscle energy reserves can be reduced after weight loss, their concentration within individual myofibers remains elevated. Weight loss does not appear sufficient to correct the potential detrimental effects of high intracellular lipid concentrations.     

Additive effects of training and high-fat diet on energy metabolism during exercise

This study was conducted to obtain additional information about the adaptations after 12 wk of high-fat diet (HFD) per se or HFD combined with endurance training in the rat using a two [diet: carbohydrate (CHO) or HFD] by two (training: sedentary or trained) by two (condition at death: rested or exercised) factorial design. Adaptation to prolonged HFD increases maximal O2 uptake (VO2max; 13%, P less than 0.05) and submaximal running endurance (+64%, P less than 0.05). This enhancement in exercise capacity could be attributed to 1) an increase in skeletal muscle aerobic enzyme activities (3-hydroxyacyl-CoA dehydrogenase and citrate synthase in soleus and red quadriceps) or 2) a decrease in liver glycogen breakdown in response to 1 h exercise at 80% VO2max. When training is superimposed to HFD, the most prominent finding provided by this study is that the diet-induced effects are cumulative with the well-known training effect on VO2max, exercise endurance, oxidative capacity of red muscle, and metabolic responses to exercise, with a further reduction in liver glycogen breakdown.     

High-fat hypocaloric diet modifies carbohydrate utilization of obese rats during weight loss

The effects of fat content in the hypocaloric diet on whole body glucose oxidation and adipocyte glucose transport were investigated in two animal-feeding experiments. Diet-induced obese rats were food restricted to 75% of their previous energy intakes with either a high (45% by calorie) or a low (12% by calorie) corn oil diet for 9 wk (experiment 1) or 10 days (experiment 2). The losses of body weight (P < 0.05) and adipose depot weight (P < 0.05) were less in the 45% compared with the 12% fat group. During the dynamic phase of weight loss (day 10 of food restriction), plasma glucose and insulin concentrations were higher (P < 0.05) in the 45% than those in the 12% fat group. Whole body carbohydrate oxidation rate in response to an oral load of glucose was increased (P < 0.001) by food restriction in both dietary groups; however, carbohydrate oxidation rates were lower (P < 0.01) in the 45% than in the 12% fat-fed rats during the weight loss period. Adipocyte glucose transport was greater (P < 0.02) in the 45% than in the 12% fat group in an intra-abdominal adipose depot but not in subcutaneous fat. These data suggest that dietary fat content modifies whole body glucose oxidation and intra-abdominal adipocyte glucose uptake during weight loss.     

High-fat diet elevates resting intramuscular triglyceride concentration and whole body lipolysis during exercise

This study determined the role of intramuscular triglyceride (IMTG) and adipose lipolysis in the elevated fat oxidation during exercise caused by a high-fat diet. In four separate trials, six endurance-trained cyclists exercised at 50% peak O2 consumption for 1 h after a two-day control diet (22% fat, CON) or an isocaloric high-fat diet (60% fat, HF) with or without the ingestion of acipimox, an adipose lipolysis inhibitor, before exercise. During exercise, HF elevated fat oxidation by 72% and whole body lipolysis [i.e., the appearance rate of glycerol in plasma (Ra glycerol)] by 79% compared with CON (P < 0.05), and this was associated with a 36% increase (P < 0.05) in preexercise IMTG concentration. Although acipimox lowered plasma free fatty acid (FFA) availability, HF still increased fat oxidation and Ra glycerol to the same magnitude above control as the increase caused by HF without acipimox (i.e., both increased fat oxidation 13-14 micromol.kg(-1).min(-1)). In conclusion, the marked increase in fat oxidation after a HF diet is associated with elevated IMTG concentration and whole body lipolysis and does not require increased adipose tissue lipolysis and plasma FFA concentration during exercise. This suggests that altered substrate storage in skeletal muscle is responsible for increased fat oxidation during exercise after 2 days of an HF diet.     

Muscle triglyceride utilization during exercise: effect of training

The respiratory exchange ratio (RER) is lower during exercise of the same intensity in the trained compared with the untrained state, even though plasma free fatty acids (FFA) and glycerol levels are lower, suggesting reduced availability of plasma FFA. In this context, we evaluated the possibility that lipolysis of muscle triglycerides might be higher in the trained state. Nine adult male subjects performed a prolonged bout of exercise of the same absolute intensity before and after adapting to a strenuous 12-wk program of endurance exercise. The exercise test required 64% of maximum O2 uptake before training. Plasma FFA and glycerol concentrations and RER during the exercise test were lower in the trained than in the untrained state. The proportion of the caloric expenditure derived from fat, calculated from the RER, during the exercise test increased from 35% before training to 57% after training. Muscle glycogen utilization was 41% lower, whereas the decrease in quadriceps muscle triglyceride concentration was roughly twice as great (12.7 +/- 5.5 vs. 26.1 +/- 9.3 mmol/kg dry wt, P less than 0.001) in the trained state. These results suggest that the greater utilization of FFA in the trained state is fueled by increased lipolysis of muscle triglyceride.     

Influence of endurance exercise training and sex on intramyocellular lipid and mitochondrial ultrastructure, substrate use, and mitochondrial enzyme activity

Impaired mitochondrial function and structure and intramyocellular lipid (IMCL) accumulation have been associated with obesity and Type 2 diabetes. We examined whether endurance exercise training and sex influenced IMCL and mitochondrial morphology using electron microscopy, whole-body substrate use, and mitochondrial enzyme activity. Untrained men (n = 5) and women (n = 7) were tested before and after 7 wk of endurance exercise training. Testing included 90 min of cycle ergometry at 60% Vo(2 peak) with preexercise muscle biopsies analyzed for IMCL and mitochondrial size/area using electron microscopy and short-chain beta-hydroxyacyl-CoA dehydrogenase (SCHAD) and citrate synthase (CS) enzyme activity. Training increased the mean lipid area density (P = 0.090), the number of IMCL droplets (P = 0.055), the number of IMCL droplets in contact with mitochondria (P = 0.010), the total mitochondrial area (P < 0.001), and the size of individual mitochondrial fragments (P = 0.006). Women had higher mean lipid area density (P = 0.030) and number of IMCL droplets (P = 0.002) before and after training, but higher individual IMCL area only before training (P = 0.013), compared with men. Women oxidized more fat (P = 0.027) and less carbohydrate (P = 0.032) throughout the study. Training increased Vo(2 peak) (P < 0.001), %fat oxidation (P = 0.018), SCHAD activity (P = 0.003), and CS activity (P = 0.042). In summary, endurance exercise training increased IMCL area density due to an increase in the number of lipid droplets, whereas the increase in total mitochondrial area was due to an increase in the size of individual mitochondrial fragments. In addition, women have higher IMCL content compared with men due mainly to a greater number of individual droplets. Finally, endurance exercise training increased the proportion of IMCL in physical contact with mitochondria.     

High-fat diet effects on gut motility,hormone, and appetite responses to duodenal lipid in healthy men

There is evidence that gastrointestinal function adapts in response to a high-fat (HF) diet. This study investigated the hypothesis that an HF diet modifies the acute effects of duodenal lipid on appetite, antropyloroduodenal pressures, plasma CCK and plasma glucagon-like peptide-1 (GLP-1) levels in humans. Twelve healthy men were studied twice in randomized, crossover fashion. The effects of a 90-min duodenal lipid infusion (6.3 kJ/min) on the above parameters were assessed immediately following 14-day periods on either an HF or a low-fat (LF) diet. After the HF diet, pyloric tonic and phasic pressures were attenuated, and the number of antropyloroduodenal pressure-wave sequences was increased when compared with the LF diet. Plasma CCK and GLP-1 levels did not differ between the two diets. Hunger was greater during the lipid infusion following the HF diet, but there was no difference in food intake. Therefore, exposure to an HF diet for 14 days attenuates the effects of duodenal lipid on antropyloroduodenal pressures and hunger without affecting food intake or plasma hormone levels.     

Evaluation of intramyocellular lipid breakdown during exercise by biochemical assay, NMR spectroscopy, and Oil Red O staining

The study compared the net decline of intramyocellular lipids (IMCL) during exercise (n = 18) measured by biochemical assay (BIO) and Oil Red O (ORO) staining on biopsy samples from vastus lateralis muscle and by (1)H-MR spectroscopy (MRS) sampled in an 11 x 11 x 18-mm(3) voxel in the same muscle. IMCL was measured before and after a 2-h cycling bout ( approximately 75% V(.)(O(2) peak)). ORO and MRS measurements showed substantial IMCL use during exercise of 31 +/- 12 and 47 +/- 6% of preexercise IMCL content. In contrast, use of BIO for IMCL determination did not reveal an exercise-induced breakdown of IMCL (2 +/- 9%, P = 0.29) in young healthy males. Correlations between different measures of exercise-induced IMCL degradation were low. Coefficients were 0.48 for MRS vs. ORO (P = 0.07) and were even lower for BIO vs. MRS (r = 0.38, P = 0.13) or ORO (r = 0.08, P = 0.78). This study demonstrates that different methods to measure IMCL in human muscles can result in different conclusions with regard to exercise-induced IMCL changes. MRS has the advantage that it is noninvasive, however, not fiber type specific and hampered by an at least 30-min delay in measurements after exercise completion and may overestimate IMCL use. BIO is the only quantitative method but is subject to variation when biopsies have different fiber type composition. However, BIO yields lower IMCL breakdown compared with ORO and MRS. ORO has the major advantage that it is fiber type specific, and it therefore provides information that is not available with the other methods.     

Substrate utilization during endurance exercise in men and women after endurance training

We investigated the effect of endurance training on whole body substrate, glucose, and glycerol utilization during 90 min of exercise at 60% peak O2 consumption (VO2(peak)) in males and females. Substrate oxidation was determined before and after 7 wk of endurance training on a cycle ergometer, with posttesting performed at the same absolute (ABS, W) and relative (REL, VO2(peak)) intensities. [6,6-2H]glucose and [1,1,2,3,3-2H]glycerol tracers were used to calculate the respective substrate tracee flux. Endurance training resulted in an increase in VO2(peak) for both males and females of 17 and 22%, respectively (P < 0.001). Females demonstrated a lower respiratory exchange ratio (RER) both pretraining and posttraining compared with males during exercise (P < 0.001). Glucose rate of appearance (R(a)) and rate of disappearance (R(d)) were not different between males and females. Glucose metabolic clearance rate (MCR) was lower at 75 and 90 min of exercise for females compared with males (P < 0.05). Glucose R(a) and R(d) were lower during exercise at both ABS and REL posttraining exercise intensities compared with pretraining (P < 0.001). Females had a higher exercise glycerol R(a) and R(d) compared with males both pre- and posttraining (P < 0.001). Glycerol R(a) was not different at either the ABS or REL posttraining exercise intensities compared with pretraining. We concluded that females oxidize proportionately more lipid and less carbohydrate during exercise compared with males both pre- and posttraining, which was cotemporal with a higher glycerol R(a) in females. Furthermore, endurance training resulted in a decrease in glucose flux at both ABS and REL exercise intensities after endurance exercise training.     

The effects of diet on muscle pH and metabolism during high intensity exercise

Five healthy male subjects exercised for 3 min at a workload equivalent to 100% VO2max on two separate occasions. Each exercise test was performed on an electrically braked cycle ergometer after a four-day period of dietary manipulation. During each of these periods subjects consumed either a low carbohydrate (3 +/- 0%, mean +/- SD), high fat (73 +/- 2%), high protein (24 +/- 3%) diet (FP) or a high carbohydrate (82 +/- 1%), low fat (8 +/- 1%) low protein (10 +/- 1%) diet (CHO). The diets were isoenergetic and were assigned in a randomised manner. Muscle biopsy samples (Vastus lateralis) were taken at rest prior to dietary manipulation, immediately prior to exercise and immediately post-exercise for measurement of pH, glycogen, glucose 6-phosphate, fructose 1,6-diphosphate, triose phosphates, lactate and glutamine content. Blood acid-base status and selected metabolites were measured in arterialised venous samples at rest prior to dietary manipulation, immediately prior to exercise and at pre-determined intervals during the post-exercise period. There was no differences between the two treatments in blood acid-base status at rest prior to dietary manipulation; immediately prior to exercise plasma pH (p less than 0.01), blood PCO2 (p less than 0.01), plasma bicarbonate (p less than 0.001) and blood base-excess (p less than 0.001) values were all lower on the FP treatment. There were no major differences in blood acid-base variables between the two diets during the post-exercise period.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of endurance training and thiamine supplementation on anti-fatigue during exercise

The purpose of this study was to find the effect of endurance training and thiamine supplementation on anti-fatigue during the exercise. Each nine students from K Women’s University went through three cross-over treatments: placebo treatment, training treatment and thiamine treatment. Training treatment was performed with bicycle ergometer exercise for four weeks (five days per week). Each exercise was performed for an hour with intensity set at 70% (50rpm) of maximal oxygen uptake. Thiamine treatment group was given 10mg of thiamine tetrahydrofurfuryl disulfide per one kilogram for four weeks. The bicycle ergometer exercise was performed at 70% of maximal oxygen uptake in exercise intensity which 60 minutes of exercise was performed at 50rpm . Lactate concentration was significantly decreased during 15 to 30 minutes of exercise for those with training treatment and 15 to 60 minutes of exercise for those with thiamine treatment compared to placebo treatment group. Ammonia concentration was significantly decreased during 15 to 60 minutes of exercise and 15 to 30 minutes of recovery for those with training and thiamine treatment compared to placebo treatment. Resting blood thiamine concentrations of placebo treatment were significantly lower than training treatment. 60 minutes after the exercise, plasma thiamine concentration was significantly increased in all treatment group. To sum up the previous, thiamine intake during exercise positively benefits carbohydrate metabolism in a way that will decrease lactate concentration, ammonia concentration, and anti- fatigue by reducing the RPE. Therefore, we can consider thiamine intake to be utilized as similar benefits as endurance training.     

Age and training effects on the lactate kinetics of master athletes during maximal exercise

To study the effects of age and training on lactate production in older trained subjects, the lactate kinetics of highly trained cyclists [HT, n = 7; 65 (SEM 1.2) years] and control subjects with low training (LT, n = 7) and of similar age were compared to those of young athletes [YA, n = 7; 26 (SEM 0.7) years], during an incremental exercise test to maximum power. The results showed that the lactacidaemia at maximal oxygen uptake (VO2max) was lower for HT than for LT (P < 0.05) and, in both cases, lower than that of YA (P < 0.001). The respective values were HT: 3.9 (SEM 0.51), LT: 5.36 (SEM 1.12), and YA: 10.3 (SEM 0.63) mmol.l-1. At submaximal powers, however, the difference in lactacidaemia was not significant between HT and YA, although the values for lactacidaemia at VO2max calculated per watt and per watt normalized by body mass were significantly lower for HT (P < 0.001) and LT (P < 0.02). These results would indicate that the decline in power with age induced a decline in lactacidaemia. Yet this loss in power was not the only causative factor; indeed, our results indicated a complementary metabolic influence. In the older subjects training decreased significantly the lactacidaemia for the same submaximal power (P < 0.01) and from 60% of VO2max onwards (P < 0.05); as for YA it postponed the increase and accumulation of lactates. The lactate increase threshold (Thla-,1) was found at 46% VO2max for LT and at 56% VO2max for HT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Green tea extract improves running endurance in mice by stimulating lipid utilization during exercise

A series of polyphenols known as catechins are abundant in green tea, which is consumed mainly in Asian countries. The effects of catechin-rich green tea extract (GTE) on running endurance and energy metabolism during exercise in BALB/c mice were investigated. Mice were divided into four groups: nonexercise control, exercise control (Ex-cont), exercise+0.2% GTE, and exercise+0.5% GTE groups. Treadmill running time to exhaustion, plasma biochemical parameters, skeletal muscle glycogen content, beta-oxidation activity, and malonyl-CoA content immediately after exercise were measured at 8-10 wk after the initiation of the experiment. Oxygen consumption and respiratory exchange ratio were measured using indirect calorimetry. Running times to exhaustion in mice fed 0.5% GTE were 30% higher than in Ex-cont mice and were accompanied by a lower respiratory exchange ratio, higher muscle beta-oxidation activity, and lower malonyl-CoA content. In addition, muscle glycogen content was high in the GTE group compared with the Ex-cont group. Plasma lactate concentrations in mice fed GTE were significantly lower after exercise, concomitant with an increase in free fatty acid concentrations. Catechins, which are the main constituents of GTE, did not show significant effects on peroxisome proliferator-activated receptor-alpha or delta-dependent luciferase activities. These results suggest that the endurance-improving effects of GTE were mediated, at least partly, by increased metabolic capacity and utilization of fatty acid as a source of energy in skeletal muscle during exercise.     

Effects of rosiglitazone on intramyocellular lipid accumulation in Psammomys obesus

Objective: To examine the effects of rosiglitazone in intramyocellular lipid (IMCL) content in diabetic Psammomys obesus using novel electron microscopy technologies. Background: P. obesus is an unique polygenic model of obesity and type 2 diabetes. Male diabetic P. obesus were treated daily with 5 mg/Kg Rosiglitazone by oral gavage for 14 days. Data were compared with a group of age-matched diabetic P. obesus treated with saline vehicle. Methods: Assessment of insulin resistance and adiposity were determine before and after the treatment period by oral glucose tolerance test (oGTT) and dual energy X-ray absorptiometry (DEXA) analysis. We used a new scanning electron microscopy technology, (WETSEM) to investigate the effects of rosiglitazone administration on IMCL content, size and distribution in red gastrocnemius muscle. Results: Rosiglitazone treatment improved glucose tolerance in P. obesus with no difference in the overall body fat content although a significant reduction in subscapular fat mass was observed. Rosiglitazone changed the distribution of lipid droplet size in skeletal muscle. Treated animals tended to have smaller lipid droplets compared with saline-treated controls. Conclusions: Since smaller IMCL droplets are associated with improvements in insulin sensitivity, we propose that this may be an important mechanism by which rosiglitazone affects glucose tolerance.     

Twitch potentiation during fatiguing exercise in the elderly: the effects of training.

Twitch potentiation was studied during a fatigue paradigm involving intermittent maximum voluntary contractions (MVCs) of the tibialis anterior muscle in the elderly and in young adults. Resting twitch torques were similar between groups, but twitch potentiation was significantly greater (241% vs 166%) in the young; the recovery of the twitch after fatigue was similar between groups. Contraction time, time to peak torque and half-relaxation time were all significantly slower in the elderly. Following 12 weeks of resistance training in the elderly, there was no significant change in the twitch contractile properties at rest, but there was a significant main effect of training on the degree of twitch potentiation during the same fatigue protocol (peak potentiation 192% post-training vs 165% pretraining). These data suggest that the mechanism(s) responsible for twitch potentiation following MVCs may be influenced by both aging and training.     

High-fat diet offsets the long-lasting effects of running-wheel access on food intake and body weight in OLETF rats

We have previously demonstrated that running-wheel access normalizes the food intake and body weight of Otsuka Long-Evens Tokushima Fatty (OLETF) rats. Following 6 wk of running-wheel access beginning at 8 wk of age, the body weight of OLETF rats remains reduced, demonstrating a lasting effect on their phenotype. In contrast, access to a high-fat diet exacerbates the hyperphagia and obesity of OLETF rats. To determine whether diet modulates the long-term effects of exercise, we examined the effects of high-fat diet on food intake and body weight in OLETF rats that had prior access to running wheels for 4 wk. We found that 4 wk of running exercise significantly decreased food intake and body weight of OLETF rats. Consistent with prior results, 4 wk of exercise also produced long-lasting effects on food intake and body weight in OLETF rats fed a regular chow. When running wheels were relocked, OLETF rats stabilized at lower levels of body weight than sedentary OLETF rats. However, access to a high-fat diet offset these effects. When OLETF rats were switched to a high-fat diet following wheel relocking, they significantly increased food intake and body weight, so that they reached levels similar to those of sedentary OLETF rats fed a high-fat diet. Gene expression determination of hypothalamic neuropeptides revealed changes that appeared to be appropriate responses to the effects of diet and running exercise. Together, these results demonstrate that high-fat diet modulates the long-lasting effects of exercise on food intake and body weight in OLETF rats.     

Effect of high-intensity exercise and high-fat diet on lipid metabolism in the liver of rats

[Purpose]

This study investigated the effects of high-intensity exercise (Ex) and high dietary fat intake on lipid metabolism in the liver of rats.

[Methods]

Male Sprague-Dawley rats were randomly assigned to one of the four groups (n=10 per group) that were maintained on a normal diet (ND) or high-fat diet (HFD) consisting of 30% fat (w/w), with or without exercise on a treadmill at 30 m/min and 8% grade) for 4 weeks (i.e., ND, ND+Ex, HFD, and HFD+Ex groups).

[Results]

Body weight (p<.001), total plasma cholesterol (TC) (p<.001), triglyceride (TG) (p<.05), and liver TG levels (p<.05) were increased in the HFD group relative to the ND groups, and serum glucose (p<.05), insulin (p<.05), homeostatic model assessment of insulin resistance (HOMA-IR) (p<.01), and liver TG levels (p<.01) were also higher in the HFD group compared to the ND+Ex group. Plasma free fatty acid was elevated in the HFD+Ex group compared to the HFD group (p<.01). With the exception of acetyl coenzyme A carboxylase, the expression of lipid metabolism-related genes in the liver was altered in the Ex groups compared to the control group (p<.05), with genes involved in lipolysis specifically up regulated in the HFD+Ex group compared to the other groups.

[Conclusion]

Vigorous exercise may increase glucose utilization and fat oxidation by activating genes in the liver that are associated with lipid metabolism compared to that in animals consuming a HFD without exercise. Therefore, high intensity exercise can be considered to counter the adverse effects of high dietary fat intake.