Effects of a 10-Week Exercise and Nutritional Intervention with Variable Dietary Carbohydrates and Glycaemic Indices on Substrate Metabolism, Glycogen Storage, and Endurance Performance in Men: A Randomized Controlled Trial

BACKGROUND

Daily nutrition plays an important role in supporting training adaptions and endurance performance. The objective of this 10-week study was to investigate the consequences of varying carbohydrate consumption and the glycaemic index (GI) together with an endurance training regimen on substrate oxidation, muscle energy storage and endurance performance under free-living conditions. Sixty-five moderately trained healthy men (29 ± 4 years; VO2 peak 55 ± 8 mL min-1 kg-1) were randomized to one of three different nutritional regimes (LOW-GI: 50-60% CHO with ≥ 65% of these CHO with GI < 50 per day, n = 24; HIGH-GI: 50-60% CHO with ≥ 65% CHO with GI > 70 per day, n = 20; LCHF: ≤ 50 g CHO daily, n = 21). Metabolic alterations and performance were assessed at baseline (T0) and after 10 weeks (T10) during a graded exercise treadmill test. Additionally, a 5 km time trial on a 400-m outdoor track was performed and muscle glycogen was measured by magnet resonance spectroscopy.

RESULTS

Total fat oxidation expressed as area under the curve (AUC) during the graded exercise test increased in LCHF (1.3 ± 2.4 g min-1 × km h-1, p < 0.001), remained unchanged in LOW-GI (p > 0.05) and decreased in HIGH-GI (- 1.7 ± 1.5 g min-1 × km h-1, p < 0.001). After the intervention, LOW-GI (- 0.4 ± 0.5 mmol L-1 × km h-1, p < 0.001) and LCHF (- 0.8 ± 0.7 mmol L-1 × km h-1, p < 0.001) showed significantly lower AUC of blood lactate concentrations. Peak running speed increased in LOW-GI (T0: 4.3 ± 0.4 vs. T10: 4.5 ± 0.3 m s-1, p < 0.001) and HIGH-GI (T0: 4.4 ± 0.5 vs. T10: 4.6 ± 0.4 m s-1), while no improvement was observed in LCHF. Yet, time trial performance improved significantly in all groups. Muscle glycogen content increased for participants in HIGH-GI (T0: 97.3 ± 18.5 vs. T10: 144.5 ± 39.8 mmol L wet-tissue-1, p = 0.027) and remained unchanged in the LOW-GI and the LCHF group. At the last examination, muscle glycogen concentration was significantly higher in LOW-GI compared to LCHF (p = 0.014).

CONCLUSION

Changes in fat oxidation were only present in LCHF, however, lower lactate concentrations in LOW-GI resulted in changes indicating an improved substrate metabolism. Compared to a LCHF diet, changes in peak running speed, and muscle glycogen stores were superior in LOW- and HIGH-GI diets. The low GI diet seems to have an influence on substrate metabolism without compromising performance at higher intensities, suggesting that a high-carbohydrate diet with a low GI is a viable alternative to a LCHF or a high GI diet.

TRIAL REGISTRATION

Clinical Trials, NCT05241730. https://clinicaltrials.gov/study/NCT05241730 . Registered 25 January 2021.

Two weeks of single-leg immobilization alters intramyocellular lipid storage characteristics in healthy, young women

Muscle disuse rapidly induces insulin resistance (IR). Despite a relationship between intramyocellular lipid (IMCL) content and IR, during muscle-disuse IR develops before IMCL accumulation, suggesting that IMCL are not related to disuse-induced IR. However, recent studies show that it is not total IMCL content, but IMCL size and location that are related to IR. Changes in these IMCL parameters may occur prior to increases in IMCL content, thus contributing to disuse-induced IR. Omega-3 fatty acids may mitigate the effects of disuse on IR by preventing a decline in insulin signaling proteins. Twenty women (age 22 ± 3 yr) received either 5 g·day^-1 omega-3 fatty acid or isoenergetic sunflower oil for 4 wk prior to, throughout 2 wk of single-leg immobilization, and during 2 wk of recovery. Changes in IMCL characteristics and insulin signaling proteins were examined in vastus lateralis samples taken before supplementation and immobilization, and following immobilization and recovery. Omega-3 supplementation had no effect. IMCL area density decreased in the subsarcolemmal region during immobilization and recovery (-19% and -56%, respectively, P = 0.009). IMCL size increased in the central intermyofibrillar region during immobilization (43%, P = 0.007), returning to baseline during recovery. PLIN5 and AKT increased during immobilization (87%, P = 0.002; 30%, P = 0.007, respectively). PLIN 5 remained elevated and AKT increased further (15%) during recovery. IRS1, AS160, and GLUT4 decreased during immobilization (-35%, P = 0.001; -44%, P = 0.03; -56%, P = 0.02, respectively), returning to baseline during recovery. Immobilization alters IMCL storage characteristics while negatively affecting unstimulated insulin signaling protein content in young women.NEW & NOTEWORTHY We report that the subcellular storage location of IMCL is altered by limb immobilization, highlighting the need to evaluate IMCL storage location when assessing the effects of disuse on IMCL content. We also found that AKT content increased during immobilization in our female population, contrary to studies in males finding that AKT decreases during disuse, highlighting that men and women may respond differently to disuse and the necessity to include women in all research.

Differences between muscle from osteoporotic and osteoarthritic subjects: in vitro study by diffusion-tensor MRI and histological findings

BACKGROUND

Osteoarthritis and osteoporosis are strongly coupled with alterations of muscles quality and fats metabolism. However, there are no studies for investigating possible differences between osteoporotic and osteoarthritic muscles. Understanding muscle-bone and muscle-cartilage interactions would be of high clinical value.

AIM

Investigate potential microstructural and physiological differences between osteoporotic and osteoarthritic muscles by diffusion Nuclear Magnetic Resonance (NMR) imaging (diffusion MRI) and histological findings.

METHODS

Vastus-lateralis muscles excised from osteoporotic (n = 26, T Score <  - 2.5, Kellgren-Lawrence ≤ 2) and osteoarthritic (n = 26, T Score >  - 2.5, Kellgren--Lawrence 3 and 4) age-matched women were investigated by NMR relaxometry, diffusion-tensor imaging (DTI) at 9.4 T, and histological techniques. Intramyocellular (IMCL) and extramyocellular (EMCL) lipid were quantified. The percentage and mean diameters of fibers I and II were evaluated. Relationship between mean diffusivity (MD), fractional anisotropy (FA), the DTI eigenvalues (λ₁, λ₂, λ₃), histological findings in muscles and clinical data (Kellgren-Lawrence and T score, age, menopausal age, body mass index) were studied. Pairwise comparisons between groups were made using one-way analysis of variance and correlation between variables was assessed with linear correlation analysis (Pearson's r coefficient).

RESULTS

Osteoporotic muscles showed higher MD, λ_1, λ₂, λ₃ compared to osteoarthritis ones. This is explainable with a significant higher density of IMCL droplets found inside the osteoarthritic muscles and a large amount of fibrotic tissue and IMCL infiltration between fibers, i.e. in endomysium and perimysium that lead to a more hindered diffusion. Furthermore, histological analysis suggests mitochondrial degeneration as the origin of the greatest amount of IMCL droplets in osteoarthritic muscles.

CONCLUSION

This work highlights differences between muscles of osteoporotic and osteoarthritic subjects that can be quantified by NMR DTI investigations.

Fat-water separation by fast metabolite cycling magnetic resonance spectroscopic imaging at 3 T: A method to generate separate quantitative distribution maps of musculoskeletal lipid components

PURPOSE

To provide a rapid, noninvasive fat-water separation technique that allows producing quantitative maps of particular lipid components.

METHODS

The calf muscles in 5 healthy adolescents (age 12-16 years; body mass index = 20 ± 3 kg/m² ) were scanned by two different fat fraction measurement methods. A density-weighted concentric-ring trajectory metabolite-cycling MRSI technique was implemented to collect data with a nominal resolution of 0.25 mL within 3 minutes and 16 seconds. For comparative purposes, the standard Dixon technique was performed. The two techniques were compared using structural similarity analysis. Additionally, the difference in the distribution of each lipid over the adolescent calf muscles was assessed based on the MRSI data.

RESULTS

The proposed MRSI technique provided individual fat fraction maps for eight musculoskeletal lipid components identified by LCModel analysis (IMC/L [CH₃ ], EMCL [CH₃ ], IMC/L [CH₂ ]_n , EMC/L [CH₂ ]_n , IMC/L [CH₂ -CH], EMC/L [CH₂ -CH], IMC/L [-CH=CH-], and EMC/L [-CH=CH-]) with mean structural similarity indices of 0.19, 0.04, 0.03, 0.50, 0.45, 0.04, 0.07, and 0.12, respectively, compared with the maps generated by the used Dixon method. Further analysis of voxels with zero structural similarity demonstrated an increased sensitivity of fat fraction lipid maps from the data acquired using this MRSI technique over the standard Dixon technique. The lipid spatial distribution over calf muscles was consistent with previously published findings in adults.

CONCLUSION

This MRSI technique can be a useful tool when individual lipid fat fraction maps are desired within a clinically acceptable time and with a nominal spatial resolution of 0.25 mL.

Local In Vivo Measures of Muscle Lipid and Oxygen Consumption Change in Response to Combined Vitamin D Repletion and Aerobic Training in Older Adults

Intramyocellular (IMCL), extramyocellular lipid (EMCL), and vitamin D deficiency are associated with muscle metabolic dysfunction. This study compared the change in [IMCL]:[EMCL] following the combined treatment of vitamin D and aerobic training (DAT) compared with vitamin D (D), aerobic training (AT), and control (CTL). Male and female subjects aged 60–80 years with a BMI ranging from 18.5–34.9 and vitamin D status of ≤32 ng/mL (25(OH)D) were recruited to randomized, prospective clinical trial double-blinded for supplement with a 2 × 2 factorial design. Cholecalciferol (Vitamin D₃) (10,000 IU × 5 days/week) or placebo was provided for 13 weeks and treadmill aerobic training during week 13. Gastrocnemius IMCL and EMCL were measured with magnetic resonance spectroscopy (MRS) and MRI. Hybrid near-infrared diffuse correlation spectroscopy measured hemodynamics. Group differences in IMCL were observed when controlling for baseline IMCL (p = 0.049). DAT was the only group to reduce IMCL from baseline, while a mean increase was observed in all other groups combined (p = 0.008). IMCL reduction and the corresponding increase in rVO₂ at study end (p = 0.011) were unique to DAT. Vitamin D, when combined with exercise, may potentiate the metabolic benefits of exercise by reducing IMCL and increasing tissue-level VO₂ in healthy, older adults.

Sex-based differences in hepatic and skeletal muscle triglyceride storage and metabolism 1

Women and men store lipid differently within the body with men storing more fat in the android region and women storing more fat in the gynoid region. Fat is predominately stored in adipose tissue as triacylglycerides (TG); however, TG are also stored in other tissues including the liver and skeletal muscle. Excess hepatic TG storage, defined as a TG concentration >5% of liver weight and known as nonalcoholic fatty liver disease (NAFLD), is related to the metabolic syndrome. Similarly, elevated skeletal muscle TG, termed intramyocellular lipids (IMCL), are related to insulin resistance in obesity and type II diabetes. Men store more hepatic TG than women and, unsurprisingly, NAFLD is more prevalent in men than women. Women store more IMCL than men, yet type II diabetes risk is not greater, which is likely due to the manner in which women store TG within muscle. Sex-based differences in TG storage between men and women are underpinned by differences in messenger RNA expression, protein content, and enzyme activities of skeletal muscle and hepatic lipid metabolic pathways. Furthermore, women have a greater reliance on lipid during exercise because of upregulation of lipid oxidative pathways. The purpose of this review is to discuss the role of sex in mediating lipid storage and metabolism within skeletal muscle and the liver at rest and during exercise and its relationship with metabolic disease.

The Muscle Fiber Profiles, Mitochondrial Content, and Enzyme Activities of the Exceptionally Well-Trained Arm and Leg Muscles of Elite Cross-Country Skiers

As one of the most physically demanding sports in the Olympic Games, cross-country skiing poses considerable challenges with respect to both force generation and endurance during the combined upper- and lower-body effort of varying intensity and duration. The isoforms of myosin in skeletal muscle have long been considered not only to define the contractile properties, but also to determine metabolic capacities. The current investigation was designed to explore the relationship between these isoforms and metabolic profiles in the arms (triceps brachii) and legs (vastus lateralis) as well as the range of training responses in the muscle fibers of elite cross-country skiers with equally and exceptionally well-trained upper and lower bodies. The proportion of myosin heavy chain (MHC)-1 was higher in the leg (58 ± 2% [34-69%]) than arm (40 ± 3% [24-57%]), although the mitochondrial volume percentages [8.6 ± 1.6 (leg) and 9.0 ± 2.0 (arm)], and average number of capillaries per fiber [5.8 ± 0.8 (leg) and 6.3 ± 0.3 (arm)] were the same. In these comparable highly trained leg and arm muscles, the maximal citrate synthase (CS) activity was the same. Still, 3-hydroxy-acyl-CoA-dehydrogenase (HAD) capacity was 52% higher (P < 0.05) in the leg compared to arm muscles, suggesting a relatively higher capacity for lipid oxidation in leg muscle, which cannot be explained by the different fiber type distributions. For both limbs combined, HAD activity was correlated with the content of MHC-1 (r² = 0.32, P = 0.011), whereas CS activity was not. Thus, in these highly trained cross-country skiers capillarization of and mitochondrial volume in type 2 fiber can be at least as high as in type 1 fibers, indicating a divergence between fiber type pattern and aerobic metabolic capacity. The considerable variability in oxidative metabolism with similar MHC profiles provides a new perspective on exercise training. Furthermore, the clear differences between equally well-trained arm and leg muscles regarding HAD activity cannot be explained by training status or MHC distribution, thereby indicating an intrinsic metabolic difference between the upper and lower body. Moreover, trained type 1 and type 2A muscle fibers exhibited similar aerobic capacity regardless of whether they were located in an arm or leg muscle.

Intramuscular triglyceride synthesis: importance in muscle lipid partitioning in humans

Intramuscular triglyceride (IMTG) concentration is elevated in insulin-resistant individuals and was once thought to promote insulin resistance. However, endurance-trained athletes have equivalent concentration of IMTG compared with individuals with type 2 diabetes, and have very low risk of diabetes, termed the "athlete's paradox." We now know that IMTG synthesis is positively related to insulin sensitivity, but the exact mechanisms for this are unclear. To understand the relationship between IMTG synthesis and insulin sensitivity, we measured IMTG synthesis in obese control subjects, endurance-trained athletes, and individuals with type 2 diabetes during rest, exercise, and recovery. IMTG synthesis rates were positively related to insulin sensitivity, cytosolic accumulation of DAG, and decreased accumulation of C18:0 ceramide and glucosylceramide. Greater rates of IMTG synthesis in athletes were not explained by alterations in FFA concentration, DGAT1 mRNA expression, or protein content. IMTG synthesis during exercise in Ob and T2D indicate utilization as a fuel despite unchanged content, whereas IMTG concentration decreased during exercise in athletes. mRNA expression for genes involved in lipid desaturation and IMTG synthesis were increased after exercise and recovery. Further, in a subset of individuals, exercise decreased cytosolic and membrane di-saturated DAG content, which may help explain insulin sensitization after acute exercise. These data suggest IMTG synthesis rates may influence insulin sensitivity by altering intracellular lipid localization, and decreasing specific ceramide species that promote insulin resistance.

Intramyocellular lipids of muscle type in athletes of different sport disciplines

The present study used magnetic resonance spectroscopy (¹H-MRS) to examine quantitative differences in intramyocellular lipid (IMCL) contents in various muscle types at rest for individual athletes from different sport disciplines. Five groups consisting of sprinters, alpine skiers, cross-country skiers, endurance runners and untrained healthy male subjects volunteered for this study. Data were acquired using ¹H-MRS from the tibialis anterior (TA), medial gastrocnemius (MG) and soleus (SOL) muscles. No significant difference was found in the cross-sectional area (CSA) of the TA, MG and SOL muscles, whereas the CSA of subcutaneous fat was significantly lower (p<0.01) for each athlete group compared with untrained subjects. In both TA and MG, IMCL concentrations in endurance runners were significantly higher than those of alpine skiers (p<0.01), sprinters (p<0.01) and untrained subjects (p<0.05). The IMCL concentrations in TA and MG of cross-country skiers were significantly higher than those of alpine skiers (p<0.05) and sprinters (TA, p<0.01; MG, p<0.05). There was no significant difference in the IMCL concentrations of TA and MG between alpine skiers or sprinters and untrained subjects. The IMCL concentration in SOL was significantly greater in endurance runners and showed no difference in cross-country skiers compared with that in alpine skiers and sprinters. There was no significant difference in the IMCL concentration of SOL between athletes and untrained subjects. These results suggest that differences in IMCL contents stored in various muscle types for athletes at rest are associated with the muscle cellular adaptation for differences in the type of exercise training and/or muscle fiber composition.

Intramyocellular lipid droplets and insulin sensitivity, the human perspective

Skeletal muscle can store excess fat as subcellular lipid droplets (LDs). While originally viewed as uninteresting static balls of triacylglycerol, it is now clear that myocellular LDs play an active role in myocellular (patho)physiology. In this review we aim to discuss the role of LDs in muscle cell insulin sensitivity and identify parameters which appear to affect this relationship. Moreover, we discuss the application of novel tools permitting detailed examination of these parameters. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.

Intramyocellular lipid content and lipogenic gene expression responses following a single bout of resistance type exercise differ between young and older men

The aim of this study was to examine the temporal relationship between intramyocellular lipid (IMCL) content and the expression of genes associated with IMCL turnover, fat metabolism, and inflammation during recovery from an acute bout of resistance type exercise in old versus young men. Seven healthy young (23±2years, 77.2±2.9kg) and seven healthy older (72±1years, 79.3±4.9kg) males performed a single bout of resistance exercise involving 6 sets of 10 repetitions of leg press and 6 sets of 10 repetitions of leg extension at 75% one-repetition maximum (1-RM). Muscle biopsy samples were obtained before and 12, 24 and 48h after the completion of exercise and analysed for IMCL content and the expression of 48 genes. The subjects refrained from further heavy physical exercise and consumed a standardized diet for the entire experimental period. The IMCL content was ~2-fold higher at baseline and 12h post-exercise in old compared with young individuals. However, no differences between groups were apparent after 48h of recovery. There was higher expression of genes involved in fatty acid synthesis (FASN and PPARγ) during the first 24h of recovery. Differential responses to exercise were observed between groups for a number of genes indicating increased inflammatory response (IL6, IkBalpha, CREB1) and impaired fat metabolism and TCA cycle (LPL, ACAT1, SUCLG1) in older compared with younger individuals. A singe bout of resistance type exercise leads to molecular changes in skeletal muscle favouring reduced lipid oxidation, increased lipogenesis, and exaggerated inflammation during post-exercise recovery in the older compared with younger individuals, which may be indicative of a blunted response of IMCL turnover with ageing.

Pioglitazone-induced improvements in insulin sensitivity occur without concomitant changes in muscle mitochondrial function

AIMS

Pioglitazone (Pio) is known to improve insulin sensitivity in skeletal muscle. However, the role of Pio in skeletal muscle lipid metabolism and skeletal muscle oxidative capacity is not clear. The aim of this study was to determine the effects of chronic Pio treatment on skeletal muscle mitochondrial activity in individuals with type 2 diabetes (T2D).

MATERIALS AND METHODS

Twenty-four participants with T2D (13M/11F 53.38±2.1years; BMI 36.47±1.1kg/m²) were randomized to either a placebo (CON, n=8) or a pioglitazone (PIO, n=16) group. Following 12weeks of treatment, we measured insulin sensitivity by hyperinsulinemic-euglycemic clamp (clamp), metabolic flexibility by calculating the change in respiratory quotient (ΔRQ) during the steady state of the clamp, intra- and extra-myocellular lipid content (IMCL and EMCL, respectively) by ¹H magnetic resonance spectroscopy (¹H-MRS) and muscle maximal ATP synthetic capacity (ATPmax) by ³¹P-MRS.

RESULTS

Following 12weeks of PIO treatment, insulin sensitivity (p<0.0005 vs. baseline) and metabolic flexibility (p<0.05 vs. CON) significantly increased. PIO treatment significantly decreased IMCL content and increased EMCL content in gastrocnemius, soleus and tibialis anterior muscles. ATPmax was unaffected by PIO treatment.

CONCLUSIONS

These results suggest that 12weeks of pioglitazone treatment improves insulin sensitivity, metabolic flexibility and myocellular lipid distribution without any effect on maximal ATP synthetic capacity in skeletal muscle. Consequently, pioglitazone-induced enhancements in insulin responsiveness and fuel utilization are independent of mitochondrial function.

Effect of biological factors on successful measurements with skeletal-muscle (1)H-MRS

Background

Our purpose in this study was to clarify whether differences in subject group attributes could affect data acquisition in proton magnetic resonance spectroscopy (¹H-MRS).

Methods

Subjects without diabetes mellitus (DM) were divided into two groups (group A, in their 20s; group B, 30–60 years old). Subjects with DM formed group C (30–60 years old). The numbers of subjects were 19, 27, and 22 for group A, B, and C respectively. For all subjects, ¹H-MRS measurements were taken of the soleus muscle (SOL) and the anterior tibial muscle (AT). We defined the success of the measurements by the detection of intramyocellular lipids. Moreover, we also measured the full width at half maximum of the water peaks for all subjects.

Results

The success rate was significantly higher for the AT (100%) than for the SOL (81.6%) (P<0.01). For the SOL, the success rate was 100% in group A, 85.2% in group B, and 77.3% in group C. There was a significant difference (P<0.05) between groups A and B, as well as between groups A and C. In all subjects, there was a significant difference (P<0.01) in the full width at half maximum (Hz) of the water peak between the AT and SOL measurements.

Conclusion

We conclude that differences in the age and DM history of subjects could affect the probability of successful ¹H-MRS data acquisition.

Decoration of intramyocellular lipid droplets with PLIN5 modulates fasting-induced insulin resistance and lipotoxicity in humans

AIMS/HYPOTHESIS

In contrast to insulin-resistant individuals, insulin-sensitive athletes possess high intramyocellular lipid content (IMCL), good mitochondrial function and high perilipin 5 (PLIN5) levels, suggesting a role for PLIN5 in benign IMCL storage. We hypothesised a role for PLIN5 in modulating fasting-mediated insulin resistance.

METHODS

Twelve men were fasted for 60 h, before and after which muscle biopsies were taken and stained for lipid droplets (LDs), PLIN5 and laminin. Confocal microscopy images were analysed for LD size, number, PLIN5 association and subcellular distribution.

RESULTS

Fasting elevated IMCL content 2.8-fold and reduced insulin sensitivity (by 55%). Individuals with the most prominent increase in IMCL showed the least reduction in insulin sensitivity (r = 0.657; p = 0.028) and mitochondrial function (r = 0.896; p = 0.006). During fasting, PLIN5 gene expression or PLIN5 protein content in muscle homogenates was unaffected, microscopy analyses revealed that the fraction of PLIN5 associated with LDs (PLIN5+) increased significantly (+26%) upon fasting, suggesting PLIN5 redistribution. The significant increase in LD number (+23%) and size (+23%) upon fasting was entirely accounted for by PLIN5+ LDs, not by LDs devoid of PLIN5. Also the association between IMCL storage capacity and insulin resistance and mitochondrial dysfunction was only apparent for PLIN5+ LDs.

CONCLUSIONS/INTERPRETATION

Fasting results in subcellular redistribution of PLIN5 and promotes the capacity to store excess fat in larger and more numerous PLIN5-decorated LDs. This associates with blunting of fasting-induced insulin resistance and mitochondrial dysfunction, suggesting a role for PLIN5 in the modulation of fasting-mediated lipotoxicity.

TRIAL REGISTRATION

trialregister.nl NTR 2042.

Lipid storage changes in human skeletal muscle during detraining

Exercise training is known to increase intramuscular triglyceride content in both trained and untrained legs. The purpose of the study was to determine the changes of intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) of both trained and untrained legs during detraining. We measured both IMCL and EMCL levels in previously trained vs. untrained legs during 4-weeks of detraining after 6-weeks of strength training. Eight young men (aged 21.4 ± 1.4 years) trained their vastus lateralis muscle in one leg using a dynamometer, whereas the contralateral leg served as untrained control. Muscle cross-sectional area (CSA), IMCL, EMCL, total creatine (creatine + phophocreatine) of extensor (vastus lateralis) muscles were assessed using magnetic resonance imaging (MRI) and proton magnetic resonance spectra (¹H-MRS) before training, 3 days after and 28 days after the last bout of training. CSA was increased in both legs by Day 3 after training, and was still high at Day 28 post-training; IMCL increased in both legs by Day 3 after training, then decreased at Day 28 post-training only in the untrained leg; EMCL shows no significant change by Day 3 after training, but at Day 28 post-training has increased in the trained leg and decreased in the untrained leg; total creatine did not change significantly.

Conclusion: Decreases of IMCL and EMCL storages in previously untrained leg during detraining indicates an ectopic influence on tissue lipid storage by different metabolic demand among tissues in the same human body.

Proton magnetic resonance spectroscopy reveals increased hepatic lipid content after a single high-fat meal with no additional modulation by added protein

BACKGROUND

Fat accumulation in nonadipose tissue is linked to insulin resistance and metabolic diseases. Earlier studies have shown that hepatic lipid accumulation can occur after 4 d of a high-fat diet in humans, and this fat accumulation can be blunted by the ingestion of additional proteins.

OBJECTIVES

In this study, we explored whether a single high-fat meal increased the lipid content in liver and skeletal muscle as measured by using in vivo proton magnetic resonance spectroscopy (¹H-MRS) and whether the addition of protein can modulate the postprandial ectopic lipid storage.

DESIGN

Intrahepatic lipid (IHL) and intramyocellular lipid (IMCL) concentrations were determined by using ¹H-MRS before and 3 and 5 h after a high-fat with added protein meal (61.5% of energy from fat) or a high-fat without added protein meal (mean ± SEM: 51.1 ± 7.9 g of protein; 191.9 ± 9.9 kcal added) in a randomized crossover study. IHL and IMCL concentrations were converted to absolute concentrations (g/kg wet weight) by using water as an internal reference.

RESULTS

Nine lean, healthy subjects [6 men and 3 women; mean (±SD) age: 22.7 ± 3.0 y; mean body mass index (in kg/m²): 21.8 ± 1.8] were included in this study. IHL concentrations increased ∼20% (P < 0.01) at 3 h after the meal and did not further increase after 5 h. In contrast, IMCL concentrations were not altered during the postprandial period (P = 0.74). The addition of protein to a single high-fat meal did not change the postprandial accumulation of fat in the liver (P = 0.93) or skeletal muscle (P = 0.84).

CONCLUSIONS

In this study, we showed that a single energy-dense, high-fat meal induced net lipid accumulation in the liver, which was detected by using in vivo ¹H-MRS. This noninvasive approach might bring new opportunities to study postprandial hepatic lipid dynamics. The addition of protein did not change the ectopic lipid retention after a single high-fat meal.

Effects of exercise and lifestyle modification on fitness, insulin resistance, skeletal muscle oxidative phosphorylation and intramyocellular lipid content in obese children and adolescents

BACKGROUND

Obesity is associated with poor fitness and adverse metabolic consequences in children.

OBJECTIVE

To investigate how exercise and lifestyle modification may improve fitness and insulin sensitivity in this population.

DESIGN AND SUBJECTS

Randomized controlled trial, 21 obese (body mass index ≥ 95% percentile) subjects, ages 10 to 17 years.

METHODS

Subjects were given standardized healthful lifestyle advice for 8 weeks. In addition, they were randomized to an in-home supervised exercise intervention (n = 10) or control group (n = 11).

MEASUREMENTS

Fasting laboratory studies (insulin, glucose, lipid profile) and assessments of fitness, body composition, skeletal muscle oxidative phosphorylation and intramyocellular lipid content (IMCL), were performed at baseline and study completion.

RESULTS

Subjects were 13.0 ± 1.9 (standard deviation) years old, 72% female and 44% non-white. Exercise improved fitness (P = 0.03) and power (P = 0.01), and increased IMCL (P = 0.02). HOMA-IR decreased among all subjects in response to lifestyle modification advice (P = 0.01), regardless of exercise training assignment. In univariate analysis in all subjects, change in cardiovascular fitness was associated with change in HOMA-IR. In exploratory analyses, increased IMCL was associated with greater resting energy expenditure (r = 0.78, P = 0.005) and a decrease in fasting respiratory quotient (r = -0.70, P = 0.02) (n = 11).

CONCLUSIONS

Change in fitness was found to be related to change in insulin resistance in response to lifestyle modification and exercise in obese children. IMCL increased with exercise in these obese children, which may reflect greater muscle lipid oxidative capacity.

Whole body fat: content and distribution

Obesity and its co-morbidities, including type II diabetes, insulin resistance and cardiovascular diseases, have become one of the biggest health issues of present times. The impact of obesity goes well beyond the individual and is so far-reaching that, if it continues unabated, it will cause havoc with the economies of most countries. In order to be able to fully understand the relationship between increased adiposity (obesity) and its co-morbidity, it has been necessary to develop proper methodology to accurately and reproducibly determine both body fat content and distribution, including ectopic fat depots. Magnetic Resonance Imaging (MRI) and Spectroscopy (MRS) have recently emerged as the gold-standard for accomplishing this task. Here, we will review the use of different MRI techniques currently being used to determine body fat content and distribution. We also discuss the pros and cons of MRS to determine ectopic fat depots in liver, muscle, pancreas and heart and compare these to emerging MRI techniques currently being put forward to create ectopic fat maps. Finally, we will discuss how MRI/MRS techniques are helping in changing the perception of what is healthy and what is normal and desirable body-fat content and distribution.

Cardiac function and lipid distribution in rats fed a high-fat diet: in vivo magnetic resonance imaging and spectroscopy

Obesity is a major risk factor in the development of cardiovascular disease, type 2 diabetes, and its pathophysiological precondition insulin resistance. Very little is known about the metabolic changes that occur in the myocardium and consequent changes in cardiac function that are associated with high-fat accumulation. Therefore, cardiac function and metabolism were evaluated in control rats and those fed a high-fat diet, using magnetic resonance imaging, magnetic resonance spectroscopy, mRNA analysis, histology, and plasma biochemistry. Analysis of blood plasma from rats fed the high-fat diet showed that they were insulin resistant (P < 0.001). Our high-fat diet model had higher heart weight (P = 0.005) and also increasing trend in septal wall thickness (P = 0.07) compared with control diet rats. Our results from biochemistry, magnetic resonance imaging, and mRNA analysis confirmed that rats on the high-fat diet had moderate diabetes along with mild cardiac hypertrophy. The magnetic resonance spectroscopy results showed the extramyocellular lipid signal only in the spectra from high-fat diet rats, which was absent in the control diet rats. The intramyocellular lipids in high-fat diet rats was higher (8.7%) compared with rats on the control diet (6.1%). This was confirmed by electron microscope and light microscopy studies. Our results indicate that lipid accumulation in the myocardium might be an early indication of the cardiovascular pathophysiology associated with type 2 diabetes.