D. Enette Larson-Meyer

Effect of 6-month calorie restriction and exercise on serum and liver lipids and markers of liver function.

Objective: Nonalcoholic fatty liver disease (NAFLD) and its association with insulin resistance are increasingly recognized as major health burdens. The main objectives of this study were to assess the relation between liver lipid content and serum lipids, markers of liver function and inflammation in healthy overweight subjects, and to determine whether caloric restriction (CR) (which improves insulin resistance) reduces liver lipids in association with these same measures.

Vitamin D and athletes.

While it is well recognized that vitamin D is necessary for optimal bone health, emerging evidence is finding that adequate vitamin D intake reduces risk for conditions such as stress fracture, total body inflammation, infectious illness, and impaired muscle function. Studies in athletes have found that vitamin D status is variable and is dependent on outdoor training time (during peak sunlight), skin color, and geographic location. Although research has found that athletes generally do not meet the U.S. dietary reference intake for vitamin D, inadequate endogenous synthesis is the most probable reason for insufficient/deficient status. Given the recent findings, it is imperative that sports dietitians and physicians routinely assess vitamin D status and make recommendations to help athletes achieve a serum 25(OH)D concentration of ≥32 and preferably ≥40 ng·mL−1. Further research is needed to determine the effect of vitamin D status on injury, training, and performance in athletes.

Vitamin D Status Relative to Diet, Lifestyle, Injury and Illness in College Athletes

UNLABELLED Vitamin D deficiency is endemic in the general population; however, there is much to be learned about the vitamin D status of athletes. PURPOSE the purposes of this study were to assess the prevalence of vitamin D insufficiency in collegiate athletes and to determine whether 25(OH)D concentrations are related to vitamin D intake, sun exposure, body composition, and risk for illness or athletic injury. METHODS 25(OH) vitamin D concentrations were measured in 41 athletes (18 men/23 women, 12 indoor/29 outdoor athletes) throughout the academic year. Dietary intake and lifestyle habits were assessed via questionnaire, bone density was measured by dual energy x-ray absorptiometry, and injury and illness were documented as part of routine care. RESULTS the 25(OH)D concentrations changed across time (P = 0.001) and averaged 49.0 ± 16.6, 30.5 ± 9.4, and 41.9 ± 14.6 ng·mL (mean ± SD) in the fall, winter, and spring, respectively, and were higher in outdoor versus indoor athletes in the fall (P < 0.05). Using 40 ng·mL as the cutoff for optimal status, 75.6%, 15.2%, and 36.0% of athletes had optimal status in the fall, winter, and spring, respectively. 25(OH)D concentrations were significantly (P < 0.05) correlated with multivitamin intake in the winter (r = 0.39) and tanning bed use in the spring (r = 0.48); however, status was otherwise not related to intake, lifestyle factors, or body composition. 25(OH)D concentrations in the spring (r = -0.40, P = 0.048) was correlated with frequency of illness. CONCLUSIONS our results suggest that collegiate athletes can maintain sufficient status during the fall and spring but would benefit from supplementation during the winter to prevent seasonal decreases in 25(OH)D concentrations. Results further suggest that insufficient vitamin D status may increase risk for frequent illness. Future research is needed to identify whether vitamin D status influences injury risk during athletic training or competition.

Muscle‐associated Triglyceride Measured by Computed Tomography and Magnetic Resonance Spectroscopy

Objective: Muscle triglyceride can be assessed in vivo using computed tomography (CT) and 1H magnetic resonance spectroscopy (MRS), two techniques that are based on entirely different biophysical principles. Little is known, however, about the cross‐correlation between these techniques and their test—retest reliability.

Caloric restriction with or without exercise: the fitness versus fatness debate.

UNLABELLED There is a debate over the independent effects of aerobic fitness and body fatness on mortality and disease risks. PURPOSE To determine whether a 25% energy deficit that produces equal change in body fatness leads to greater cardiometabolic benefits when aerobic exercise is included. METHODS Thirty-six overweight participants (16 males/20 females) (39 +/- 1 yr; 82 +/- 2 kg; body mass index = 27.8 +/- 0.3 kg x m2, mean +/- SEM) were randomized to one of three groups (n = 12 for each) for a 6-month intervention: control (CO, weight-maintenance diet), caloric restriction (CR, 25% reduction in energy intake), or caloric restriction plus aerobic exercise (CR + EX, 12.5% reduction in energy intake plus 12.5% increase in exercise energy expenditure). Food was provided during weeks 1-12 and 22-24. Changes in fat mass, visceral fat, VO2peak (graded treadmill test), muscular strength (isokinetic knee extension/flexion), blood lipids, blood pressure, and insulin sensitivity/secretion were compared. RESULTS As expected, VO2peak was significantly improved after 6 months of intervention in CR + EX only (22 +/- 5% vs 7 +/- 5% in CR and -5 +/- 3% in CO), whereas isokinetic muscular strength did not change. There was no difference in the losses of weight, fat mass, or visceral fat and changes in systolic blood pressure (BP) between the intervention groups. However, only CR + EX had a significant decrease in diastolic BP (-5 +/- 3% vs -2 +/- 2% in CR and -1 +/- 2% in CO), in low-density lipoprotein (LDL) cholesterol (-13 +/- 4% vs -6 +/- 3% in CR and 2 +/- 4% in CO), and a significant increase in insulin sensitivity (66 +/- 22% vs 40 +/- 20% in CR and 1 +/- 11% in CO). CONCLUSIONS Despite similar effect on fat losses, combining CR with exercise increased aerobic fitness in parallel with improved insulin sensitivity, LDL cholesterol, and diastolic BP. The results lend support for inclusion of an exercise component in weight loss programs to improve metabolic fitness.

Relation between in vivo and in vitro measurements of skeletal muscle oxidative metabolism

The relationships between in vivo 31P magnetic resonance spectroscopy (MRS) and in vitro markers of oxidative capacity (mitochondrial function) were determined in 27 women with varying levels of physical fitness. Following 90‐s isometric plantar flexion exercises, calf muscle mitochondrial function was determined from the phosphocreatine (PCr) recovery time constant, the adenosine diphosphate (ADP) recovery time constant, the rate of change of PCr during the initial 14 s of recovery, and the apparent maximum rate of oxidative adenosine triphosphate (ATP) synthesis (Qmax). Muscle fiber type distribution (I, IIa, IIx), citrate synthase (CS) activity, and cytochrome c oxidase (COX) activity were determined from a biopsy sample of lateral gastrocnemius. MRS markers of mitochondrial function correlated moderately (P < 0.05) with the percentage of type IIa oxidative fibers (r = 0.41 to 0.66) and CS activity (r = 0.48 to 0.64), but only weakly with COX activity (r = 0.03 to 0.26, P > 0.05). These results support the use of MRS to determine mitochondrial function in vivo.

Influence of Running and Walking on Hormonal Regulators of Appetite in Women

Nine female runners and ten walkers completed a 60 min moderate-intensity (70% VO2max) run or walk, or 60 min rest in counterbalanced order. Plasma concentrations of the orexogenic peptide ghrelin, anorexogenic peptides peptide YY (PYY), glucagon-like peptide-1 (GLP-1), and appetite ratings were measured at 30 min interval for 120 min, followed by a free-choice meal. Both orexogenic and anorexogenic peptides were elevated after running, but no changes were observed after walking. Relative energy intake (adjusted for cost of exercise/rest) was negative in the meal following running (−194 ± 206 kcal) versus walking (41 ± 196 kcal) (P = 0.015), although both were suppressed (P < 0.05) compared to rest (299 ± 308 and 284 ± 121 kcal, resp.). The average rate of change in PYY and GLP-1 over time predicted appetite in runners, but only the change in GLP-1 predicted hunger (P = 0.05) in walkers. Results provide evidence that exercise-induced alterations in appetite are likely driven by complex changes in appetite-regulating hormones rather than change in a single gut peptide.

Impaired Insulin Sensitivity and Elevated Ectopic fat in Healthy Obese vs. Nonobese Prepubertal Children

Insulin sensitivity is impaired and ectopic fat (accretion of lipids outside of typical adipose tissue depots) increased in obese adults and adolescents. It is unknown how early in life this occurs; thus, it is important to evaluate young children to identify potential factors leading to the development of metabolic syndrome. We examined an ethnically diverse cohort of healthy, exclusively prepubertal children (N = 123; F = 57, M = 66; age 8.04 ± 0.77 years) to examine differences in insulin sensitivity and ectopic and visceral fat deposition between obese and nonobese youth. Obesity was categorized by age‐ and sex‐adjusted BMI z‐scores (nonobese = z‐score <2 (N = 94) and obese = z‐score ≥2 (N = 29)). Insulin sensitivity was assessed by both a frequently sampled intravenous glucose tolerance test (Si) and the homeostatic model assessment of insulin resistance (HOMAIR). Intramyocellular lipids (IMCLs) from soleus and intrahepatic lipids (IHLs) were assessed by magnetic resonance spectroscopy, visceral adipose tissue (VAT) by magnetic resonance imaging, and total body fat by dual‐energy X‐ray absorptiometry. We also examined serum lipids (total cholesterol, triglycerides, high‐density lipoprotein cholesterol (HDL‐C) and low‐density lipoprotein cholesterol) and blood pressure (diastolic and systolic). Obese children exhibited significantly lower Si (5.9 ± 5.98 vs. 13.43 ± 8.18 (mµ/l)−1·min−1, P = 0.01) and HDL‐C and higher HOMAIR (1.68 ± 1.49 vs. 0.63 ± 0.47, P < 0.0001), IMCL (0.74 ± 0.39 vs. 0.44 ± 0.21% water peak, P < 0.0001), IHL (1.49 ± 1.13 vs. 0.54 ± 0.42% water peak, P < 0.0001), VAT (20.16 ± 8.01 vs. 10.62 ± 5.44 cm2, P < 0.0001), total cholesterol, triglycerides, low‐density lipoprotein cholesterol, and systolic blood pressure relative to nonobese children. These results confirm significantly increased ectopic fat and insulin resistance in healthy obese vs. nonobese children prior to puberty. Excessive adiposity during early development appears concomitant with precursors of type 2 diabetes and the metabolic syndrome.

Hemoglobin, muscle oxidative capacity, and VO2max in African-American and Caucasian women.

PURPOSE The purpose of this paper was to determine whether differences in hemoglobin (Hb) and muscle aerobic capacity exist between African-American (AA) and Caucasian (CA) premenopausal women and to determine whether Hb and aerobic capacity of the muscle are associated with the racial differences in maximum oxygen uptake (VO2max). METHODS 43 AA and 46 CA sedentary premenopausal women were subjects. Percent body fat was determined by four-compartment model, leg lean tissue by dual energy x-ray absorptiometry, VO2max during a graded exercise test, aerobic capacity of the calf muscle by 31P magnetic resonance spectroscopy, and serum Hb by the cyanide method. RESULTS AA women had reduced VO2max (AA 29.3 +/- 3.0 vs CA 33.6 +/- 5.6 mL.kg(-1) bdw(-1).min, P < 0.01), reduced muscle aerobic capacity (AA 24.3 +/- 5.8 vs CA 21.3 +/- 4.8 s, P = 0.01, where lower values indicate higher aerobic capacity), and reduced Hb (AA 11.8 +/- 1.3 vs CA 12.9 +/- 0.8 g.dL(-1), P < 0.01). The racial difference in VO2max persisted whether the values were unadjusted or adjusted for fat-free mass or leg lean tissue. Multiple regression analysis revealed that both Hb and muscle aerobic capacity were related to VO2max after adjusting for each other, race, and either fat-free mass or leg lean tissue. Being AA was associated with reduced VO2max in mL O2.kg leg lean tissue(-1).min(-1) (zero-order simple Pearson-product correlation -0.60, P < 0.01). When multiple regression was used, the correlation between race and VO2max decreased but persisted (-0.40, <0.01) after adjusting for Hb and muscle aerobic capacity. CONCLUSIONS These data suggest that differences in Hb and aerobic capacity of muscle are related to reduced VO2max in AA women. However, Hb and aerobic capacity of the muscle can only partially explain the racial differences in VO2max.

Cod Liver Oil, Vitamin A Toxicity, Frequent Respiratory Infections, and the Vitamin D Deficiency Epidemic

John J. Cannell, MD; Reinhold Vieth, MS, PhD; Walter Willett, MD, DrPH; Michael Zasloff, MD, PhD; John N. Hathcock, MSc, PhD; John H. White, PhD; Sherry A. Tanumihardjo, MSc, PhD; D. Enette Larson-Meyer, PhD; Heike A. Bischoff-Ferrari, MD, MPH; Christel J. Lamberg-Allardt, PhD; Joan M. Lappe, PhD, RN; Anthony W. Norman, PhD; Armin Zittermann, PhD; Susan J. Whiting, MSc, PhD; William B. Grant, PhD; Bruce W. Hollis, PhD; Edward Giovannucci, MD