[Show abstract][Hide abstract] ABSTRACT: TO THE EDITOR: We are writing this letter in response to Dr. Chacko's second letter to the editor (1). It was not our intent to devalue her opinions with our rebuttal to her first letter. We fully respect and value her opinions, and it was our intention to respond to her remarks with our own evidence-based opinions. One of our first opinions was " Unfortunately, no study has directly examined how the intensity of exercise performed in the postprandial period alters glycemia in the same individual with type 2 diabetes " (2). We thank Dr. Chacko for correcting this statement, as we overlooked the study by Manders et al. (4). They show that neither high-nor low-intensity postpran-dial exercise significantly improves postprandial glucose concentrations , a finding that Dr. Chacko does not mention and it does not support her original remarks. However, 24 h glycemia (including both fasting and postprandial glucose concentrations) was improved with low-intensity exercise, not high-intensity exercise (4). Whether these acute changes would translate into longer term improvements in glycemic control is not known, but the study by Mitranun et al. (see Ref. 2, Ref. 4 therein) provides evidence that this may not be the case. In fact, this study demonstrates that higher intensity exercise may be more beneficial, because glycosylated hemoglobin (a clinical marker of long term glycemic control including both fasting and postprandial glucose) only improved with higher exercise intensity. The timing of exercise relative to meal ingestion was not mentioned, and this topic warrants further investigation. Although our comments about the incremental vs. total area under the curve (AUC) in our first letter are based on a triglyceride study, it was not our intent to provide an all-inclusive literature review because of space limitations. To clarify this, in another study the glucose incremental AUC was shown to better reflect the postprandial glucose response, whereas the total AUC better reflects fasting glucose concentrations (3). Because our subjects were not in a fasting and resting state before the meal using incremental AUC was the legitimate way to go.
Journal of Applied Physiology 07/2015; 119(2). · 3.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We prospectively evaluated adolescent organized physical activity (PA) as a factor in adult female bone traits. Annual DXA scans accompanied semi-annual records of anthropometry, maturity and PA for 42 participants in this preliminary analysis (criteria: appropriately timed DXA scans at ~1 year pre-menarche [predictor] and ~5 years post-menarche [dependent variable]). Regression analysis evaluated total adolescent inter-scan PA and PA over 3 maturity sub-phases as predictors of young adult bone outcomes: 1) bone mineral content (BMC), geometry and strength indices at non-dominant distal radius and femoral neck; 2) sub-head BMC; 3) lumbar spine BMC. Analyses accounted for baseline gynecological age (years pre- or post-menarche), baseline bone status, adult body size and inter-scan body size change. Gymnastics training was evaluated as a potentially independent predictor, but did not improve models for any outcomes (p<0.07). Pre-menarcheal bone traits were strong predictors of most adult outcomes (semi-partial r2 = 0.21-0.59, p≤0.001). Adult 1/3 radius and sub-head BMC were predicted by both total PA and PA 1-3 years post-menarche (p<0.03). PA 3-5 years post-menarche predicted femoral narrow neck width, endosteal diameter and buckling ratio (p<0.05). Thus, participation in organized physical activity programs throughout middle and high school may reduce lifetime fracture risk in females.
[Show abstract][Hide abstract] ABSTRACT: This study assessed if walking at a self-selected pace could improve postprandial glucose and insulin concentrations in obese adolescents consuming high-fructose (HF) or high-glucose (HG) diets.
Journal of physical activity & health 10/2014; DOI:10.1123/jpah.2014-0105 · 1.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A frequent eating pattern may alter glycaemic control and augment postprandial insulin concentrations in some individuals due to the truncation of the previous postprandial period by a subsequent meal. The present study examined glucose, insulin, C-peptide and glucose-dependent insulinotropic peptide (GIP) responses in obese individuals when meals were ingested in a high-frequency pattern (every 2 h, 6M) or in a low-frequency pattern (every 4 h, 3M) over 12 h. It also examined these postprandial responses to high-frequency, high-protein meals (6MHP). In total, thirteen obese subjects completed three 12 h study days during which they consumed 6276 kJ (1500 kcal): (1) 3M - 15 % protein and 65 % carbohydrate; (2) 6M - 15 % protein and 65 % carbohydrate; (3) 6MHP - 45 % protein and 35 % carbohydrate. Blood samples were collected every 10 min and analysed for glucose, insulin, C-peptide and GIP. Insulin total AUC (tAUC) and peak insulin concentrations (P< 0·05) were higher in the 3M condition than in the 6M condition, but there were no differences in glucose tAUC between the conditions. The 6MHP regimen (glucose: 3569 (se 83) mmol/l × min (64·3 (se 1·5) g/dl × min), insulin: 1·577 (se 0·146) pmol/l (22·7 (se 2·1) μIU/dl) for 12 h) lowered glucose and insulin excursions more so over 12 h than either the 3M regimen (glucose: 3913 (se 78) mmol/l × min (70·5 (se 1·4) g/dl × min), insulin: 2·195 (se 0·146) pmol/l × min (31·6 (se 2·1) μIU/dl × min) for 12 h) or the 6M regimen (glucose: 3902 (se 83) mmol/l × min (70·3 (se 1·5) g/dl × min), insulin: 1·861 (se 0·174) pmol/l × min (26·8 (se 2·5) μIU/dl × min) for 12 h; P< 0·01). Insulin secretion, GIP concentrations and the glucose:insulin ratio were not altered by meal frequency or composition. In obese subjects, ingestion of meals in a low-frequency pattern does not alter glucose tAUC, but increases postprandial insulin responses. The substitution of carbohydrates with protein in a frequent meal pattern results in tighter glycaemic control and reduced postprandial insulin responses.
British Journal Of Nutrition 09/2014; 112(9):1-10. DOI:10.1017/S0007114514002128 · 3.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Adolescents consume more sugar-sweetened beverages than do individuals in any other age group, but it is unknown how the type of sugar-sweetened beverage affects metabolic health in this population.OBJECTIVE: The objective was to compare the metabolic health effects of short-term (2-wk) consumption of high-fructose (HF) and high-glucose (HG)-sweetened beverages in adolescents (15-20 y of age).DESIGN: In a counterbalanced, single-blind fashion, 40 male and female adolescents completed two 2-wk trials that included 1) an HF trial in which they consumed 710 mL of a sugar-sweetened beverage/d (equivalent to 50 g fructose/d and 15 g glucose/d) for 2 wk and 2) an HG trial in which they consumed 710 mL of a sugar-sweetened beverage/d (equivalent to 50 g glucose/d and 15 g fructose/d) for 2 wk in addition to their normal ad libitum diet. In addition, the participants maintained similar physical activity levels during each trial. The day after each trial, insulin sensitivity and resistance [assessed via Quantitative Insulin Sensitivity Check Index (QUICKI) and homeostatic model assessment of insulin resistance (HOMA-IR) index] and fasting and postprandial glucose, lactate, lipid, cholesterol, insulin, C-peptide, insulin secretion, and clearance responses to HF or HG mixed meals were assessed.RESULTS: Body weight, QUICKI (whole-body insulin sensitivity), HOMA-IR (hepatic insulin resistance), and fasting lipids, cholesterol, glucose, lactate, and insulin secretion or clearance were not different between trials. Fasting HDL- and HDL3-cholesterol concentrations were ∼10-31% greater (P < 0.05) in female adolescents than in male adolescents. Postprandial triacylglycerol, HDL-cholesterol, HDL3-cholesterol, and glucose concentrations were not different between HF and HG trials. The lactate incremental area under the curve was ∼3.7-fold greater during the HF trial (P < 0.05), whereas insulin secretion was 19% greater during the HG trial (P < 0.05).Conclusions: Moderate amounts of HF- or HG-sweetened beverages for 2 wk did not have differential effects on fasting or postprandial cholesterol, triacylglycerol, glucose, or hepatic insulin clearance in weight-stable, physically active adolescents. This trial was registered at clinicaltrials.gov as NCT02058914.
American Journal of Clinical Nutrition 07/2014; 100(3). DOI:10.3945/ajcn.113.081232 · 6.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background/Objectives:The purpose of the current study was to determine whether increased physical activity (PA) altered glycemic control while ingesting an energy-balanced high-fructose diet.Subjects/Methods:Twenty-two normal-weight men and women (age: 21.2±0.6 years; body mass index: 22.6 ±0.6 kg/m(2)) participated in a randomized, cross-over design study in which they ingested an additional 75 g of fructose for 14 days while either maintaining low PA (FR+inactive) (<4500 steps/day) or high PA (FR+active) (>12 000 steps/day). Before and following the 2-week loading period, a fructose-rich meal challenge was administered and blood was sampled at baseline and for 6 h after the meal and analyzed for glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), c-peptide, glucose and insulin concentrations.Results:Plasma insulin, glucose, c-peptide, GIP and GLP-1 concentrations significantly increased in response to the test meal on all test visits (P<0.05). C-peptide incremental area under the curve (AUC) decreased by 10 208 ±120 pmol/l × min for 6 h from pre to post Fr+active intervention (P=0.02) leading to a decrease in plasma insulin total AUC (pre: 58 470.2±6261.0 pmol/l; post: 49 444.3±3883.0 pmol/l; P=0.04) resulting in a decrease Δpeak[Insulin] (P=0.009). Following the FR+active intervention, GIP total AUC significantly decreased (P=0.005) yet only males had a lower total GLP-1 AUC after both interventions (P=0.049). There were no sex differences in GIP levels.Conclusions:Increased PA attenuates the deleterious effects on glycemic control caused by a high-fructose diet. These changes in glycemic control with PA are associated with decreases in insulin and GIP concentrations.European Journal of Clinical Nutrition advance online publication, 21 May 2014; doi:10.1038/ejcn.2014.90.
European Journal of Clinical Nutrition 05/2014; 68(9). DOI:10.1038/ejcn.2014.90 · 2.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective: This study aimed to determine the interaction between a high-fructose diet and PA levels on postprandial lipidemia and inflammation in normal-weight, recreationally active individuals. Methods: Twenty-two men and women (age, 21.2 +/- 0.6 yr; body mass index, 22.5 +/- 0.6 kg.m(-2)) consumed an additional 75 g of fructose for 14 d on two separate occasions: high physical activity (PA) (approximately 12,500 steps per day) (FR+active) and low PA (approximately 4500 steps per day) (FR+inactive). A fructose-rich test meal was given before and at the end of each intervention. Blood was sampled at baseline and for 6 h after the meal for triglycerides (TG), VLDL, total cholesterol, glucose, insulin, tumor necrosis factor-alpha, interleukin 6, and C-reactive protein. Results: Log-transformed TG area under the curve (AUC) significantly increased from before (10.1 +/- 0.1 mg.dL(-1) x min for 6 h) to after (10.3 +/- 0.08 mg.dL(-1) x min for 6 h, P = 0.04) the FR+inactive intervention, with an 88% increase in Delta peak TG (P = 0.009) and an 84% increase in Delta peak VLDL (P = 0.002). Delta Peak interleukin 6 also increased by 116% after the FR+inactive intervention (P = 0.009). Insulin total AUC significantly decreased after FR+ active intervention (P = 0.04), with no change in AUC after the FR+ inactive intervention. No changes were observed in glucose, tumor necrosis factor-alpha, and C-reactive protein concentrations (P > 0.05). Conclusions: Low PA during a period of high fructose intake augments fructose-induced postprandial lipidemia and inflammation, whereas high PA minimizes these fructose-induced metabolic disturbances. Even within a young healthy population, maintenance of high PA (912,500 steps per day) decreases susceptibility to cardiovascular risk factors associated with elevated fructose consumption.
Medicine & Science in Sports & Exercise 05/2014; 46(11). DOI:10.1249/MSS.0000000000000343 · 4.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Obesity and high-fructose corn syrup (HFCS)-sweetened beverages are associated with an increased risk of chronic disease, but it is not clear whether obese (Ob) individuals are more susceptible to the detrimental effects of HFCS-sweetened beverages. The purpose of this study was to examine the endocrine and metabolic effects of consuming HFCS-sweetened beverages, and whether weight classification (normal weight (NW) vs. Ob) influences these effects. Ten NW and 10 Ob men and women who habitually consumed ≤355 mL per day of sugar-sweetened beverages were included in this study. Initially, the participants underwent a 4-h mixed-meal test after a 12-h overnight fast to assess insulin sensitivity, pancreatic and gut endocrine responses, insulin secretion and clearance, and glucose, triacylglycerol, and cholesterol responses. Next, the participants consumed their normal diet ad libitum, with 1065 mL per day (117 g·day(-1)) of HFCS-sweetened beverages added for 2 weeks. After the intervention, the participants repeated the mixed-meal test. HFCS-sweetened beverages did not significantly alter body weight, insulin sensitivity, insulin secretion or clearance, or endocrine, glucose, lipid, or cholesterol responses in either NW or Ob individuals. Regardless of previous diet, Ob individuals, compared with NW individuals, had ∼28% lower physical activity levels, 6%-9% lower insulin sensitivity, 12%-16% lower fasting high-density-lipoprotein cholesterol concentrations, 84%-144% greater postprandial triacylglycerol concentrations, and 46%-79% greater postprandial insulin concentrations. Greater insulin responses were associated with reduced insulin clearance, and there were no differences in insulin secretion. These findings suggest that weight classification does not influence the short-term endocrine and metabolic effects of HFCS-sweetened beverages.
[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to compare the effects of short-term low-fat (LF) and high-fat (HF) diets on fed-state hepatic triacylglycerol (TAG) secretion, the content of proteins involved in TAG assembly and secretion, fatty acid oxidation (FAO), and the fatty acid profile of stored TAG. Using selectively bred obese-prone Sprague-Dawley rats, we directly measured fed-state hepatic TAG secretion, using Tyloxapol (a lipoprotein lipase inhibitor) and a standardized oral mixed meal (45% carbohydrate, 40% fat, 15% protein) bolus in animals fed a HF or LF diet for 2 weeks, after which the rats were maintained on their respective diet for 1 week (washout) prior to the liver being excised to measure protein content, FAO, and TAG fatty acid profiles. Hepatic DGAT-1 protein expression was ∼27% lower in HF- than in LF-fed animals (p < 0.05); the protein expression of all other molecules was similar in the 2 diets. The fed-state hepatic TAG secretion rate was ∼39% lower (p < 0.05) in HF- (4.62 ± 0.18 mmol·h(-1)) than in LF- (7.60 ± 0.57 mmol·h(-1)) fed animals. Hepatic TAG content was ∼2-fold higher (p < 0.05) in HF- (1.07 ± 0.15 nmol·g(-1) tissue) than in LF- (0.50 ± 0.16 nmol·g(-1) tissue) fed animals. In addition, the fatty acid profile of liver TAG in HF-fed animals closely resembled the diet, whereas in LF-fed animals, the fatty acid profile consisted of mostly de novo synthesized fatty acids. FAO was not altered by diet. LF and HF diets differentially alter fed-state hepatic TAG secretion, hepatic fatty acid profiles, and DGAT-1 protein expression.
[Show abstract][Hide abstract] ABSTRACT: The aim of the study is to evaluate central and peripheral neuromuscular function in the knee extensors (KE) and plantar flexors (PF) after 30 days of unilateral lower limb suspension (ULLS) and to examine the effects of low-load blood flow restricted (BFR) resistance training on the KE during ULLS.
Strength, cross-sectional area (CSA), central activation, evoked force, and rates of force development and relaxation were assessed in the KE and PF before and after ULLS in sixteen subjects (9 M, 7F; 18-49 years). Eight of those subjects participated in BFR on the KE three times per week during ULLS (ULLS + Exercise).
The ULLS group had decrements in strength and CSA of the KE (16 and 7 %, respectively) and PF (27 and 8 %, respectively) and the ULLS + Exercise maintained strength and CSA of the KE (P > 0.05), but significantly lost strength and CSA in the PF (21 and 5 %; P > 0.05). KE central activation declined 6 % in the ULLS group and was maintained in the ULLS + Exercise group, but a time × group interaction was not evident (P = 0.31). PF central activation was reduced in both groups (ULLS: -7.6 ± 9.9 and -7.9 ±11.6 %; time main effect P = 0.01). A time × group interaction for KE-evoked twitch force (P = 0.04) demonstrated a 9 % decline in the ULLS + Exercise group following the intervention. Evoked PF doublet torque decreased 12 % in both groups (P = 0.002).
Central and peripheral neuromuscular function is compromised during unloading. While BFR resistance training on the KE during unloading can maintain muscle mass and strength, it may only partially attenuate neuromuscular dysfunction.
[Show abstract][Hide abstract] ABSTRACT: Background. Exercise training intervention is underused in the management of type 2 diabetes mellitus in East Africa.
Methods. 41 physically-active males with type 2 diabetes mellitus living in Mozambique were recruited and randomly assigned to 12 weeks of supervised exercise of low intensity exercise (LEX), vigorous intensity exercise (VEX), or to a control group (CON). Since there were no differences for any outcome variables between the exercise groups, VEX and LEX were combined into one exercise group (EX). Results. Age and baseline body weight were similar between EX and CON. Plasma glucose at 120 min following glucose load (Glu 120) was significantly reduced in the EX group after training (Glu 120 : 17.3 mmol/L to 15.0 mmol/L, P < 0.05), whereas Glu 120 remained unchanged in the CON (Glu 120 : 16.6 mmol/L to 18.7 mmol/L). After controlling for baseline blood pressure (BP), posttraining systolic BP and diastolic BP were lower in the EX group than in the CON group (EX: 129/77 mm Hg, CON: 152/83 mm Hg, P < 0.05). Conclusion. Adding exercise to already active African men with type 2 diabetes improved glucose control and BP levels without concomitant changes in weight.
[Show abstract][Hide abstract] ABSTRACT: Type 2 diabetes is associated with poor exercise tolerance and peak aerobic capacity (VO2peak) even when compared to obese non-diabetic peers. Exercise training studies have demonstrated improvements in VO2peak among T2D, yet there is a large amount of variability in this response. Recent evidence suggests that cardiac autonomic modulation may be an important factor when considering improvements in aerobic capacity.
To determine the effects of a 16 wk aerobic exercise program on VO2peak in obese individuals, with and without T2D, who were classified as having either high or low cardiovagal modulation (HCVM or LCVM) at baseline.
Obese individuals (38 women/19 men; BMI = 36.1 kg/m) were studied in the fasted state. ECG recordings were obtained while seated for 3 min, prior to and after 4 mo of exercise training (4 d/wk, 65% VO2peak). The ECG recording was analyzed for HRV in the spectral domain. Groups were split on a marker of CVM (normalized high frequency (HFnu)) at the 50th percentile, as either high (H) or low (L) CVM.
VO2peak only increased with exercise training among those classified as having HCVM, regardless of diabetes status (T2D: HCVM 20.3 to 22.5 mL/kg/min, LCVM 24.3 to 25.0 mL/kg/min; Obese non-diabetics: HCVM 24.5 to 26.3 mL/kg/min, LCVM 23.1 to 23.7 mL/kg/min) (p<0.05). No change in VO2peak was observed for the LCVM group. Changes in weight do not explain the change in VO2peak among the HCVM group. Glucose tolerance only improved among the LCVM group with T2D.
Obese individuals, with or without T2D, when classified as having relatively HCVM prior to exercise training, have a greater propensity to improve VO2peak following a 16-week aerobic training program.
Medicine and science in sports and exercise 07/2013; 46(2). DOI:10.1249/MSS.0b013e3182a66411 · 4.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Elevated postprandial glycemic excursions (PPG) are significant risk factors for cardiovascular disease in type 2 diabetes patients. Here we tested if and for how many meals a single bout of exercise would reduce PPG responses to subsequent meals in type 2 diabetes (T2D) patients using continuous glucose monitors (CGMS).
We recruited 9 sedentary (<30 minutes/week of exercise) individuals with T2D (BMI: 36.0 ± 1.1 kg/m; age 60.3 ± 1.0 years; HbA1c: 6.3 ± 0.2 %). The subjects consumed a eucaloric diet (51% carbohydrate, 31% fat, 18% protein) consisting of 3 meals, identical in composition, over a 2-day period while wearing CGMS in two different conditions (exercise (EX; one 60 minute bout at 60-75% of heart rate reserve performed prior to breakfast) vs. a sedentary (SED) condition). We quantified 24-h average glucose, PPG-AUC (4 h glucose AUC following meals) and PPG-2 h (2 hour post-prandial glucose).
EX significantly reduced average [glucose] during the first 24 hour period (p=0.03). EX caused a reduction in PPG-AUC (p=0.02) for all of the meals over the two days (main effect between conditions). Comparison between the EX and SED conditions at each meal revealed that EX reduced PPG-AUC following the second meal of day 1 (lunch) (p=0.04). PPG-2 h was not significantly different between EX and SED.
Although a single EX bout does lower 24-h average [glucose], it only significantly lowered PPG-AUC at the second meal following the bout suggesting that daily exercise may be needed to most effectively improve PPG at the advent of exercise training in T2D patients.
Medicine and science in sports and exercise 07/2013; 46(2). DOI:10.1249/MSS.0b013e3182a54d85 · 4.46 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Adiposity alters acylated ghrelin concentrations, but it is unknown if adiposity alters the effect of exercise and feeding on acylated ghrelin responses. Therefore, the purpose of this study was to determine if adiposity (normal-weight [NW] vs. obese [Ob]) influences the effect of exercise and feeding on acylated ghrelin, hunger, and fullness. Fourteen NW and 14 Ob individuals completed two trials in a randomized counterbalanced fashion including a prior exercise trial (EX) and a no exercise trial (NoEX). During the EX trial the participants performed 1 h of treadmill walking (55-60% VO2peak) during the evening, 12 h prior to a 4 h standardized mixed meal test. Frequent blood samples were taken and analyzed for acylated ghrelin and a visual analogue scale was used to assess perceived hunger and fullness. In NW individuals, EX, compared to NoEX, reduced fasting acylated ghrelin concentrations by 18% (P=0.03) and in response to feeding the change in acylated ghrelin (P=0.02) was attenuated by 39%, but perceived hunger and fullness were unaltered. In Ob individuals, despite no changes in fasting or postprandial acylated ghrelin concentrations with EX, postprandial fullness was attenuated by 46% compared to NoEX (P=0.05). In summary, exercise performed the night prior to a meal suppresses acylated ghrelin concentrations in NW individuals without altering perceived hunger or fullness. In Ob individuals, despite no changes in acylated ghrelin concentrations, EX reduced the fullness response to the test meal. Acylated ghrelin and perceived fullness responses are differently altered by acute aerobic exercise in NW and Ob individuals.