Recommended Levels of Physical Activity and Insulin Resistance in Middle-Aged Women

Purpose

The purpose of this study was to examine the relationship between recommended levels of physical activity (PA) and insulin resistance, as estimated by the homeostasis model assessment of insulin resistance (HOMA-IR) in middle-aged women without diabetes.

Methods

This was a cross-sectional study of 264 women located in the Mountain West region of the United States. Sedentary time and moderate- and vigorous-intensity PA were determined objectively, via accelerometry, over 7 days. HOMA-IR was calculated from fasting insulin and glucose. Body mass index (kg/m2) was calculated from measured weight and height; body fat percentage was assessed using air displacement plethysmography; and abdominal circumference was measured at the umbilicus. Moderate- and vigorous-intensity PA levels were based on recommendations for PA and health from the American College of Sports Medicine.

Results

Total time spent in sedentary activity was significantly related to insulin resistance. Time spent in moderate-intensity or vigorous-intensity activity, at recommended levels, was also significantly and inversely related to insulin resistance. However, after statistically adjusting for body fat percentage or abdominal circumference individually, the relationship between sedentary activity, moderate-intensity, or vigorous-intensity activity and HOMA-IR was eliminated.

Conclusions

Achieving recommended levels of PA is associated with lower HOMA-IR in healthy women without diabetes; however, adiposity accounts for part of this relationship.

Weight loss-induced alterations in serum markers of bone turnover persist during weight maintenance in obese men and women

OBJECTIVE

Moderate weight loss alters bone turnover and reduces bone mineral density in overweight men and women. However, it is not known whether bone turnover is normalized during weight maintenance postweight loss. Thus, the objective of the present study was to examine changes in serum bone turnover markers during 9 months of weight maintenance following weight reduction on a very low-energy diet (VLED) in obese men and women.

METHODS

Thirty-seven men (n = 13) and women (n = 24) aged 50 +/- 9.8 years underwent 3 months of weight reduction on a VLED ( approximately 500 kcal/d) followed by 9 months on either a low-carbohydrate or low-fat weight maintenance diet ( approximately 1600 kcal/d). Concentrations of osteocalcin (OC) and C-terminal peptide of type I collagen (CTX) in serum were measured using enzyme-linked immunosorbent assay at baseline and at months 3, 6, and 12. Serum parathyroid (PTH) concentrations were measured using a chemiluminescent immunoassay at all 4 time points. Data were analyzed using a 3-factor-repeated measures analysis of variance.

RESULTS

Average weight loss was 19% +/- 3% and, during the 9-month weight maintenance period, average weight gain was approximately 3%, with no differences due to diet composition. Serum concentrations of OC and CTX significantly increased after weight reduction and remained elevated during weight maintenance. Serum PTH was reduced after weight loss. Percent changes in OC and CTX were correlated during weight maintenance (r = -0.437, p = 0.008), but not during weight loss. Percent changes in CTX and body weight were negatively correlated during weight loss (r = -0.474, p = 0.003) and maintenance (r = -0.455, p = 0.006).

CONCLUSIONS

Weight loss induced via a VLED may result in an imbalance between bone formation and resorption and accelerate remodeling. The deleterious effect of energy restriction on bone remodeling rate appears to persist during weight maintenance.

Comparison of a reduced carbohydrate and reduced fat diet for LDL, HDL, and VLDL subclasses during 9-months of weight maintenance subsequent to weight loss

OBJECTIVES

This study compared LDL, HDL, and VLDL subclasses in overweight or obese adults consuming either a reduced carbohydrate (RC) or reduced fat (RF) weight maintenance diet for 9 months following significant weight loss.

METHODS

Thirty-five (21 RC; 14 RF) overweight or obese middle-aged adults completed a 1-year weight management clinic. Participants met weekly for the first six months and bi-weekly thereafter. Meetings included instruction for diet, physical activity, and behavior change related to weight management. Additionally, participants followed a liquid very low-energy diet of approximately 2092 kJ per day for the first three months of the study. Subsequently, participants followed a dietary plan for nine months that targeted a reduced percentage of carbohydrate (approximately 20%) or fat (approximately 30%) intake and an energy intake level calculated to maintain weight loss. Lipid subclasses using NMR spectroscopy were analyzed prior to weight loss and at multiple intervals during weight maintenance.

RESULTS

Body weight change was not significantly different within or between groups during weight maintenance (p>0.05). The RC group showed significant increases in mean LDL size, large LDL, total HDL, large and small HDL, mean VLDL size, and large VLDL during weight maintenance while the RF group showed increases in total HDL, large and small HDL, total VLDL, and large, medium, and small VLDL (p<0.05). Group*time interactions were significant for large and medium VLDL (p>0.05).

CONCLUSION

Some individual lipid subclasses improved in both dietary groups. Large and medium VLDL subclasses increased to a greater extent across weight maintenance in the RF group.

Effects of long-term aerobic exercise on EPOC

This study sought to determine the influence of 16 months of progressive aerobic exercise on excess postexercise oxygen consumption (EPOC) and the extent EPOC contributed to weight management. Twenty-five overweight/obese women and 16 overweight/obese men participated in a 16-month exercise program (moderate-intensity treadmill walking) that progressed across the first 26 weeks to 5 days.wk(-1), 45 min.session(-1), and 75% HRR. Three-hour EPOC was measured at baseline, 9 months, and 16 months by indirect calorimetry in response to an exercise session (treadmill walking), in which energy expenditure (EE) was estimated from the participant's previous 10 exercise sessions. For women, EPOC was 7.5 +/- 4.9, 9.6 +/- 7.6, and 6.5 +/- 6.5 L at baseline, 9 months, and 16 months, respectively (p > 0.05). For men, EPOC increased from baseline (11.8 +/- 6.8 L) to 9 months (13.5 +/- 8.6 L) (p < 0.05) with no further increase at 16 months (13.5 +/- 11.0 L). Change in EPOC was correlated with change in EE at 9 months (r = 0.65; p < 0.05) and 16 months (r = 0.58; p < 0.05) for men but not women. Progressive long-term exercise significantly influenced EPOC in overweight/obese men but not women. Change in volume of exercise likely explained the increase in energy expenditure during EPOC in men. EPOC contributed modestly to EE compared to the exercise itself.

SIX MONTHS OF SUPERVISED HIGH-INTENSITY LOW-VOLUME RESISTANCE TRAINING IMPROVES STRENGTH INDEPENDENT OF CHANGES IN MUSCLE MASS IN YOUNG OVERWEIGHT MEN

To determine the effects of a 6-month supervised low-volume resistance training (RT) program (1 set, 85-90%, one repetition maximum, 1RM, 3 d x wk(-1)) on muscular strength (1RM) and skeletal muscle mass (SMM) in previously sedentary, overweight men on an ad libitum diet. Nineteen men were randomly assigned to a control (CON, n = 8) or RT (n = 11) group. The exercise protocol consisted of 5 upper- and 4 lower-body exercises using weight machines. CON maintained their sedentary lifestyle. One RM for upper body (chest press [CP] + lat pull-down [LPD]) and lower body (leg press [LP]) and SMM were assessed at baseline, and at 3 and 6 months. Adherence was 96 +/- 2% with an average time to complete each exercise session of 15 +/- 2 minutes. Volume completed per exercise session significantly increased from baseline (2,812 +/- 670 kg) to 6 months (6,411 +/- 2,128 kg). There was a group by time interaction in 1RM for CP, LPD, and LP. Upper-body strength increased significantly (p < 0.001) (31.3 +/- 9.3%) from baseline to 3 months and from 3 to 6 months (17.9 +/- 8.7%). Lower-body strength also increased significantly from baseline to 3 months (17.8 +/- 16.6%) and from 3 to 6 months (32.0 +/- 33.7%). No changes in upper- or lower-body strength occurred in the CON group. There was no group by time interaction for SMM (CON, 34.5 +/- 2.9 kg vs. RT, 34.2 +/- 2.9 kg; p > 0.05) or for energy intake (p > 0.05). In conclusion, a single set resistance training program at 85% of 1RM, 3 d x wk(-1) resulted in continued increases in muscular strength and a very high adherence rate over a 6-month period in sedentary, overweight men independent of significant changes in SMM. This training protocol may increase adherence and produce long-term increases in muscular fitness as part of an adult fitness program.

A comparison of meal replacements and medication in weight maintenance after weight loss

OBJECTIVE

To compare the use of meal replacements or medication during weight maintenance subsequent to weight loss using a very low-energy diet (VLED) in overweight or obese adults.

DESIGN

Participants followed a liquid VLED of 2177 kJ for 12 weeks followed by 4 weeks of re-orientation to solid foods. Participants were randomized at week 16 to receive either meal replacements or Orlistat both combined with a structured meal plan containing an energy value calculated to maintain weight loss.

SUBJECTS

Sixty-four women (age = 49.9 +/- 10 y, weight = 101.6 +/- 17.1 kg, height = 164.9 +/- 6.0 cm, BMI = 36.7 +/- 5.4 kg/m(2)) and 28 men (age = 53.7 +/- 9.6 y, weight = 121.8 +/- 16.0 kg, height = 178.7 +/- 5.6 cm, BMI = 37.8 +/- 4.9 kg/m(2)) completed a 1 year weight management program. Behavioral weight management clinics included topics on lifestyle, physical activity (PA), and nutrition. Participants met for 90 min weekly for 26 weeks, and then biweekly for the remaining 26 weeks.

OUTCOMES

Minutes of PA, fruits and vegetables (FV), and pedometer steps were recorded on a daily basis and reported at each group meeting. Body weight was obtained at each group meeting.

RESULTS

During VLED, the MR group decreased body weight by 22.8 +/- 6.1 kg and the Orlistat group decreased body weight by 22.3 +/- 6.1 kg. During weight maintenance, there was no significant group by time interaction for body weight, PA, FV consumption, or pedometer steps. At week 16, the meal replacement group had a body weight of 85.4 +/- 14.3 kg that increased to 88.1 +/- 16.5 kg at 52 weeks (p < 0.05). At week 16, the Orlistat group had a body weight of 85.7 +/- 17.9 kg that increased to 88.5 +/- 20.3 kg at 52 weeks (p < 0.05).

CONCLUSIONS

Subsequent to weight loss from a VLED, meal replacements and Orlistat treatments were both effective in maintaining weight significantly below baseline levels over a 52 week period of time. Meal replacements may be a viable alternative strategy to medications for weight maintenance.

A comparison of three methods of analyzing post-exercise oxygen consumption

Oxygen consumption after exercise is frequently plotted as a function of time and then the area under the curve (AUC) is calculated. Subsequently, this AUC is further manipulated and thus, differences between these manipulations may impact the interpretation of changes in oxygen consumption after exercise. The purpose of this study was to determine if the method of calculating AUC influences the interpretation of changes in post-exercise oxygen consumption in response to long-term aerobic exercise. Forty-three moderately obese, sedentary participants volunteered to participate in this study (26 women and 17 men). All participants performed verified supervised exercise during the study. Supervised treadmill exercise was initially conducted for 3 d/week at 60 % of heart rate reserve (HRR) for 30 min and progressed to 5 d/week at 75 % of HRR for 45 min across the first 4 months. Pre-exercise, exercise, and post-exercise oxygen consumption was measured at baseline and 9 months. AUC was calculated by three methods; total, incremental, and positive incremental. Descriptive statistics and dependent T-tests were calculated for each method of calculating the AUC. In addition, the intra-individual coefficient of variation was determined for each individual for each AUC method. A pearson product moment correlation was calculated for each method to determine the strength of the relationship between pre- and post-training values. The change in post-exercise oxygen AUC after nine months of training was 5.36+/-10.90 L, 2.17+/-7.61 L, and 1.74+/-9.10 L for the total, incremental, and positive incremental methods, respectively. There was significant change in post-exercise total AUC from baseline to 9-months (5.36 +/- 10.90 L), while there was no significant change in incremental or positive incremental AUC. There was a moderately high correlation (r=0.67, p <0.05) between baseline and 9-months for the total AUC method, while there was no significant correlation for incremental and positive incremental AUC methods. These results suggest that the method used to calculate AUC can lead to a different interpretation of the effects of training on post-exercise oxygen consumption. From this data, it appears that analyzing post exercise oxygen consumption with the total area under the curve method has a greater ability to detect a change from aerobic training, than either the positive or incremental area under the curve methods.

Reporting quality of randomized trials in the diet and exercise literature for weight loss

Background

To adequately assess individual studies and synthesize quantitative research on weight loss studies, transparent reporting of data is required. The authors examined the reporting quality of randomized trials in the weight loss literature, focusing exclusively on subject characteristics as they relate to enrollment, allocation, and follow-up.

Methods

An extensive literature review, which included a computerized search of the MEDLINE database, manual searches of bibliographic references, and cross-referencing of 92 review articles was conducted. A checklist, based on CONSORT recommendations, was used to collect information on whether or not authors reported age, gender, co-morbid disease, medication use, race/ethnicity, and postmenopausal status. Also tracked was whether or not initial and final sample size was reported and stratified by gender.

Results

Of 604 possible articles, 231 articles met eligibility criteria. Important subject characteristics were not reported as the following breakdown indicates: age (11%), gender (4%), race/ethnicity (86%), co-morbid disease states (34%), and medication use (92%). Additionally, 21% of articles failed to report initial sample size by gender while 69% neglected to report final sample size by gender.

Conclusion

Inadequate reporting can create difficulties with interpretation and can lead to biased results receiving false credibility. The quality of reporting for weight loss studies needs considerable improvement.