Decline In Resting Metabolic Rate Research Articles

Tissue losses and metabolic adaptations both contribute to the reduction in resting metabolic rate following weight loss

ObjectiveTo characterize the contributions of the loss of energy-expending tissues and metabolic adaptations to the reduction in resting metabolic rate (RMR) following weight loss.MethodsA secondary analysis was conducted on data from the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy study. Changes in RMR, body composition, and metabolic hormones were examined over 12 months of calorie restriction in 109 individuals. The contribution of tissue losses to the decline in RMR was determined by weighing changes in the size of energy-expending tissues and organs (skeletal muscle, adipose tissue, bone, brain, inner organs, residual mass) assessed by dual-energy X-ray absorptiometry with their tissue-specific metabolic rates. Metabolic adaptations were quantified as the remaining reduction in RMR.ResultsRMR was reduced by 101 ± 12 kcal/d as participants lost 7.3 ± 0.2 kg (both p < 0.001). On average, 60% of the total reduction in RMR were explained by energy-expending tissues losses, while 40% were attributed to metabolic adaptations. The loss of skeletal muscle mass (1.0 ± 0.7 kg) was not significantly related to RMR changes (r = 0.14, p = 0.16), whereas adipose tissue losses (7.2 ± 3.0 kg) were positively associated with the reduction in RMR (r = 0.42, p < 0.001) and metabolic adaptations (r = 0.31, p < 0.001). Metabolic adaptations were correlated with declines in leptin (r = 0.27, p < 0.01), triiodothyronine (r = 0.19, p < 0.05), and insulin (r = 0.25, p < 0.05).ConclusionsDuring weight loss, tissue loss and metabolic adaptations both contribute to the reduction in RMR, albeit variably. Contrary to popularly belief, it is not skeletal muscle, but rather adipose tissue losses that seem to drive RMR reductions following weight loss. Future research should target personalized strategies addressing the predominant cause of RMR reduction for weight maintenance.

Longitudinal Changes in Resting Metabolic Rates with Aging Are Accelerated by Diseases.

Resting metabolic rate (RMR) declines with aging and is related to changes in health status, but how specific health impairments impact basal metabolism over time has been largely unexplored. We analyzed the association of RMR with 15 common age-related chronic diseases for up to 13 years of follow-up in a population of 997 participants to the Baltimore Longitudinal Study of Aging. At each visit, participants underwent measurements of RMR by indirect calorimetry and body composition by DEXA. Linear regression models and linear mixed effect models were used to test cross-sectional and longitudinal associations of RMR and changes in disease status. Cancer and diabetes were associated with higher RMR at baseline. Independent of covariates, prevalent COPD and cancer, as well as incident diabetes, heart failure, and CKD were associated with a steeper decline in RMR over time. Chronic diseases seem to have a two-phase association with RMR. Initially, RMR may increase because of the high cost of resiliency homeostatic mechanisms. However, as the reserve capacity becomes exhausted, a catabolic cascade becomes unavoidable, resulting in loss of total and metabolically active mass and consequent RMR decline.

Impact of Hepatic Steatosis on Resting Metabolic Rate and Metabolic Adaptation in Response to Intentional Weight Loss.

Weight loss is the primary intervention for nonalcoholic fatty liver disease (NAFLD). A decrease in resting metabolic rate (RMR) out of proportion to the degree of weight loss may promote weight regain. We aimed to determine the impact of hepatic steatosis on weight loss‐associated changes in RMR and metabolic adaptation, defined as the difference between predicted and measured RMR after weight loss. We retrospectively analyzed prospectively collected data from 114 subjects without diabetes (52 with NAFLD), with body mass index (BMI) >35, and who enrolled in a 6‐month weight loss intervention. Hepatic steatosis was determined by unenhanced computed tomography scans by liver:spleen attenuation ratio <1.1. RMR was measured by indirect calorimetry. At baseline, patients with hepatic steatosis had higher BMI, fat mass (FM), fat‐free mass (FFM), and RMR (RMR, 1,933 kcal/day; 95% confidence interval [CI], 841‐2,025 kcal/day; versus 1,696; 95% CI, 1,641‐1,751; P < 0.0001). After 6 months, the NAFLD group experienced larger absolute declines in weight, FM, and FFM, but percentage changes in weight, FFM, and FM were similar between groups. A greater decline in RMR was observed in patients with NAFLD (−179 kcal/day; 95% CI, −233 to −126 kcal/day; versus −100; 95% CI, −51 to −150; P = 0.0154) for the time × group interaction, and patients with NAFLD experienced greater metabolic adaptation to weight loss (−97 kcal/day; 95% CI, −143 to −50 kcal/day; versus −31.7; 95% CI, −74 to 11; P = 0.0218) for the prediction × group interaction. The change (Δ) in RMR was significantly associated with ΔFM, ΔFFM, and baseline RMR, while metabolic adaptation was significantly associated with female sex and ΔFM only. Conclusion: Hepatic steatosis is associated with a greater reduction in FM, which predicts RMR decline and a higher metabolic adaptation after weight loss, potentially increasing the risk of long‐term weight regain.

Contribution of Changes in Body Composition and Adaptive Thermogenesis to the Decline in Resting Metabolic Rate During Prolonged Calorie‐Restricted Weight Loss

In the United States, 2 out of 3 adults are overweight or obese. To lose weight, individuals engage in a variety of dietary and exercise interventions. Despite successful weight loss initially, weight loss is typically less than expected and most individuals regain weight. Both phenomena have been linked to a reduction in resting metabolic rate (RMR) secondary to weight loss.ObjectiveTo characterize the independent contributions of changes in body composition, the major predictor of RMR, and adaptive thermogenesis to the observed decline in RMR associated with weight loss. We predict that changes in fat‐free mass and adaptive thermogenesis will both contribute to RMR decline.MethodsSecondary data analysis was conducted on a publically available data set from CALERIE (Comprehensive Assessment of Long‐term Effects of Reducing Intake of Energy), a 2‐year observational calorie restriction study. CALERIE data used for the present analysis examined changes in RMR, body composition, and metabolic hormones over 12 months of 25% calorie restriction in 117 non‐obese (BMI between 22–27.9 kg/m2) men and women with complete data. Changes in RMR were compared between quartiles based on loss of body weight, fat‐free mass, and fat mass. Adaptive thermogenesis was quantified as the reduction in RMR that exceeded the reduction in RMR predicted from changes in organ mass, which was assessed by Dual‐energy X‐ray absorptiometry.ResultsAfter 12 months, mean weight loss was 7.9 ± 0.3 kg (−10.9 ± 0.4%, p&lt;0.001 vs. baseline), and RMR declined by 101 ± 11 kcal/d (−6.8 ± 0.8%, p&lt;0.001 vs. baseline). Individuals who lost the most weight (Q1ΔBW) demonstrated a greater RMR decline than individuals who lost the least weight (Q4ΔBW, p&lt;0.01). The change in RMR did not differ between quartiles based on fat free mass loss (p=0.15), but it was positively associated with the amount of fat loss (p=0.03). In addition, participants who lost the greatest amount of fat mass (Q1ΔFM) exhibited a more pronounced adaptive thermogenic effect (−79 ± 19 kcal/d) than participants with the least amount of fat loss (Q4ΔFM; −10 ± 26 kcal/d, p&lt;0.05 vs. Q1ΔFM). Adaptive thermogenesis was correlated with declines in leptin (r=0.27, p&lt;0.01), T3 (r=0.19, p &lt; 0.05), and insulin (r=0.25, p&lt;0.05).ConclusionsDuring weight loss, the loss of fat mass and adaptive thermogenesis appear to be stronger predictors of RMR decline when compared to the loss of fat‐free mass.Support or Funding InformationThis work was funded in part by the University of Nebraska‐Lincoln McNair Scholars Program and the Undergraduate Creative Activities and Research Experience.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Effect of Engaging in a Lifestyle Weight Loss Program on Adaptive Thermogenesis in Older Adults

ObjectiveStudies in younger adults show that weight loss results in adaptive thermogenesis, a reduction in resting metabolic rate (RMR) beyond what is predicted by changes in body composition. However, whether adaptive thermogenesis occurs in response to weight loss in older adults is not as well documented. The objective of this analysis was to determine whether adaptive thermogenesis occurs in older adults engaging in a lifestyle weight loss program involving aerobic exercise training (AEX) and dietary caloric restriction (CR).MethodsOlder (65–79 yrs) sedentary men and women with obesity (BMI: 30–45 kg/m2) participated in a 20‐week study assessing the effects of adding CR to AEX on cardiorespiratory fitness and physical function outcomes. Participants were randomly assigned to CR+AEX (n=107) or AEX only (n=41). All participants engaged in the same treadmill walking program of 4 days/week for 30 minutes at 65–70% heart rate reserve. Baseline and post‐intervention RMR and body composition were measured with indirect calorimetry and dual‐energy x‐ray absorptiometry, respectively. Baseline measures of body composition, age, and sex were used to generate a linear regression equation to predict RMR. To determine metabolic changes resulting from the intervention, post‐intervention measures were applied to the same regression equation. Adaptive thermogenesis was calculated as the difference between predicted and measured RMR post‐intervention; a value &lt;0 indicated the presence of adaptive thermogenesis.ResultsThe CR+AEX group lost more body weight (−8.9 ± 4.4 vs. −1.5 ± 3.5 kg, p&lt;0.01) and fat free mass (FFM; −2.4 ± 2.2 vs. −0.5 ± 2.1 kg, p&lt;0.01) compared with AEX. Measured RMR was similar in CR+AEX compared with AEX before (1365 ± 275 vs. 1378 ± 256 kcal/d, p=0.79) and after (1294 ± 259 vs. 1332 ± 252 kcal/d, p=0.42) the intervention. Adaptive thermogenesis was similar in CR+AEX compared with AEX (−23 ± 159 vs. −33 ± 189 kcal/d, p=0.73). There was large individual variability in the degree of adaptive thermogenesis in both groups (CR+AEX: −409 to 376 kcal/d; AEX: −534 to 359 kcal/d), which did not correlate with the individual degree of relative or absolute CR or to the individual amount of weight lost (all p&gt;0.05).ConclusionsCompared with AEX alone, older adults engaging in weight loss by CR and AEX did not experience a greater decline in RMR beyond what was expected from changes in body composition. Since individual variability in adaptive thermogenesis was not related to amount of weight lost or CR, further research is needed to identify factors that cause adaptive thermogenesis in some older individuals.Support or Funding InformationNIH R01 HL093713 (BJN), NIA P30 AG021332, NIH T32 AG033534This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Perfluoroalkyl substances and changes in body weight and resting metabolic rate in response to weight-loss diets: A prospective study.

BackgroundThe potential endocrine-disrupting effects of perfluoroalkyl substances (PFASs) have been demonstrated in animal studies, but whether PFASs may interfere with body weight regulation in humans is largely unknown. This study aimed to examine the associations of PFAS exposure with changes in body weight and resting metabolic rate (RMR) in a diet-induced weight-loss setting.Methods and findingsIn the 2-year POUNDS Lost randomized clinical trial based in Boston, Massachusetts, and Baton Rouge, Louisiana, that examined the effects of energy-restricted diets on weight changes, baseline plasma concentrations of major PFASs were measured among 621 overweight and obese participants aged 30–70 years. Body weight was measured at baseline and 6, 12, 18, and 24 months. RMR and other metabolic parameters, including glucose, lipids, thyroid hormones, and leptin, were measured at baseline and 6 and 24 months. Participants lost an average of 6.4 kg of body weight during the first 6 months (weight-loss period) and subsequently regained an average of 2.7 kg of body weight during the period of 6–24 months (weight regain period). After multivariate adjustment, baseline PFAS concentrations were not significantly associated with concurrent body weight or weight loss during the first 6 months. In contrast, higher baseline levels of PFASs were significantly associated with a greater weight regain, primarily in women. In women, comparing the highest to the lowest tertiles of PFAS concentrations, the multivariate-adjusted mean weight regain (SE) was 4.0 (0.8) versus 2.1 (0.9) kg for perfluorooctanesulfonic acid (PFOS) (Ptrend = 0.01); 4.3 (0.9) versus 2.2 (0.8) kg for perfluorooctanoic acid (PFOA) (Ptrend = 0.007); 4.7 (0.9) versus 2.5 (0.9) kg for perfluorononanoic acid (PFNA) (Ptrend = 0.006); 4.9 (0.9) versus 2.7 (0.8) kg for perfluorohexanesulfonic acid (PFHxS) (Ptrend = 0.009); and 4.2 (0.8) versus 2.5 (0.9) kg for perfluorodecanoic acid (PFDA) (Ptrend = 0.03). When further adjusted for changes in body weight or thyroid hormones during the first 6 months, results remained similar. Moreover, higher baseline plasma PFAS concentrations, especially for PFOS and PFNA, were significantly associated with greater decline in RMR during the weight-loss period and less increase in RMR during the weight regain period in both men and women. Limitations of the study include the possibility of unmeasured or residual confounding by socioeconomic and psychosocial factors, as well as possible relapse to the usual diet prior to randomization, which could have been rich in foods contaminated by PFASs through food packaging and also dense in energy.ConclusionsIn this diet-induced weight-loss trial, higher baseline plasma PFAS concentrations were associated with a greater weight regain, especially in women, possibly explained by a slower regression of RMR levels. These data illustrate a potential novel pathway through which PFASs interfere with human body weight regulation and metabolism. The possible impact of environmental chemicals on the obesity epidemic therefore deserves attention.Trial registrationClinicalTrials.gov NCT00072995

Changes in resting metabolic rate and body composition after bariatric surgery in two severely obese adolescent patients attending a bariatric healthy weight clinic: A clinical case report

BackgroundThe literature supports the concept that resting metabolic rate (RMR) decreases significantly after bariatric surgery and that there is a relationship between body composition changes and decline in RMR. Research also indicates that the greater the decline in RMR through weight loss, the greater the chance for weight regain. There are currently no data describing RMR changes of severely obese adolescent bariatric patients in the clinical setting.AimThis current clinical observation describes changes in RMR and body composition in two severely obese adolescents who were part of a healthy weight bariatric clinic and who underwent laparoscopic sleeve gastrectomy.MethodsPatients who were eligible for bariatric surgery were recruited as part of a nine‐ month pilot study which aimed to observe changes in RMR in adolescents pre‐ and post –surgery. Institutional Review Board (IRB) approval was obtained and patients interested in the study signed an informed consent and assent for the measurement of RMR via indirect calorimetry. Eight patients signed informed consent for RMR testing; four patients were lost to clinical follow‐up. Four patients underwent pre‐surgery RMR testing, two of those patients underwent bariatric surgery and completed post‐surgery RMR testing. Patients participated in their usual clinical care. Patients arrived at the clinic approximately 30–45 minutes before their regularly scheduled clinic appointment and were fasting. Protocol for indirect calorimetry was followed.ResultsPre‐surgery (one month before surgery) weight for Patient 1: 124.4kg, BMI 36.8; Patient 2 : 149.4kg, BMI 55.5. Both patients demonstrated a decline in RMR post‐surgery (Patient 1: 25% of baseline, 68 days post‐surgery; Patient 2: 5% of baseline, 94 days post‐surgery). Patient 1 lost 12.8% body weight with a decrease of RMR from 21.28kcal/kg body weight to 18.28kcal/kg. Patient 2 lost 14.8% body weight with change in RMR from 15.29kcal/kg body weight to 17.26 kcal/kg. Interestingly, patient 2 lost more muscle mass (14.1%) than patient 1 (9.4%) through surgery yet had less of a decline in RMR when compared to patient 1. Overall total percent body fat changes post‐surgery was quite small for both patients (Patient 1: −2.8%; Patient 2: −1.6%)ConclusionCurrently, best‐practice guidelines are used in the nutrition management of adolescent bariatric patients; however, there is no standardization of nutrition care. Further research investigating the changes in RMR and body composition in severely obese adolescents undergoing bariatric surgery in the clinical setting and what may be the clinical implications of these changes is still needed. Tracking RMR and body composition over‐time may help guide clinical practice for individualized nutrition and exercise recommendations that could help prevent weight regain post‐surgery.Support or Funding InformationGeorgia State University, Lewis School of Nursing and Health Professions Intramural Grant Program 2013–2014

Aging and the Energetic Cost of Life

Aging and the Energetic Cost of Life

Changes in resting metabolic rate in an elderly German population: cross-sectional and longitudinal data.

This study investigates age-dependent changes in resting metabolic rate (RMR) considering changes in body composition and fat distribution within the longitudinal study on nutrition and health status in an aging population in Giessen (GISELA), Germany, using three different approaches. In approach 1 cross-sectional data from 358 female and 155 male participants of the GISELA study were evaluated (mean age of 67.4 +/- 5.9 and 66.9 +/- 5.2 y, respectively). In approach 2 longitudinal data of 107 female and 55 male subjects who participated over a follow up period of 10 years were analysed. In approach 3 all data obtained at a total of 3033 visits from 363 women and 153 men between 1994 and 2006 were evaluated. The mean duration of follow-up was eight years. RMR was assessed by indirect calorimetry. Approach 1: RMR correlates significantly negatively with age in women and men. Considering fat free mass, fat mass, and WHR, age proved to be a significant predictor of RMR in both sexes in multiple regression analysis; RMR falls by 11.2 kJ/d and 34.1 kJ/d per year in females and males, respectively. Approach 2: In males but not in females RMR decreases significantly in the course of the follow up. After ten years measured RMR is significantly lower than expected RMR predicted on the basis of body composition and fat distribution in females and males. Deviations correspond to a decline in RMR by 11.4 and 27.5 kJ/d per year independently of changes in body composition and fat distribution. Approach 3: Results of the mixed linear model show that RMR decreases in the course of aging in both women and men; after considering changes in body composition and fat distribution respective decreases were 8.7 and 30.7 kJ/d per year. These results indicate that the decline in RMR with advancing age cannot be totally due to changes in body composition.

Losers Can Win at Weight Maintenance

LOSING WEIGHT AND KEEPING IT OFF is a tough business—no one succeeds without really trying. But some long-held beliefs about the difficulties of maintaining weight loss are changing. As a result, experts are developing a more complete picture of weight loss maintenance and a more hopeful message for millions who are overweight or obese. Experts who presented data on maintaining weight loss during the Endocrine Society’s annual meeting in Toronto last month said the proportion of overweight individuals who succeed at long-term weight loss—losing at least 10% of body weight and keeping the weight off for 1 year—is higher than many might expect, about 20% (McGuire MT et al. Int J Obes Relat Metab Disord. 1999;23[12]:1314-1319). An even more optimistic outlook appears in a recent study. Researchers from the Centers for Disease Control and Prevention report that nearly 60% of 1310 individuals in the National Health and Nutrition Examination Survey who lost 10% of body weight maintained 95% of the loss for 1 year (Weiss EC et al. Am J Prev Med. 2007;33[1]: 34-40). “Weight maintenance following weight loss is doable,” lead author Edward C. Weiss, MD, MPH, said in a statement. Holly Wyatt, MD, an associate professor at the University of Colorado Health Sciences Center, Denver, agreed. “A lot of people say you can’t succeed at maintaining weight loss long-term,” she noted during a press briefing at the meeting in Toronto. “We do have some data now that say that’s not true.” METABOLIC ROLE Wyatt said the theory that weight loss lowers the resting metabolic rate (RMR), which in turn pushes the body to regain lost pounds, is not a catchall explanation for weight regain. She examined the existing medical literature and found several studies that contradict the theory. Among them is a study of 24 overweight, postmenopausal women who, after 4 phases of weight loss and weight maintenance, lost a mean of 12.9 kg (Weinsier RL et al. Am J Clin Nutr. 2000; 72[3]:1088-1094). After measuring changes in the women’s RMR and thyroid hormone levels compared with 24 control participants, researchers from the University of Alabama School of Medicine, Birmingham, and the Mayo Clinic, in Rochester, Minn, reported a temporary decline in RMR and thyroid hormones in the study participants. However, measures of both returned to baseline after the women stopped losing weight. The RMR in the women who had lost weight was not significantly different than in controls, and women with lower RMRs were not more likely than those with higher rates to regain more weight over the next 4 years. “The idea that absolutely, your body is fighting you, I don’t think really holds out in the literature,” said Wyatt. “Other things like our environment or other behaviors may overpower [metabolic] change.”

Lower resting metabolic rate in the elderly may not be entirely due to changes in body composition

To investigate whether or not the lower resting metabolic rate (RMR) in the elderly is entirely due to changes in body composition. Cross-sectional data of 132 female (age 69.9+/-5.5 y, body mass index (BMI) 26.5+/-4.0 kg/m(2)) and 84 male (age 68.9+/-5.1 y, BMI 26.1+/-2.8 kg/m(2)) participants of the longitudinal study on nutrition and health status in an aging population of Giessen, Germany, as well as that of 159 young women (age 24.8+/-3.0 y, BMI 21.1+/-2.5 kg/m(2)) and 67 young men (age 26.8+/-3.4 y, BMI 23.3+/-2.4 kg/m(2)) were analysed. RMR was measured by indirect calorimetry after an overnight fast and body composition was estimated by bioelectrical impedance analysis and predictive equations from the literature. Analysis of covariance was used to adjust RMR for body composition, body fat distribution and smoking habits. Additionally, RMR that is to be expected theoretically, was calculated on the basis of the subjects' body composition and the specific metabolic rate of the different organs and was compared to measured RMR. Compared to young subjects adjusted RMR was significantly lower in elderly women (5432+/-82 vs 5809+/-70 kJ/day, P<0.01) and men (6971+/-99 vs 7558+/-121 kJ/day, P<0.001). In both elderly women and men, measured RMR was markedly lower than calculated RMR (-625+/-404, -515+/-570 kJ/day). By contrast, measured and calculated RMR were nearly the same in young men (159+/-612 kJ/day); in young women the difference between measured and calculated RMR was only -300+/-457 kJ/day. In both sexes, these differences are significantly larger in the elderly when compared to young adults. These results support the point of view that the decline in RMR with advancing age cannot be totally due to changes in body composition.

Effects of a low-calorie diet on resting metabolic rate and serum tri-iodothyronine levels in obese children.

The purpose of the study was to examine the effects of weight loss on resting metabolic rate (RMR) and on serum T3 levels in obese children and to investigate whether RMR changes are related to T3 changes. Sixty-four healthy, overweight, children (age: 12.1+/-1.1 years, body mass index 29.3+/-4.3 kg/m2) were studied during a 6-week weight reduction programme. RMR (by indirect calorimetry) total T3, total T4, TSH and fat-free mass (FFM) (by anthropometry) were measured at baseline and after 6 weeks of dietary treatment. Weight loss resulted in a 10.1% decline in RMR (P < 0.01) and a 23.4% decrease in serum T3 levels (P < 0.001). RMR was correlated with FFM before (r = 0.78, P < 0.001) and after weight loss (r = 0.76, P < 0.001). The changes in RMR were positively correlated with the changes in FFM (r = 0.48, P < 0.05) but also with the changes in serum T3 levels (r = 0.47, P < 0.05). The initial T3 levels predicted the subsequent fall in T3 that occurred after 6 weeks of dietary treatment (r = -0.60, P < 0.001). A significant decrease in serum T3 concentrations and resting metabolic rate occurred as a result of a 6-week weight reduction programme in an obese child population. The decline in T3 levels combined with fat-free mass loss could be responsible for the reduction in resting metabolic rate.

Regular exercise and the age-related decline in resting metabolic rate in women.

A low resting metabolic rate (RMR) is a risk factor for future weight gain. We tested the hypothesis that the age-related decline in RMR in sedentary women is not observed in women who exercise regularly. Sixty-five healthy, weight-stable women, aged 21-35 or 50-72 yr, were studied: 12 premenopausal and 15 postmenopausal sedentary women, 13 premenopausal and 15 postmenopausal distance runners, and 10 endurance-trained postmenopausal swimmers. RMR was measured by indirect calorimetry (ventilated hood system) after an overnight fast, and values were adjusted for fat mass and fat-free mass (RMRadj). The RMRadj was approximately 10% lower in the postmenopausal vs. premenopausal sedentary women (52 +/- 2 vs. 57 +/- 2 Cal/h; P < 0.002). In contrast, RMRadj was not significantly different in the premenopausal (59 +/- 2 Cal/h) and postmenopausal (57 +/- 1 Cal/h) distance runners. The postmenopausal swimmers had a RMRadj (57 +/- 2 Cal/h) identical to that of the postmenopausal runners, suggesting a generalized influence of the endurance exercise-trained state in postmenopausal women. Group differences in RMRadj were not associated with differences in total energy intake or composition or with plasma concentrations of norepinephrine, T3, or T4. However, maximal oxygen consumption (aerobic fitness) accounted for 35% of the individual variance in RMRadj in the overall population (r = 0.59; P < 0.001). Our results are consistent with the concept that the age-related decline in RMR in sedentary women is not observed in women who regularly perform endurance exercise. The elevated level of RMR observed in middle-aged and older exercising women may play a role in their lower levels of body weight and fatness compared to those in sedentary women.

Effects of strength or aerobic training on body composition, resting metabolic rate, and peak oxygen consumption in obese dieting subjects

Given that resting metabolic rate (RMR) is related largely to the amount of fat-free mass (FFM), the hypothesis was that strength training, which stimulates muscle hypertrophy, would help preserve both FFM and RMR during dieting. In a randomized controlled intervention trial, moderately obese subjects (aged 19-48 y) were assigned to one of three groups: diet plus strength training, diet plus aerobic training, or diet only. Sixty-five subjects (25 men and 40 women) completed the study. They received a formula diet with an energy content of 70% of RMR or 5150 +/- 1070 kJ/d (x +/- SD) during the 8-wk intervention. They were seen weekly for individual nutritional counseling. Subjects in the two exercise groups, designed to be isoenergetic, trained three times per week under supervision. Those in the strength-training group performed progressive weight-resistance exercises for the upper and lower body. Those in the aerobic group performed alternate leg and arm cycling. After 8 wk, the mean amount of weight lost, 9.0 kg, did not differ significantly among groups. The strength-training group, however, lost significantly less FFM (P < 0.05) than the aerobic and diet-only groups. The strength-training group also showed significant increases (P < 0.05) in anthropometrically measured flexed arm muscle mass and grip strength. Mean RMR declined significantly, without differing among groups. Peak oxygen consumption increased the most for the aerobic group (P = 0.03). In conclusion, strength training significantly reduced the loss of FFM during dieting but did not prevent the decline in RMR.

Malnutrition in children with cystic fibrosis: the energy-balance equation.

Malnutrition in children with cystic fibrosis: the energy-balance equation.

Regulation of energy expenditure in aging humans.

The regulation of daily energy expenditure and its components in aging humans in considered in this review. Specifically, the effects of age on resting metabolic rate (RMR), the thermic effect of a meal, body composition, and the interaction of these variables with physical activity in both men and women are considered. The possible modulators of the age-related decline in RMR are examined by exploring the influence of alterations in body composition, physical activity, and the sodium-potassium pump. Thereafter, the status of energy requirements in healthy and diseased individuals is examined. New information is presented regarding the use of the doubly-labeled water technique to measure daily energy expenditure and its applicability to the determination of daily energy requirements in free-living older persons.

Sodium-potassium pump activity contributes to the age-related decline in resting metabolic rate.

We examined the hypothesis that a decline in Na-K pump activity contributes to the lower resting metabolic rate (RMR) in older males, independent of the loss of fat-free mass. Plasma and erythrocyte Na and K concentrations were measured using flame photometry. Changes in these concentrations after incubation with and without ouabain were used to calculate erythrocyte Na-K pump rate and rate constant in 27 younger (28 +/- 7 yr) and 25 older (67 +/- 6 yr) men. Older men showed an 18% lower erythrocyte Na-K pump rate constant (0.32 +/- 0.09 vs. 0.39 +/- 0.10 h-1; P < 0.01), a 12% lower RMR (1.10 +/- 0.14 vs. 1.25 +/- 0.14 kcal/min; P < 0.01) and an 8% lower level of fat-free mass (61.7 +/- 5.8 vs. 67.4 +/- 8.1 kg; P < 0.01) relative to younger men. A lower RMR persisted in older men (1.14 +/- 0.12 kcal/min) compared to younger men (1.21 +/- 0.12 kcal/min; P < 0.05) after control for the effect of fat-free mass. No differences in RMR were found, however, between older (1.17 +/- 0.13 kcal/min) and younger men (1.20 +/- 0.13 kcal/min) after controlling for both fat-free mass and the erythrocyte Na-K pump rate constant. A positive relation was noted between RMR and the erythrocyte Na-K pump rate constant, after removing the effects of fat-free mass (partial r = 0.30; P < 0.05). Our results support the conclusions that: 1) the in vivo activity of the Na-K pump is related to RMR, and 2) the age-related reduction in Na-K pump activity is a partial contributor to the decline in RMR in older men.

Influence of aerobic capacity, body composition, and thyroid hormones on the age-related decline in resting metabolic rate

It has been suggested that changes in fat-free weight may not fully explain the decline of resting metabolic rate (RMR) that occurs with aging. We therefore examined the hypothesis that a reduction in maximal aerobic capacity (V o 2max) may partially explain the lower RMR in older men, after accounting for differences in fat-free weight and fat weight. We also considered differences in energy intake and plasma thyroid hormones as possible modulators of the age-related decline in RMR in men. Three-hundred healthy men (aged 17 to 78 years) were characterized for: (1) RMR (kcal/min) from indirect calorimetry; (2) body composition from underwater weighing; (3) maximal aerobic capacity from a test of V o 2max; (4) plasma thyroid hormones (total triiodothyronine [T 3], free T 3, total thyroxine [T 4], and free T 4); and (5) estimated energy intake (kcal/d) from a 3-day food diary. A curvilinear decline of RMR with age was found ( P < .01), in which no relationship was found in men less than 40 years of age ( r = .10, slope = 0.002 kcal/min/yr), whereas in men older than 40 years, RMR was negatively related to age ( r = −.52, slope = −0.008 kcal/min/yr). After statistical control for differences in fat-free weight and fat weight, a negative relationship between age and RMR persisted (partial r = −.30, P < .01). It was only after control for fat-free weight, fat weight, and V o 2max (partial r = −.10, P > .05) that no association between age and RMR was noted. When subgroups of younger and older individuals were paired for age and fat-free weight, but different V o 2max values, a higher RMR was noted in the trained younger (8%) and trained older men (11%) compared with untrained younger and older men, respectively. Thyroid hormones and daily energy intake were negatively related to age on a univariate basis, but no independent association was noted after control for fat-free weight. We conclude that, in addition to the loss of fat-free weight, the decline in V o 2max is an additional factor associated with the decline of RMR in aging men. Age-related changes in energy intake, fat weight, and thyroid hormones appear to be less important in explaining the reduction of RMR in aging men. Maintenance of fat-free weight and V o 2max by regular physical activity may attenuate the age-related RMR in healthy men.

Weight loss and change in resting metabolic rate

The relation between change in resting metabolic rate (RMR) and change in fat-free mass (FFM) after weight loss is not well understood and is often inappropriately expressed in kilocalories per unit of FFM. We measured RMR and FFM in 35 obese patients enrolled in a conservative weight-loss program. RMR per kilogram FFM was not different after weight loss. However, the regression of delta RMR on delta FFM revealed that the decline in RMR tended to be greater than could be accounted for by loss of FFM. At initial test and retest, body fat (Fat) was not a predictor of RMR after FFM had been taken into account but delta Fat significantly contributed to the prediction of delta RMR when added to the equation after delta FFM. Thus, people losing larger amounts of weight had declines in RMR greater than could be accounted for by loss of FFM. Self-reported age of onset of obesity was not related to delta RMR.

Thermic effect of feeding in relation to energy balance in elderly men.

Resting metabolic rate (RMR) and the thermic effect of feeding (TEF) two meals of differing energy densities were measured in 8 healthy elderly men aged 63-74 years. Similar measurements were made on 8 healthy young men aged 22-28 years. TEF was related to the meal size in both groups. Metabolic rate increased by 20.7 and 27.9% in the elderly group (EG) and 25.8 and 37.7% in the control group (CG) in response to the 2.0-and 4.0-MJ meals, respectively. Although the EG were fatter than the CG, they consumed a smaller daily food intake: we suggest that the decline in RMR and TEF as indicated by the study would explain his paradox.