Exercise and obesity

Physiology of energy homeostasis: Models, actors, challenges and the glucoadipostatic loop

The aim of this review is to discuss the physiology of energy homeostasis (EH), which is a debated concept. Thus, we will see that the set-point theory is highly challenged and that other models integrating an anticipative component, such as energy allostasis, seem more relevant to experimental reports and life preservation. Moreover, the current obesity epidemic suggests that EH is poorly efficient in the modern human dietary environment. Non-homeostatic phenomena linked to hedonism and reward seem to profoundly impair EH. In this review, the apparent failed homeostatic responses to energy challenges such as exercise, cafeteria diet, overfeeding and diet-induced weight loss, as well as their putative determinants, are analyzed to highlight the mechanisms of EH. Then, the hormonal, neuronal, and metabolic factors of energy intake or energy expenditure are briefly presented. Last, this review focuses on the contributions of two of the most pivotal and often overlooked determinants of EH: the availability of endogenous energy and the pattern of energy intake. A glucoadipostatic loop model is finally proposed to link energy stored in adipose tissue to EH through changes in eating behavior via leptin and sympathetic nervous system activity.

The Role of Physical Exercise in Obesity and Diabetes

The prevalence of obesity is increasing world-wide. Obesity is associated with a plethora of metabolic and clinical constraints, which result in a higher risk for the development of cardiovascular complications and metabolic disease, particularly insulin resistance and type 2 diabetes. Obesity is an acknowledged determinant of glycemic control in patients with type 1 diabetes and accounts for the majority of premature death due to cardiovascular events. Physical exercise is generally recommended in patients with diabetes in order to prevent the development of or reduce existing obesity, as adopted by every international treatment guideline so far. Regular physical exercise has a beneficial impact on body composition, cardiovascular integrity, insulin sensitivity and quality of life. However, only a minority of patients participates in regular physical exercise, due to individual or disease-related barriers. In type 2 diabetes, there is robust evidence for beneficial effects of physical exercise on glycemic control, cardiovascular health and the development of diabetes-related long-term complications. In type 1 diabetes and patients treated with insulin, a higher risk for exercise-related hypoglycemia has to be considered, which requires certain prerequisites and adequate adaptions of insulin dosing. Current treatment guidelines do only incompletely address the development of exercise-related hypoglycemia. However, every patient with diabetes should participate in regular physical exercise in order to support and enable sufficient treatment and optimal glycemic control.

Non-exercise activity thermogenesis (NEAT): a component of total daily energy expenditure

[Purpose]

The purpose of this review is to promote awareness of non-exercise activity thermogenesis (NEAT) as a new strategy to increase energy expenditure, and to manage obesity.

[Methods]

The content of this review is based on a literature search of PubMed and the Google Scholar search engine, using the search terms obesity, energy expenditure, non-exercise activity thermogenesis (NEAT), and sitting disease.

[Results]

Daily energy expenditure is of great interest because most obese individuals have no exercise activity-related thermogenesis (EAT); thus their physical activity-related energy expenditure (PEE) is comprised almost entirely of NEAT. Consequently, NEAT represents the main variable component of daily total energy expenditure (TEE); this varies considerably, both within among individuals. These somewhat unplanned and unstructured low level physical activities are associated with energy expenditure in excess of the resting metabolic rate (RMR). They may therefore have the potential to stimulate greater energy expenditure over time with a higher rate of adherence.

[Conclusion]

In conclusion, NEAT is a highly variable component of daily TEE and a low level of NEAT is associated with obesity. NEAT enhances lifestyle, and variations in individual and environmental factors can significantly affect daily energy expenditure. Therefore, well designed longitudinal studies that focus on personal behavioral approaches and re-engineered environments to increase NEAT should be conducted in the future.

Exercise Therapy for Patients With Type 2 Diabetes: A Narrative Review

To achieve excellent glycemic control in patients with type 2 diabetes, an adequate prescription of exercise therapy is required. The meta-analyses proposed that high-intensity training improves metabolic parameters in patients with pre-diabetes or type 2 diabetes and low physical activity is associated with an increased risk of incident type 2 diabetes. Here, we would introduce literatures about effects of physical activity on mortality, cardiovascular events, and metabolic parameters, to encourage understanding of exercise therapy, and then describe how to prescribe exercise therapy for patients with type 2 diabetes. We also show the usefulness of non-exercise activity thermogenesis for diabetic patients who cannot perform volitional sporting-like exercise because of diabetic complication and/or comorbidity, by presenting results of our previous studies.

Group Cohesion Effects in Exercise Classes

Membership in cohesive groups has a powerful influence on individual behaviors such as adherence and conformity. Although the psychological andphysiological benefits of exercise have been well documented, individual adherence has proven to be problematic. Given that exercise classes are minimal groups at best, the purpose of the present study was to determine whether measures of cohesion secured during the early stages of group development could be used to predictsubsequent drop-out behavior In Study 1, participants in universityfitness classes were administered the Group Environment Questionnaire after the third week of a 13-week session. Adherence behavior, as measured by absenteeism, was monitored for 4 weeks and used to form two extreme groups-regular attenders and drop-outs. The regular attenders (n = 20) were those individuals who attended at least 66% of the monitored classes; drop-outs (n = 17) were those individuals who were absent for all classes in the monitored period. Discriminant function analysis showed that regular attenders held significantly greater perceptions of task cohesion than the drop-outs. Study 2 was a replication with exercise participants in private fitness clubs. A protocol identical to Study 1 was used to measure cohesion, operationalize adherence and analyze the data. Perceptions of cohesion again were a reliable predictor of adherence in the private club setting. However, it was measures of social cohesion that significantly discriminated between regular attenders (n = 30) and drop-outs (n = 16). The results were discussed in terms of their implications for (a) the dynamics of minimal groups, (b) the generality of the cohesion-adherence relationship in exercise groups, (c) the importance of considering the setting, and (d) health behavior change intervention programs.

Measuring energy expenditure in clinical populations: rewards and challenges

The measurement of energy expenditure (EE) is recommended as an important component of comprehensive clinical nutrition assessments in patients with altered metabolic states, who failed to respond to nutrition support and with critical illness that require individualized nutrition support. There is evidence that EE is variable in patients with metabolic diseases, such as chronic renal disease, cirrhosis, HIV, cancer cachexia, cystic fibrosis and patients under intensive care. By using appropriate techniques and interpretations of basal or resting EE, clinicians can facilitate the adequate nutrition support with minimum negative impacts from under- or overfeeding in these patients. This review is based on our current understanding of the different components of EE and the techniques to measure them, and to re-examine advances and challenges to determine energy needs in clinical populations with more focuses on the obese, pediatric and elderly patients. In addition, technological advances have expanded the choices of market-available equipments for assessing EE, which also bring specific challenges and rewards in selecting the right equipment with specific performance criteria. Lastly, analytical considerations of interpreting the results of EE in the context of changing body composition are presented and discussed.

Obesity: attitudes of undergraduate student nurses and registered nurses

AIM

To investigate undergraduate student nurses' and registered nurses' attitudes towards obese persons and towards the management of obese patients.

BACKGROUND

Obesity is a global public health problem. Escalating rates of overweight and obesity are also taking a toll in Asian countries that have historically had much lower rates. Despite the growing prevalence of obesity worldwide, studies show that nurses and other health professionals hold negative attitudes towards obese people, which may affect the care of obese patients.

DESIGN

Cross-sectional study.

METHODS

A self-administered questionnaire was completed by 352 undergraduate student nurses and 198 registered nurses. The questionnaire consisted of the Fat Phobia Scale, the Attitudes Toward Obese Adult Patients Scale and a demographic profile. Data were analysed using descriptive statistics and student's t-tests.

RESULTS

Overall mean scores on the Fat Phobia Scale (3.53 SD 0.47) indicated average levels of fat phobia and mean scores on the Attitudes Toward Obese Adult Patients scale (2.64 SD 0.51) indicated neutral attitudes towards obese patients. Registered nurses had significantly higher levels of fat phobia and more negative attitudes than did student nurses. The majority of participants perceived that obese people liked food, overate, and were shapeless, slow and unattractive. Additionally, over one-half of participants believed that obese adults should be put on a diet while in hospital.

CONCLUSIONS

Results of this study show that both registered nurses and student nurses have negative perceptions of obesity and are unlikely to attribute positive characteristics to obese individuals. That registered nurses hold more negative attitudes towards obese person is cause for concern.

RELEVANCE TO CLINICAL PRACTICE

Given the increasing prevalence of obesity and the disproportionate number of obese persons affected by many health conditions, current and future nurses should have positive professional attitudes towards obese individuals. Obesity needs to be more adequately addressed, both in basic nursing education programs and in continuing professional education for practising nurses.

Spontaneous activity responses to exercise in males and females

OBJECTIVE

This study examines the impact of a short-term exercise programme, prescribed on the basis of current exercise recommendations, on energy balance in males and females to assess whether this type of exercise induces compensatory changes in spontaneous activity energy expenditure (SAEE) and energy intake (EI).

DESIGN

Individuals were monitored for 16 days, 8 days of habitual physical activity (C) and 8 days when exercise was imposed (E). Total energy expenditure (TEE) was calculated from individual relationships of VO2 and VCO2 to heart rate (HR) records of HR and physical activity obtained during waking hours of the C and E periods and basal metabolic rate (BMR) measurements (Deltatrac System, Datex Instrumentation). Changes in nude body mass (BM) were estimated by using a digital scale (Sartorius AG, Gottigen, Germany).

SETTING

Laboratory and free-living.

SUBJECTS

Eight lean females (body fat: 17.5+/-4.5%) and eight males of similar percentage body fat participated in this study. All subjects were Caucasian and aged between 20 and 25 years.

INTERVENTION

During the E period, a supervised exercise session was conducted every second day, each consisting of a total net energy expenditure of 2092 kJ+BMR at 90% lactate threshold.

RESULTS

During the E period, TEE was higher than C in males and females (exercise: 95.2+/-13.9, 78.3+/-15.9 MJ; control: 82.4+/-10.4, 68.8+/-16.7 MJ, respectively; P<0.00; P=0.02). SAEE, calculated as TEE minus the energy expended during exercise, was not significantly different between C (males: 82.4+/-4.8 MJ; females: 68.8+/-7.6 MJ) and E (males: 86.8+/-6.3 MJ; females: 70.0+/-7.2 MJ) periods in either gender. Males showed no change in BM over the C (pre-intervention: 83.4+/-7.2 kg; post-intervention: 83.1+/-6.8 kg) or E (pre-intervention: 83.4+/-6.8 kg; post-intervention: 83.4+/-6.8 kg) periods. Females' BM over the C period did not alter (pre-intervention: 63.3+/-2.8 kg; post-intervention 63.7+/-3.1 kg); however, there was a significant decrease (P<0.00) in BM over the E period (pre-intervention: 63.0+/-2.7 kg; post-intervention: 62.4+/-2.7 kg).

CONCLUSION

The exercise programme was achieved in males and females without any impact on SAEE. Therefore, differences between genders in relation to BM reduction can be explained by differences in the EI response to exercise.

Overnutrition and undernutrition as modifiers of metabolic processes in disease states

Both overnutrition and undernutrition affect energy metabolism, with overnutrition raising energy expenditure and undernutrition lowering it. Fever is a powerful stimulator of thermogenesis. In diseases such as cancer, AIDS, diabetes mellitus, and rheumatoid arthritis, whether energy expenditure is increased or decreased often depends on how advanced the disorder is. Early on, when the greater protein turnover characteristic of these conditions is paramount, energy expenditure is increased. In addition, in diseases such as cancer, AIDS, and rheumatoid arthritis in which cytokines are released, the cytokines' thermogenic effect initially increases the metabolic rate. However, as the disease becomes more advanced and leads to cachexia, energy expenditure drops below normal. Acute conditions such as burns and trauma significantly raise energy expenditure, primarily by increasing sympathetic response and the release of catecholamines, which are powerful stimulators of energy expenditure.

Low impact aerobic dance as a useful exercise mode for reducing body mass in mildly obese middle-aged women

The purpose of this study was to test the hypothesis that a low impact aerobic dance is a useful exercise mode for weight loss in obese middle-aged women. Sixty Japanese women, aged 50.9 +/- 6.7 years (initial %fat = 35.2 +/- 5.3%), participated in our 3-month weight-loss program consisting of diet and exercise prescription. To compare the effectiveness of exercise modes, the subjects were divided into the following two groups: aerobic dance group and jogging and/or cycling group. As a result, body mass (-3.1 and -3.3 kg respectively) and %fat (-6.1 and -5.3% respectively) significantly decreased (P < 0.05) in both groups, while fat-free mass remained essentially unchanged. Aerobic power such as maximal oxygen uptake and oxygen uptake corresponding to lactate threshold significantly increased (P < 0.05) in both groups. Significant difference in the alterations in these variables between groups could not be seen. The data of this study indicates that our weight-loss program with a low impact aerobic dance is as useful as jogging or cycling in improving body composition and aerobic power for mildly obese middle-aged women.

Energy balance: role of genetics and activity

It is clear from the above discussion that much remains to be learned about both energy intake and energy expenditure. Obesity in humans is not likely to be caused by one gene, as it is in certain rodent models of obesity, such as the ob/ob mouse and the fa/fa rat. It is likely to be a polygenic condition in which numerous genes interact with each other and the environment to express the obesity phenotype. It is likely that genes that affect energy intake as well as genes that affect energy expenditure are involved. The role of leptin as a putative factor in signaling the extent of the fat mass to the central nervous system and controlling both food intake and energy expenditure is unclear at this time. The genetics of energy expenditure are also not clear at this time. There are mechanisms of nutrient partitioning, such as respiratory quotient and lipoprotein lipase activity, that are being discovered to be important. In addition, insulin sensitivity is likely to play a role in the etiology of obesity. Much more investigation will be required before we have a clearer picture of how the above-named factors interact, what the genetic contribution to this is, and how important each factor is to the overall phenotypic expression of obesity.

Prediction of oxygen uptake and energy expenditure during exercise in obese women

PURPOSE

For patients concerned with weight loss, monitoring the energy balance between daily dietary intake and exercise expenditure can be useful. Formulas commonly used to estimate the energy costs of exercise were previously derived from healthy men of normal body weight. The purpose of this study was to determine the relationship between measured and predicted exercise energy expenditure for obese women.

METHODS

Oxygen uptake (VO2) was measured using respiratory gas analysis in 45 obese (92 +/- 16 kg; 40 +/- 7% fat) and 10 normal weight (control) (58 +/- 5 kg; 21 +/- 6% fat) women during progressive exercise on a motorized treadmill. VO2 was also calculated at matched workrates using a regression equation published by the American College of Sports Medicine. The relationship between predicted versus measured VO2 was determined using least squares regression analysis.

RESULTS

The slope of the regression line for measured versus predicted VO2 for controls (y = 0.98x +/- 0.56; P < .001) was different than that of obese women (y = 0.75x +/- 3.06; P < .001). The slope of the regression line for controls was in close approximation to the line of identity, whereas the slope for obese was below it. Using VO2 to calculate kcal, measured energy expenditure, was significantly lower than predicted energy expenditure for obese subjects, but not for controls at several matched workrates: Stage III (213 +/- 40 versus 225 +/- 38 kcal per 30 minutes, P < .001); stage 4 (292 +/- 55 versus 340 +/- 58 kcal per 30 minutes, P < .001); and stage 5 (330 +/- 55 versus 412 +/- 70 kcal per 30 minutes, P < .001) obese measured versus obese predicted, respectively.

CONCLUSIONS

The authors conclude that the standard prediction equation gives a better estimation of VO2 for women who have average body weight and body fat than for obese women. This may, in part, be due to the differences in weight and/or fat mass between these subjects and those used to derive this equation. These findings should be considered when estimates of VO2 and energy expenditure are used rather than direct measures for obese women.

Comparison of 2-year weight loss trends in behavioral treatments of obesity: diet, exercise, and combination interventions

OBJECTIVE

The effects of three cognitive-behavioral weight control interventions for adults were compared: diet only, exercise only, and a combination of diet and exercise. This article reports 2-year follow-up data.

DESIGN

The three interventions were compared in a randomized, experimental design.

SUBJECTS

A total of 127 men and women who were at least 14 kg overweight (according to height-weight tables) were recruited from an urban community and assigned randomly to the experimental conditions.

INTERVENTION

The dietary intervention was a low-energy eating plan adjusted to produce a 1 kg/week loss of weight. The exercise component involved training in walking and a home-based program of up to five exercise periods per week. There were 12 weekly instructional sessions, followed by 3 biweekly and 8 monthly meetings. All sessions were led by registered dietitians.

OUTCOME MEASURES

Changes in body weight.

STATISTICAL ANALYSES

Analysis of variance for weight changes and repeated measures analysis of variance for weight change trends.

RESULTS

At 1 year, no significant differences were noted among the three groups. The diet-only group lost 6.8 kg, the exercise-only group lost 2.9 kg, and the combination group lost 8.9 kg (P=.09). During the second year, the diet-only group regained weight--reaching 0.9 kg above baseline; the combination group regained to 2.2 kg below baseline; and the exercise-only group regained slightly to 2.7 kg below baseline (P=.36). Repeated measures analysis of variance showed a group-by-time interaction (P=.001); data for the dieting groups best fit a U-shaped regain curve (P=.001).

APPLICATIONS

The results suggest that dieting is associated with weight loss followed by regain after treatment ends, whereas exercise alone produced smaller weight losses but better maintenance. The large outcome variability and unequal difficulty of the regimens across groups limit the generalizability of the findings.

Distribution of anthropometric variables and the prevalence of obesity in populations of west African origin: the International Collaborative Study on Hypertension in Blacks (ICSHIB)

A survey of the prevalence of hypertension and associated risk factors including obesity was carried out among persons of West African heritage currently living in societies at different stages of social, economic and technological development. We present here the distribution of several anthropometric variables and the prevalence of obesity in these populations. Using a standard protocol with centralized training of field staff, 7,439 men and women aged 24 to 75 from six multinational sites were recruited and examined. Although men were taller, women were more obese across sites. Body mass index (BMI) and consequently the prevalence of overweight and obesity increased with westernization from rural African subsistence farming communities to suburban Chicago. Average BMI increased with age until about age 54, and then began to decline or at least level off. The mean BMI for African-American men and women was 27.1kg/m2 and 30.8kg/m2, respectively. Men displayed high levels of centripetal fatness, measured as the waist-to-hip ratio (WHR), compared to the women across site. Based on the US Department of Agriculture guidelines, 22.6% and 56.9% of the African-American men and women had elevated WHR. Although account must be taken of the important contribution of an individual's genetic background, this multinational study of persons with similar heritage clearly shows the potent impact of current environmental factors on the distribution and level of obesity.

Biracial differences in physical activity and body composition among women

Overweight among black females is almost two times as frequent as among white females. Genetics, caloric intake, and physical activity have been identified as possible explanatory factors. This study assessed the differences in physical activity and body composition in 76 white and 66 black adult females. Black women had significantly higher (p = .0001) percent body fat (32.2 +/- 7.1) than white women (27.7 +/- 6.5) with a similar difference in weight (4.4 kg) approaching significance (p = .055). Physical activity was assessed using a structured 24-hour recall instrument. A purposive sampling design was implemented to control for age, education and occupation. A summary physical activity value unit for the 24-hour period revealed a significantly greater mean value for white females (41.93 +/- 4.7) than for black females (40.01 +/- 3.9) suggesting white females were more physically active (p = .02) although this was not a function of biracial differences in play/recreation and exercise/sport type of activities. Although both black and white females were found to be sedentary (MET value < or = 2) over 90 percent of the time, black women are significantly more sedentary (p = .03). Biracial differences in discretionary non-exercise oriented activities may contribute to different rates of overweight observed between black and white women.

Traditional treatment of obesity: does it work?

Obesity is the most important nutritional disorder in the developed world, since up to 10% of the population are obese. The place of physical activity and diet in the aetiology of obesity is discussed. The traditional treatment of obesity includes change in lifestyle, nutritional education and modification and increase in exercise. These changes are important for long-term success. There are a number of other treatment options including anorectic drugs, the use of very low calorie diets and surgical techniques which may have some clinical role. For the extremely obese patient with established complications surgery may be the most appropriate intervention and may be life-saving. Most studies of traditional treatment have demonstrated limited success. The prevention of obesity is therefore of great importance. Large-scale studies have shown that it is possible to modify behaviour and cardiovascular risk factors. The prevention of obesity requires a coordinated approach with targeting of children and their carers. Governmental involvement and legislation is essential. The future holds the promise of more imaginative and coordinated therapies for obesity using the skills of physicians, nutritionists, exercise physiologists and psychologists. Different forms of treatment may be appropriate for different groups of obese patients.

Dietary fat, sugar, and fiber predict body fat content

OBJECTIVE

This study was conducted to determine the relationships among the specific components of dietary fat and carbohydrate and body fatness in lean and obese adults.

DESIGN

Body composition determination was performed on each subject by hydrostatic weighing at residual volume. Subsequently, the individual components of dietary fat and carbohydrate were examined relative to body fatness using a 3-day food diary and a food frequency questionnaire.

SUBJECTS

Subjects were 23 lean (11.1 +/- 2.9% body fat) men, 23 obese (29.2 +/- 3.8% body fat) men, 17 lean (16.7 +/- 3.3% body fat) women, and 15 obese (42.7 +/- 3.9% body fat) women who volunteered for free diet and body composition analyses. Inclusion criteria were 15% body fat for lean men, 25% for obese men, 20% for lean women, and 35% for obese women.

STATISTICAL ANALYSIS PERFORMED

Group comparisons for dietary variables were made with a multivariate analysis of variance.

RESULTS

No differences were found between lean and obese subjects for energy intake or total sugar intake, but obese subjects derived a greater portion of their energy from fat (33.1 +/- 2.6% and 36.3 +/- 2.3% for obese men and women, respectively, vs 29.1 +/- 1.3% and 29.6 +/- 2.0%, lean men and women, respectively). Percent of fat intake for saturated, monounsaturated, and polyunsaturated fats was not different among groups. Obese subjects derived a greater percentage of their sugar intake from added sugars than lean subjects (38.0 +/- 3.5% vs 25.2 +/- 2.0%, respectively, for men; 47.9 +/- 8.0% vs 31.4 +/- 3.4%, respectively, for women). Dietary fiber was lower for obese men (20.9 +/- 1.8 g) and women (15.7 +/- 1.1 g) than for lean men (27.0 +/- 1.8 g) and women (22.7 +/- 2.1 g).

APPLICATIONS/CONCLUSIONS

Obesity is maintained primarily by a diet that is high in fat and added sugar and relatively low in fiber. Alterations in diet composition rather than energy intake may be a weight control strategy for overweight adults.

Treating Overweight Patients

Many psychological barriers keep overweight people from being physically active. Too often, these patients think being large and being athletic simply don't mix. But with the right approach, physicians can help sedentary overweight patients overcome barriers and start enjoying the many benefits that regular exercise offers- regardless of whether the patients lose weight.

Long-term effect of physical activity on energy balance and body composition

We studied the effect of an increase in physical activity on energy balance and body composition without interfering with energy intake (EI). Sixteen women and sixteen men, aged 28-41 years, body mass index 19.4-26.4 kg/m2, not participating in any sport before the start of the experiment, prepared to run a half-marathon competition after 44 weeks. Measurements of body composition, EI and energy expenditure (EE) were performed before (0 weeks), and 8, 20, and 40 weeks after the start of training. Body composition was measured with hydrodensitometry and isotope dilution, and EI with a 7 d dietary record. EE was measured overnight in a respiration chamber (sleeping metabolic rate (SMR)) and in a number of subjects over 2-week intervals with doubly-labelled water (average daily metabolic rate (ADMR)). ADMR showed an average increase of 30% in both sexes from the start of training onwards while SMR tended to decrease. EI showed a tendency to drop from week 20 to week 40 in the men and a tendency to increase from week 20 to week 40 in the women. Body mass (BM) did not change in both sexes until the observation at 40 weeks when the median value of the change in men was -1.0 kg (P < 0.01; Wilcoxon signed-rank) while the corresponding change of -0.9 kg in the women was not statistically significant. Body composition changes were most pronounced in men as well. Based on changes in BM, body volume and total body water, men lost 3.8 kg fat mass (FM) (P < 0.001; Wilcoxon signed-rank) and gained 1.6 kg protein mass (P < 0.01; Wilcoxon signed-rank) while the corresponding changes in women were 2.0 kg (P < 0.05; Wilcoxon signed-rank) and 1.2 kg (P < 0.05; Wilcoxon signed-rank). In men the loss of FM was positively correlated with the initial percentage body fat (Pearson r 0.92, P < 0.001). In conclusion, body fat can be reduced by physical activity although women tend to compensate for the increased EE with an increased EI, resulting in a smaller effect on BM and FM compared with men.

Independent effects of obesity and insulin resistance on postprandial thermogenesis in men

The putative blunted thermogenesis in obesity may be related to insulin resistance, but insulin sensitivity and obesity are potentially confounding factors. To determine the independent effects of obesity and insulin resistance on the thermic effect of food, at rest and after exercise, lean and obese men were matched at two levels of insulin sensitivity determined by insulin-stimulated glucose disposal (milligrams per kilogram fat-free mass [FFM] per minute) during the euglycemic, hyperinsulinemic (40 mU/m2.min) clamp: 5.4 mg/kg FFM for the lean and obese groups with low insulin sensitivity, and 8.1 mg/kg FFM for the groups with high insulin sensitivity. The two lean groups were matched for percent fat (approximately 15 +/- 1% fat), as were the two obese groups (approximately 33 +/- 2% fat). Energy expenditure was measured for 3 h in the fasting state and for 3 h after a 720-kcal mixed meal, each at rest and immediately after 1 h of cycling at 100 W. The thermic effect of food (TEF) was calculated as the postprandial minus fasting energy expenditure (kcal/3 h) during rest and after exercise. During rest, TEF was blunted by both obesity (24 +/- 5 and 34 +/- 6 kcal/3 h for obese groups with low and high insulin sensitivity vs. 56 +/- 6 and 74 +/- 6 kcal/3 h for the lean groups with low and high insulin sensitivity; P less than 0.01 lean vs. obese) and insulin resistance (insulin-resistant less than insulin-sensitive, at both levels of obesity; P less than 0.01). After exercise, TEF was also impaired in the obese (47 +/- 6 and 44 +/- 5 kcal/3 h for the insulin-resistant and -sensitive groups) and in the lean insulin-resistant (55 +/- 5 kcal/3 h), compared with the lean insulin-sensitive men (71 +/- 3 kcal/3 h), P less than 0.01. Compared with rest, TEF after exercise was improved, but not normalized, in both obese groups (P less than 0.05), but unchanged in the lean groups. These results suggest that both insulin resistance and obesity are independently associated with impaired TEF at rest, but the responsiveness of thermogenesis to exercise before a meal is related to the obese state and not independently to insulin resistance per se.

The role of exercise in weight regulation in nonathletes

Obesity is an extremely prevalent condition that is associated with a range of deleterious health effects. While traditionally considered a disorder primarily of energy intake, accumulating evidence underscores the importance of energy expenditure in the development and treatment of obesity. As the most variable component of energy expenditure, physical activity can influence the development of obesity as well as success in achieving both initial and long term weight loss. Among the types of exercise-related physiological and behavioural factors most likely to be involved in the development of obesity are reductions in the amount of physical activity actually performed, differences in the effect of physical activity on diet-induced thermogenesis, and modeling of deleterious dietary and exercise patterns on the part of the family and other facets of the environment. In contrast, there is relatively little evidence supporting the common belief that obese individuals have a significantly greater energy intake than nonobese individuals. With respect to weight reduction in the already obese, while increased physical activity levels often augment caloric restriction programmes in aiding initial weight loss, evidence suggests that physical activity may be particularly important in helping to sustain initial losses through increased total energy output, preservation of lean body mass, and changes in substrate utilisation. The psychological benefits received from regular participation in a physical activity programme may serve as an additional impetus for engaging in such activities over the long run. Developing programmes to aid in long term adherence to physical activity regimens remains the most critical challenge. Recent results suggest the utility of regular, brief contacts in aiding sustained physical activity participation in individuals attempting to control their weight.