The hypothalamus and energy balance

In recent years the growing number of molecules implicated in energy homeostasis has raised nearly limitless possibilities for how body-weight regulation might occur. To better understand how energy homeostasis can be achieved, we describe the roles of individual hormonal and neuropeptide signalling pathways in the control of food intake and the means by which obesity can arise from defects in their function. The hypothalamus links the sensing of nutrients to the control of metabolism and feeding behaviour. Disruptions in the mechanisms of central nervous system (CNS) nutrient-sensing alter these homeostatic responses and contribute to the pathophysiology of obesity and type 2 diabetes mellitus. Experimental and epidemiological studies suggest that sleep loss may also play a role in the increased prevalence of diabetes and obesity. The molecular components of the circadian clock are present in the anterior hypothalamus. It is not therefore surprising that there is a close link between sleep and energy metabolism. In this review we also focus on physical exercise as a mechanism to restore physiological rhythm preventing hyperphagia and obesity in humans. Given its ability to reduce cerebral energy demands and therefore promote sleep, physical exercise could be beneficial for maintaining brain function and improving brain plasticity.     

Exercise training bradycardia: the role of autonomic balance

We used an algebraic model of resting heart rate (HRr), HRr-mn (HRo), to compare resting parasympathetic (n) and sympathetic (m) influence, intrinsic heart rate (HRo), and resting autonomic balance (Abal) in ten endurance-trained (ET) and ten nontrained (NT) men. The values of m, n, and Abal were determined by selective pharmacological blockade with atropine and metoprolol. HRo was obtained during double blockade with atropine and metoprolol. HRo and HRr were significantly lower (P less than or equal to 0.04 and P less than or equal to 0.01, respectively) in the ET subjects (79.5 +/- 2.8 beats.min-1 and 54.7 +/- 3.0 beats.min-1, respectively) when compared to the NT subjects (86.6 +/- 2.5 beats.min1 and 70.2 +/- 3.1 beats.min-1, respectively). Parasympathetic influence (n) was greater in the ET subjects (P less than or equal to 0.04), while sympathetic influence (m) was slightly (P less than or equal to 0.05) less in the ET subjects. Consequently, the value of Abal was significantly less in the ET subjects (P less than or equal to 0.02), indicating that resting parasympathetic predominance was significantly greater in the ET subjects. We concluded that the exercise training bradycardia, observed in this group of subjects, was due to both a lower HRo and an Abal with an augmented parasympathetic dominance.     

Relation between bone turnover, oestradiol, and energy balance in women distance runners

OBJECTIVE: To explore relations between biochemical markers of bone turnover, indices of nutritional status, and serum oestradiol concentration in women distance runners. METHODS: Thirty three women distance runners of mean age (SD) 27.2 (1.8) years participated. Eighteen were defined as eumenorrhoeic, nine as amenorrhoeic, and six as oligomenorrhoeic. Mean (SD) running distance was 47.6 (22.4) km/week. Using bivariate correlation and regression analysis, serum levels of osteocalcin and bone alkaline phosphatase (BAP) and also urine deoxypyridinoline/creatinine (Dpyr/Cr) were correlated with mean daily energy balance, body mass index (BMI; kg/m2), and serum levels of total 3,5,3'-triiodothyronine and oestradiol within each group by menstrual status. RESULTS: All the amenorrhoeic women were in negative energy balance; they had a lower BMI, lower serum levels of oestradiol, triiodothyronine, osteocalcin and BAP and a lower urine Dpyr/Cr than any of the oligomenorrhoeic or eumenorrhoeic women. These variables were also lower in oligomenorrhoeic than in eumenorrhoeic women. Positive correlations were observed between serum levels of osteocalcin or BAP and both BMI and serum oestradiol concentration in amenorrhoeic, but not in oligomenorrhoeic or eumenorrhoeic women. Urine Dpyr/Cr did not correlate with any other variable within any group. Serum oestradiol concentration correlated positively with BMI in amenorrhoeic and oligomenorrhoeic, but not eumenorrhoeic women. CONCLUSIONS: Positive correlations between serum levels of bone formation markers, BMI and serum oestradiol concentration in our amenorrhoeic runners suggested that their reduced bone formation was linked to a low BMI and an oestrogen deficiency. Reduced bone turnover in amenorrhoeic distance runners has not previously been shown. These findings emphasise the importance of body mass and its possible link with a chronic energy deficit and hypothalamic dysfunction on bone remodelling balance in amenorrhoeic runners.


     

Exercise, stress, and the immune conversation

The role of exercise in meaningful alterations in immune function is unclear. The recent demonstration that stress proteins are potent modulators of immune cell activation and cytokine production, coupled with the role of exercise in stress protein production, suggest that exercise-associated alterations in immune function may be related to exercise associated alterations in the cellular stress response.     

Resting metabolic rate and energy balance in amenorrheic and eumenorrheic runners

This study investigated metabolic and nutritional factors in association with athletic menstrual dysfunction (AMD). Three groups of women were studied: amenorrheic runners (amenorrheic), eumenorrheic runners (eumenorrheic), and eumenorrheic sedentary controls (sedentary). Amenorrheic and eumenorrheic were similar in age, weight, percent body fat by hydrodensitometry, training pace and mileage, best 10 km race time, years running, and maximal oxygen consumption. When adjusted for body weight or for fat-free mass by analysis of covariance, RMR was significantly lower in amenorrheic than in eumenorrheic and sedentary. The daily caloric intakes of the groups did not differ significantly, but the amenorrheic scored significantly higher than the eumenorrheic and sedentary on a scale of aberrant eating patterns. Amenorrheic high mileage runners seem to have a less adequate diet than eumenorrheic runners but appear to maintain energy balance and stable weight through a reduction in RMR.     

Exercise training and energy restriction decrease neutrophil phagocytic activity in judoists

PURPOSE: To investigate the effects of weight reduction as the result of exercise training and energy restriction on neutrophil function. METHODS: Eighteen male competitive college judoists participated in the study. In a whole blood assay, oxidative burst activity, phagocytic activity, expressions of Fc gamma receptor 3 (CD16), and complement receptor 3 (CD11b) of neutrophils were measured on a per cell basis by flow cytometry at day 20, 5, and 1 before and at day 7 after the competition. RESULTS: The rate of neutrophil producing reactive oxygen species decreased before the competition, whereas the oxidative burst activity per cell increased significantly in all subjects, which resulted in a significant increase of the total oxidative burst activity. However, there were no significant effect of energy restriction on oxidative burst activity. The rate of neutrophils incorporating opsonized zymosan decreased significantly with energy restriction. The total phagocytic activity of 10,000 neutrophils and the phagocytic activity per cell also decreased significantly by severe energy restriction. The surface antigen expressions of CD11b and CD16 were unaffected by weight reduction. CONCLUSIONS: The results suggest that with respect to the management of health conditions, weight reduction for judoists should be composed of exercise training and energy restriction should be moderate.     

Response of beta-endorphin and estradiol to resistance exercise in females during energy balance and energy restriction.

The acute effect of weightlifting on beta-endorphin and estradiol was studied in experienced female recreational weightlifters. Five eumenorrheic females completed two months of testing, each with a different sequence of testing conditions (SEQ1 and SEQ2). In SEQ1, a week of weight maintenance diet and prescribed exercise (3 d.wk-1, 3 sets, approximately 85% 1 RM, 10-12 reps, eight lifts) beginning on d 11 of their menstrual cycle was followed by measurement of hormone response to a weightlifting bout during energy balance (EBAL) on d 18. This included blood sampling via a catheter before, just after, and at 15 and 30 min of recovery. The women consumed 500 kcal per day for the next 48 hrs and then repeated the weightlifting test during negative energy balance (NEBAL). SEQ2 was similar except that the 48 hrs of NEBAL preceded the EBAL test condition. Estradiol and beta-endorphin increased from baseline to immediately post exercise under both dietary conditions but was significant only during NEBAL. Estradiol increased 1.6 fold and beta-endorphin 3.7 fold by the end of the resistance exercise bout during NEBAL. Both hormones were also elevated for a longer time during recovery in the NEBAL condition. Since estradiol and beta-endorphin can suppress gonadotropin release, it is possible that repeated elevations in these hormones during weightlifting, especially concurrent with energy restriction, could contribute to disruption of the menstrual cycle.     

The energy cost for balance control during upright standing

The aim of this study was to investigate whether balance control during a static upright standing task with and without balance perturbations elicits a significant and meaningful metabolic energy demand and to test whether this energy demand correlates with conventional posturography measures for balance control. Ten healthy subjects were assessed in four 4-min upright standing conditions on a force platform while energy consumption was measured using open circuit respirometry. In the reference condition subjects stood upright in parallel stance without balance perturbation (PS). In the other conditions balance was perturbed by placing the subjects in tandem stance (TS), in tandem stance blind folded (TSBF) and in tandem stance on a balance board (TSBB). Gross and net energy consumption was assessed and various conventional posturography measures were derived from the excursion of the center of pressure (CoP) of the ground reaction force. Energy consumption was substantially affected by all balance perturbations, compared to the reference condition. The highest increase in energy consumption was found for the TSBF condition (increase of 0.86 J kg^?1 s^?1 or 60% of PS). Significant correlations were found between energy consumption and posturography measures. The strongest correlation was found between gross energy consumption and the CoP path and normalized CoP path along the anterior–posterior axis (resp. r = 0.57 and r = 0.66, p < 0.001). It was concluded that the effort for balance control can elicit a meaningful metabolic energy demand. Conventional posturography provided significant, though moderate, predictors of this metabolic effort for balance control.     

Increased protein maintains nitrogen balance during exercise-induced energy deficit

PURPOSE: This study examined how a high-protein diet affected nitrogen balance and protein turnover during an exercise-induced energy deficit. METHODS: Twenty-two men completed a 4-d (D1-4) baseline period (BL) of an energy balance diet while maintaining usual physical activity level, followed by 7 d (D5-11) of 1000 kcal.d increased energy expenditure via exercise (50-65% V O2peak). One group consumed 0.9 g of protein per kilogram per day and maintained energy balance throughout the 11-d intervention (BAL, N = 8). The other two groups consumed their BL energy intake throughout the 11 days, resulting in a 7-d, 1000-kcal.d energy deficit. These groups consumed either 0.9 g of protein per kilogram per day (DEF, N = 7) or 1.8 g of protein per kilogram per day (DEF-HP, N = 7). Mean nitrogen balance (NB), calculated per kilogram of fat-free mass (FFM), was determined for BL, days 5-8 (EX1), and days 9-11 (EX2). Whole-body protein turnover was derived from phenylalanine and tyrosine kinetics assessed while fasting at rest on days 4, 7, and 12, using a priming dose of L-[ring-N]tyrosine and a 4-h, primed, continuous infusion of L-[N]phenylalanine and L-[ring-H4]tyrosine. RESULTS: DEF experienced a decrease in NB from BL to EX 1 that was maintained in EX 2. No changes in NB occurred for BAL or DEF-HP over time. No within- or between-group differences were found over time for Phe flux (Qp), conversion rate of Phe to Tyr (Qpt), or the derived protein synthesis value (Sp). CONCLUSION: Increased dietary protein maintained NB during exercise-induced energy deficit, but this did not impact resting whole-body protein turnover.     

Exercise, mobility and aging

The elderly population is growing both in size and in proportion of the total population. The costs to the community of the elderly being in poor health are also growing proportionately. The beneficial effects of exercise on various physiological and psychological parameters in the elderly have been well established. The effects of exercise on the mobility and independence of the elderly are also of primary concern, their maintenance being an important exercise goal. Impaired balance and gait are the 2 most significant risk factors for limited mobility and falls in the elderly. It is important to understand the effects of aging and exercise on these risk factors.     

Exercise, Intestinal Absorption, and Rehydration

KEYPOINTS 1. The proximal small intestine (duodenum & jejunum) is the primary site of fluid absorption. It absorbs about 50% to 60% of any given fluid load. The colon or large intestine absorbs approximately 80 to 90% of the fluid it receives, but accounts for only about 15% of the total fluid load.     

Exercise,Intestinal Absorption,and Rehydration

ＫＥＹＰＯＩＮＴＳ1.Ｔｈｅｐｒｏｘｉｍａｌｓｍａｌｌｉｎｔｅｓｔｉｎｅ(ｄｕｏｄｅｎｕｍ＆ｊｅｊｕｎｕｍ)ｉｓｔｈｅｐｒｉｍａｒｙｓｉｔｅｏｆｆｌｕｉｄａｂｓｏｒｐｔｉｏｎ .Ｉｔａｂｓｏｒｂｓａｂｏｕｔ 50 %ｔｏ 60 %ｏｆａｎｙｇｉｖｅｎｆｌｕｉｄｌｏａｄ .Ｔｈｅｃｏｌｏｎｏｒｌａｒｇｅｉｎｔｅｓ ｔｉｎｅａｂｓｏｒｂｓａｐｐｒｏｘｉｍａｔｅｌｙ 80ｔｏ 90 %ｏｆｔｈｅｆｌｕｉｄｉｔｒｅ ｃｅｉｖｅｓ ,ｂｕｔａｃｃｏｕｎｔｓｆｏｒｏｎｌｙａｂｏｕｔ 15%ｏｆｔｈｅｔｏｔａｌｆｌｕｉｄｌｏａｄ .2 .Ｉｎｔｅ…     

The effects of exercise-training on energy balance and adipose tissue morphology and metabolism

The effects of exercise training on energy expenditure, energy intake, fat cell size and adipose tissue lipolysis have been reviewed. Individuals engaged in regular and intense training programmes, e.g. long distance runners, seem to exhibit an elevated resting metabolic rate but moderate training is not accompanied by any important change. Diet-induced thermogenesis is a significant component of daily energy expenditure. It is still unclear whether or not exercise or training causes significant alteration in the thermic response to food intake. Energy expenditure associated with physical activity can play a meaningful role in body composition and adipose tissue metabolism. Largest weight losses have been achieved with programmes of long duration, presumably without marked compensation in food intake. However, it has been shown repeatedly that an increase in energy expenditure with exercise training tends to be associated with an elevation in food intake in free-living individuals. Weight loss is concomitant with a reduction in fat cell diameter and, when caused by an exercise training programme, it is generally accompanied by an increase in fat cell lipolytic activities. There are clear indications that weight loss induced by exercise training has a much higher fat content than weight loss caused by dieting. In addition, data suggest that exercise training may result in a greater depletion of fat stores than a low calorie diet, thus delaying the advent of the resistance phase to fat loss. Data on human subjects derived from well controlled energy balance and metabolic experiments are needed to further advance our understanding about the effects of exercise training on the adipose tissue.