Metabolic Effects of Mental Stress during Over ... - Wiley Online Library

Metabolic Effects of Mental Stress during Over- and Underfeeding in Healthy Women Ge´rald Seematter, Mirjam Dirlewanger, Valentine Rey, Philippe Schneiter, and Luc Tappy

Abstract SEEMATTER, GE´RALD, MIRJAM DIRLEWANGER, VALENTINE REY, PHILIPPE SCHNEITER, AND LUC TAPPY. Metabolic effects of mental stress during over- and underfeeding in healthy women. Obes Res. 2002;10:49 –55. Objective: To assess the short-term consequences of carbohydrate or fat overfeeding or of food restriction on the metabolic effects of mental stress in healthy lean women. Research Methods and Procedures: The effects of a sympathetic activation elicited by mental stress were evaluated in a group of healthy women after standardized isocaloric feeding (ISO) or after a 3-day overfeeding with 40% excess calories as either carbohydrate overfeeding (CHO OF) or fat overfeeding (FAT OF). Oxygen consumption rate (VO2) was measured as an index of energy expenditure, and subcutaneous glycerol concentrations were monitored with microdialysis. The same measurements were performed in another group of healthy women after ISO and after a 3-day period of underfeeding with a protein sparing modified fast (UF). Results: In all conditions, mental stress significantly increased heart rate, blood pressure, plasma norepinephrine and epinephrine concentrations, and VO2, and produced a nonsignificant increase in subcutaneous glycerol concentrations. CHO OF and FAT OF did not alter the effects of mental stress on VO2 and subcutaneous glycerol concentrations. In contrast, UF increased basal VO2 but significantly reduced its stimulation by mental stress. UF also enhanced the increase in subcutaneous glycerol concentrations during mental stress. Discussion: UF reduces the stimulation of energy expenditure and enhances lipolysis during sympathetic activation. These adaptations may be involved in mobilization of endogenous fat while limiting weight loss. In contrast, short-

Submitted for publication April 5, 2001. Accepted for publication in final form October 31, 2001. Institute of physiology, University of Lausanne, 1005 Lausanne, Switzerland. Address correspondence to Dr. Luc Tappy, Institut de Physiologie, 7 Rue du Bugnon, 1005 Lausanne, Switzerland. E-mail: [email protected] Copyright © 2002 NAASO

term overfeeding fails to alter the sympathetic control of energy expenditure and lipolysis. Key words: overfeeding, underfeeding, sympathetic nervous system

Introduction An energy intake in excess of energy expenditure invariably leads to body weight gain. However, there is evidence that the amount of weight gained under standardized overfeeding varies considerably among individuals (1,2), suggesting that an adaptive increase in energy expenditure occurs concomitantly. This concept has been supported by studies showing that, in lean and obese individuals overfed for several weeks, 24-hour energy expenditure increases more than what would be predicted from changes in body composition (3,4). Interestingly, this increase in 24-hour energy expenditure was not accounted for by an increase in basal metabolic rate, thermic effect of food, or a change in muscular efficiency, suggesting that physical activity was increased to prevent weight gain. In contrast, energy restriction imposed until a 10% weight loss led to a significant reduction in 24-hour energy expenditure (3). Energy imbalance also affects the sympathoadrenal system. Overfeeding stimulates sympathetic nervous system activity, whereas underfeeding (UF) produces the opposite effect (5). We have recently observed that a sympathetic activation elicited by mental stress acutely increases energy expenditure through ␤-adrenergic mechanisms (6). Therefore, it is possible that the changes in 24-hour energy expenditure observed during under- or overfeeding are partially accounted for by alterations of the metabolic rate during sympathetic activation. Lipolysis is also stimulated by mental stress through ␤-adrenoceptors (7,8). This parameter is likely to change during energy imbalance not only because of the changes in the sympathetic nervous system tone (5), but also as a consequence of an increased sensitivity of adipocytes to catecholamines (9) and a decreased antilipolytic effect of insulin (10). To further assess the effects of alterations of energy balance on the sympathetic control of metabolism, we, OBESITY RESEARCH Vol. 10 No. 1 January 2002

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Mental Stress and Energy Imbalance, Seematter et al.

therefore, monitored the changes in energy expenditure and lipolysis induced by 15 minutes of mental stress in healthy women volunteers after 3 days of either an isocaloric diet (ISO) or a hypercaloric high-carbohydrate or high-fat diet and after 3 days of a severe energy restriction.

Research Methods and Procedures Subjects Ten healthy lean women were selected to take part in the overfeeding protocol. They had a mean body weight of 60.9 ⫾ 2.4 kg, a mean height of 1.67 ⫾ 0.03 m, a mean body fat free mass (determined by skinfold thickness measurements) (11) of 44.4 ⫾ 1.7 kg, and a mean age of 22.4 ⫾ 1.1 years. Eight healthy lean women were selected to take part in the UF protocol. They had a mean body weight of 58.9 ⫾ 2.0 kg, a mean height of 1.70 ⫾ 0.01 m, a mean body fat free mass of 45.4 ⫾ 1.0 kg, and a mean age of 22.1 ⫾ 0.5 years. All subjects were in good physical condition; they were not taking any medication and had no family history of diabetes mellitus or metabolic disorders. The experimental protocol was approved by the Ethical Committee of Lausanne Medical School and all participants provided informed, written consent. Dietary Conditions Overfeeding Protocol. At inclusion, resting energy expenditure was measured by indirect calorimetry during a 30to 60-minute period. In the morning after an overnight fast, a ventilated hood was used for respiratory gas collections (12). Twenty-four-hour energy requirement was estimated as equal to resting energy expenditure multiplied by 1.3. The subjects were then placed on a controlled diet during three periods of 3 days, separated by at least 10 days. On one occasion , they received an ISO containing 50% carbohydrate, 35% lipid, and 15% protein, which consisted mainly of a liquid formula (Fresubin Energy; Fresenius, Stans, CH) supplemented with orange juice, yogurt, and cream, to be consumed at specific time periods. They were instructed not to consume any other food or drink. On a second occasion, they received a hypercaloric diet providing 40% excess energy as carbohydrate (carbohydrate overfeeding [CHO OF]). For this, the ISO was supplemented with bread, rice biscuits, and sugar. On a third occasion, they received a hypercaloric diet providing 40% excess energy as fat (fat overfeeding [FAT OF]). For this, the ISO was supplemented with cheese, potato chips, and chocolate. The order by which the three diets were administered was randomized and each test was separated by an interval of at least 7 days. All subjects spent the third day of each dietary condition in a metabolic chamber as part of another protocol (13). This allowed documentation of the dietary goals that were actually attained during each condition (13). 50

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UF Protocol. At inclusion, resting energy expenditure and 24-hour energy requirements were assessed as in the overfeeding protocol. Thereafter, the subjects received in randomized order during 3 days an ISO providing 50% of energy as carbohydrate, 35% as fat, and 15% as protein or an hypocaloric diet (protein-sparing modified diet, providing 1 g of protein/kg of body weight per day and 800 to 1000 kcal/d) (14). Experimental Protocol All studies were performed during the follicular phase of the menstrual cycle. In the morning of the third day of each dietary condition, the subjects came to the Institute of Physiology after an overnight fast. A microdialysis catheter (CMA 100; CMA Microdialysis AB, Stockholm, Sweden) was inserted into the periumbilical subcutaneous adipose tissue and was perfused with 0.3 ␮L/min phosphate-buffered saline by means of a portable infusion pump (CMA 106; CMA). One indwelling venous cannula was inserted into a wrist vein of the right arm to allow serial blood samples collections. The right hand was placed in a thermostabilized box heated at 56 °C to achieve partial arterialization of venous blood. Throughout the study, indirect calorimetry was performed using a ventilated hood, as described (12). Because mental stress produced significant hyperventilation, only oxygen consumption rates (VO2) measurements were used as an index of energy expenditure. The experiment started between 8:00 AM and 8:30 AM. After 60 minutes baseline, a 15-minute mental stress, consisting in 5-minute periods of mental arithmetics (15) alternated with 5-minute periods of Stroop’s color word conflict test (7) was applied. Indirect calorimetry was continued until time 105 minutes, i.e., 20 minutes after the termination of the mental stress. Blood samples were collected at times 30 and 40 minutes during the baseline period; at times 67 and 75 minutes during the mental stress, and at time 105 minutes, i.e., 20 minutes after the end of the mental stress. Blood pressure and heart rate (electrocardiogram) were recorded at 30, 40, 45, 50, 55, 60, 65, 67, 70, 75, 80, 85, 90, 95, 100, and 105 minutes. Analytical Measurements Plasma glucose concentration in plasma was determined with a Beckman glucose analyzer 2 (Beckman Instrument, Brea, CA). Plasma norepinephrine and epinephrine concentrations were determined by high performance liquid chromatography (16). Plasma insulin concentration was determined by a radioimmunoassay (RIA) kit (Biodata Guidoni, Montecello, Italy) and plasma glucagon and leptin concentrations by RIA kits (Linco Research, St. Charles, MO). Plasma free fatty acid concentrations were measured colorimetrically, using a kit from Wako (Freiburg, Germany). Plasma ␤-hydroxybutyrate concentrations were measured enzymatically.


Table 1. Postabsorptive plasma substrate and hormone concentrations in the overfeeding protocols

Glucose (mM) Non-esterified fatty acids (mM) ␤ hydroxybutyrate (mM) Insulin (mU/liter) Leptin (␮g/liter) Epinephrine (pM) Norepinephrine (pM)

Isocaloric diet

Carbohydrate overfeeding

Fat overfeeding

4.12 ⫾ 0.07 0.495 ⫾ 0.031 0.143 ⫾ 0.023 9.8 ⫾ 1.2 9.8 ⫾ 1.7 26 ⫾ 4 205 ⫾ 22

4.40 ⫾ 0.11 0.374 ⫾ 0.035* 0.077 ⫾ 0.015* 10.7 ⫾ 1.4 12.5 ⫾ 1.6* 26 ⫾ 3 207 ⫾ 17

4.30 ⫾ 0.04 0.458 ⫾ 0.030 0.148 ⫾ 0.030 10.0 ⫾ 1.2 10.9 ⫾ 1.4 26 ⫾ 3 199 ⫾ 13

* p ⬍ 0.05 vs. isocaloric diet.

Statistics All results are expressed as mean ⫾ SEM unless stated otherwise. The effect of mental stress on all parameters mentioned was assessed with ANOVA for repeated measurements. Between groups comparison was done using a two-way ANOVA for all parameters except for the increase in energy expenditure for which the Wilcoxon signed rank test was used.

in plasma leptin concentration, a 161% increase in plasma non-esterified fatty acid concentration, a 6000% increase in plasma ␤-hydroxybutyrate concentration, and a 77% de-

Results Overfeeding Protocol Compared with an ISO, 3 days of carbohydrate overfeeding led to a 28% increase in postabsorptive plasma leptin concentration, a 24% decrease in plasma nonesterified fatty acid concentration, and a 59% decrease in plasma ␤-hydroxybutyrate concentration, but did not change basal plasma concentration of insulin, catecholamines, and glucose or VO2. Fat overfeeding did not significantly alter any of these parameters (Table 1). Mental stress increased plasma norepinephrine and epinephrine to the same extent in ISO, CHO OF, and FAT OF (Figure 1), increased heart rate and blood pressure (ISO from 58 ⫾ 2 to 84 ⫾ 2 bpm, p ⬍ 0.01; GLU OF from 62 ⫾ 2 to 91 ⫾ 2 bpm, p ⬍ 0.01; FAT OF from 57 ⫾ 1 to 84 ⫾ 2 bpm, p ⬍ 0.01) and blood pressure (ISO from 77 ⫾ 1 to 91 ⫾ 2 mm Hg, p ⬍ 0.01; GLU OF from 78 ⫾ 1 to 89 ⫾ 1 mm Hg, p ⬍ 0.01; FAT OF from 80 ⫾ 1 to 90 ⫾ 2 mm Hg, p ⬍ 0.01), increased VO2 by 22% ⫾ 3% in ISO (p ⬍ 0.001), by 22% ⫾ 2% in CHO OF (p ⬍ 0.001), by 21% ⫾ 2% in FAT OF (p ⬍ 0.001; Figure 2), and produced nonsignificant increases in subcutaneous interstitial glycerol concentrations (ISO from 293 ⫾ 44 to 421 ⫾ 39 ␮M; GLU OF from 321 ⫾ 30 to 404 ⫾ 35 ␮M; FAT OF from 360 ⫾ 41 to 408 ⫾ 40 ␮M, all not significant; Figure 3). UF Protocol Compared with the isocaloric diet, UF led to a 24% decrease in plasma glucose concentration, a 60% decrease

Figure 1: Plasma norepinephrine and epinephrine concentrations during a 15-minute mental stress in healthy women studied after isocaloric nutrition (ISO) or a 3-day period of carbohydrate overfeeding (CHO OF) or fat overfeeding (FAT OF). *p ⬍ 0.05 or less vs. basal (time, 60 minutes). MS, mental stress.


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Table 2. Postabsorptive plasma substrate and hormone concentrations in the underfeeding protocol Isocaloric diet

Underfeeing

Glucose (mM) 4.01 ⫾ 0.10 3.04 ⫾ 0.21* Non-esterified fatty acids (mM) 0.36 ⫾ 0.05 0.94 ⫾ 0.07† ␤-hydroxybutyrate (mM) 0.054 ⫾ 0.021 3.258 ⫾ 0.843‡ Insulin (mU/liter) 8.1 ⫾ 0.7 1.9 ⫾ 0.7 Leptin (␮g/liter) 8.2 ⫾ 2.2 3.3 ⫾ 0.4† Epinephrine (pM) 46 ⫾ 8 43 ⫾ 4 Norepinephrine (pM) 200 ⫾ 22 204 ⫾ 16 Figure 2: Oxygen consumption (VO2 mL standard pressure and temperature, dry [STPD]), in basal conditions and during mental stress in healthy women studied after isocaloric nutrition (ISO) or a 3-day period of carbohydrate overfeeding (CHO OF) or fat overfeeding (FAT OF). *p ⬍ 0.05 or less vs. basal (time, 60 minutes).

crease in plasma insulin concentration but did not change plasma catecholamines concentrations or basal metabolic rate (Table 2). Mental stress increased plasma norepinephrine and epinephrine concentrations similarly in ISO and hypocaloric (HYPO) conditions (Figure 4). The stimulation by mental stress of heart rate (ISO from 67 ⫾ 5 to 93 ⫾ 5 bpm, p ⬍

* p ⬍ 0.05. † p ⬍ 0.01. ‡ p ⬍ 0.001 or less vs. ISO.

0.01; HYPO from 70 ⫾ 5 to 91 ⫾ 7 bpm, p ⬍ 0.01) and blood pressure (ISO from 80 ⫾ 2 to 93 ⫾ 3 mm Hg, p ⬍ 0.01; HYPO from 80 ⫾ 2 to 91 ⫾ 3 mm Hg, p ⬍ 0.01), were similar under both conditions. Mental stress increased less VO2 in HYPO (by 13% ⫾ 3%) than in ISO (by 19% ⫾ 3%, p ⬍ 0.05; Figure 5) and increased more subcutaneous interstitial glycerol concentrations in HYPO (from 304 ⫾ 13 to 497 ⫾ 51␮M, p ⬍ 0.01) than in ISO (from 309 ⫾ 34 to 355 ⫾ 53 ␮M ⫽ not significant; Figure 6).

Discussion

Figure 3: Concentration of glycerol in the dialysate collected from a microdialysis catheter inserted into the subcutaneous, periumbilical tissue. Values obtained in basal conditions and during a 15-minute mental stress in healthy women studied after isocaloric nutrition (ISO) or a 3-day period of carbohydrate overfeeding (CHO OF) or fat overfeeding (FAT OF). MS, mental stress.

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The effects of energy imbalance on the sympathetic control of energy expenditure remain debated. Energy imbalance may possibly affect energy expenditure through alterations of either sympathetic nervous system activity or responsiveness to the stimulating actions of catecholamines on energy expenditure. In this study, we assessed the effects of mental stress, a procedure that acutely activates the sympathetic nervous system on whole body energy expenditure. Because mental stress also produces a significant degree of hyperventilation, which invalidates the measurement of respiratory exchange ratio, the sole oxygen consumption was used as an index of energy expenditure. The major novel observation of this study is that a 3-day calorie restriction decreased significantly the stimulation of oxygen consumption induced by a mental stress, indicating a reduced stimulation of energy expenditure. This blunted metabolic response occurred in the absence of significant differences in the degree of sympathetic stimulation elicited by mental stress; the increase in plasma catecholamines concentrations and in heart rate and blood pressure were


Figure 6: Concentration of glycerol in the dialysate collected from a microdialysis catheter inserted into the subcutaneous, periumbilical tissue. Values obtained in basal conditions and during a 15-minute mental stress in healthy women studied after isocaloric nutrition (ISO) or a 3-day period of underfeeding (UF). *p ⬍ 0.05 or less vs. basal (time, 60 minutes). MS, mental stress.

Figure 4: Plasma norepinephrine and epinephrine concentrations during a 15-minute mental stress in healthy women studied after isocaloric nutrition (ISO) or a 3-day period of underfeeding (UF). *p ⬍ 0.05 or less vs. basal (time, 60 minutes). MS, mental stress.

Figure 5: Oxygen consumption (VO2, mL standard pressure and temperature, dry [STPD]), in basal conditions (left panel) and during mental stress (middle panel) in healthy women studied after isocaloric nutrition (ISO) or after a 3-day period of underfeeding (UF). Right panel represents the change in VO2 observed during mental stress. *p ⬍ 0.05 or less vs. ISO.

indeed similar in isocaloric conditions and after energy restriction. Our results seem in opposition with those of Mansell et al. (17), who showed that the stimulation of energy expenditure by epinephrine infusion was increased in normal volunteers after 48 hours of starvation. The reason for this discrepancy is not readily apparent. The nutritional condition (48 hours of starvation in the Mansell study vs. 3 days of protein-sparing modified fasting in the present study) may play a role. Sex differences (men in the Mansell studies vs. women in our study) may also be involved. Finally, our observation of a reduced stimulation of energy expenditure during mental stress in calorie-restricted women may be specifically due to a blunted effect of endogenous catecholamine released at nerve endings. Resting VO2 was significantly increased after calorie restriction before mental stress. Such an increase in resting energy expenditure has been reported by other investigators (18) and is believed to correspond to the energy cost of enhanced gluconeogenesis during short-term UF. This rise in basal energy expenditure, however, is expected to be transient and to decrease when UF continues for extended periods. We considered the possibility that this increase in basal energy expenditure may interfere with the evaluation of the effects of mental stress. However, such interference seems unlikely. Sympathetic activation elicited by mental stress is not expected to inhibit gluconeogenesis; hence, it is improbable to acutely decrease basal energy expenditure. Moreover, the acute increase in energy expenditure induced by mental stress cannot be attributed to stimulation of OBESITY RESEARCH Vol. 10 No. 1 January 2002

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gluconeogenesis because we have previously observed that it does not increase hepatic glucose production (6). Our observation of a reduced stimulation of oxygen consumption by mental stress in calorie-restricted women contrasted with an enhanced activation of lipolysis, as documented by increased interstitial subcutaneous glycerol concentrations. This finding is consistent with the enhanced adipose tissue sensitivity to catecholamines of food-restricted individuals (9,17). Furthermore, it points to differential effects of food restriction on sympathetically mediated processes, i.e., a simultaneous enhancement of lipolysis and a reduced activation of energy expenditure. In contrast with these effects of calorie restriction, overfeeding had no significant effects on the metabolic processes that were monitored. Neither carbohydrate nor fat overfeeding produced any detectable alterations on basal oxygen consumption or on the stimulation of sympathetic nervous system, oxygen consumption, or subcutaneous adipose tissue lipolysis during mental stress. The present data suggest that a reduction of sympathetically mediated energy expenditure contribute to limit weight loss during UF. In contrast, no significant adaptation of energy expenditure was observed during UF. This may indicate that stimulation of energy expenditure is not a major mechanism to prevent weight gain in humans. Altogether this indicates that the mechanisms involved in the preservation of weight are more effective during UF than during OF. Similar differential adaptations to overfeeding or UF are observed with leptin. UF decreased markedly plasma leptin levels after only 3 days, i.e., before major changes in body composition occurred. Such a rapid decline in plasma leptin concentrations has been reported by other investigators (19,20). In contrast, OF led to only modest increases in plasma leptin concentrations, as reported previously (13). Furthermore, it is recognized that the increased plasma leptin concentrations observed in obese or lean subjects after chronic OF have little effectiveness in reducing body weight due to a simultaneous appearance of leptin resistance, possibly related to an impaired transport through the blood– brain barrier (21). A decrease in plasma leptin concentrations during fasting may indeed be instrumental in several adaptations to calorie restriction, regarding not only preservation of body weight, but also regulation of reproductive functions and of the pituitary–adrenal axis (22,23). Altogether, our present data are consistent with the concept that the organism develops potent adaptations when subjected to caloric deprivation, whereas excess caloric intake elicits little adjustments to prevent weight gain. All these measurements were performed during the follicular phase of the menstrual cycle. This was done to ensure that interindividual variations in sex hormone concentrations did not interfere with our measurements. However, it remains possible that the effects of mental stress and the interactions between feeding and mental 54


stress are different during the follicular and the luteal phases of the cycle. Additional experiments will be required to assess this hypothesis. In summary, our present observation indicates that calorie restriction leads to significant alterations of sympathetically mediated process, characterized by a reduction of energy expenditure and an enhancement of subcutaneous adipose tissue lipolysis during sympathetic activation. These adaptations to UF may be involved in the mobilization of endogenous fat while contributing to limit weight loss during extended periods of calorie restriction. In contrast, short-term overfeeding fails to elicit remarkable alterations of the sympathetic control of energy expenditure or lipolysis, regardless of the nature of substrate ingested in excess.

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