Resting Metabolic Rate and Diet-Induced Thermogenesis During Each Phase of the Menstrual Cycle in Healthy Young Women Summary Th

J. Clin. Biochem. Nutr., 25, 97-107, 1998

Resting Metabolic Rate and Diet-Induced Thermogenesis during Each Phase of the Menstrual Cycle in Healthy Young Women

Tatsuhiro MATSUO,1 * Shinichi SAITOH,2 and Masashige SUZUKI,2

1 Division of Nutrition and Biochemistry, Sanyo Women's College, Hatsukaichi 738-8504, Japan 2 Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba 305-8576, Japan

(Received June 20, 1998)

Summary The effects of the menstrual cycle on resting metabolic rate (RMR) and diet-induced thermogenesis (DIT) were studied in nine healthy young women aged 18-19 years. All subjects were eumenorrheic, with regular menstrual cycles ranging from 28 to 32 days. RMR and DIT were measured in the mid follicular phase and in the mid luteal phase. On the experimental days, subjects fasted overnight; then the RMR was measured by indirect calorimetry. For the measurement of DIT, subjects were fed a meal containing a uniform amount of energy (2.53 MJ) eaten within 15 min, and then indirect calorimetry was performed during rest for 180 min. The RMR was significantly higher in the luteal phase than in the follicular phase (67.0 vs. 62.5 J/kg/min, p<0.01). DIT was also significantly higher in the luteal phase (4.0 vs. 3.2 kJ/kg/3 h, p<0.01). The postprandial respiratory exchange ratio was slightly lower in the luteal phase than in the follicular phase (0.78 vs. 0.81). These results suggest that the menstrual cycle phase affects both the RMR and DIT. Higher postprandial energy expenditure and fat utilization in the luteal phase may be related to sympathetic and endocrinal actions.

Key Words: resting metabolic rate, diet-induced thermogenesis, fat utilization, menstrual cycle, women

Interest in the possible variability of energy expenditure during the menstrual cycle has increased in recent years. Although studies to assess the effect of the menstrual cycle on the basal metabolic rate were conducted as early as the 1920's [1-10], the findings were not conclusive. An increased basal metabolic rate during

* To whom correspondence should be addressed .

97 98 T. MATSUO, S. SAITOH, and M. SUZUKI the luteal phase was found by some researchers, whereas others did not observe such a rise. More recent studies by Tai et al. [11] and Piers et al. [12] found no significant variations in the resting metabolic rate (RMR) during the different phases of the cycle. Diet-induced thermogenesis (DIT) has not been studied as extensively as the influence of the menstrual cycle on the RMR. Weststrate [l0] measured both RMR and DIT in 23 women during the follicular and luteal phases over the course of three menstrual cycles and reported no significant differences between the two phases for either variable. Metha and Pande [13] compared DIT during the premenstrual and postmenstrual phases of the cycle in subjects who drank 200 ml of milk and found no significant difference between the two phases. However, Piers et al. [12] reported a significant increase in DIT during the luteal phase of the cycle; whereas Tai et al. [11] suggested that DIT decreased significantly during postovulation phases (average of luteal and late luteal) compared with preovulation phases (average of early follicular and follicular). Because of the difficulty of studying women at a particular phase of the menstrual cycle, most studies on DIT in women have not taken potential periodic- ity into account. However, any variation in DIT during the different phases of the menstrual cycle could be important in energy balance. Such a difference could have considerable implications for the validity of previous studies as well as an effect on future methods. This study was thus carried out to establish whether there are consistent changes in the RMR and DIT over a single menstrual cycle in healthy young women.

SUBJECTSAND METHODS

Subjects. Nine young Japanese women (aged 18-19 years) who did not have a habit of daily exercise were recruited from Sanyo Women's College (Hiroshima, Japan) to participate in this study. All procedures were approved in advance by the Institutional Review Board of Sanyo Women's College and were in accordance with the Helsinki Declaration of 1975, as revised in 1983. After a detailed explana- tion of this study, each subject gave her informed written consent. The subjects were found to be free of disease by a medical examination before the study. Subject characteristics are shown in Table 1. The subjects' height and weight, from which the body mass index (BMI) was calculated, were measured by conventional methods. Percentage of body fat, fat mass, and fat free mass (FFM) were measured with a bioelectrical impedance analyzer (Model TBF-102, Tanita Co., Ltd., Tokyo). All subjects had normal menstrual cycles that ranged from 28 to 32 days. The phase of the menstrual cycle was determined as described previously [11] (follicular phase, days b-10; luteal phase, days 21-25). Experimental design. During the period of the study, each subject maintain- ed a normal life style and ate ad libitum except for the day before the experimental period. That evening each subject ate the same supper (50 kJ kg' body weight) at

J. Clin. Biochem. Nutr. MENSTRUAL CYCLE AND ENERGY METABOLISM 99

Table 1. Subject characteristics measured during a single menstrual cycle.a

aValues are means±SE for nine subjects .

19:00 h. Subjects fasted overnight and entered the experimental laboratory room at 08:00 h where they rested until the start of experiment at 10:00 h. The experiment was performed on the subjects in the follicular phase and luteal phase. RMR and DIT tests were performed by indirect calorimetry at 10:00-13:30 h after the subject had rested comfortably, in a supine position, while trying not to move or fall asleep. The DIT test meal consisted of bread and butter, boiled egg, bone-less ham, orange juice, apple, and yogurt and provided energy as carbohydrate (58%), fat (24%), and protein (18%). The energy of the test meal was 2.53 MJ. The subjects were fed a test meal at 10:15-10:30 h. The subjects then rested for 3 h (10:30-13:30 h). During rest, oxygen consumption and respiratory exchange ratio (R) were measured. Blood samples were collected from the cephalic vein at the level of the forearm to obtain serum and plasma at 10:15, 10:45, 11:15, 11:45, 12:15, and 13:15 h. The voided urine volume was noted and acidified with concen- trated hydrochloric acid (0.01 liter acid/liter urine). All procedures were performed in a laboratory under uniform conditions (temperature: 22± 1°C, humidity: 60%). Measurements. Indirect calorimetry was performed by the ventilated hood technique. For measurement of oxygen consumption and R, the subjects wore face masks (Takei Co., Ltd., Tokyo) continuously for 210 min, except for meal time (15 min). All expired gas was collected into a Douglas bag (Takei Co., Ltd., Tokyo), and the bag was changed every 15 min during rest. The concentrations of oxygen and carbon dioxide in the expired collected gas were immediately analyzed by a gas analyzer (Model RAS-30, RAS-40, AIC Co., Ltd., Tokyo). Urinary nitrogen excretion over the metabolic test was determined by the micro-Kjeldhal method [14]. RMR and postmeal total energy output (PTEO) were calculated from oxygen consumption and carbon dioxide production, corrected for urinary nitrogen loss as described by Consolazio et al. [15]. The R was also calculated from the ratio of the volume of carbon dioxide production to the volume of oxygen consumption per unit of time and used as an index of carbohydrate and fat utilization [15]. DIT was determined by the following formula: PTEOi8o min- RMRi8o min. Plasma glucose, serum immunoreactive insulin (IRI), triacylglycerol, and free fatty acids were determined by methods reported previously [16-20]. Evaluations

Vol. 25, No. 2, 1998 100 T. MATSUO, S. SAITOH, and M. SUZUKI of serum triiodothyronine (T3), thyroxine (T4), luteinizing hormone (LH), follicle- stimulating hormone (FSH), estradiol, and progesterone levels in fasting serum from the subjects were requested from Scripps Reference Laboratory (SRL Co., Ltd., Tokyo). Urinary epinephrine and norepinephrine excretions were assayed by high-performance liquid chromatography with electrochemical detection as modi- fied by the method of Refshauge et al. [20]. Statistical analysis. The statistical analysis was conducted with a personal computer (Macintosh LC 575, Apple Japan, Inc., Tokyo) using a statistical package program (Stat View 4.02, Abacus Concepts, Inc., Berkeley, CA). The statistical significance of the difference between phases was tested by Student's t-test.

Fig. 1. Oxygen consumption (top) and respiratory exchange ratio (R, bottom) before and after meal ingestion measured during a single menstrual cycle. Oxygen consumption and carbon dioxide production were measured, and the R was calculated from these values. Each point represents the mean value±SE for nine subjects.

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RESULTS

Oxygen consumption and R Oxygen consumption and R during rest were measured for 3.5 h to assess RMR and DIT (Fig. 1). Basal and postprandial metabolic test results calculated from the data in Fig. 1 are shown in Table 2. RMR, DIT, and PTEO were significantly higher in the luteal phase than in the follicular phase (p<0.01, p < 0.05). On the other hand, basal and postprandial R were lower in the luteal phase than in the follicular phase, but the differences were not statistically significant.

Substrates and hormones in plasma, serum, and urine Fasting serum estradiol and progesterone were significantly higher in the luteal phase than in the follicular phase (p<0.01, p<0.05) (Table 3). On the other hand, fasting serum LH and FSH were lower in the luteal phase than in the follicular phase, but the differences were not statistically significant (Table 3). The concentrations of these hormones in both menstrual phases were normal compared with standard values [21]. Plasma glucose and serum IRI concentrations increased after meal ingestion

Table 2. Basal and postprandial metabolic indices measured during a single menstrual cycle.a

aValues are means±SE for nine subjects . *** Statistically significant difference from follicular phase (*p <0.05, * *p <0.01, Student's paired t-test).

Table 3. Fasting serum and 24-h urine hormone concentrations measured during a single menstrual cycle.a

aValues are means± SE for nine subjects . *, * * Statistically significant difference from follicular phase (*p<0.05, * *p < 0.O1, Student's paired t-test). LH, luteinizing hormone; FSH, follicle-stimulating hormone.

Vol. 25, No. 2, 1998 102 T. MATSUO, S. SAITOH, and M. SUZUKI

Fig. 2. Plasma glucose and serum IRI concentrations before and after meal ingestion measured during a single menstrual cycle. Total area was calculated from the left figure. Values are means±SE for nine subjects.

(Fig. 2). The total areas under the curve for glucose and IRI did not differ between the follicular phase and the luteal phase (Fig. 2). Figure 3 shows that serum triacylglycerol concentration increased after meal ingestion. The total area under the curve for serum triacylglycerol was lower in the luteal phase than in the follicular phase (Fig. 3), but the difference was not statistically significant. Serum free fatty acids concentrations decreased with intake of a test meal. The value at 11:15 h (60 min after a meal) was significantly higher in the luteal phase than in the follicular phase (p <0.05) (Fig. 3). The total area of serum free fatty acids was higher in the luteal phase (Fig. 3), but the difference was not statistically significant. The meal ingestion did not affect serum T3 and T4 concentrations (Fig. 4). The total areas under the curve for T3 and T4 did not differ between the follicular phase and the luteal phase (Fig. 4).

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Fig. 3. Serum triacylglycerol and free fatty acids concentrations before and after meal ingestion measured during a single menstrual cycle. Total area was calculated from the left figure. Values are means±SE for nine subjects. *Statistically significant difference from the value for the follicular phase (p <0.05, Student's paired t-test).

Urinary excretion of epinephrine and norepinephrine was significantly higher in the luteal phase than in the follicular phase (p<0.01) (Table 3).

DISCUSSION

All subjects had normal menstrual cycles that ranged from 28 to 32 days, and fasting serum pituitary hormones and sex steroid concentrations were normal compared with standard values [21]. These results confirmed that this study was performed safely and correctly. The results in the present study show that both RMR and DIT were significantly higher in the luteal phase than in the follicular phase. Because subjects in

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Fig. 4. Serum triiodothyronine and thyroxine concentrations before and after meal ingestion measured during a single menstrual cycle. Total area was calculated from the left figure. Values are means ±SE for 9 subjects. both menstrual phases were treated identically throughout the experimental period, the differences in RMR and DIT were ascribed to the different menstrual phases. Several previous studies suggested a significant increase in basal metabolic rate and/or RMR during the luteal phase [1-7] . Rubinstein [22] and Hessemer and Bruch [23] reported a postovular rise in RMR and attributed it to increased progesterone secretion. Because the serum progesterone concentration in our study was higher in the luteal phase, our results concerning RMR support these previous findings. There are relatively few studies on the effects of the menstrual cycle on DIT . Metha and Pande [13] measured preovulation and postovulation DIT in 10 women at 0, 5, and 15 min after they consumed 200 ml milk and found no statistically significant difference between preovulation and p0stovulation values . These findings are explained by the short postprandial period over which the

J. Clin. Biochem. Nutr. MENSTRUAL CYCLE AND ENERGY METABOLISM 105 measurements were conducted. The postprandial 15-min period resulted in exclud- ing most of total DIT, therefore precluding an accurate estimation. Recently, Reed and Hill [24] found, in a 6-h measurement of DIT, that 60% of total DIT was measured after 3 h. Segal et al. [25] reported that 60-70% of measured DIT is sufficient for comparisons of DIT groups of subjects. Because our measurements were taken after 3 h, it is safe to compare the DIT in both phases. Tai et al. [11] measured each phase of DIT in eight subjects over 205 min and suggested that DIT was significantly lower in the luteal phase than in the follicular phase. The discrepancy between our study and that of Tai et al. may be partly ascribed to the difference in the meals consumed. We provided 2.53 MJ whereas Tai et al. provided 3.14 MJ. The composition of the meals varied considerably; 75% compared with 58% carbohydrate, 15% compared with 24% fat, and 10% compared with 18% protein. The volume and consistency of the meals were also different. Our study used a normal solid meal with drink (cf., Subjects and Methods) as a test meal whereas the study by Tai et al. used a 711 ml liquid meal with an appearance and consistency similar to those of milk. On the other hand, Piers et al. [12] reported a significant increase in DIT after consumption of 1.88 MJ of semisolid food during the luteal phase of the menstrual cycle. DIT in the luteal phase was 18%higher than in the follicular phase. The result obtained in the present study, i.e., DIT 25% higher in the luteal phase, is consistent with these findings. We show here that postprandial R was lower in the luteal phase than in the follicular phase, indicating that the fat oxidation rate was higher in the former than in the latter. In this context, it should be noted that serum free fatty acid concentrations and total free fatty acids were higher in the luteal phase. Fatty acids released from adipose tissues (fat catabolism) are regulated by adrenergic function, sympathetic activity, and catecholamines [26, 27]. In this study, urinary epinephrine and norepinephrine levels were higher in the luteal phase than in the follicular phase. These findings suggest that the reduction of lipolysis after meal ingestion was prevented by catecholamines from sympathetic nerves or the adrenal medulla. Elevation of catecholamines in the luteal phase is thought to be related to higher estradiol concentrations that reduce the uptake of catecholamine by tissues [28], or competitive inhibition of catechol-0-methyl transferase [29]. Serum thyroid hormones were not affected by the menstrual cycle in our study, which agrees with previous reports [12]. The serum triacylglycerol level was slightly lower in the luteal phase, suggest- ing that blood triacylglycerol was taken into muscles by lipoprotein lipase (LPL) at a higher rate in the luteal phase. LPL plays a critical role in the supply of triacylglycerol fatty acids to various tissues and in the removal of triacylglycerol from the bloodstream [30]. LPL activity in the skeletal muscles and heart is enhanced by catecholamines [31, 32]. Blood triacylglycerol presented higher in the luteal phase after test meal ingestion. This would also contribute to greater fat utilization.

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In conclusion, the present study suggests that there is a significant increase in RMR and DIT during the luteal phase of the menstrual cycle in healthy young women. Postprandial R was lower in the luteal phase because of higher lipolytic activity and uptake of blood triacylglycerol fatty acids related to sympathetic and endocrinal action. However, further studies are needed to clarify details concerning the effects of the menstrual cycle on DIT.

We would like to convey our appreciation to the subjects who participated faithfully in the experiment. This study was supported by a grant from the program Grants-in-Aid for Encourage- ment of Young Scientists of the Ministry of Education, Science, Sports, and Culture of Japan.

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