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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 8  |  Issue : 4  |  Page : 330-335

Association of basal metabolic rate with respiratory function among middle-aged obese and nonobese subjects


1 Department of Physiology, All India Institute of Medical Sciences (AIIMS), Mangalagiri, Andhra Pradesh, India
2 Department of Physiology, Navodaya Medical College and Research Center, Raichur, Karnataka, India
3 A. B. N. Seal College, Cooch Behar, West Bengal, India
4 Department of Microbiology, Dattameghe Institute of Medical Sciences, Wardha, Maharashtra, India
5 Department of Public Health Dentistry, ESIC Dental College, Kalaburagi, Karnataka, India

Date of Submission08-Sep-2021
Date of Acceptance25-Oct-2021
Date of Web Publication22-Dec-2021

Correspondence Address:
Dr. Afreen Begum H Itagi
Department of Physiology, All India Institute of Medical Sciences (AIIMS), Mangalagiri 522503, Andhra Pradesh.
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mgmj.mgmj_68_21

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  Abstract 

Background: Obesity is proved to be a comorbid condition in various metabolic, cardiovascular, and pulmonary disorders. Only a few investigations analyzed the relationship between basal metabolic rate (BMR) and lung function in middle-aged obese individuals. Objectives: The aim of this study was to determine the relationship of BMR to that of pulmonary functions among middle-aged obese subjects. Materials and Methods: This cross-sectional study was undertaken in obese and nonobese healthy subjects (50 each) of age 35–55 years. Body mass index (BMI), body fat percentage (BF%), fat mass (FM), and fat-free mass (FFM) were estimated, and BMR was calculated using predicted equations. Spirometric measures such as forced expiratory volume in one second (FEV1), forced vital capacity (FVC), FEV1/FVC, and peak expiratory flow rate (PEFR) were measured. Maximum voluntary ventilation (MVV) and mean forced expiratory flow during the middle of FVC (FEF25%–75%) were determined. Descriptive statistics, t test (unpaired), and Pearson’s correlation test were used for the analysis of the variables. Values of P ≤ 0.05 were considered statistically significant. Results: Mean BMR among obese was significantly higher than nonobese. The pulmonary function parameters FVC, FEV1, and FEF25%–75% were significantly reduced in obese. A significant positive correlation of BMR was found with FVC, FEV1, PEFR, FEF25%–75%, and MVV among both obese and nonobese. An inverse correlation existed between BMR and FEV1-to-FVC ratio in the study participants. Conclusions: Pulmonary functions are more closely associated with fat distribution than with the extent of obesity. The study outcome suggests that, in the context of early lung function alterations in the middle-aged obese subjects, it is necessary to take into account the BMR and body composition instead of BMI alone.

Keywords: Anthropometrics, basal metabolism, lung functions, obesity


How to cite this article:
Itagi AB, Kalaskar A, Dukpa PT, Chandi DH, Yunus G Y. Association of basal metabolic rate with respiratory function among middle-aged obese and nonobese subjects. MGM J Med Sci 2021;8:330-5

How to cite this URL:
Itagi AB, Kalaskar A, Dukpa PT, Chandi DH, Yunus G Y. Association of basal metabolic rate with respiratory function among middle-aged obese and nonobese subjects. MGM J Med Sci [serial online] 2021 [cited 2022 Jan 18];8:330-5. Available from: http://www.mgmjms.com/text.asp?2021/8/4/330/333327




  Introduction Top


Obesity is one of the twenty-first century’s most significant public health concerns. The problem is worldwide, and it has approached epidemic proportions in India with morbid obesity afflicting over 5% of the population.[1] The daily rate of energy metabolism that a human must sustain to maintain the integrity of vital functions is referred to as the basal metabolic rate (BMR). It is the minimum amount of energy required to maintain life in a neutrally temperate environment in a post-absorptive condition, taking into account the energy cost of physiological activities such as muscular contractions, breathing, and brain activity.[2] It is hypothesized that reduced BMRs are common in obese people and sedentary adults; BMR accounts for 60% of total energy expenditure.[3] On the contrary, differential BMRs are unlikely to be the cause of growing obesity rates.[4]

Obesity impedes the mobility of the diaphragm and the expansion of the thoracic cage, which reduces chest compliance. Its negative impacts on respiratory mechanics, respiratory resistance, respiratory muscle function, lung volumes, effort, and energy cost of breathing, breathing control, and gas exchange can drastically change pulmonary function and cut down exercise capacity.[5],[6] The mechanism that impacts lung function in obesity is still being disputed, and hence the appropriate indicator of adiposity in connection to dynamic pulmonary function is yet not clear.[7],[8],[9] Multiple studies have found that obese persons had inferior lung volumes, with an inverse relationship between respiratory functioning and numerous indices of obesity or fat distribution.[5],[6],[7],[8],[9],[10],[11] Only a few investigations, however, have looked at the association between BMR and the components of ventilatory dysfunction.[12],[13],[14]

To the best of our knowledge, the relationship between obesity and BMR as a risk factor for pulmonary dysfunction has not been thoroughly investigated and documented among the Indian population, who are regarded to be at higher risk of obesity-related problems. Furthermore, there is a dearth of research evidence on the association between BMR and ventilatory dysfunction in middle-aged people. Hence, the study aimed at investigating the relationship between BMR and its effects on pulmonary function in middle-aged obese and nonobese individuals.


  Materials and methods Top


This cross-sectional research was conducted at the Medical Institute and Research Center in southern India. The healthy individuals between the ages of 35 and 55 years were taken as participants.

Initially, a pilot study was undertaken on eight middle-aged obese adults (not included in the final study) yielded a standard deviation (SD) of 9. The required sample size for the study was estimated using the formula N = (Z/2)2 s2/d2, with the power of the study set at 80% and an error rate of 5%. The minimum sample size was estimated to be 45 subjects; after allowing for 10% nonrespondents, the sample size required in each group was at least 49.

A detailed history of extended exposure to drugs that can lead to altered lung functions, medical issues, and medications taken during the last 6 months was taken, followed by a clinical and systemic examination. Subjects with physical chest wall abnormalities established obstructive pulmonary illness, unstable coronary syndromes, presently smokers, and alcoholics were excluded from the study. The study was approved by Institute’s Ethical Committee and informed written consent was obtained from participants after briefing about the objectives of the study.

After a minimum of 2 h of light breakfast and according to the specified guidelines, anthropometric measures were obtained in the physiology laboratory. All spirometric measurements were obtained from 10 am to 12 noon to eliminate circadian variations.[15] In a light dress without shoes, weight was measured to the nearest 0.5 kg. The stature was measured in centimeters (cm) using a measuring tape to the nearest 0.2 cm, with heels close to the wall, feet close together and the head in Frankfort’s plane.[16] Body mass index (BMI) was calculated as weight/height,[2] where weight is expressed in kg and height in square meters (m2). Body fat percentage (BF%), fat mass (FM), fat-free mass (FFM), and BMR were estimated using the formulae mentioned in [Table 1].[17],[18],[19]
Table 1: Measures and formulae used for calculation of basal metabolic rate (BMR)

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The pulmonary function tests were performed using “NDD – Easy on PC” (Royal Medi Systems, Hyderabad, India) a portable, computerized, precalibrated, electronic, dry-type spirometer. At least three appropriate maneuvers of forced vital capacity (FVC), forced expiratory volume in one second (FEV1), mean forced expiratory flow during the middle of FVC (FEF25%–75%), peak expiratory flow rate (PEFR), and maximum voluntary ventilation (MVV) were performed. The highest volumes of three acceptable FVCs, FEV1, and PEFR were recorded. The ratio of FEV1-to-FVC was expressed as a percentage. MVV was assessed by making the subject rapidly and deeply inhale and exhale for at least 15 s.

Statistical analysis

The data was analyzed by using the Statistical Package for the Social Sciences (SPSS) software program, version 20.0 (SPSS, IBM, Chicago, Illinois). The results are expressed as mean ± SD or percentages. The difference between measured variables was determined using the inferential statistical test (unpaired t test). The degree of correlation was assessed using the Pearson correlation coefficient and a value of P ≤ 0.05 was considered statistically significant.


  Results Top


The mean age and anthropometric measurements of both the obese (n = 50) and nonobese (n = 50) groups are presented in [Table 2]. In comparison to nonobese middle-aged individuals, the BMR was significantly higher among the obese group.
Table 2: Comparison of anthropometric parameters and BMR between obese and non-obese subjects

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The pulmonary function test (PFT) parameters namely FVC, FEV1, and FEF25%–75% were substantially lower in the obese group (P ≤ 0.05). However, FEV1/FVC%, PEFR, and MVV were not significantly different in comparison to nonobese [Table 3]. In both obese and nonobese patients, a significantly positive correlation of BMR was identified with FVC and FEV1. In comparison to obesity (r = +0.66 FVC and r = +0.62 for FEV1), the degree of correlation was higher for nonobese compared to obese (r = +0.57 FVC and R = +0.56 FEV1) [Table 4] and [Figure 1]. This positive association implies that whenever the BMR increases, the FVC and FEV1 levels will increase significantly. An inverse correlation of BMR with FEV1/FVC was observed among both obese and nonobese subjects, which showed comparatively higher strength of the relationship in the obese group (r = –0.02) than the nonobese middle-aged individuals (r = –0.002). BMR showed a positive correlation with PEFR, FEF25%–75%, and MVV in both groups, with the strength of correlation being comparatively slightly high and significant in nonobese subjects as shown in [Table 4] and [Figure 1].
Table 3: Comparison of pulmonary functions between obese and nonobese subjects

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Table 4: Comparison of BMR with relation to pulmonary functions between obese and nonobese subjects

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Figure 1: Relationship of BMR with pulmonary functions in obese subjects

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  Discussion Top


Obesity is a condition of excessive adiposity influenced by various neural, hormonal, and metabolic factors. BMR accounts for 45%–70% of total daily energy expenditure, depending on age and lifestyle, and is largely determined by age, gender, body size, and body composition; hence, BMR is the principal focus of development and treatment of obesity.[20],[21] Spirometry is among the easiest tools to detect pulmonary function impairments at an early stage and to adopt preventive measures. Our study evaluates the relationship between BMR and pulmonary functions in obese and nonobese male subjects of age group 35–55 years.

There existed a positive correlation of pulmonary functions with BMR, which implies higher the BMR, the higher were the levels of FVC, FEV1, FEF25%–75% in both obese and nonobese groups; however, the levels of PEFR showed a nonsignificant correlation in obese subjects only. These possibly suggest that pulmonary functions are more closely associated with fat distribution rather than with the extent of obesity. Spirometric variables, such as FEV1 and FVC, tend to decline with increasing BMR.[11],[12],[13],[22] The effect is however quite minimal and in healthy, obese adults, and children, both FEV1 and FVC are generally within the normal range. The FEV1-to-FVC ratio even in morbid obesity is either well maintained or increased, indicating that both FEV1 and FVC are affected to the same extent. This finding signifies that obesity has a substantial impact on lung volume but has no direct effect on airway obstruction.[12],[13],[14],[22]

In our study, the level of FEF25%–75% was significantly higher in subjects with increased BMR reflecting a positive correlation of BMR. A study done on pulmonary function in obese subjects with normal FEV1/FVC reported that a far greater degree of obesity is needed to impact pulmonary functioning.[23] Similarly, other studies have shown that the effect of obesity on total lung capacity and vital capacity is modest.[5],[24],[25],[26] Our investigation is consistent with the results of Ofuya et al.,[27] which reported a decrease in PEFR in obesity.

Zeng et al.[14] and Ofuya et al.[28] confirmed fat deposition reduces the movement of the thoracic wall and also that in obese subjects maximal expiratory flow rates were reduced at low lung volumes suggesting peripheral airflow limitation and resistance. The negative effect of abnormal metabolism and obesity on lung function is confirmed in many previous studies.[29],[30],[31],[31] In line with these results, we found a significant correlation between BMR and values of lung functions indicators. There is, however, a considerable variation in BMR between individuals with obesity and nonobese as BMR calculations are based directly on participants’ weight.

Limitations

The moderate sample size of our study has limits, and it may be useful to assess maximal inspiratory and expiratory pressures, which are markers of diaphragm strength and abdominal/intercostal muscle strength, respectively, along with FVC and FEV1. FVC and FEV1 are the pulmonary variables that are most commonly used in clinical investigations and appear to be the most closely associated with fat distribution. To further validate the existence of this association, a practical assessment of BMR based on direct oxygen consumption measurement is recommended.


  Conclusion Top


The study outcome suggests that it does give a glimpse into direct relationships of BMR with pulmonary functions in middle-aged healthy subjects with obesity. To the best of our knowledge, this is one of the few studies of its kind that has sought to determine and assess the association between BMR and pulmonary functioning in obese and normal-weight individuals. The study found that the BMR is a stronger predictor of pulmonary function changes in both obese and nonobese people; therefore, when identifying early changes in lung function it is vital to look at BMR rather than taking into account BMI alone.

Ethical policy and institutional review board statement

The study was approved by Institute’s Ethical Committee vide their letter no. JJMMC/IEC/2012/Phy/01 dated November 7, 2012 and informed written consent was obtained from participants after briefing about the objectives of the study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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