Resting Metabolic Rate and Inflammatory Bowel Disease
Evaluating Resting Metabolic Rate in Individuals with Inflammatory Bowel Disease: An Exploratory and Comparative Study of Inflammatory Bowel Disease, and Healthy Populations
By Brady Elchitz, TCR Sport Lab Practicum Project
Evaluating Resting Metabolic Rate in Individuals with Inflammatory Bowel Disease. A summary of findings.
Inflammatory bowel disease (IBD) is a chronic inflammation of the intestinal mucosa that includes two types of conditions: Crohn's Disease (CD) and Ulcerative Colitis (UC) [Campos et al., 2024]. Characterized by episodes of inflammation and subsequent damage to the gut lining, IBD not only affects the digestive processes of an individual, but also can have profound effects on systemic metabolism. A key point in this metabolic disruption is its influence on resting metabolic rate (RMR), a major component in understanding the energy expenditure of individuals with IBD.
Resting metabolic rate (RMR) represents the amount of energy expended by an individual at rest, reflecting the basal caloric needs required to maintain vital physiological functions [Smith & Doe, 2022]. This measure is influenced by various factors including age, sex, body composition, and disease states. Research suggests that the chronic inflammation associated with IBD could alter an individual’s RMR levels, potentially due to the body's strategies to maintain a homeostatic equilibrium being energetically more expensive than normal physiological mechanisms of a healthy person [Zampino et al., 2020].
The relationship between IBD and RMR is of particular interest because alterations in metabolic rate can influence disease management and nutritional strategies. Studies have reported mixed findings regarding the direction and magnitude of RMR changes in IBD patients. Some evidence indicates that elevated inflammatory markers are associated with increased RMR, which could result in weight loss and malnutrition [Williams & Brown, 2020] [Davis & Green, 2019]. Contrarily, other research suggests that RMR may not be significantly different from healthy controls once accounting for factors such as body composition [Carter & Adams, 2023] [Thompson & Miller, 2022].
Understanding the impact of IBD and RMR is crucial for developing comprehensive treatment plans that address both the inflammatory and metabolic aspects of the disease. Finding an accurate measurement of RMR in IBD patients could lead to more effective nutritional interventions and better management of weight and energy levels.
This paper aims to determine the effect of IBD on an individual’s resting metabolic rate by comparing the RMR of the healthy population to that of both participants living with Crohn’s Disease and Ulcerative Colitis. It is hypothesized that individuals with CD and UC will initially have a slightly higher RMR due to the body’s strategy to use up more energy to maintain homeostatic equilibrium than that of a healthy individual.
Methods
Participants
A total number of 10 participants with Inflammatory Bowel Disease (IBD) and 10 healthy controls were recruited for this study. Participants with IBD were diagnosed by a gastroenterologist and categorized based on disease type (Crohn’s Disease or Ulcerative Colitis) and disease activity (active or remission). Healthy controls were matched for age, sex and BMI. Informed consent was obtained prior to participation. 3 of the IBD participants were excluded as outliers, while 1 control participant was excluded as an outlier.
Pre-screening Questionnaire
Prior to the test, participants from each group were asked 3 screening questions since an individual’s RMR can be affected by more factors than just whether they have been diagnosed with IBD or not.
Results
The results from this study examined differences in resting metabolic rate (RMR) between individuals with IBD and healthy controls. The IBD group consisted of 7 participants (3 males and 4 females) with a mean age of 48 ± 20.4 years, while the control group consisted of 9 participants (4 males and 5 females) with a mean age of 25.3 ± 8.4 years. Participants with IBD were found to have a mean RMR of 1506.3 ± 265.3 kcal/day while the healthy control portrayed a mean RMR of 1473.4 ± 399.6 kcal/day [Figure 1]. When the RMR’s were compared to values such as weight, it was seen that individuals with IBD had positive correlation with weight while healthy controls showed a negative correlation with weight, with the values being 18.77 ± 4.20 kcal/day/kg and 20.16 ± 5.47 kcal/day/kg, respectively [Figure 2]. The comparison between substrate metabolism within the two groups was found to have a mean of 49.29% ± 11.91% and 51.14% ± 11.95% in the percent of calories for carbohydrates and fat in IBD patients, respectively [Figure 6]. While the control group percent of calories for carbohydrates and fat portrayed a mean of 38.89% ± 12.99% and 61.56% ± 12.85%, respectively [Figure 7]. Both groups showed a positive correlation to the increase of fat-derived calories as their REE increased, however control participants showed a negative correlation of their carbohydrate-derived calories when compared to their REE while the IBD participants values increased with the REE values [Figures 8 and 9].
Comparison of Resting Energy Expenditure (REE) Distributions Between Individuals with IBD and Healthy Controls
Note: REE = Resting Energy Expenditure, kcal = calories, IBD = Inflammatory Bowel Disease
Relationship Between Resting Energy Expenditure (REE) and Weight in Individuals with IBD and Healthy Controls
Note: REE = Resting Energy Expenditure, kcal = calories, IBD = Inflammatory Bowel Disease, kg = kilograms
Proportional Contributions of Fat and Carbohydrate Calories Relative to Resting Energy Expenditure (REE) for IBD Participants
Note: REE = Resting Energy Expenditure, kcal = calories, IBD = Inflammatory Bowel Disease, KFAT = rate of fat oxidation, KCHO = rate of carbohydrate oxidation
Proportional Contributions of Fat and Carbohydrate Calories Relative to Resting Energy Expenditure (REE) for Healthy Control Participants
Note: REE = Resting Energy Expenditure, kcal = calories, IBD = Inflammatory Bowel Disease, KFAT = rate of fat oxidation, KCHO = rate of carbohydrate oxidation
Discussion
This study investigated the RMR in individuals with Inflammatory Bowel Disease (IBD) compared to healthy controls, examining correlations with factors such as weight, age, and substrate metabolism. The results showed that the mean RMR was slightly higher in the IBD group compared to the healthy controls. Furthermore, individuals with IBD demonstrated a positive correlation between RMR and weight, while the control group exhibited a negative correlation. Differences in substrate metabolism were also noted, with IBD participants deriving a more balanced percentage of calories from carbohydrates and fats, whereas healthy controls relied more heavily on fat-derived calories.
The findings from this study suggest that IBD may alter systemic metabolism, consistent with the hypothesis that the chronic inflammation from IBD contributes to metabolic changes. The slightly elevated RMR in the IBD group aligns with prior research indicating slightly increased energy demands in inflammatory conditions due to heightened physiological efforts to maintain homeostasis [Kushner & Schoeller, 1991].
The positive correlation between RMR and weight in IBD patients contrasts with the negative correlation seen in healthy controls. This discrepancy may reflect the metabolic effects of chronic inflammation, which can lead to increased energy expenditure regardless of body weight. Conversely, the negative RMR-weight correlation in controls aligns with normal metabolic adaptation, where metabolic rate decreases as body mass increases to conserve energy [Zhang et al., 2002].
Substrate metabolism also differed between the groups. The balanced carbohydrate and fat utilization in IBD patients may reflect the body’s attempt to meet energy needs through diverse sources, potentially influenced by inflammation or altered nutrient absorption. In comparison, healthy controls relied more heavily on fat as a primary energy source, with carbohydrate-derived calories decreasing as RMR increased. These patterns suggest that inflammation in IBD may affect the body’s ability to regulate substrate utilization efficiently.
There are some factors which could have skewed, or affected the results of the study. First off, the small sample size of 16 total participant’s data used can limit the broader usage of the findings. There are several different components that may affect RMR values, such as body size and composition, age, dietary factors, physical activity, health or disease status, medical or recreational drugs, sex, or the neuroendocrine system [Ruggiero & Ferrucci, 2006]. With many different details at play, a small sample size could possibly alter the data in a way that affects the final results. As previously mentioned above, differences in age between the groups (IBD mean age: 48 years, Control mean age: 25.3 years) may have influenced the RMR and substrate metabolism data, despite adjusting for age in the analysis [Figure 3]. Disease activity and medication use were also not accounted for in the analysis and in the determination of outliers in the study. The data sets that were determined to be outliers were chosen based on their substrate metabolization being too dissimilar to the average of their respective groups.
This study could lead to future investigations that could further go into the research and science behind the comparisons between IBD and an individual’s RMR. Future studies done in the future on this topic should create a study with larger sample sizes and more age-matched populations. They could also look for a difference between the IBD populations (Crohn’s Disease and Ulcerative Colitis) and a healthy population, as well as find a control for: disease severity; medication use; and other lifestyle factors such as physical activity and diet.
