2.1. Obesity and Functional Constipation:
Functional constipation (FC) is one of the most prevalent gastrointestinal disorders reported in adults and children worldwide [
8]. The reported prevalence of FC ranges between 0.5% to 32.2% among the pediatric population, with a pooled prevalence of 9.5% (95% CI, 7.5-12.1%) [
9]. With abdominal pain(in as high as 47.5% [
10]) and fecal incontinence. FC further degrades an already compromised lifestyle in obese children.
The available literature on obesity and FC is contradictory at first glance. FC has been reported to be the most common GI-related morbidity in obese children [
11]. It was reported in 23% of obese children, compared to 8.9% in the general population [
12]. When compared to the age and sex-matched healthy controls, there was a preponderance of constipation among the obese children (21% versus 1%) [
13]. Such association was consistent with the findings (18.44% versus 7.82%) of another clinic-based Italian study [
14]. A US-based study reported that obesity increased the risk of developing constipation in children by almost 2-folds (odds’ ratio1.83, p-value 0.01) [
15]. In a retrospective observational study on children referred to the sub-speciality clinic for functional constipation, we observed a significantly higher number of overweight children among the constipation group than the control group (p-value <0.05) [
16]. Another study on children referred to a pediatric gastroenterology clinic reported a higher prevalence of obesity in constipated children (22.7% versus 11.7%) than the controls (p-value <0.001) [
17]. A prospective clinic-based case-control study also observed a higher obesity rate (8%) in constipated children [
11]. Similar results were reported from outside Europe and North America as well. A study from India on 186 children reported obesity in 23.66% of cases with functional constipation. Encopresis with constipation was significantly higher among the obese children (88.64%, p<0.0001) [
18].
On the other hand, two school-based studies from Columbia (N=2820) and Brazil (N=1077), did not document increased incidence of constipation in obese children (Obese/control; Columbia 14.9%/12.9%, p=0.73; Brazil 19.4%, 18%, p=0.76) [
19,
20]. Another study from the Netherlands (N=2420) found no significant increase in the incidence of obesity among children with constipation (OR 1.01; 95% CI: 0.69-1.46) compared to those with normal weight [
21].
Figure 1.
Constipation and Obesity in Children.
Figure 1.
Constipation and Obesity in Children.
On close analysis, it appears that while most of the clinic-based studies reported an association between obesity and constipation, community-based studies refuted such claims (Figure -1). We reviewed the charts of 955 children in the primary care clinic. [
22] We concluded that there was no association between constipation and obesity in the community setting. But obese children with constipation were 3 times more likely to be referred to the subspecialty clinic, for apparent treatment failure. This may explain the preponderance of obesity among constipated children in clinic-based studies. A prospective study is warranted to test this hypothesis as weight management may be another non-pharmacological tool for treating constipation.
Several mechanisms have been proposed as the causes of both constipation and obesity. High carbohydrate, low-fiber diet and a sedentary lifestyle are associated with both obesity and constipation [
21].A study on middle-aged post-menopausal women found significant improvement in constipation symptoms and quality of life after 12 weeks of increased physical activity and low-calorie diet intake [
23]. The “ileal break” concept, where a high-fat diet slows down intestinal motility and causes constipation in obese adults, has been proposed [
24]. However, a study involving morbidly obese children didn’t find any difference between the diet of children with or without constipation, including fiber and fat intake [
13].
Daily exercise enhances colonic motility and accelerates gut peristalsis by stimulating the vagus nerve, increasing gut blood flow, and augmenting the release of GI hormones. Gut hormones like ghrelin and motilin take a pivotal role in the pathogenesis of constipation in overweight persons. Ghrelin, a “hunger hormone”, augments initiation of the migrating motor complex in the stomach, and stimulates gastrointestinal motility [
25]. In obese children, lower serum concentrations of ghrelin may contribute to decreased gut motility, which, in turn, causes constipation. Fat intake potentiates increased release of Glucagon-like peptide-1, 2 (GLP-1, GLP-2), cholecystokinin (CCK), and inhibition of peptide YY (PYY), which leads to constipation by colonic smooth muscle relaxation. Obesity mediates tumor necrosis factor-alpha (TNF-a), IL-1, IL-6, and toll-like receptor (TLR) signalling, which are responsible for immunoinflammation [
26]. It causes morphological changes in the interstitial cells of Cajal of the enteric nervous system and impairs the contractile function of intestinal smooth muscles.
Finally, psychosocial and behavioral abnormalities are postulated to play important roles in the co-occurrence of obesity and FC. Children with obesity have a 43% higher risk of anxiety and depression than the general population (p<0.0001). Moreover, obesity makes children and adolescents more vulnerable to having low self-esteem (risk estimate 1.53; 95% CI: 1.16-2.02; p=0.003) and body dissatisfaction (risk estimate 4.05; 95% CI: 2.34-7.023; p=0.0001) [
27]. On the other hand, studies have identified childhood constipation as a potential risk factor for depression, attention difficulties, and poor school performance. Though there is little direct evidence identifying depression as a connecting bridge between constipation and obesity, we reported an increased incidence of psychological and behavioral problems in the group of overweight children with treatment-resistant chronic constipation [
22]. A correlation between increased body weight and psychological stress [
28]. Chronic stressful condition increases catecholamine production, especially epinephrine (E) and norepinephrine (NE). Both of these catecholamines affect GI blood flow, causes beta-receptor mediated GI smooth muscle relaxation, and ultimately, alter GI motility and increase GI transit time [
24]. Additionally, stress releases cortisol by increasing corticotrophin releasing factor (CRF) and adrenocorticotropic hormone (ACTH). Cortisol increases plasma zinc concentration, which augments secretion of CCK, an inhibitor of colonic contraction. Weight reduction interventions might help in reduction of emotional stress, anxiety, poor self-esteem and thus augment the overall emotional and psychological well-being.
Gut microbiota is believed to hold the secrets of many human ailments. Disruption of gut microbiota, or dysbiosis, deranges the homeostasis between the ‘good’ and ‘bad’ bacteria of the colon and results in disease states. The role of the microbiome in obesity was dramatically revealed when a lean person became overweight after receiving fecal transplant from an obese donor [
29]. At this point, research mostly focuses on changes in the composition of gut microbiota that can alter the energy metabolism and develop obesity [
30]. In both mono and dizygotic twins studies, there were fewer
Bacteroides (p=0.003), and abundant
Actinobacteria(p=0.002) in the obese sibling [
30]. It has been further suggested in mice studies, that alteration in gut microbiota affects the efficiency of energy harvest from diet, along with utilization and storage of the calories, causing differences in weight gain. Similarly, studies have suggested the involvement of gut microbiota in the development of constipation in obese children. A cross-sectional study examined the stool samples of children using rRNA gene pyrosequencing and found that the fecal microbiota of constipated obese children had decreased representation of
Prevotella and abundance of genera of
Firmicutes spp. compared with the non-constipated obese controls [
31].Those with early insults to the gut microbiome due to necrotizing enterocolitis, sepsis, delayed enteral feeding, and other perinatal events were at greater risk of developing FC in later life [
32]. These studies suggest that gut microbial population of constipated children contains less amount of
Prevonella compared to healthy children. Increased levels
Proteobacteria sp, Bacteroides sp., Parabacteroides sp., and
Bifidobacterium longum, and decreased
Alistipesfinegoldii and
Ruminococcusspas were found in stool samples of children with intractable constipation.
Over the counter probiotic combinations have gained popularity for treatment of FC without any scientific proof of efficacy. From the scanty evidence available from the literature, probiotic supplements containing Prevotella and L.rhamnosus strains are more likely to be effective than the random mix of probiotics available over the counter.