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Being underweight was associated with functional dyspepsia (FD) in adults, independently of the presence of anxiety, an Asian cross-sectional study found, although anxiety was additionally associated with FD.

No relation was found between high body mass index (BMI) and other functional gastrointestinal disorders (FGIDs), according to Kee Huat Chuah, MD, of the University of Malaysia in Kuala Lumpur, and colleagues.

The results, published online in , showed that across different FGIDs, including irritable bowel syndrome (IBS) and functional diarrhea and constipation, FD affected more underweight adults (defined as BMI less than 18.5) compared with a non-FGID control group (13.3% vs 3.5%, P=0.002).

On multivariable analysis, being underweight maintained an independent association with FD, for an odds ratio (OR) of 3.648 (95% CI 1.494-8.905, P=0.004), the researchers reported.

When psychological morbidity was explored in a second phase of the study, anxiety, but not depression, was independently associated with FD (OR 2.032, 95% CI 1.034-3.991, P=0.040). In addition, a BMI less than 18.5 was also independently associated with FD (OR 3.231, 95% CI 1.066-9.796, P=0.038).

Study Details

The questionnaire-based study of 1,002 adults, conducted in the primary care setting at a staff health facility during 2019-2020, found that the Rome III criteria–based prevalence of common FGIDs was 20.7%, a rate very similar to that in a 2020 Rome Foundation , which found an FGID prevalence of 20.9%.

The median age of participants in the new study for both those with (207 patients) and without (795 patients) these disorders was 32, and females predominated (65% of participants overall). More than 90% were of Malay ethnicity. A large proportion of participants were obese (39.2%) – the team noted that obesity is a growing health problem in Malaysia – and of these, 51.7% had "central" obesity (51.7%), while 6.1% had metabolic syndrome. The great majority of participants were non-smokers and did not drink alcohol.

By different FGID types, the study cohort showed the following prevalence rates:

• FD: 7.5% (75 patients)

• IBS: 4.0% (40 patients)

• Functional diarrhea: 1.2% (12 patients)

• Functional constipation: 10.5% (105 patients)

Overall, the prevalence of low or high BMI was similar in individuals both with and without FGIDs:

• Underweight: 6.3% vs 3.5% (P=0.123)

• Obese: 35.7% vs 40.1% (P=0.555)

Neither central obesity nor metabolic syndrome correlated with FGIDs.

The researchers noted that the findings are also consistent with those from a large from France, in which being underweight was independently associated with FD in females.

The Malaysian study additionally suggested that functional diarrhea may have been associated with central obesity, but this association could not be confirmed by multivariate analysis since only a small number of individuals had functional diarrhea. A 2019 large in the U.S. reported that obesity was positively associated with chronic diarrhea.

Which Comes First?

Eating disorders, often linked with anxiety neurosis, have been in bidirectional association with a low BMI and FD simultaneously. "Hence, it may be postulated that FD subjects with a low BMI in our study may have resulted from anxiety and/or eating disorders," Chuah and co-authors wrote. "Alternatively, dietary restrictions by subjects due to persistent FD symptoms may have led to a low BMI and anxiety."

The team called for further studies of longitudinal design to explore whether anxiety causes a low BMI in FD or vice versa.

William D. Chey, MD, of Michigan Medicine in Ann Arbor, who was not involved with the research, called the results interesting and said they may be applicable to the U.S. population since obesity rates are comparable to those in Malaysia.

"But I do agree it's important to consider whether these observations are cause or effect," he commented. "In other words, FD might cause people to lose weight or thin people might be more prone to developing FD. I do think there's face validity to these observations. Remember that patients with functional dyspepsia that have meal-related symptoms of fullness and early satiety are unable to eat very much without feeling ill."

Previous studies have shown that patients with postprandial distress syndrome often lose weight from their illness, Chey continued. "On the other hand, patients with anorexia often have measurable abnormalities in gastric emptying, but that's not to say all FD patients have eating disorders. My point is that certain non-GI conditions associated with weight loss can also be associated with abnormal GI function."

Ultimately, however, an observational study such as this can't answer questions about cause and effect but should lead to hypotheses that can be more formally tested in further studies, he said.

Gerard E. Mullin, MD, MS, of Johns Hopkins University School of Medicine in Baltimore and also not involved with the research, agreed that anxiety can limit caloric intake and result in lower BMI.

"Also, the gut microbiome can have negative effects on behavior and mood and is altered in functional bowel disorders," he told 番茄社区app. His group recently published a of disordered gut microbiome in functional bowel disease -- in particular in patients with diarrhea and IBS -- and concluded that IBS is characterized by gut microbial dysbiosis. In addition, obesity has been linked to disordered communities of gut microbes, he said.

Study limitations, the researchers noted, included that it was not population based, with the cohort consisting mainly of well-educated hospital and university staff members receiving primary care. In addition, the data on psychological disorders were obtained only from a subgroup of original participants in the study's second phase; that the number of participants with functional diarrhea was low; the cross-sectional design did not permit evaluation of the causality of BMI associations with FGID; and the study questionnaire did ask about dietary habits.

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