Diarrhea linked significantly to weight gain

A new study shows that having higher body weight is related to chronic diarrhea, independent of other lifestyle or dietary habits. Obesity is a concern in more than 40% of Americans, and is already known to be linked to a number of diseases like heart disease, gut disorders and diabetes.

However, the current research looks at body mass index in relation to bowel habits while accounting for most other factors that could make a difference in this association, and finds that the two are strongly connected. This could help professionals to make better medical decisions in treating obese patients who have more than sporadic bouts of diarrhea.

Our research confirms a positive association between obesity and chronic diarrhea and reveals for the first time that this relationship is not driven by confounding factors such as diet or physical activity level.”

Researcher Sarah Ballou

diarrhoea-obesitySyda Productions / Shutterstock

The study

The current study used data from the National Health and Nutrition Examination Survey (NHANES) 2019-2010, which is a survey run by the Centers for Disease Control and Prevention (CDC) to examine health and nutritional parameters in Americans.

The researchers looked at the responses on bowel movements from over 5,000 patients over 20 years who had no history of irritable bowel syndrome, celiac disease or bowel cancer. They also looked at the BMI and classified patients in five categories: underweight, normal weight, overweight, obese and severely obese.

They looked at the bowel habits in these groups as well. They adjusted the results for the effects of other factors like diet, exercise, the use of laxatives, diabetes and the age, sex, socioeconomic status, ethnicity, and other demographic factors.

What did the study show?

The results were striking: a 60% higher risk of chronic diarrhea compared to constipation or normal bowel habits when the individual was obese or severely obese.

Overall, only 4.5% of individuals who were of normal weight had chronic diarrhea, in contrast to 8.5% of obese and 11.5% of severely obese individuals. Of all the respondents, only 21% were obese and 17% severely obese.

Obese individuals were two times more likely and severely obese individuals were three times as likely to have diarrhea compared to people with normal BMI.

This is in agreement with other studies, both from the US and from Australia, New Zealand and Australia, which show higher rates of diarrhea in obese people. However, this is the first nationally based study that also covers all categories of BMI.

The present study used the Bristol stool form scale (BSFS) which standardizes the definition of diarrhea across all ranges, by using both pictures and descriptive terms. It is also recommended by the Federal Drug Administration to standardize the measures of treatment outcomes in diarrhea.

Why the connection?

Of course, this doesn’t tell us the reason for the difference. The current study controlled for the intake of carbohydrates and fat and found out that this alone could not account for the different rate of chronic diarrhea.

This study also controlled for factors like diabetes, mental status or ill-health (such as depression) and other factors that could independently affect stool frequency and form. Dietary factors were also not addressed by other studies.

Other studies indicate that obese people are more likely to have bile acid malabsorption compared to those with normal weight.

They also have a higher rate of colonic food transport, higher intestinal permeability, a more imbalanced gut microbiome, and higher levels of bacterial lipopolysaccharides due to Gram-negative bacteria.

The two predominant gut bacterial phyla are Firmicutes and Bacteroidetes, and the ratio between them is higher in obesity, which is also the case in those patients who have diarrhea in relation to irritable bowel syndrome. All these could be the reason for the connection between obesity and diarrhea.

Study limitations include the non-usage of validated Rome criteria to diagnose diarrhea, the lack of data on fermentable carbohydrate intake, which can cause diarrhea, and on the use of drugs or medications over the counter which stimulates the bowel.

The treatment of obesity and obesity-related medical conditions requires multidisciplinary management.”

Anthony Lembo, Researcher

Journal reference:

Sarah Ballou, Prashant Singh, Vikram Rangan, Johanna Iturrino, Judy Nee, & Anthony Lembo. (2019). Obesity is associated with significantly increased risk for diarrhoea after controlling for demographic, dietary and medical factors: a cross‐sectional analysis of the 2009‐2010 National Health and Nutrition Examination Survey. Alimentary Pharmacology & Therapeutics. https://doi.org/10.1111/apt.15500.

Dr. Liji Thomas

Written by

Dr. Liji Thomas

Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.


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