Being underweight may take a toll on more than energy and immunity; it could also disrupt the gut’s delicate balance.
Researchers at Fujita Health University in Japan found that young women with low body weight had significantly lower gut microbiota diversity than women of normal weight, despite eating similar diets. The findings, published in Nutrients, suggest that gut health may influence how the body regulates weight and responds to nutrient intake.
The study compared 40 underweight women (body mass index below 17.5) with 40 women of normal weight between ages 20 and 39. Both groups reported similar eating patterns based on detailed food questionnaires, yet stool samples told a different story.
“Among Japanese women aged 20-39, those in the underweight group showed a greater decrease in gut microbiota diversity compared to the normal-weight group, rather than differences in dietary patterns,” said Katsumi Iizuka, M.D., Ph.D., professor in the Department of Clinical Nutrition at Fujita Health University. “Underweight women demonstrated reduced gut microbiota diversity and enrichment of taxa associated with inflammatory tendencies.”
The underweight group had higher levels of Bacteroides, Bifidobacterium and Erysipelatoclostridium, bacteria often linked to inflammation. Women with normal weight had more Prevotella and Dorea, species associated with balanced gut function.
Dr. Iizuka said that beyond calorie intake, fiber and fermented foods could play a role in supporting a healthier gut and body weight.
“Actively consuming dietary fiber and fermented foods may lead to weight improvement in underweight individuals by causing changes in the gut microbiota,” he explained.
The results highlight that gut diversity is vital at both ends of the weight spectrum. A balanced microbiome may be just as important for those trying to gain weight as it is for those looking to lose it.
This research was supported by Fujita Health University through its departmental research budget.