What effect does weight have on GI disorders?

Being overweight or obese presents a significant risk factor for the development and progression of a range of gastrointestinal (GI) disorders.

These include (but are not limited to):

• inflammatory bowel disease
• irritable bowel syndrome
• non-alcoholic fatty liver disease
• diverticular disease
• GI cancer
• gastroesophageal reflux

Mechanisms by which obesity influences the disease state

Changes to gut microbiome

Obesity changes the makeup of the gut’s microbiome, and in turn alters the fermentative capacity of otherwise non-digestible compounds in the gut. This can have many downstream consequences leading to an increased risk of inflammatory bowel disease, irritable bowel syndrome, non-alcoholic fatty liver disease, and diverticular disease¹⁵ (where small bulging sacs develop on the intestines which can then become inflamed and painful). The mechanisms involved are summarised in the figure below.

_{Figure adapted from Emerenziani et al 2019}

Systemic inflammation

In addition to causing changes to the gut’s microbiome, the visceral fat present in people with obesity also causes the release of pro-inflammatory factors which contributes to the development and progression of inflammatory bowel disease, pancreatitis and non-alcoholic fatty liver disease. Visceral fat also releases pro-tumoral factors which increase the risk of GI cancer¹⁵.

Mechanical factors

Obesity also induces some mechanical changes, whereby increased abdominal pressure leads to the relaxation of the lower esophageal sphincter, which in turn increases the risk of hiatus hernia (where the upper part of the stomach bulges through the diaphragm), as well as gastroesophageal reflux disease (also known as acid reflux).

Benefits of weight loss

Weight gain is associated with an increase in acid reflux symptoms, and weight loss with a reduction in symptoms. Research has shown that weight loss achieved via dietary advice can improve reflux symptoms in individuals who are overweight¹⁶. Interestingly, improvement in reflux symptoms was seen even with only modest weight loss (2-3kg) following dietary change, inferring that improving dietary intake may contribute to reflux symptoms as well as actual weight loss¹⁷.

Research also shows that irritable bowel syndrome symptoms were improved in individuals with obesity following weight loss surgery¹⁸, inferring that weight loss may be worth considering as part of a management strategy.