Constipation and Weight Management
Constipation is more common in people carrying excess weight and is often worsened by low fibre, inactivity, some medicines and the appetite-suppressing injections - all of it manageable.
Plain English
Patient-Friendly Explanation
Constipation usually means opening the bowels fewer than three times a week, or passing hard stools with straining and a feeling that the bowel has not emptied. It is more common in people with obesity, and several reasons overlap: diets low in fibre and fluid, less physical activity, and a long list of medicines including iron tablets, calcium supplements, some antidepressants, opioid painkillers and certain blood pressure drugs. The modern appetite-suppressing injections - the GLP-1 type medicines - deliberately slow the stomach and can slow the gut, so constipation is one of their commonest side effects; it usually settles as the body adapts, or when the dose is raised more slowly. What helps is unglamorous and effective: build fibre up gradually towards 25 to 30 grams a day from fruit, vegetables, oats, beans and wholegrains, drink enough fluid, keep moving, and add a bulk-forming supplement such as psyllium if food alone is not enough. Do not leave straining untreated, because it causes haemorrhoids and anal fissures. See a doctor if constipation is new after the age of 50, if there is blood, unintended weight loss, anaemia or a change in stool shape, if it alternates with diarrhoea, or if it does not respond to the measures above.
Medical
Clinical Definition
Chronic constipation is defined by Rome IV criteria as two or more of straining, hard or lumpy stools, incomplete evacuation, a sensation of anorectal obstruction, manual manoeuvres to defecate, or fewer than three spontaneous bowel movements per week, present for at least three months with symptoms in more than a quarter of defecations; worldwide prevalence is around 16% of adults and a weighted analysis of American national survey data put constipation prevalence at 9.42%. Obesity is associated with constipation in several large datasets, with adjusted odds ratios of about 1.5 for the highest body mass index quartile and a reported prevalence of 24.7% in class II and III obesity, although the relationship is confounded by diet quality, physical activity, socioeconomic factors and polypharmacy - in one series the adjusted prevalence ratio for constipation with five or more medicines was 2.99. Organic causes must be excluded before symptoms are attributed to weight and diet: hypothyroidism, hypercalcaemia, diabetes with autonomic neuropathy, hypokalaemia, coeliac disease, colorectal malignancy and drug effects. Incretin-based therapies produce constipation through delayed gastric emptying and reduced colonic motility; constipation and nausea are among their most frequently reported adverse effects and are usually dose-related and transient. Management is a stepwise combination of adequate dietary fibre, fluid, activity and a bulk-forming or osmotic laxative - polyethylene glycol is preferred for long-term use - with stimulant laxatives reserved for short courses and alarm features requiring colonoscopy.
Key Insight
Why It Matters
Slower bowels after starting a weight-loss injection or a very low calorie diet are almost always the diet and the drug rather than something new and dangerous - fibre, fluid and a gentler dose increase sort out most cases.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: September 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
