Question

What exactly does a laxative do? How do you take them if you want to lose weight?

Answer

Laxatives should never be taken to lose weight. They are a treatment for constipation and if you want to lose weight you should go on an appropriate diet, supervised by a dietician or your doctor.

There are many different types of laxative, which use different methods to accelerate expulsion of the intestinal contents. The laxatives are classified by their general mode of action. Some increase the bulk of the stool by combining with it as a non-absorbable solid residue (bulk laxatives). Others increase the water content of the stool in the colon (the part of the intestine just before the rectum), attracting water into the stool and so making it larger and softer (osmotic laxatives). Others may affect the consistency of the stool in different ways (faecal softeners). Finally, there are laxatives that increase the motility of the intestine, causing decreased absorption of salt and water secondary to decreased transit time in the intestine (stimulant laxatives).

Bulk laxatives are rich in fibre. They are not broken down in the normal process of digestion and therefore enter the colon intact. They retain water. The osmotic laxatives comprise a poorly absorbed compound such as lactulose and they act by increasing the volume of fluid in the lumen (space) of the intestine, because of their osmotic effects (basically, the process whereby fluids move from the dilute to the less dilute). The resulting distension of the intestine lumen acts as the stimulus for increased muscle action. Those laxatives that soften the faeces also do so by increasing the water content. The stimulant laxatives increase motility by stimulating the muscle of the gut wall.

Laxatives are therefore taken to relieve constipation, increasing the bulk of the stool and softening it so it is easier to pass. They are not indicated to lose weight, for which there are better, safe and more acceptable techniques.

Links

• Constipation in older people