Updated 05 August 2013

Causes of underweight

Desperate to gain weight? In this article, DietDoc takes a closer look at underweight and factors that may be causing it.

More and more Health24 readers are "desperate to gain weight".

Definition of underweight

Anyone who is 15 to 20% below the normal weight for age and height is classified as underweight, according to Krause (2000).

  • Medication – many medicines either suppress appetite or actually cause weight loss. Check with your pharmacist if you have recently started a new medication and now are losing weight without wanting to.
  • Excessive exercise – you may well be overdoing your exercise sessions to such an extent that your diet cannot keep up with the increased demands.
  • Excessive stress – individuals who are very stressed may stop eating due to a lack of appetite, nausea or being preoccupied with their worries.
  • Enzyme deficiencies – deficiencies of digestive enzymes and/or stomach acid may also hamper digestion and absorption of food thus causing weight loss.
  • Other medical conditions such as coeliac disease (gluten allergy), or cystic fibrosis are associated with inability to gain weight.


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