Can anyone suggest postures that might help someone who suffers with Iritable Bowel Syndrom?

absolutely
One of the major benefits that yoga can help in relation to IBS, is helping to stabilize the digestive system.
Stress or emotional trauma may also trigger IBS or Irritable Bowel Syndrome and could make your problem even worse. So you need to keep yourself calm and stress free to get rid of it. Yoga helps by helping you calm down. You can safely practice Dhyana or meditation as that will help you calm down and will make you feel peaceful. Thus it will relieve the stress and tension that might be the cause of triggering the IBS in your case. You could also try the Pranayama or the breathing exercises, as they will help to increase the blood and oxygen flow to your body. It will also correct your breathing pattern and once that happens your body will be able to cope with IBS in a better way. Besides this you may try the following yoga asanas or poses:

* Vajra asana or the Diamond or Thunderbolt Pose– This asana or pose is great for your digestive system as it promotes excellent digestion.

* Jathara Parivritta or the Revolved Twist – This asana consists of twists and is great for your internal organs.

* Uttana Asana or the Standing Forward Bend – This asana or pose helps to stimulate your liver and the kidneys and thus helps to treat IBS.

* Ardha Matsyendrasana or the Twist Pose – This too helps to stimulate your kidneys and liver and helps to keep your internal organs in good health.

* Shavasana or the Corpse Pose – This fully relaxes your body right from your head to toe and brings about a feeling of relaxation and calm.
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