You may lose your appetite at altitude and AMS may make you feel sick. Changing food may affect appetite or cause the runs.
Many altitude trips are in areas where water and sanitation are poor, so the risk of the runs is higher. Prevention is better than cure. Bottled water and water filters can be unreliable. Iodine is the best, unless you have thyroid disease or are pregnant.
If you do get the runs keep hydrated by drinking plenty of purified water or rehydration solution. Traveller’s diarrhoea is likely to be caused by bacteria so antibiotics may be needed.
If you have indigestion or piles at home, see your doctor well before travelling. Piles can be a misery at altitude. With indigestion, avoid indigestion causing painkillers. Milky drinks, curd or yoghurt may sooth the problem.
Rotting toilet paper and piles of poo ruin places. Don’t just leave it!
Never forget to wash your hands.
Drink plenty.
Take your favourite snacks to eat when you're off the food.
Always wash your hands.
Plan how to get clean water so you are not afraid to drink plenty.
Take rehydration sachets and / or know how to make up your own.
Find out about traveller’s diarrhoea and how to treat it.
Have a group plan for disposal of toilet paper 'in the field'.
When high on a Patagonian glacier a climber had to demand a sudden stop to drop his salopettes whilst roped due to traveller’s diarrhoea. On a bivouac that evening he took some antibiotics and was able to continue the next day.