Travel changes the gut before you realise it.
Meals become irregular. Water intake drops because clean toilets are uncertain. Breakfast becomes tea and toast. Lunch is airport food or roadside snacks. Sleep changes. Movement reduces. For many people, this is enough to disturb digestive health and cause travel constipation.
Fibre can help, but the routine has to be travel friendly. Carry roasted chana, nuts, seeds, fruit that travels well, or a simple fibre supplement if you already tolerate it. Do not start a new high dose psyllium routine on the first day of a trip. Test it at home first. If you use psyllium husk, carry a bottle and use enough water.
Choose easy upgrades. Add dal to hotel meals. Pick fruit at breakfast. Choose curd, vegetables or sprouts when available. Avoid making every snack a biscuit or fried item. Walk after long sitting when possible.
Also respect your body clock. Do not ignore the urge to use the toilet for many days.