Traveling on long international flights can expose you to various negative physical conditions.  These can be easily mitigated by preparing your body, before, during and after a flight to stay healthy throughout the trip.  First, start taking probiotics a week before a trip to prime your stomach with good bacteria to help digest different kinds of food you will enjoy along the way more easily. Probiotics can be found widely at most supermarkets, convenience stores or online health food sources.  

Second, always use compression socks during a trip.  This is probably the most important thing you can do. It helps keep feet from swelling and from creating blood clots that can find their way to your lungs and block blood flow.  This is medically know as DVT (Deep Vein Thrombosis).  

Third, drink natural psyllium fiber to keep your digestive pipes flowing, diminishing bloating and constipation associated with eating food and not being very mobile.  Lastly, I recommend using anti bacterial gel, washing hands often, and using a nasal spray to keep your sinuses moist to shield germs from entering your body thru your nose.  These simple measures will keep you healthy while traveling.