Thought this might help:-
Water retention that pops up as weight gain on a scale can be very disheartening to the average dieter. With the holidays quickly approaching, more people will be flying. Unfortunately, being in a plane causes even more fluid retention due to the lack of movement and cabin pressure. However, there are things you can do to alleviate this challenge.
Some people believe that, drinking more water when they are bloated makes them puffier. This is not true. Drink your daily water quota. This is a must! The kidneys perceive inadequate water intake as a threat to survival and then hold on to more water! When you are flying, drink at least eight ounces for every hour in the air.
Fluid retention also has to do with your lack of activity and poor blood circulation on the plane. Shift in your seat every half hour, prop your legs on your carry-on bag, and try leaning forward and stretching if you can. Get up and go to the bathroom regularly. When you land, try to walk around for 15 minutes or so to get the blood moving
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Lastly, avoid salty snacks, alcohol, and caffeine. These will all dehydrate you further.
To prevent water retention you can add fresh lemon juice to your water. (Do this during and after a flight.) You might also try 50 mg. of vitamin B6 a few times a day for a couple of days around your flight, as this helps to reduce excess fluids.You will have to purchase a separate B6 supplement to obtain the recommended amount.