Actually the amount is miniscule, regardless of what your scale may show and here is the reason why – water retention. When on vacation, we tend to eat saltier foods. Because our body wants to level out the amount of sodium, it tends to hang on to water to keep the ppm at a safe level. Once back home and on your normal diet lower in sodium, the excess water and sodium will excrete out as urine.
Another reason why we retain water is climate change. Since you will be vacationing in a place that is hotter than what you are used to in the US or Europe, your body will retain fluids in the form of swelling in the hands and feet. If you stayed long enough for your body to acclimate, the swelling would go down, but it takes at least 14 days for that to happen.
A third reason for retaining water is eating more carbs than you are used to. When carbs are digested, they are turned into a sugar called glycogen and stored in the muscles. Because there are 3 molecules of water for every molecule of glycogen, and you are storing more glycogen than normal, you will retain more water.
So even though your scale may show a perceived weight gain of 3 to 5 pounds after a week’s vacation, your real increase in mass is probably around 1 pound. The rest of the gain you’ll lose fast once home.
Most people don’t maintain their same level of exercising while on vacation, and eat more than normal, but don’t fret. The tightness you feel in your clothes is only temporary, so have fun while on vacation. As far as a decrease in your fitness level … it takes at least a month of no exercising to have an appreciable decrease.
People tend to go on an extreme diet before going on vacation in hopes of losing a few pounds, because they know they will gain a few while gone. The problem is the body senses the reduction of calories as famine, so it becomes more efficient and burns fewer calories. Instead eat normally so your body is burning calories normally.
As part of eating healthy, you should be intuitive to your body’s clues as far as when hungry and when full. You’ll get these same cues while on vacation. All you have to do is heed them sensibly.
Don’t deprive yourself of food you really want. If you want to have that decedent dessert, have it. Just be sure to include it in your daily maintenance calorie count. That might mean having one or two fewer drinks during the day, or maybe not eating dessert at lunch too.