HELP! Weigh more in heat?

Um.. I've never really heard about the heat making you weigh more, I think I'd be looking at other factors before that.

Drink water, eat watermelon, bananas, parsley...

It is absolutely possible, in fact, it is likely, especially at the beginning of a heat wave. While it is true that your body does increase the amount of sweat secreted to try and cool your body when it is hot, there is also a hormonal reaction that is triggered to retain water by sending more water back into the blood stream when your blood meets your kidney for filtration. Increasing your water intake will help to stop the feedback loop responsible for telling your kidneys to send back the water. Consuming fluids with electrolytes (salt) will also help....despite what people tend to think "More salt = more water retention". More salt will lead to water retention, but the mechanism in matters where the body is sweating but also trying to hold on to as much water as possible, the salt helps establish an equilibrium so that water output can return to normal.

If you've heard before that after a period of starvation the body hoards calories even if the person is eating very little, then you can think of this phenomena in the same manner. Whenever equilibrium is thrown off homeostatic maintenance mechanisms kick into action (like those hormonal cascades responsible for calorie hoarding and decreased water output).

If I were to offer a suggestion, it would be to consume some sports drinks, like Powerade or Gatorade. If you are concerned about the sugar content you can either purchase forms of these types of drinks that have lowered or no sugar (which means they have artificial sweetners in them) or dilute the contents of bottle with water and sip it throughout the day. This is somewhat akin to an IV drip, which creates a stable inflow of solutes and water and consequently, leads to a stable and steady outflow of solutes and water

I see you are female, so you might also consider what point you may be at in your menstrual cycle. Some women also put on temporary weight during their ovulation period, which is roughly a point between your periods.

So in short, consider trying to stabilize your electrolytes and your urine output should become much more diluted (more water output), which should halt your body from 'hoarding' water, so to speak.

Best Regards,
- Mharren