The heat waves streaking across the country bring up questions in people's minds about whether they should change their eating and drinking habits in such conditions.
Do our calorie needs change, or does our metabolism increase during the hot summer temps? Well, maybe yes, but probably no. Our bodies are well-tuned to keep things at status quo. If anything, our metabolism may go up when we're cold, as our bodies need to work harder to maintain our temperature (by shivering). In the heat, our bodies actually slow down a bit to try to conserve energy so as not to overheat. But none of this really makes any significant change in our BMR or how many calories our body needs.
What is important to note is that in hot weather your body is prone to dehydration, and this actually can have an effect on your metabolism. In the course of an average day, sweating, breathing, and waste elimination together leach more than 10 cups of water out of your body -- and that's without exercise. If you don't replace what you've lost, you may become dehydrated; your system literally begins to dry out.
Some people say that their appetite decreases when it's hot outside. If that's the case, you should still try to eat small, frequent healthy meals throughout the day. Many people find cool gazpacho refreshing in hotter weather. Try my easy recipe for Icy Gazpacho With Fresh Lime.