For these types of low-intensity activities, a snack isn't necessary (unless you wake up famished), but hydration is. "Most people think, 'I won't be sweating much, so I don't need to drink anything,'" says Rosenbloom. But dehydration can make the workout feel much harder than it really is. A 60- to 90-minute class is a long time to go without water.
The snack: 8 ounces of a low-calorie sports drink, a full-calorie sports drink cut with water, or fruit juice diluted with water. These will still give you some carbohydrates for energy, and the electrolytes in the sports drink are a must if you're attending an intense hot-yoga class.
When: On your way to the yoga studio (the body digests liquids very quickly).