Carbon dioxide is a by product of metabolism and creation of energy. When you eat less, your body turns fat to energy and releases CO2, that where this is from.

Carbon dioxide is a by product of metabolism and creation of energy. When you eat less, your body turns fat to energy and releases CO2, that where this is from. When you exercise your body needs more oxygen to get more energy and release more CO2. Some tips/hacks to eat less: coffee is an appetite suppressant, so is nicotine, weed is the opposite. Some foods keep you fuller for longer like meat and fibrous veg or brocolli. Its easier (and more time efficient) to avoid eating the calories than exercising the same number off, a piece of cake 500cal is something like an hour or more jogging. Get busy and sleep earlier/longer, less time to think of food or snack.