 His research was informed by the first law of thermodynamics, taking into account that energy can be transformed but it cannot be created or destroyed, despite the belief at the time that the law only applied to animals because humans were unique.Earlier experiments concerning calorie intake and expenditure had proven that the first law applied to animals and Atwater's findings demonstrated the law applied to humans as well.Through the experiments he demonstrated that whatever amount of energy consumed by humans that could not be used was stored in the body.