Calorie surplus and deficit both have direct effects on weight. A calorie surplus, when more calories are consumed than the body uses, can lead to weight gain and potential increase in body fat over time. Conversely, a calorie deficit occurs when calories burned exceed those consumed, resulting in weight loss. Individuals use either strategy depending on their fitness goals, but both must be approached carefully to avoid negative health effects. A sudden or extreme imbalance can lead to metabolic issues or loss of lean muscle mass, emphasizing the need for balanced dietary practices.