The concept of calorie deficit in weight loss involves consuming fewer calories than the body expends, leading to stored fat being used for energy. To create a sustainable calorie deficit, individuals should focus on balanced nutrition and exercise rather than extreme restriction. A deficit of about 500-1000 calories per day generally leads to a healthy weight loss of 1-2 pounds per week. However, it is essential to ensure that nutrient needs are met while reducing calories. Incorporating whole foods and engaging in physical activity can enhance fat loss while preserving lean muscle mass.