People gain weight when they eat more calories than they burn and lose weight when they burn up more calories than they eat. Therefore, to lose weight, you need to create an energy deficit by eating fewer calories or increasing the number of calories you burn through physical activity or both.
To demonstrate this we monitored a male subject on a recent trek to Everest who lost 4kg over 13 days. This is an Energy Deficit of 30,800Kcal or 2,369 Kcal per day. Based on a food diary the estimated energy consumed was 3,999 Kcal/day. This indicates that the Total Energy Expenditure (TEE) was 6,368Kcal/day. Thus the food consumed was only providing 63% of TEE with the remainder being supplied from the body’s own internal stores.
The use of indirect calorimetry to assess Resting Metabolic Rate (RMR) and set energy intake goals positively influences weight loss success (McDonieletal). Measured on the GEM Indirect Calorimeter, the subject had an RMR of 1968Kcal/day. This indicates a TEE at normal living of 2558Kcal/day. Thus the TEE whilst trekking was approximately 2.5 times greater, which shows the effects of cold, altitude and exercise.
The foundation for weight loss continues to be based on the balance between physical activity and diet. Measure how many calories you need and take in fewer calories than you burn, and you lose weight.