Final answer:
If you consume fewer calories than you need, you have a negative energy balance, which can result in weight loss as your body burns stored energy.
Step-by-step explanation:
If you take in fewer calories than you need, you have a negative energy balance. Consuming fewer calories than your body requires for daily activities and basic metabolic functions leads to the depletion of energy stores within your body.
It's a straightforward matter of thermochemistry: the number of calories you ingest compared to the amount of calories you burn determines your overall weight. In order to lose weight, you must burn more calories than you consume, which can be achieved through a combination of dietary changes and increased physical activity to raise your metabolic rate.