Einstein to the Rescue

In 1905, Einstein published his theory of special relativity. In this it is stated that:

Energy is equal to the mass multiplied by the speed of light squared.

This means gaining energy means a gain in mass, losing energy means losing mass. The reverse must be true.

Gaining mass means a gain in energy, losing mass means a loss in energy.

The energy we are losing is the binding energy.

where ∆m is the mass defect and E is binding energy