There may be some misunderstandings about this problem.

Theoretically, if you exercise on an empty stomach, for example, for one night, before breakfast the next day, because the blood sugar level is relatively low at this time, the blood insulin level is also low. To maintain a stable blood sugar level, you need to decompose fat and protein products to supplement gluconeogenesis.

At this time, the energy consumed by muscle exercise naturally comes mainly from fat.

In other words, fasting exercise consumes more fat.

As for whether you will lose weight, that is another concept.

Because the increase or decrease of weight is the result of the balance of total calorie intake and consumption over a period of time.

If you eat more, consume less, and the energy is balanced, you will gain weight; On the contrary, if you eat less and eat more, you will lose weight.