Training fasted

It is healthy to train in the morning before breakfast for some people, but it very much depends on the individual. Some research indicates that training before breakfast works better in men than in women, but this is not always the case.
In the morning your body is usually in a fasted state with low blood sugar as you have not eaten since the evening. Therefore once any stored energy (glycogen) is used your body will go into fat-burning mode for energy to fuel your training. This system of energy production is less efficient than using carbohydrate so it may make training feel more difficult. The upside is that if you are trying to lose weight you will start to burn fat reserves. The down side is that your performance may not be as good as when you have eaten and therefore you may find it difficult to train to the same degree (especially if you are doing intense resistance training or high intensity interval training). Also training in a fasted state may cause more muscle breakdown compared to if you have eaten.