While there is sugar in the system then, the body is not getting the energy it needs. This sends signals to the brain to tell it that you need more energy and thus more food.
The result is that you can feel hungry a lot of the time despite eating. If you’re looking for the earliest symptoms, then unusual hunger coupled with tiredness is a combination to be aware of.
Of course, there are many other potential causes for these symptoms, so it’s important that you consider all of the symptoms together rather than in an isolated fashion. Likewise, it’s important to think of ‘change’ as being the most worrying sign. If you suddenly feel different to normal, then this is the most alarming sign to look out for.