Or even just manage blood sugar levels. It would be an immense help to the folks with type 2 diabetes.

There are already small devices that regulate insulin levels. How would this improve on those?

Insulin causes blood sugar to be deposited as fat. A fuel cell causes blood sugar to be turned into electricity, and eventually some combination of work and heat, which could be far more desirable than fat.

Type 2 diabetics have the issue where body parts become increasingly "deaf" to insulin. This keeps blood sugar levels higher for longer periods of time.