Tests on rabbits have showed that the lenses work and can detect even very low glucose levels, says Dr Parviz.

Food with a low-glycemic index (LGI) causes blood glucose levels to increase more slowly and to lower levels compared to high-carbohydrate foods with a high glycemic index.

And because glucose fuels the neurons, a transitory low level in the brain may signal the stomach to get the hands to fill up the mouth, even though the energy actually spent has gone up just a hair.