Check out this site for normal range for glucose readings:WebMD

Since for fasting (12 hours) any reading below 110 is considered good, your reading of 72 is fine.

When we don't eat glucose or things that easily turn into glucose, our body can create glucose out of protein IF it really needs it. It's called 'gluconeogenesis'. Those who say "you must eat glucose" have yet to explain how the Inuit/Eskimo of the Arctic regions managed to survive through the winters for centuries on a diet of meat and fat for more than 6 months of every year. Not many potato farms north of the Arctic circle (like NONE!). It's only now that a "normal North American diet" is available year round that the Inuit are developing diabetes at a remarkably rapid rate. Just like the rest of the population.