When
carbohydrates are in short supply, the tree tends to use what's left for short growth at the expense of fruit growth.»
It can be a source of energy when
carbohydrates are in short supply, but it's not a major source of fuel during exercise you're well - fed.
Your brain is so picky in fact, it is specifically designed to operate on glucose for 99.9999 % of your waking life, and only switches to oxidizing ketones when
carbohydrates are in short supply in your diet.