When you start exercising working muscles need extra energy, this energy demand triggers a hormonal cocktail that stimulates the breakdown and release of stored energy (fat and carbs) into the blood stream as free fatty acids and glucose for muscles to use as needed.
In the majority of cases the presence of ketones in the urine prior to exercise indicates insufficient insulin in the body. If you have insufficient circulating insulin the glucose in blood cannot get from blood into muscles (see e-coach module 3 how glucose gets into muscle). Yet exercising muscles keep asking for glucose and the body keeps trying to meet the call by sending more and more glucose into blood, this causes your BGL to skyrocket upward while your muscles are starved of the glucose they need to fuel exercise. Of course the body is a clever thing, when it can’t get enough glucose to add to the exercise fuel mix it looks for an alternate fuel source to meet exercise energy demand. When there’s no glucose the body relies on fat (free fatty acids) only for fuel (body fat is broken down, then released into blood as free fatty acids). This may sound like a positive thing to people wanting to lose or manage their weight but be assured it’s a BIG NEGATIVE!
When the body breaks-down fat for energy in the absence of glucose it produces ketones which are acidic. Ketones leave the body in urine, perspiration and the breath. Another thing about ketones is they don’t smell so good, that’s why malodorous (tec talk for bad smelling) breath is a common indicator of undiagnosed type 1 diabetes. If ketones build-up to high enough levels they can cause an imbalance in the body’s delicate pH balance and this can lead to a serious, potentially life threatening condition called diabetic ketoacidosis.
Whenever your pre-exercise BGL is high for no obvious reason the smart thing to do is test your urine or blood for ketones. Exercising on top of an already high BGL with ketones showing in urine or blood only makes things worse. As much as I hate saying it, this is a time when you shouldn’t exercise. Exercise at this time will further increase BGL, burn extra fat absent of glucose in muscle and produce even more ketones! This can fast track you to diabetic ketoacidosis – that’s a place none of us want to go!