Dr Kate Thomas has exercise on the brain. As an exercise physiologist, she researches how exercise and fasting can change the energy sources our brain uses. And as an ultramarathon runner, she chases that runner's high on gruelling mountain races.

Dr Kate Thomas is a self-described "exercise evangelist". An exercise physiologist, she spends her time researching the impacts exercise has on the body.

But she also practises what she preaches.

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Based at the University of Otago, Kate is investigating what energy sources the brain uses when you put the body under stress due to exercise and/or fasting. While glucose is the preferred energy source for the brain, it can switch things up if glucose is depleted, and this opens different metabolic pathways and products.

"As we age our brain's ability to use glucose declines and that's even more the case in neurodegenerative diseases like Alzheimer's," Kate explains.

"What is important is that the brain can actually use other fuels. And some of these for example are ketone bodies produced during fasting and lactate produced during high intensity exercise.

"One of the theories and what we're trying to explore in this study is whether if we provide the brain with alternative substrates, how it chooses to use those and what that does for the brain's environment. We think that by switching the brain away from using glucose as its main fuel to one of those other substrates, ketone bodies or lactate, that that triggers a bunch of pathways in the brain that help promote neuroplasticity, cognitive function and general resilience to stress."

In particular, Kate is trying to figure out what combination of fasting and exercise might trigger release of a protein called BDNF - brain-derived neurotrophic factor. BDNF plays a role in preserving existing nerve cells and encouraging the growth of new ones. Our levels of BDNF decrease naturally as we age, and in some chronic neurological conditions such as Parkinson's disease.

Dr Kate Thomas monitors data during an exercise experiment.

Study participants are asked to do a series of four trials - the hardest of which involves a three-hour cycle and a three day fast - while Kate monitors effort, blood glucose, products of metabolism and cognitive ability. In this mechanistic study, Kate is "pulling the levers" as she terms it, to figure out which conditions promote greater production of BDNF. …

Go to this episode on rnz.co.nz for more details