Exercise is supposed to be good for you. But for some people, exercise can become a deadly obsession.

My guest in this podcast episode is Vanessa Alford, author of the new book "Fit, Not Healthy", which is a warning to all high achievers driven to extremes to excel.

As a young girl growing up in Melbourne, Australia, Alford loved sports: she began gymnastics at age six, netball at seven, and tennis at age ten. She was, in her words, "born to compete", and both her gymnastics and netball teams won the state championships in her age group. During her early years of sports, she ran to train and to keep fit, but describes it as an obligation, not a pleasure.

After graduating college, Alford began to run regularly: she would set the alarm for 6am, jog for 8k (around an hour) along the beach and be home by 7am, which gave her time to eat breakfast before cycling 15k to work. But soon, her 8k runs became 10k runs, and 12k runs on the weekends.

Soon, both the runs and the ride became mandatory morning rituals, "just like a shot of coffee or booze", that left her euphoric, floating for the rest of the day on dopamine and adrenaline. "This feeling of elation would sweep over me," she says, "I just couldn't get enough of it."

Within months, she had dropped over 10 pounds and a dress size, and then she started running marathons. Nike and PowerBar sponsored her. Her runs became longer and more grueling, and were soon accompanied by a strict dietary protocol in which she counted every calorie, and monitored every morsel that entered her mouth.

Soon she was running up to 160k a week while surviving on a diet low in fat and low in carbohydrates too. Her body began wasting away, slowly cannibalizing itself, and shutting down non-essential physiological systems. She was exercising herself to death. People warned her, they told her to stop, and her boyfriend told her she had lost her mind. But she couldn't stop.

Then finally, Vanessa's body stopped for her, as she collapsed in the middle of a race after losing sensation in her legs.

In today's podcast interview, you're going to find out exactly what happened, how exercise addiction occurs, how you can recover from adrenal fatigue, how you can test your body to see if you're exercising too much, and much more, including:

-The difference between exercise addiction and a runner's high...

-What's going on psychologically that makes some people feel like they need to go do things like triathlons, marathons or adventure races...

-Why you often need more and more exercise to achieve the same "high"...

-What happens chemically that is making you feel so down, so lazy, or so depressed if you stop exercising at the same volume or frequency that you were at before...

-Why will rats run until they drop dead on an exercise wheel...

-And much more!

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Do you have questions, comments or feedback about Vanessa's story, or being "fit not healthy"? Leave your thoughts at http://www.BenGreenfieldFitness.com/fitnothealthy, and be sure to check out Vanessa's book "Fit Not Healthy".