Jonny Bowden, author, nutritionist and weight loss coach cuts through all the misconceptions about diet and fitness to help you transform your body, your health and your life.

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Ever wonder why it's so easy to succumb to the lure of a Krispy Kreme on days when you're really stressed?

Scientists are beginning to discover that there's a method to the madness of overindulging. And that key may explain a great deal about both overeating and under-exercising.

Emerging research is suggesting that willpower and self-control may be a limited resource. When we use it up on a given day -- say, by concentrating intensely on a stressful job -- we have less left over to "spend" on things like resisting Häagen-Dazs.

In one clever experiment, Stanford researcher Baha Shiv gave one group of subjects a two-digit number to memorize and a second group a seven-digit number; the subjects then had to walk to another building. Shiv arranged for them to pass a little "buffet" on the way, from which they could eat freely from two choices: Fruit salad or cake. A higher percentage of the seven-number group chose the cake over the fruit salad.

Shiv hypothesized that having to hold seven numbers in memory actually draws cognitive "juice" away from from the self-control muscles. That's not as far-fetched as it might seem -- both "working memory" and "self-control" are located in the same place in the brain, the pre-frontal cortex. "Having to remember seven numbers occupied neurons that would otherwise help us decide what to eat, which causes us to become more reliant on impulsive emotions," writes Jonah Lehrer, author of "How We Decide."

Experiments done at Florida State University draw the same conclusion. The researchers basically ask people to do a challenging activity that requires some self-control, then they quickly assign one or two other tasks and compare performance. One result that shows up time and time again: When you "spend" energy on self-control in the first task, there's less left over for the ones that follow. Like staying out of the Krispy Kreme store. Or going to the gym.

Researchers recently got 61 university students who didn't normally exercise to start working out. They were then given a difficult task called the Stroop test which involves showing words for colors printed in different color ink and then saying the color they saw rather than the word. For example, the word "red" might be printed in bright blue, and the task is to say "blue." (The temptation is to say the word that's printed out -- red -- so saying "blue" takes some discipline.) Then the researchers subjected the students to a second round in the gym. Those who had gone through the Stroop test worked out much less intensely than those who didn't. Not only that, they worked out less over the next eight weeks!

"[Willpower] is like a muscle -- the more you use it, the stronger it gets," psychologist Kathleen Martin Ginis tells the LA Times. Try resisting something small to start with -- much like you'd start bicep curls with a low weight.

You can give your willpower a shot in the arm by keeping your blood sugar from going on a roller coaster ride. And when you're exercising, try "stacking the deck" so you have less to think about. Pick the machine, the number of minutes and the time of day so you have to use less brain power on decisions and have some "juice" left for actually doing the workout. And if all else fails, Gillis suggests listening to your favorite song or watching a funny or endearing video on YouTube.

For more information on health and nutrition, visit Jonny's website!