On Monday, July 9, 2007, Robert Lustig – Professor of Pediatric Endocrinology at the University of California, San Francisco – was featured on Norman Swan’s ABC Radio show. The topic of discussion was obesity and associated factors.

Prof. Lustig clearly identified a number of important areas when considering the prevalence and development of obesity in adults and children.

For many years I have been explaining the need for more exercise in the community and have discussed that exercise is not about burning calories. Here is what Prof. Lustig had to say on that front:

“The question is why does exercise work in obesity? Because it burns calories? That’s ridiculous. Twenty minutes of jogging is one chocolate chip cookie, I mean you can’t do it. One Big Mac requires three hours of vigorous exercise to work that off, that’s not the reason that exercise is important, exercise is important for three reasons exclusive of the fact that it burns calories.

“The first is it increases skeletal muscle insulin sensitivity, in other words it makes your muscle more insulin sensitive, therefore your pancreas can make less, therefore your levels can drop, therefore there’s less insulin in your blood to shunt sugar to fat. That’s probably the main reason that exercise is important and I’m totally for it.

“The second reason that exercise is important is because it’s the single best treatment to get your cortisol down. Cortisol is your stress hormone, it’s the hormone that goes up when you are mega-stressed, it’s the hormone that basically causes visceral fat deposition which is the bad fat and it has been tied to the metabolic syndrome. So by getting your cortisol down you’re actually reducing the amount of fat deposited and it also reduces food intake. People think that somehow exercise increases food intake, it does not, it reduces food intake.

“And then the third reason that exercise is important, which is somewhat not well known, but I’m trying to evaluate this at the present time, is that it actually helps detoxify the sugar fructose. Fructose actually is a hepato-toxin; now fructose is fruit sugar but we were never designed to take in so much fructose. Our consumption of fructose has gone from less than half a pound per year in 1970 to 56 pounds per year in 2003.”

Read the full transcript here.