Obesity. The Real Reason for the Epidemic?

Robert Lustig: I'm very interested in what's happened over the last 30 years that has fomented this obesity epidemic. And of course everyone says well, that's because you're eating too much, and you're exercising too little and of course that's true. But the question is what about our physiology allows this to happen, we have some built-in negative feedback mechanisms that are supposed to stop us from gaining too much weight but clearly they are not working. The question I've been interested in now for the last ten years is what is actually blocking that signal to the brain to tell our bodies to eat less and exercise more? Clearly something is getting in its way ...

About exercise ...

Exactly, in fact exercise is the best treatment. 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.

Pointing the finger at a critical factor ...

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.

Norman Swan: It's the dominant sugar in these so-called sugar free jams for example that you buy, these sort of natural fruit jams.

Robert Lustig: Right, originally it was used because since it's not regulated by insulin it was thought to be the perfect sugar for diabetics and so it got introduced as that. Then of course high fructose corn syrup came on the market after it was invented in Japan in 1966, and started finding its way into American foods in 1975. In 1980 the soft drink companies started introducing it into soft drinks and you can actually trace the prevalence of childhood obesity, and the rise, to 1980 when this change was made.

Cutting to the chase ...

Norman Swan: So what you're saying in fact is that whilst we are clearly eating too much, we're passively eating too much of the wrong thing, that the food manufacturing industry is putting stuff in which is fuelling the epidemic?

Robert Lustig: Absolutely, we're being poisoned to death, that's a very strong statement but I think we can back it up with very clear scientific evidence.

And ...

Robert Lustig: I've heard those same concerns you know, why, if we have so many calories why aren't we fatter. Well there are a few reasons why that might be. I do want to mention that the American food industry produces 3,900 calories per capita per day. We can only eat 1,800 calories per capita per day. In other words the American food industry makes double the amount of food that we can actually use. Who eats the rest? We do, through this mechanism, they actually know that by putting fructose into the foods that we eat, for instance pretzels -- why do you need fructose in pretzels, why do we need fructose in hamburger buns?

Norman Swan: Are you postulating here a fructose conspiracy, the way the tobacco industry had a nicotine conspiracy?

Robert Lustig: Well I can't call it a conspiracy per se. I certainly know, and they certainly know that they sell more of it when they add the fructose to it. That's why it's in there, otherwise why would it be in there? Do they know that this is actually harmful? That's what I don't know. There's no smoking gun, ultimately we found the smoking gun for smoking, you know we found the documents. I'm not prepared to say that about the food companies. I do not know that they know that they are hurting us. However, they definitely know they sell more, and it temporarily coincides with the advent of fructose being added to our diet.

Norman Swan: And of course you could argue that it's going up because they are responding to the market and they've got sugar-free, fat-free etc. etc.

Robert Lustig: Well in fact fat-free doesn't help, if anything as the fat content of our foods has gone down, and it has gone down, it's gone from 40% to 30%, in fact our obesity prevalence has gone way up. So that's not the answer.

I've always thought it strange that the population is so much bigger now than when I was in my twenties. We certainly weren't starving ourselves at that time.

It would be naive to conclude that this was the only contributing factor for present day obesity, however, Lustig's case, backed by scientific research, certainly points the finger at processed foods and the food industry.