Is sugar toxic?

Sanjay Gupta reports on new research showing that beyond weight gain, sugar can take a serious toll on your health, worsening conditions ranging from heart disease to cancer.

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Lewis Cantley: In fact-- I-- you know, I live my life that way. I rarely eat sugar.

Dr. Sanjay Gupta: When you see a sugary drink or if I were to offer you one, what-- with all that you know, what's going through your mind?

Lewis Cantley: I probably would turn it down and get a glass of water.

But for most of us, that's easier said than done...

Eric Stice: It turns out sugar is much more addictive than I think we had sort of realized early on.

Eric Stice, a neuroscientist at the Oregon Research Institute, is using functional MRI scanners to learn how our brains respond to sweetness.

Eric Stice: Sugar activates our brain in a special way. That's very reminiscent of, you know, drugs like cocaine.

That's right. Cocaine.

Dr. Sanjay Gupta: Let's give it a shot...

I climbed into the MRI scanner to see how my brain would respond. That's a straw that's been rigged to deliver a tiny sip of soda into my mouth.

Eric Stice: Stay as still as you can, ok?

Just as it hit my tongue, the scanner detected increased blood rushing to certain regions of my brain. In these images, the yellow areas show that my reward region is responding to the sweet taste. Dopamine - a chemical that controls the brain's pleasure center - is being released, just as it would in response to drugs or alcohol.

Dr. Sanjay Gupta: So dopamine is released. That sort of makes me feel good. I'm experiencing some pleasure from having this Coke.

Eric Stice: Right, that euphoric effect.

Dr. Sanjay Gupta: So far be it for people to realize this 'cause sugar is everywhere, but you're saying this is one of the most addictive substances possibly that we have?

Eric Stice: It certainly is very good at firing the reward regions in our brain.

Eric Stice says by scanning hundreds of volunteers, he's learned that people who frequently drink sodas or eat ice cream or other sweet foods may be building up a tolerance, much like drug users do. As strange as it sounds, that means the more you eat, the less you feel the reward. The result: you eat more than ever.

Eric Stice: If you overeat these on a regular basis it causes changes in the brain that basically it blunts your reward region response to the food, so then you eat more and more to achieve the same satisfaction you felt originally.

With all this new science emerging, we wanted to hear from the sugar industry, so we visited Jim Simon, who's on the board of the Sugar Association, at a sugar cane farm in Louisiana.

Dr. Sanjay Gupta: Would it surprise you that almost every scientist that we talked to in researching this story told us they are eliminating all added sugars. They're getting rid of it because they're concerned about the health impacts.

Jim Simon: To say that the American consuming public is going to completely omit, eliminate, sweeteners out of their diet I don't think gets us there.

Simon cautions that eliminating sugar wrongly vilifies one food, rather than working towards the long-term solution of reducing calories and exercising.

Dr. Sanjay Gupta: You know, a lot of people, Jim, are saying that sugar is different. That it is bad for your heart and is causing a lot of the problems we're talking about. It is addictive and in some cases might even fuel cancers. What would you - I mean you've looked at this. You must have looked at some of these studies. What do you say about that?

Jim Simon: The science is not completely clear here.

Dr. Sanjay Gupta: But some of that's, but some of these studies exist. I mean, what is a consumer, what are they to make of all that?

Jim Simon: Well, I would say to them, that they've got to approach, their diet in balance.

Dr. Robert Lustig agrees -- we need a balanced diet -- but his idea of balance is a drastic reduction in sugar consumption. To that end he co-authored an American Heart Association report recommending men should consume no more than 150 calories of added sugars a day. And women, just 100 calories. That's less than the amount in just one can of soda.

Dr. Robert Lustig: Ultimately this is a public health crisis. And when it's a public health crisis, you have to do big things and you have to do them across the board. Tobacco and alcohol are perfect examples. We have made a conscious choice that we're not going to get rid of them, but we are going to limit their consumption. I think sugar belongs in this exact same wastebasket.