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.

CBS All Access
This video is available on CBS All Access

Dr. Robert Lustig: We love it. We go out of our way to find it. I think one of the reasons evolutionarily is because there is no food stuff on the planet that has fructose that is poisonous to you. It is all good. So when you taste something that's sweet, it's an evolutionary Darwinian signal that this is a safe food.

Dr. Sanjay Gupta: We were born this way?

Dr. Robert Lustig: We were born this way.

Central to Dr. Lustig's theory is that we used to get our fructose mostly in small amounts of fruit -- which came loaded with fiber that slows absorption and consumption -- after all, who can eat 10 oranges at a time? But as sugar and high fructose corn syrup became cheaper to refine and produce, we started gorging on them. Americans now consume 130 pounds per person a year -- that's a third of a pound every day.

Dr. Lustig believes those sweeteners are helping fuel an increase in the most deadly disease in America: heart disease. For years, he's been a controversial voice.

[Kimber Stanhope: Here is our oral isotope...]

But now, studies done by Kimber Stanhope, a nutritional biologist at the University of California, Davis are starting to back him up. She's in the middle of a groundbreaking, five-year study which has already shown strong evidence linking excess high fructose corn syrup consumption to an increase in risk factors for heart disease and stroke. That suggests calories from added sugars are different than calories from other foods.

Dr. Sanjay Gupta: The mantra that you hear from most nutritionists is that a calorie is a calorie is a calorie.

Kimber Stanhope: And I think the results of the study showed clearly that is not true.

Stanhope's conclusions weren't easy to come by. Nutrition studies are expensive and difficult. Stanhope has paid groups of research subjects to live in this hospital wing for weeks at a time, under a sort of 24-hour lockdown. They undergo scans and blood tests - every calorie they ingest, meticulously weighed and prepared.

Kimber Stanhope: They're never out of our sight. So we do know that they are consuming exactly what we need them to consume.

Dr. Sanjay Gupta: And they're not sneaking any candy bars on the side.

Kimber Stanhope: Yeah, right, exactly.

For the first few days, participants eat a diet low in added sugars, so baseline blood levels can be measured.

[Research assistant: So remember you guys have to finish all of your Kool-Aid. ]

Then, 25 percent of their calories are replaced with sweetened drinks and Stanhope's team starts drawing blood every 30 minutes around the clock. And those blood samples? They revealed something disturbing.

Dr. Sanjay Gupta: And what are you starting to see?

Kimber Stanhope: We found that the subjects who consumed high fructose corn syrup had increased blood levels of LDL cholesterol and other risk factors for cardiovascular disease.

Dr. Sanjay Gupta: How quickly did these changes occur?

Kimber Stanhope: Within two weeks.

Kimber Stanhope's study suggests that when a person consumes too much sweet stuff, the liver gets overloaded with fructose and converts some of it into fat. Some of that fat ends up in the bloodstream and helps generate a dangerous kind of cholesterol called small dense LDL. These particles are known to lodge in blood vessels, form plaque and are associated with heart attacks.