Since the 1970s, sugar consumption has gone down nearly 40 percent, but high fructose corn syrup has more than made up the difference. Dr. Lustig says they are both toxic because they both contain fructose — that’s what makes them sweet and irresistible.

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.