Mark Bittman in the New York Times:
One of the challenges of arguing that hyperprocessed carbohydrates are largely responsible for the obesity pandemic (“epidemic” is no longer a strong enough word, say many experts) is the notion that “a calorie is a calorie.”
Accept that, and you buy into the contention that consuming 100 calories’ worth of sugar water (like Coke or Gatorade), white bread or French fries is the same as eating 100 calories of broccoli or beans. And Big Food — which has little interest in selling broccoli or beans — would have you believe that if you expend enough energy to work off those 100 calories, it simply doesn’t matter.
There’s an increasing body of evidence, however, that calories from highly processed carbohydrates like white flour (and of course sugar) provide calories that the body treats differently, spiking both blood sugar and insulin and causing us to retain fat instead of burning it off.
In other words, all calories are not alike.