Both milkshakes had the same number of calories and similar ingredients, but one contained more fast-digesting carbs and the other was made of slower-digesting carbohydrates. The concept here is that so-called high-glycemic index foods such as sugar and highly processed breads move through the body faster than low-glycemic index foods such as fruit and whole grains.
After the participants drank the rapidly digesting carb shake, their blood sugar spiked and then crashed four hours later. And it's at this point that researchers documented activation of a part of the brain called the nucleus accumbens, a small area that is involved in emotions and addiction. Ludwig told The Salt: "The scans showed intense activation in brain regions involved in addictive behavior."
The idea that certain foods may be addictive is controversial. Some scientists think it's overstating the matter. And clearly it's not settled as to whether activity in these brain regions would be seen widely in the population, or perhaps only among those who are overweight or prone to overeating.
As Dr. Robert Lustig, a professor of clinical pediatrics at the University of California, San Francisco, points out, this research can't tell us if there's a cause and effect relationship between eating certain foods and triggering brain responses, or if those responses lead to overeating and obesity.
"[The study] doesn't tell you if this is the reason they got obese," says Lustig, "or if this is what happens once you're already obese."
Nonetheless, Lustig told The Salt that he thinks this study offers another bit of evidence that "this phenomenon is real." He has been a leading voice in suggesting that sugar is the cause of obesity and other health problems.
Increasingly, the concept of food addiction is gaining attention from researchers. There's a body of work exploring the connection, says Nicole Avena, a neuroscientist at the University of Florida who studies food and the brain.
This study, she says, adds to the growing literature that suggests that high-sugar foods can affect the brain "in ways that can alter reward processing and potentially fuel overeating."