"The views in this opinion piece I found to be biased and speculative," said Theresa Hedrick, nutrition and scientific affairs specialist for the Calorie Control Council, a lobbying group for the manufacturers of artificial sweeteners. "She's presented only the research that supports her opinion and ignored the large body of scientific research that demonstrates the safety and benefits of low-calorie sweeteners."
"I think it's important to remember that low-calorie sweeteners are one aspect of a multifaceted approach to health or obesity prevention," Hedrick said. "They aren't magic bullets."
But Swithers said her animal studies support the counterintuitive notion that artificial sweeteners may lead to weight gain, even if they don't have any calories.
She said she's seen evidence of metabolic disruptions caused by artificial sweeteners in rats.
It basically goes something like this: In a world without artificial sweeteners, a taste of something sweet preps the brain and the gut for digestion of incoming calories. When the calories don't show, as happens with artificial sweeteners, those metabolic responses don't fire the way they should. Insulin doesn't increase; hormones that increase the feeling of fullness and satisfaction aren't triggered; and the brain doesn't get a feeling of reward from the dopamine that sugars release.
After a while, Swithers said, it's like the mouth keeps crying wolf, and the brain and gut stop listening. As a result, when real sugar and real calories come along, the body doesn't respond to them as strongly as it normally might. Calories don't end up making you feel as full as they should. They aren't as rewarding. So you don't get the signals that might stop you from eating when you should.
Artificial sweeteners may also facilitate something psychologists call cognitive distortions. That is, they allow us to trick ourselves into thinking we can eat more calories than we really should. Saving calories with a diet soda now means a slab of chocolate cake is OK later.
"I think there are multiple things that are contributing to this," Swithers said. "Psychology is a factor, but physiology can also be altered."