Sweetness without calories sounded like the ultimate free lunch, and when sweeteners like aspartame and sucralose were introduced they were thought to be the answer to both our sugar cravings and to our desire to be slim.
Alas, quite surprisingly, diet drinks are associated with weight gain in several long-term large studies, even after results are controled for the fact that heavier people are more likely to choose diet drinks. To be fair, not all studies have shown the diet-drink obesity link, and it remains unclear exactly how a drink with no calories can make you fat. Do diet drinks mess with our satiety signals? Do they create a craving for sweetness that triggers overeating? Or are we feeling good about opting for a non-caloric drink and rewarding ourselves with compensatory calories later?
To find out how non-caloric sweeteners affect our food thoughts and food choices, new research, published ahead of print in Appetite, served Solo cups with either Sprite, Sprite Zero, or unsweetened Kroger lemon-lime sparkling water to students and conducted three neat experiments.
What pops into your mind after a diet drink?
The first experiment was designed to gauge the volunteers' thoughts -- not an easy thing to measure! The 116 students were presented with strings of letters that spelled either a high-calorie word (such as cookie), a low-calorie word (such as carrot) or gibberish, and were asked -- after distracting them as to the goal of their task and some practice -- to identify as quickly as they can if the letters spell a word or not. Those who had the non-caloric sweetened drink responded more quickly to the names of the high caloric foods, compared to those who had the sugary drink or the unsweetened drink.
So according to this, brains might be more receptive to high-calorie foods after a non-caloric sweetened drink.
Which foods do you choose following a diet drink?
The next experiment was more straightforward. Again, the participants did not know what was tested, but 115 of them were served one of the three test drinks, and after answering a few unrelated questions (about shampoo), were given a box with three items, from which they were instructed to choose one to take along: natural spring water, Trident gum or M&M candies. Those who had the non-caloric sweetened drink were three times more likely to pick the M&Ms than those who had the sugary drink or the unsweetened drink.
Do diet drinks decrease satisfaction?
The third experiment was designed to see if a drink's sweetener affects satisfaction from sweet foods. The volunteers, again blinded as to the goal of the research, were given mini Oreos, were instructed to eat at least one of them, and were asked how satisfied they were with the cookie. Those who had the non-caloric sweetened drink were less satisfied with their cookie compared to those who had the sugary drink or the unsweetened drink.
Do non-caloric sweeteners really make us eat more?
While health experts agree about the need to reduce added sugar in the diet, replacing sugar with non-caloric sweeteners might be useful only as a transitional aid. The long term effects of these sweeteners on appetite, intake and weight is still unclear, but most of the research shows these sweeteners are associated with weight gain (and other adverse health outcomes on top of that), and this study offers us clues regarding their effect on our food regulation psychology.
The question of what these sweeteners do to our body -- and by what mechanism -- is far from settled, but this study adds to the realization that looking just at calorie counts, without thinking a little more about the actual ingredients, might not be enough to lead to long-term weight control and health.
Dr. Ayala
Full disclosure: I'm vice president of product development for Herbal Water, where we make organic herb-infused waters that have zero calories and no sugar or artificial ingredients. I'm also a pediatrician and have been promoting good nutrition and healthy lifestyle for many years.