After suggesting last week that artificial sweeteners may lead to insulin resistance, I wanted to call your attention to a new study that calls this theory into question.
In a new study published in the New England Journal of Medicine, researchers fed 8 ounces of soda per person per day to a group of children between the ages of 4 and 12, and 8 ounces of diet soda per person per day to a second group of children the same age.
The researchers intended to discover whether substituting diet soda, with artificial sweeteners, for regular soda, with actual sugar, had any impact on weight gain.
They found that it did: The children drinking the artificially sweetened beverage gained less weight, and put on less fat, during the 18 month trial, than did the children drinking the sugared beverage. The numbers for body weight are impressive. Body mass index increased by only 0.02 standards of deviation in the sugar-free group, compared to 0.15 standards of deviation in the sugar group. This looks like a major difference.
So, was I wrong that diet sodas, and other artificially sweetened foods and beverages, may lead to weight gain through insulin resistance? Not necessarily.
The difference, in the short term anyway, between eating sugar and eating artificial sweeteners seems pretty clear in this study. You won’t put on a fraction of the weight using artificial sweeteners as you will using sugar, in the short term (up to 18 months).
The difference between kids drinking artificially sweetened beverages and kids not drinking artificially-sweetened beverages is also clear: it’s very little. Kids in the artificial sweetener group seem to have gained 0.02 standards of deviation more than normal kids, but the study’s authors don’t consider this to be a statistically significant finding. In fact, they suggest that their study fails to support the idea that diet sodas can cause weight gain.
Still, it doesn’t seem statistically to exclude that possibility, and even a small difference in weight gain over an 18 month period can add up to meaningful differences over the course of a decade or two. So, even though it’s clear that sugar makes us more prone to weight gain in the near term than artificial sweeteners do, artificial sweeteners may still make us somewhat more prone to weight gain than avoiding sweet foods and drinks altogether.
Perhaps more importantly, note that this study only lasted 18 months. There may be many reasons why people gain weight, and some of the forces driving weight gain may be very slow acting. In my post last week, I surmised that artificial sweeteners may make us gain weight in the long run (there’s evidence that consumption of diet soda is correlated strongly to weight gain over periods of 10 years or more) by driving up insulin resistance. Artificial sweeteners may cause the same burst of insulin in our bodies that sugar causes, and over time our tissue cells may well start to resist insulin because they deal with so darned much of it. This means we need to eat more and more for our tissue cells to take in energy from food, and more and more of that energy gets stored as fat.
And that may be a very slow-working process. So, it’s possible that the effect of 18 months of drinking artificially sweetened beverages has an adverse effect on insulin resistance, but that that effect doesn’t cause immediate, significant weight gain. But over years of this insulin resistance building and building, we may well see weight gain starting and then gaining speed. So it’s very possible that, if this study went on for a decade, rather than 18 months, you’d see the kids drinking artificially sweetened beverages gaining just as much weight as those drinking sugary beverages.
But in the near term, the sugary beverages may be making kids gain weight for other reasons (e.g., empty calories) in addition to insulin resistance, and so have a bigger impact on the scale over this short time period.
All this is possible. But far from certain. This study is certainly an encouraging sign for those of us who love diet soda but fear that the artificial sweeteners are somehow bad for us. But it’s no guarantee that they’re OK. Insulin resistance may still be a major concern, as it may take years, even decades, to start showing results on the scale.