05/28/2015 10:39 pm ET | Updated May 28, 2016

Calorie for Calorie, Fructose Packs On More Pounds

My two boys recently brought home their elementary-school class pictures, and my wife and I decided it would be fun to show them our class photos back when we were their age. One thing we all noticed right away was how many more overweight or obese kids there are in our sons' class photos than in our old pictures from the early '80s, when we were kids. Something has changed in a big way, no pun intended. More inactivity and poor diets are likely to blame. People are eating more calories than ever before, but they are also changing the source of their calories. More kids today are eating highly processed foods and drinks instead of fresh fruits, vegetables and prepared foods. Does the source of the calories matter? I used to think not. I used to think that what we are eating is fine but that we just need to eat less of it. However, I've proved myself wrong.

As you no doubt have realized, fructose consumption has increased astronomically in recent years, because it is the dominant sugar added to processed foods and drinks, mostly in the form of high-fructose corn syrup. Fructose is what is in fruit, but when you eat a piece of fruit, you are full. When you drink a big-gulp soda, you take in not only huge numbers of calories but huge amounts of fructose, way more than you could ever eat in fruit. We already know that the excess calories are bad when we are trying to lose weight, but what about the large amount of fructose?

We recently conducted a simple experiment in which two groups of mice were fed identical diets except for the type of sugar added. In one group 18 percent of the calories in the diet were composed of fructose, whereas in the other group 18 percent of the calories were composed of glucose, an alternative sugar with the same number of calories. The maximum recommended level of added sugar in the diet is 5 percent, so 18 percent is ridiculously high but common among adolescent males in our society. The mice did not prefer one diet over the other and ate the same amount of food, and the normal amount of food for a mouse starting in adolescence and continuing through adulthood. However, the fructose animals accumulated twice the body fat, had larger livers, and gained significantly more weight than the glucose group. The fructose animals were also less physically active. Moreover, when we did some rough energetic calculations, we discovered that the reduced physical activity could completely explain the weight gain. It was previously known that fructose increases fat deposition more than alternative sugars do, because of the way it is metabolized in the body, but it was not known that, calorie for calorie, it produces more pounds.

So the source of the calorie does matter, and fructose is a bad choice, especially if the goal is to reduce body fat and increase physical activity. So my family and I are going to try to stay away from the sugary drinks and reduce the processed foods. Sometimes it is best to go back to the basics.'

The original paper can be found here.