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When Dave Scott was growing up in Davis, California, in the 1960s, he had ice cream after dinner almost every night. That was normal. Dessert used to be an almost obligatory part of the evening meal in America. It wasn’t just meat and potatoes—it was meat, potatoes, and ice cream.
In college at UC Davis Scott studied nutrition as a physical education major and learned how bad his dessert habit was for his body. (He had recently eaten eight-and-a-half pounds of ice cream in one sitting at a local ice cream parlor on a dare.) He immediately eliminated all confections from his diet, and no doubt this helped him become a six-time champion of Ironman.
After-dinner ice cream may not be quite the ritual it used to be, but Americans still eat as many sweets as ever. Ironically, triathletes, who generally try harder than the average person to be careful about their diet, often find themselves craving dessert more and more as they train harder and harder. A new study explains why.
Researchers at Yale University and the University of Southern California sought to investigate the connection between blood sugar levels and cravings for sweets, and also how this connection is mediated by the brain. Volunteers had their blood sugar levels manipulated intravenously while being exposed to images of high-calorie foods, low-calorie foods, and non-food items. And while all of this was going on, the subjects were also having their brains scanned by fMRI.
The researchers found that when blood glucose levels were lowered, activity levels of particular brain areas changed dramatically in response to images of high-calorie foods. Specifically, activity in the insula and the striata increased. Both of these brain regions are associated with rewards and the desire to eat. At the same time, activity in the prefrontal cortex, which is called upon to inhibit such urges, was reduced. The net effect was that, when blood sugar levels dropped, the urge to eat high-calorie foods such as ice cream was intensified while the ability to suppress the urge was weakened.
Interestingly, these effects were found to be especially pronounced in obese subjects. But I suspect that triathletes might have a heightened susceptibility as well, due to a phenomenon known as glucose flux. Through frequent, prolonged, and intensive training, triathletes use more glucose than non-athletes, which means we challenge our blood-sugar homeostasis more than couch potatoes do. This constant drawing upon our glucose stores may intensify our cravings for sugary treats in much the same way intravenous manipulation did in these study subjects.
So, what do we do about it? While the elevated rate of daily calorie expenditure that comes with training does give triathletes a certain allowance to “get away with” eating dessert that the sedentary person lacks, we’re still better off strictly limiting our consumption of ice cream and other such fare. Doing so will make us that much leaner and faster.
There are a couple of effective ways to deal with the heightened dessert cravings that typically attend high training volumes. One is suggested by the very study I was just discussing. If plummeting glucose levels increase dessert cravings, then preventing your blood sugar from plummeting stands to reduce such cravings. This can be done by eating healthy sources of carbohydrate such as fruit frequently throughout the day, and especially after exercise.
A second option is to go ahead and eat dessert, but to make better dessert choices than ice cream. For example, a small bowl (½ cup) of ice cream has 143 calories. A large serving (1 cup) of mixed berries with a heaping tablespoon of low-fat vanilla yogurt drizzled on top contains exactly half as many calories. Another dessert substitution that I both recommend and rely on myself is dark chocolate. Dark chocolate releases mood-boosting chemicals in the brain, so just a single 50-calorie piece can satisfy you better than a whole bowl of sorbet. Dark chocolate is calorically dense, however, so it’s important that you limit yourself to just one small piece. But again, dark chocolate is so uniquely satisfying that, if you’re like me, one small piece will fully satisfy your training-enhanced sweet tooth.
Matt Fitzgerald is the author of Iron War: Dave Scott, Mark Allen & The Greatest Race Ever Run (VeloPress 2011) and a Coach and Training Intelligence Specialist for PEAR Sports. Find out more at mattfizgerald.org.