While it’s very possible, and advisable, to lose weight while training for a triathlon (check out “Racing Weight: How to Get Lean for Peak Performance” by Matt Fitzgerald), be sure to do it during the nutrition phase of your eating and not the fueling phase. This means that you shouldn’t attempt to run caloric deficits around and during long workouts for the sole purpose of weight loss. While it is very tempting to try to apply the calories you burned towards those few extra pounds on your midsection, this is not the time to undereat. A good rule of thumb is to take in calories on any workout 90 minutes or longer, and try to replace at least 50% of the calories you’re burning (this can include your pre- and post-workout snacks).
Mike Tyson made over $300 million during his boxing career, yet declared bankruptcy in 2003. Why? Because, no matter who you are, you cannot out-earn bad spending habits. Similarly, you cannot out-train bad eating habits. When you are spending 10 or more hours per week training for a triathlon it can be tempting to think you can eat all the cheeseburgers and drink all the beer you want. You can’t. The math just doesn’t work. It takes me an hour of running to burn 800 calories but I can eat that much in about 3 minutes at a buffet (ask my wife). You will, of course, have more leeway than if you weren’t working out at all, but that doesn’t give you free rein to stuff your mouth with everything in sight. I usually have one food cheat day per week, commonly the day I do my brick workout, in which I let myself eat whatever I want. I try to eat clean and avoid empty calories during the other six days. If you do have to cheat a bit on these other days and eat a grilled cheese sandwich or bowl of chocolate ice cream, any post-workout meal is by far the best time to do this.
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