You are a human. You store your most accessible form of energy (as glycogen) in your liver and muscles. Now your ordinary standard human can store about 1 pound of glycogen and pretty much an unlimited amount of fat. There is a good reason for this; God didn’t get it backwards but that’s for another training blog. You’re a superstar triathlete and your training is teaching your body to store and use glycogen (from complex carbs like potatoes and pasta or at least mine is...no judging!) more efficiently. During your training sessions your body draws on this stored glycogen as a source of quick energy. It does so because it can bring this energy to bear at twice the speed as it can from your fat stores. As your workouts progress in length you actually do begin to also draw from your fat stores but very slowly – it just requires much more metabolic transformation to convert fatty acids to glycogen (which becomes ATP for your cells but THAT'S another blog.) None-the-less your fabulous bod through weeks and weeks of torturous training by a sadistic coach begins to also become more efficient using these fat and glycogen stores. Also because you listen to everything the coach says you have a quick carb like a PowerGel or Gu and Gatorade to help prolong your stores. By the way all these processes require lots water – know what I mean?
So if you stick to your training, eat right, rest, carry your gels, and make sure that you at least have that 1 pound of glycogen in you then you’ll be fine. But don’t go dissing that little bit of chubbiness either: it’s CHUBBY POWER! Also now that you know that if you swim, bike, and run at a smart pace then the mixture of your glycogen and fat stores can bring you all the way home.