Fat is the enemy right? If you are trying to achieve a more effective power to weight ratio body fat is the ballast you want to drop, however, during endurance training and events fat is the fuel source you want to utilize the most. Endurance sport efficiency is largely dependant upon access and utilization of fat as a fuel source. Working at an intensity that results in the highest fat oxidation (Fatmax) is the key to success in long endurance events.

• Working at intensities higher intensities above Fatmax are costly in terms of carbohydrate usage. Not only does fat utilization decrease but carbohydrate calorie contribution increases dramatically. Typical Fatmax is 35-40 grams per hour.
• Carbohydrate has less than half the energy per gram as fat. This means you use twice the carbohydrate calories to equal the cost of one gram of fat.
• When carbohydrate stores are depleted in the body the amount of energy you can produce is significantly reduced.
• A typical athlete will have enough energy stored in body fat to perform several marathons back to back.
• Even though you may burn hundreds of calories in carbohydrate per hour you can only take in a limited amount, usually 60-80g per hour on the bike or 240-320 calories. The harder you are working the harder it will be to take consume calories.
• Fast twitch muscle fibers utilize more carbohydrate than slow twitch fibers. This means higher cadences and less pedal forces will utilize more slow twitch fibers and fat as a fuel source.

So, that extra spare tire you are carrying is actually good then? Sorry, body fat is not metabolically active, does not directly contribute to speed, may hinder cooling, increases aerodynamic drag, and indirectly increases VO2 max if you were to compare yourself at a lower body fat percentage. Even if you are as low as 5% body fat you have plenty for your event. But being aerobically efficient and utilizing fat stores for events such as road races or long course triathlon is very important. These events are as much about conserving energy as utilizing it. Utilizing fat optimally will depend on you knowing your energy sources, at what intensity they are utilized at, and how to pace yourself appropriately.

References
Peak Performance Cycling; number 224: 1-4