Think of it this way: You can spend $$$$$ eliminating a few ounces from your tri-bike. That's great—but if your body fat percentage is in the teens, or higher, then be aware it's like your lugging around a weight vest. Eliminate the excess fat and go faster.
To shed the weight vest, experts like Tim Noakes and Mark Sisson advise endurance athletes to do the counterintuitive: Cut carbs and up fat intake. "The low fat diet is probably the worst mistake we've ever made in the history of human medicine," Noakes says. "The mainstream dietary advice that we are currently giving to the world has simply not worked. It's time to talk about how we can make a real change." Professor Noakes, an ultra runner, an MD, a sports scientist, and author of books like "The Lore of Running" and "Waterlogged," has become a controversial character in the academic and sports science worlds because of a vigorous reversal in the belief of a high-carb diet for endurance athletes. He's now a proponent of a low-carb, high-fat diet (not just for endurance athletes—for everyone. Check out The Noakes Foundation to learn more).
I spoke with Dr. Noakes recently and he uses himself as an example: Through a simple change in his diet, he not only lost a significant amount of weight (that he had not been able to burn off in his running), he restored a comprehensive state of health to his life, and, now in his 60s, is running more than he has in a long time. "I just got a stress fracture from running too much," he told me, with a note of humor. "How many 60-somethings can say something like that?" The gist of what Noakes has to say to runners and triathletes is this: Want to improve performance? Then a first order of business is to shed excess body fat. Read more from Noakes and former elite triathlete (and also former ITU official) Mark Sisson about why a high-carb diet can be the nemesis of a triathlete.