Strict carbohydrate deprivation in training has never been shown to enhance racing performance. The few studies that have compared the effects of training with and without supplemental carbohydrate on actual performance have found no advantage. In my view the “train low, race high” method is unnecessarily extreme. I prefer a more moderate approach that I call high-low training. In this approach some workouts are performed with supplemental carbohydrate and some without. Relying on this approach is likely to increase your fat-burning capacity as much as would withholding carbs in every workout. You’ll also enjoy the benefits of the performance boost that comes from carbohydrate supplementation in key workouts—benefits that you’ll miss out on if you never use sports drinks or energy gels.
The benefits of training with and without carbohydrate are equal even though they are achieved by different means, with carb supplementation enhancing workout performance and carb deprivation enhancing fat-burning capacity. The fact that the benefits of training with and without carbs are achieved by different means indicates that these benefits might be additive, and the two methods complementary. Runners who consume carbs in some workouts and withhold carbs in other workouts may improve more than may runners who do just one or the other because they reap the benefits of enhanced performance in key workouts and increased fat-burning capacity.
Another reason it’s best to consume carbs in some workouts is that it serves as practice for carb consumption in races. No one disputes that runners should take in carbs during marathons and, in most cases, half marathons. Practicing with sports drinks and energy gels ahead of races enables you to take in carbs more comfortably in races. Research has shown that while it is not possible to train the gut to absorb more carbs on the run, most runners are able to absorb the same amount of carbs more comfortably after getting some practice. Practicing with sports drinks and gels also gives you the opportunity to develop a personalized fueling plan. Individual runners vary widely in their tolerances and preferences for fluid and carbohydrate intake on the run. The only way you can identify your own tolerances and preferences is through trial and error.