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The Science/Hype Behind Carb Back-Loading

Mark Gilbert
BSc. Nutrition, CISSN

In the physique world there are so many types of diets floating around that even I get confused! Not only that, but the industry ascribes different meanings to the same words, and words can have different meanings in different contexts. “Front-loading” and “back-loading” are examples of this phenomenon.

One definition of carb back-loading refers to a specific diet that recommends eating very little during the day, training late, and then getting most of your calories (via carbs) in the evening. In terms of contest prep, there is the idea of front-loading your repletion in the days leading up to a show versus back-loading them. This refers to when you’re depleted and near the end of your dieting phase, you should start upping your carbs/calories four to eight days before hitting the stage, versus in the three days leading up to the show.

As a lifestyle, Carb back-loading dictates that you eat very few (or, as many advocates suggest, “zero”) carbs in the morning and afternoon, and then in the evening, after weight training, you gorge on carbs until bedtime. Last time I looked into this diet, the main advocate espoused that those carbs can be composed of junk and/or high-glycemic carbs! I recall there is also an “induction” period in which you eat only 30 grams of carbs daily for ten days to force your body to be metabolizing and burning fat as its primary energy source when you start adding the carbs back in.

When I looked at the studies that were referenced to support this diet, one was conducted in weight-training humans and showed no fat loss, and the other studies were in underfed children. Regardless, carb back-loading does seem to work for some, but probably for the wrong reasons. Most people’s problem is that they eat too much and eat too many of the wrong carbs/foods; so it’s not a question of “when” they eat. Restricting carb intake to within a small window of the day will reduce their intake.

In fact, back-loading seems to have it backwards, probably because of better insulin function in the morning, the majority of the research shows that eating breakfast is associated with lower body fat and people who eat most of their calories at night have higher body fat. So not only is the theory that you’ll store more fat from eating morning carbs not supported by research, but the other back-loading claim that it causes lipogenesis (the production of fat from carbohydrates) is also incorrect. Lipogenesis only occurs to a very small extent in humans. Studies show that even with huge carbohydrates intake, lipogenesis doesn’t occur to a great enough extent to “cause an increase in the body’s fat content.”

While carb back-loading may work for some guys who need a simple way to justify eating excess carbs after training late in the day, there’s no reason to believe that it’s the best way to diet.

As far as front- versus back-loading in the week or so pre-contest, while I know front-loading works for some people, I prefer back-loading. Reason number one is that the science of carb loading (one of the oldest strategies in sports nutrition) only demonstrates brief super compensation of glycogen, so you may only hold those extra carb and water levels in the muscle for a day or so. Secondly, by doing a few “dry runs” and seeing how your body responds to various carb-loading strategies and by carefully monitoring your condition, you can avoid any “spillover” (which is what most people use front-loading to avoid).