The theory is that eating prior to sleep increases the risk of fat gain, and although there is no inherent harm to body fat levels when consuming a late meal, because many diet routines are designed with an incorrect use of calories and carbohydrates, not to mention improper meal division, which can detract from metabolic rate, eating before sleep encourages fat increase for many, and some in the bodybuilding world classify later eating as harmful towards body fat control.
The common mistake made is to either use greater than necessary carbohydrates for a bedtime meal, or implement a food intake that is beyond the body's core requirements for muscle growth or maintenance, which then clearly will result in fat gain, as energy needs during an overnight fast are less than at any other time. Yet, unlike certain flawed bodybuilding trainers may suggest, a weight lifter is in great need of calories during sleep, as this is when the majority of muscle growth occurs. In fact, since the body has a lengthy uninterrupted period to repair and grow lean muscle mass, enough calories and protein must be present in order to maximize such progress, which is why a bedtime meal becomes critical. When nutrients are neglected prior to a lengthy sleep period, although muscles seek to grow during such hours, they are unable to do so, and if an individual is consuming a lower calorie diet for fat loss, many times muscle mass will even decline dramatically.
During fat loss periods, one of the most challenging obstacles for many weight lifters is muscle maintenance, and making dramatic changes to a diet, whether it be reducing food intake below the maximum necessary for fat loss due to impatience, or eliminating food later in the evening, will greatly increase the chance for lost muscle, which further suppresses metabolism, making future fat loss difficult. Unbeknownst to many, a properly structured bedtime meal can actually aid in fat reduction, as metabolism benefits from a frequent meal structure, and withholding food for extended periods can cause the body to limit calorie burn. This can occur not only when reducing the number of meals during early hours, but also by skipping a moderately sized meal prior to sleep. This is contradictory to the notion that food before rest increases the chance of fat gain or slows fat loss, but far too many who integrate bedtime meals are consuming a larger intake than is necessary to properly fuel metabolism and maintain muscle mass, or are using excessive carbohydrates, as if the meal were preceding a weight lifting workout as opposed to a lengthy sleep session. A meal prior to sleep should be composed of mostly protein, as the body during sleep craves primarily recovery and growth (by way of protein synthesis), but eliminating carbohydrates completely will cause the body to waste protein for energy, which robs nutrients for muscle recuperation, and places metabolism at risk.
Certain weight lifters understand the importance of bedtime meals, and try to integrate several during the evening, waking up once or twice for additional food, believing this will aid muscle gain, but such a technique is harmful to overall progress, as consuming one properly designed bedtime meal is sufficient to promote muscle gains and proper metabolic stimulation, while waking up for another one or two meals will disrupt proper sleep patterns, which are just as critical for muscle gains and proper metabolism as the meal itself. Waking up for additional food during time which should be devoted to rest prevents the body from utilizing calories properly, so for maximum muscle gain and fat loss, aiming for a bedtime meal with limited carbohydrate intake and sufficient protein once before a lengthy sleep is the most efficient method.