Low-carbohydrate diets generally do not restrict calorie intake. This is done to promote anabolic processes stimulated by certain amino acids, particularly leucine, to maintain metabolically active lean mass; support gluconeogenesis to maintain a baseline glucose concentration; and stimulate fatty acid oxidation.7 Hypocaloric diets generally do not recommend reducing daily calories lower than a 500-calorie per day deficit.8 This prevents the rapid onset of catabolic processes, hypoglycemia, and wasting.
Very low-calorie diets, restricting subjects to 800 calories per day or less, are only recommended in extreme cases under the close supervision of qualified health care personnel, due to the risks involved.9
If both pathways to weight (fat) loss are followed simultaneously— hypocaloric and low-carbohydrate dieting— the additive effect on metabolism can be catastrophic for an athletic man. Following such a diet long-term would likely result in Sally Struthers appearing at your door in tears. Consider the following effect of the relevant diets as evidence against committing to either (or both) low-carbohydrate or low-calorie diets long-term, if muscularity and strength are one’s goals.
In the setting of adequate nutrition (not dieting), reducing carbohydrate content of the diet to levels that are considered low in comparison to the standard Western diet (roughly 55 percent) while exercising intensely results in greater decreases in testosterone; sometimes free, sometimes total, sometimes both.10 It is difficult to establish a cut-off, as exercise intensity, duration, and tolerance vary considerably among individuals. However, it appears that the decrement in circulating testosterone concentration can be seen at moderate carbohydrate intake (30 percent of calories). High-carbohydrate intake was able to prevent the rise in cortisol that normally follows intense exercise in experienced athletes, but the amount was far in excess of what a very active man who lifts heavy weights would consume (12 grams per kg bodyweight per day).
A recent study published in the European Journal of Applied Physiology demonstrated how carbohydrate intake is related to the balance between anabolic and catabolic processes during intensive exercise.11 Hormonally, the anabolic versus catabolic balance is approximated by the free testosterone-to-cortisol ratio (fT:C).<sup12
Research has shown that athletes who are subjected to overly intense or prolonged training reach a point where the efforts are counterproductive. In fact, pushing harder results in: reduced athletic performance; delayed reaction time; loss of muscle mass and strength; mood and sleep disturbances. This condition, called overreaching or overtraining, is associated with a falling fT:C. For the average person who is not pushing himself, the effects of a dietary insufficiency (low carbohydrates or low calories) generally does not manifest in visible deteriorations in performance or physique. Look at the person in the next cubicle or at the cash register— would anyone notice if they lost 20 percent of their 1RM bench press?
The study followed two groups of trained athletes who trained for one hour at 70-75 percent maximal oxygen consumption. This is a pace that keeps one breathing heavy, but not gasping. Most experienced lifters have evolved training into a pace that is closer to the anaerobic threshold, making this study design relevant for this group. The subjects were conditioned athletes, and the training was not so extreme that it was unrealistic; most people train for 45-90 minutes and the intensity was consistent with serious, committed lifters.