of muscle gains. it is impossible to promote protein synthesis without the existence of insulin, which means that without ingesting carbohydrates or protein—which also induces the release of insulin—it is impossible to add muscle mass. bodybuilders seek out low-glycemic polysaccharides and other slowly digesting carbohydrates, which release energy in a more stable fashion than high-glycemic sugars and starches. this is important as high-glycemic carbohydrates cause a sharp insulin response, which places the body in a state where it is likely to store additional food energy as fat. however, bodybuilders frequently do ingest some quickly digesting sugars (often in form of pure dextrose or maltodextrin) just before, during, and/or just after a workout. this may help to replenish glycogen stored within the muscle, and to stimulate muscle protein synthesis. protein protein milkshakes, made from protein powder (center) and milk (left), are a common supplement. the motor proteins actin and myosin generate the forces exerted by contracting muscles. cortisol decreases amino acid uptake by muscle and inhibits protein synthesis. current recommendations suggest that bodybuilders should consume 25–30% of protein per total calorie intake to further their goal of maintaining and improving their body composition. this is a widely debated topic, with many arguing that 1 gram of protein per pound of body weight per day is ideal, some suggesting that less is sufficient, while others recommending 1.5, 2, or more. it is believed that protein needs to be consumed frequently throughout the day, especially during/after a workout, and before sleep. there is also some debate concerning the best type of protein to take. chicken, turkey, beef, pork, fish, eggs and dairy foods are high in protein, as are some nuts, seeds, beans, and lentils. casein or whey are often used to supplement the diet with additional protein. whey is the type of protein contained in many popular brands of protein supplements and is preferred by many bodybuilders because of its high biological value (bv) and quick absorption rates. whey protein also has a bigger effect than casein on insulin levels, triggering about double the amount of insulin release. that effect is somewhat overcome by combining casein and whey. bodybuilders were previously thought to require protein with a higher bv than that of soy, which was additionally avoided due to its alleged estrogenic (female hormone) properties, though more recent studies have shown that soy actually contains phytoestrogens which compete with estrogens in the male body and can block estrogenic actions. soy, flax, and other plant-based foods that contain phytoestrogens are also beneficial because they can inhibit some pituitary functions while stimulating the liver's p450 system (which eliminates hormones, drugs, and waste from the body) to more actively process and excrete excess estrogen. meals some bodybuilders often split their food intake into 5 to 7 meals of equal nutritional content and eat at regular intervals (e.g., every 2 to 3 hours). this approach serves two purposes: to limit overindulging in the cutting phase, and to allow for the consumption of large volumes of food during the bulking phase. eating more frequently does not increase basal metabolic rate when compared to 3 meals a day. while food does have a metabolic cost to digest, absorb, and store, called the thermic effect of food, it depends on the quantity and type of food, not how the food is spread across the meals of the day. well-controlled studies using whole-body calorimetry and doubly labeled water have demonstrated that there is no metabolic advantage to eating more frequently. dietary supplements main article: bodybuilding supplement the important role of nutrition in building muscle and losing fat means bodybuilders may consume a wide variety of dietary supplements. various products are used in an attempt to augment muscle size, increase the rate of fat loss, improve joint health, increase natural testosterone production, enhance training performance and prevent potential nutrient deficiencies. performance-enhancing substances some bodybuilders use drugs such as anabolic steroids and precursor substances such as prohormones to increase muscle hypertrophy. anabolic steroids cause hypertrophy of both types (i and ii) of muscle fibers, likely caused by an increased synthesis of muscle proteins. they also provoke undesired side effects including hepatotoxicity, gynecomastia, acne, the early onset of male pattern baldness and a decline in the body's own testosterone production, which can cause testicular atrophy. other performance-enhancing substances used by competitive bodybuilders include human growth hormone (hgh). hgh is also used by female bodybuilders to obtain bigger muscles "while maintaining a 'female appearance'". muscle growth is more difficult to achieve in older adults than younger adults because of biological aging, which leads to many metabolic changes detrimental to muscle growth; for instance, by diminishing growth hormone and testosterone levels. some recent clinical studies have shown that low-dose hgh treatment for adults with hgh deficiency changes the body composition by increasing muscle mass, decreasing fat mass, increasing bone density and muscle strength, improves cardiovascular parameters, and affects the quality of life without significant side effects. in rodents, knockdown of metallothionein gene expression results in activation of the akt pathway and increases in myotube size, in type iib fiber hypertrophy, and ultimately in muscle strength. injecting oil into muscles a recent trend in bodybuilding is to inject synthol into muscles to create larger bulges, or injecting pmma into muscles to shape them. use of pmma to shape muscles is prohibited in the united states. however, it is not illegal to use synthol. site enhancement oil, often called santol or synthol (no relation to the synthol mouthwash brand), refers to oils injected into muscles to increase the size or change the shape. some bodybuilders, particularly at the professional level, inject their muscles with such mixtures to mimic the appearance of developed muscle where it may otherwise be disproportionate or lacking. this is known as "fluffing". synthol is 85% oil, 7.5% lidocaine, and 7.5% alcohol. it is not restricted, and many brands are available on the internet. the use of injected oil to enhance muscle appearance is common among bodybuilders, despite the fact that synthol can cause pulmonary embolisms, nerve damage, infections, sclerosing lipogranuloma, stroke, and the formation of oil-filled granulomas, cysts or ulcers in the muscle. rare cases might require surgical intervention to avoid further damage to the muscle and/or to prevent loss of life. sesame oil is often used in such mixtures, which can cause allergic reactions such as vasculitis. as the injected muscle is not actually well-developed, it might droop under gravity. rest although muscle stimulation occurs when lifting weights, muscle growth occurs afterward during rest periods. without adequate rest (48 to 72 hours) and sleep (6 to 8 hours a night), muscles do not have an opportunity to recover and grow. additionally, many athletes find that a daytime nap further increases their body's ability to recover from training and build muscles. some bodybuilders add a massage at the end of each workout to their routine as a method of recovering. overtraining main article: overtraining overtraining occurs when a bodybuilder has trained to the point where their workload exceeds their recovery capacity. there are many reasons why overtraining occurs, including lack of adequate nutrition, lack of recovery time between workouts, insufficient sleep, and training at a high intensity for too long (a lack of splitting apart workouts). training at a high intensity too frequently also stimulates the central nervous system (cns) and can result in a hyperadrenergic state that interferes with sleep patterns. to avoid overtraining, intense frequent training must be met with at least an equal amount of purposeful recovery. timely provision of carbohydrates, proteins, and various micronutrients such as vitamins, minerals, phytochemicals, even nutritional supplements are critical. a mental disorder, informally called bigorexia (by analogy with anorexia), may account for overtraining in some individuals. sufferers feel as if they are never big enough or muscular enough, which forces them to overtrain in order to try to reach their goal physique. an article by muscle & fitness magazine, "overtrain for big gains", claimed that overtraining for a brief period can be beneficial. overtraining can be used advantageously, as when a bodybuilder is purposely overtrained for a brief period of time to super compensate during a regeneration phase. these are known as "shock micro-cycles" and were a key training technique used by soviet athletes.