A popular belief appears to have emerged among bodybuilders that using insulin can assist in achieving substantial gains in muscle mass and muscle definition. The purpose of this paper is not to support or refute these claims but rather, to bring it to the attention of people who are considering the use of insulin for these purposes that this practice carries with it a significant risk, and to provide risk reduction advice to those who choose to use insulin regardless of this risk. It is of relevance to note that there have been reports of several insulin-related deaths among bodybuilders recently.

The Physiological Role of Insulin in the Body

        Insulin is a hormone which is manufactured in the pancreas and which has a number of important physiological actions in the body. It is an essential hormone in maintaining the body's blood glucose level so that the brain, muscles, heart and other tissues are adequately supplied with the fuel they require for normal cellular metabolism and normal function. Insulin also plays an essential role in fat and protein metabolism. For example, it promotes transport of amino acids from the bloodstream into muscle and other cells.  Within these cells, insulin increases the rate of incorporation of amino acids into protein (amino acids are the building blocks of protein) and reduces protein break down in the body ("catabolism"). These physiological actions probably form the basis of speculation regarding the additional anabolic gains which might be made through the use of exogenously administered   insulin.

        Normally, blood glucose and  blood insulin levels are not both elevated for any extended period of time as these two chemicals influence each other through a feedback system in the body.  In the post-absorptive state, the blood insulin concentration tends to decrease during exercise, allowing the blood glucose to be maintained at or above resting levels and to provide increased energy supplies (fuel) to muscle cells.  Following a meal, the blood glucose and amino acid levels rise (the absorptive state) and this triggers an increase in insulin release from the pancreas, driving glucose and amino acids from the blood into cells and maintaining the blood glucose level within a certain physiological (operating) range.

        Intending users should also be aware that insulin stimulates lipid (fat) synthesis from carbohydrate ("lipogenesis"), decreases fatty acid release from tissues ("lipolysis") and leads to a net increase in total body lipid stores. The development of such increased body fat stores runs counter to the training goals of most body builders, athletes and those seeking to improve their physical appearance.

        In striving to become bigger, stronger, more competitive or more physically attractive you should also remember that no matter what you do, your genetic make-up will have an influence on what you are able to achieve. It is important to realize that you cannot look exactly like the role model you admire because you have inherited a different set of genes.

The Glycemic Index Factor

        Scientists have discovered that carbohydrate containing foods can be measured and ranked on the basis of the rate and level of blood glucose increase they cause when eaten. This measurement is called the "Glycemic Index" or "G.I. factor". The rate at which glucose enters the bloodstream affects the insulin response to that food and ultimately affects the rate at which this glucose (fuel) is made available to exercising muscles. (2)

        Low G.I. foods are those measuring less than 50 on a scale of 1-100.  Moderate G.I. foods are those with a reading of 50-70 and high G.I. foods are those measuring 71 or greater on this scale. Pure glucose has a G.I. of 100.

        Foods which have a high G.I. produce a rapid increase in blood glucose and blood insulin levels. Examples of such high G.I. foods are potatoes, ice cream, many cereals particularly those with a high sugar content, some varieties of rice (e.g. Calrose) and sweets.

        Foods with an moderate G.I. include some brands of muesli, some varieties of rice, white or brown bread, honey and some cereals.

        Foods with a low G.I. produce a slower, smaller but more sustained increase in blood glucose levels.  Examples of such low G.I. foods are pasta, varieties of high amylose rice, barley, instant noodles, oats, heavy grain breads, lentils, and many fruits such as apples and dried apricots. Low G.I foods are advantageous if consumed at least two hours before an event. This gives time for this food to be emptied from the stomach into the small intestine. Since these foods are digested and absorbed slowly from the gastro-intestinal tract, they continue to provide glucose to muscle cells for a longer period of time than moderate or high G.I. foods, particularly towards the end of an event when muscle glycogen stores may be running low. In this way, low G.I. foods can increase a person's exercise endurance and prolong the time before exhaustion sets in.(2)

        High G.I. foods, preferably in the form of liquid foods or glucose drinks of approximately 6% in concentration, can enhance endurance during a very strenuous event lasting more than 90 minutes. ("strenuous" being defined as an athlete exercising at more than 65% of their maximum capacity).   Some athletes may prefer food rather than liquid replenishment. Miller(2) suggests glucose enriched honey sandwiches, which have a G.I. factor of 75 or jelly beans, which have a G.I. factor of 80.
 

          Miller suggests that an athlete who is engaged in a prolonged strenuous event
          should consume between 30 and 60 grams of carbohydrate per hour during the event.
 

        High G.I. foods are also desirable after completing an exhausting sporting or training event when muscle and liver glycogen stores have been depleted, as they provide a rapidly absorbed source of glucose and stimulate insulin release from the pancreas. This insulin in turn stimulates the absorption of glucose into liver and muscle cells and its storage as hepatic and muscle glycogen, optimizing recovery and preparation for the next training or competitive event.

        It has been shown that greatest benefit can be had if an athlete consumes these high G.I. carbohydrate foods as soon as possible after an event, preferably within an hour or less. It is further recommended that a high carbohydrate intake be maintained during the next 24 hours. Miller suggests eating at least one gram of carbohydrate per kilogram body weight each 2 hours after prolonged heavy exercise and at least 10 grams of high G.I. carbohydrate per kilogram body weight over the 24 hour period following this exercise.

        For these reasons, an athlete who needs to maintain a high level of activity and performance on consecutive days or more extended periods of time should eat large amounts of high G.I. foods. However, a reasonable quantity of low G.I. carbohydrate food should be consumed before an event in order to improve endurance.

A Natural Method of Maintaining an Elevated Blood Insulin Level

        Noting the hypothesis that an elevated blood insulin level may be of some advantage to bodybuilders, Fahey and his colleagues (1993) undertook an experiment in which they fed athletes a liquid meal of "Metabolol", which consisted of 13.0 g protein, 31.9 g carbohydrate and 2.6 g fat per 100 ml and provided 825 kJ of energy.

        These researchers demonstrated that it is possible with such intermittent feeding during intense weight training to maintain a person's blood glucose at or above resting levels and at the same time, significantly increase insulin levels for the duration of the workout.  This suggests a potentially effective and safe non-drug method for achieving a sustained elevation of blood insulin levels.

        The authors of this research commented that "theoretically, this could provide a biochemical environment conducive to accelerating the rate of muscle hypertrophy and inhibiting protein degradation."   However, the writer knows of no scientific studies which support this theory.

        It is also relevant to note that muscle repair and growth begins in the hours and days following heavy exercise. It is doubtful that the use of insulin just prior to a workout will have any anabolic effects over and above natural processes, at this time. However, use of insulin prior to a workout will certainly expose you to much greater risk of serious harm. If you believe it is beneficial to have a higher insulin blood level during workouts, use the natural method outlined here.

Level of Risk Associated with Insulin Use

        The use of all drugs carries some risk along with potential or perceived benefits, whether used for legitimate medical reasons or for other purposes. Insulin carries some risk even when used by an insulin dependent diabetic, as demonstrated by the observation that some diabetics run into difficulties with their treatment from time to time and often  require assistance to restabilize their medical condition and insulin requirements.  If used by a healthy non diabetic person in whom there is no natural deficiency in insulin production or reduced insulin sensitivity and in the absence of medical advice and monitoring, the risks may be substantially increased.

        The major risk associated with insulin is a physical state known as hypoglycemia or "low blood sugar".  This occurs  when the level of glucose in the blood falls below a certain level required for normal body function. If the blood glucose level is substantially reduced below this normal level and if this is not quickly corrected, there is a risk of disorientation, collapse, coma, permanent brain damage and even death. Exercise and reduced food intake decreases the body's need for insulin and increases the risk of hypoglycemia associated with non-medical use of insulin.

        It is difficult to provide a quantitative estimate of risk for any drug but on a scale of risk in relation to other non-medical and unsanctioned drug use, the use of insulin in this manner would rank towards the higher end of the scale. If zero equals "no risk" of harm to a person's health and ten equals "extreme risk", the use of anabolic steroids in a non-medical context might rate towards the middle of the scale of risk (particularly in the medium to long term) whilst insulin would rate higher. This level of risk associated with insulin use will depend on a number of factors: