Anabolism: The phase of metabolism in which simple substances are synthesized into the complex materials of living tissue.
Catabolism: The metabolic breakdown of complex molecules into simpler ones, often resulting in a release of energy.
Both of my sources for these definitions (through the clickable links) are worth looking at, because they include dictionary definitions from several sources, as well as Wikipedia articles which explain in more depth.
Basically, anabolism means taking simpler stuff & using it to build more complex stuff within the body: amino acids into protein into muscle, blood glucose into adipose tissue (body fat), etc. Catabolism does the opposite: it breaks larger, more complex molecules into simpler stuff, usually with a release of energy, for example, burning off fat through exercise or going on a low-calorie starvation diet that leads to the loss of lean muscle mass.
Insulin is anabolic in these ways:
- Insulin tranfers blood glucose to the liver & to muscle cells to either be burned for energy, or to be synthesized (that is, built into) glycogen. Glycogen is “animal carbohydrate” which can be burnt (catabolized) when quick energy is needed for exercise or an emergency. Insulin is anabolic because it helps build glycogen.
[Edit: I misstated that. Actually, glycogen itself isn’t burnt for energy. Rather, it’s converted back into glucose (a conversion stimulated by the catabolic hormone glucagon) & the resulting glucose can then be burnt for energy.]
- Insulin transfers excess blood glucose, that is more than the body needs for its immediate energy requirements or for replenishment of its glycogen stores, to fat cells for storage as adipose (fat) tissue. Insulin is anabolic because it helps build body fat.
- Insulin transfers amino acids in the blood for uptake by the muscle cells to be synthesized into proteins for muscle growth. Insulin is anabolic because it helps build muscle.
There are other hormones which are catabolic, such as cortisol & glucagon, which specialize in breaking down muscle proteins, glycogen, etc. Cortisol, for example, is a stress hormone that (amongst other things) breaks down muscle proteins, which will lead to an increase of glucose in the blood. Insulin then goes to work to take care of the glucose, & if (as in point 2 above) that’s more glucose than you need for energy or glycogen replenishment, insulin will exercise its anabolic function with respect to body fat by dumping that insulin into your fat muscles.
In a healthy person, all these hormones & more act in balance with each other to keep you healthy. But if something is thrown out of whack, your hormones will still keep doing the jobs they were made to do even if doing their jobs might mess you up even further.
That’s what happens with insulin resistance. It’s not insulin itself that is the problem, but the insulin resistance that comes from eating too many carbohydrates, especially highly refined carbs that are digested quickly. By eating too many carbs, you put your body into a chronic state of too high blood sugar. High blood glucose leads to high insulin levels, because the insulin is trying to take care of all that sugar. You become insulin resistant, high insulin levels in your blood becomes chronic, all that excess blood sugar gets dumped as fat, & as you get fatter you also get more & more unhealthy & begin the progression to diabetes, cancer, heart disease, etc. Not only are the natural, healthy functions of insulin thrown off, but so are the functions of the other hormones & systems in the body.
Unless you do something to change your situation.
Let me put it very clearly: my view is that insulin resistance & chronic high insulin levels are very bad things. That’s why I have been working my butt off to increase my insulin sensitivity.
A healthy body is insulin sensitive, & so needs relatively little insulin to take care of the jobs that insulin was made to do, including shuttling blood glucose & amino acids to the places where they’re needed to keep on building & maintaining a healthy body. That includes shuttling amino acids to where they’re needed — in the muscles — & participating in the anabolic process of muscle-building.
In the body that is unhealthy because of insulin resistance, more & more insulin is required to do the job, not because insulin isn’t doing its job, but almost always because the body’s owner is making its job very hard for it by eating too much lousy food, not getting enough sleep, not getting enough exercise, & making other bad lifestyle choices. Probably insulin & the other hormones are all having problems doing their job exactly right because of the challenges the bad lifestyle choices are putting to them. Your entire metabolic system goes out of whack, out of balance.
Finally, about insulin’s anabolic role in building muscle: I learned of this just last week at John Berardi’s website, & have researched it quite a bit since, & based on scientific articles, medical dictionary definitions, & some of the sources I’ve cited in this message I believe that Berardi is right. But Berardi does not say, nor do I, that high insulin levels are a good way to take advantage of this fact. His approach (as mine) is not to increase insulin levels, but on the contrary: to increase insulin sensitivity so that less insulin is necessary to do the job & do it right.
I learned doing research that there are a lot of bodybuilders who actually take insulin shots in order to take advantage of insulin’s anabolic properties re: muscle. This is a stupid & dangerous thing to do. Because of course insulin is also anabolic with respect to body fat, not to mention that high insulin levels leads to insulin resistance. So these abusers of insulin are actually making themselves less healthy. Needless to say, Berardi recommends against this idiotic kind of supplementation.
These are the definitions I’m using, & the understandings I have at the present moment, which are subject to modification as I increase my understanding.