If you ask most bodybuilders what “eating clean” means, they will probably tell you it means cutting out all the junk food. If you probe further, they narrow it down to avoiding sugar and fat. What they are left with is skinless and boneless chicken breasts, steamed broccoli, and maybe part of a baked yam with nothing on it. Throw a few protein drinks on top, and the daily food routine is complete. This type of diet is very effective for staying lean, but I see many guys who forget that losing fat and gaining muscle might call for different diets. Putting aside fat for another discussion, I want to focus on the importance of carbs, insulin, and insulin-like growth factor-1 (IGF-1) when planning your diet.
Eating low carb or what I call “too clean” can exert the same effect on your body as fasting.(1) This has proved to be an effective way of reducing body fat, but when trying to put on muscle, there are metabolic adaptations to chronic low-carb intake that directly interfere with muscle growth. I’m speaking specifically of a negative regulator of muscle growth called AMP-activated protein kinase (AMPK).(2)
Now I’m going to use a bit of scientific jargon here, but try to stay with me. The primary purpose of a bodybuilder’s diet is to facilitate if not stimulate muscle growth. Staying lean is of secondary importance to gaining muscle mass. This is accomplished not only by eating quality proteins, but also by supplying the body with enough carbohydrate that anabolic activity is unrestricted. Here’s how it works. With sufficient carb intake you will increase insulin levels. Increased insulin levels lead to an increase of free IGF-1 and a decrease in sex hormone-binding globulin (SHBG).(3) Decreases in SHBG increase the level of free testosterone. Binding of insulin and IGF-1 to their receptors on muscle cells activates phosphatidylinositol 3-kinase (PI3K). Further downstream, PI3K signaling causes activation of the serine/threonine kinase Akt. Akt activates mammalian target of rapamycin (mTOR), a critical regulator of muscle growth. Carbohydrates “unrestrict” growth by suppressing AMPK activity and enhance muscle growth through this IGF-1/insulin receptor/PI3K/Akt/mTOR signaling pathway. When you don’t eat enough carbs or do too much cardio, you increase the activity of AMPK within muscle cells, which directly inhibits mTOR, putting the kibosh on muscle growth.(4)
In simplest terms, eating sufficient carbs is not just about replenishing glycogen stores. Eating carbs is mandatory for optimizing the anabolic environment within muscle tissue if you want to see real gains in size and strength.
REFERENCES : 1. S. Klein and R.R. Wolfe, Am J Physiol., 262:e631–36, 1992; 2. D.M. Thomson and s.e. Gordon, J. Appl. Physiol. 98:557–64, 2005; 3. d.m. selva et al., J Clin Invest., 117(12):3979–87, 2007; 4. R. Mounier et al., FASEB J., 23(7):2264–73, 2009.