Daniel Gwartney, M.D.
Big Gut Dilemma - Is Insulin to Blame?
Raw Mass, Not Quality Muscle
How does insulin contribute to what has been known as “GH belly” in bodybuilders? Is there any proof it happens? Of course, there has not be a randomized, double-blind, placebo-controlled trial approved by an institutional review board; nor will there ever be. Yet, would the word of another Mr. Olympia legend add credence to the hypothetical association?
In an interview published in Muscular Development, six-time Mr. Olympia Dorian Yates noted his experience with growth hormone and insulin, commenting that whereas growth hormone (8 IU/day) did have a positive effect on his size and condition, insofar as insulin was concerned, “I got bigger than ever, but it wasn’t quality muscle, and my midsection was distended.” In fact, Yates only used insulin one year during the off-season. He further stated, “For me, insulin had a negative overall impact on my physique. It kept me from getting into my usual condition that I prided myself on. Raw mass is not the same thing as quality muscle tissue. I got a bit bigger, but at the expense of my separation, crispness and clear muscle separations. I see that same lack of separation constantly today with the guys, as well as the distended abs.”
Despite the cacophony of disrespect for “broscience” from the wonder boys of academia, there is great relevance and value in the observations of these men. Such “reports from the field” offer insights that more often than not raise questions, but also offer guidance as to the correct direction to explore in the scientific literature. Note, Yates reports that the appearance of today’s competitors is similar to what he experienced while experimenting with insulin.
Insulin’s Double Whammy
This is going to be a deep-end splash into physiology, so hold your hat and look for the general concepts. First, insulin increases adipocyte lipogenesis— basically, fat storage in the fat cell. This is particularly unhealthy in the intra-abdominal fat depots where much of the growth is due to adipocyte hypertrophy.5 Further, in the overfed state, cortisol (the “stress” hormone) increases the growth of individual fat cells and increases the rate of lipogenesis from insulin’s signal.6 Though testosterone replacement may produce smaller, healthier visceral fat cells in older men with low testosterone, excessively high testosterone may increase adipocyte hypertrophy— bigger but unhealthy fat cells that release harmful hormone-like signals.7 In part, this happens because testosterone increases the enzyme that activates cortisol in fat cells.8 Also, hypertrophic adipocytes have a higher aromatase activity that converts testosterone to estradiol in the cell, further promoting fat storage.9 Insulin resistance is harmful to the overall metabolism, but fat cells and muscle cells that are overloaded with stored fat make cellular modifications to become less sensitive to insulin as a “last resort” act of self-preservation.
So, not only fat cells become more resistant to insulin, but also muscle cells. The increase in cellular energy (ATP/AMP ratio) turns on the anabolic pathway of mTOR and suppresses the metabolically beneficial AMPK pathways.10 Further, stored fat inside the muscle cells increases just as it does in fat cells. Though this is beneficial if it is a response to chronic aerobic conditioning, where the stored fat is there to be used instead of deposited as overflow from overburdened fat cells, it reduces the activity of insulin in muscle cells.11 Thus, the muscle cell is less efficient. Eventually it becomes less efficient at increasing muscle protein synthesis in response to insulin, similar to aging.12
Not only does stored fat interfere with muscle insulin signaling, but also with circulating fat (free fatty acids). Though it has not been studied, the conglomerate of drugs used by professional bodybuilders (e.g., growth hormone, thyroid hormone, clenbuterol, etc.) results in a near-continuous release of free fatty acids. This has been shown to reduce muscle response to insulin.13 Competitors seeking continued gains may unwisely increase the insulin dose— increasing not only fat mass, but also the risk of side effects. Lastly, insulin promotes the accumulation of a class of lipids called ceramides in muscle cells by increasing the rate of production of these signaling molecules.14 The types of ceramides that accumulate in insulin-resistant muscle cells are associated with abdominal obesity and insulin resistance, though they have not been shown to damage muscle function.15
Water Retention
One final matter to consider with insulin’s effect on appearance is water retention. Perhaps the experience of a puffy face and doughy skin after a three-day buffet binge or just a heavy Thanksgiving meal is familiar to many? Insulin acts on the kidneys, promoting water and sodium retention, among other effects.16 Edema (water retention) is common among diabetics using prescribed doses of insulin on restricted diets, so one can only imagine the greater effect among bodybuilders using supraphysiologic doses while consuming the number of calories required to maintain the mass and growth they display. Typical to the sport, the response of the bodybuilder is more drugs to treat this side effect— primarily diuretics during the pre-contest preparation. Some might attempt a low-carbohydrate diet, but this increases the vulnerability to hypoglycemia, shock and organ damage.
Bigger Not Always Better
There is little question that insulin has fueled much of the mass differential in modern-day bodybuilders. However, as voiced by Mr. Olympia legends Arnold Schwarzenegger and Dorian Yates, bigger has not resulted in better. Some of the abdominal distension seen is likely due to growth hormone abuse. However, the role of insulin has been underappreciated, adding to the “bottle-shaped bodies” that provoked a comment from Arnold. The professional places himself at great risk by abusing insulin for size gains. However, the greater fear is that impressionable young men are following their lead with little understanding. Further, the anabolic effect of insulin comes at the cost of greater insulin resistance, and edema. Too often, this leads to additional drug seeking to counter these effects, with a greater risk of an adverse drug interaction.
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