Take a look at the last decade’s worth of Olympia lineups and you’ll notice that competitors’ biceps and delts aren’t the only body parts getting bigger—their guts are, too. Known as the “bubble gut,” top-tier competitors like seven-time Mr. O, Phil HeathKai Greene; and 8-time Mr. O, Ronnie Coleman, have all stepped onstage sporting bloated, engorged midsections, begging us to ask—why the heck does that happen?

“There’s no data; it’s all anecdotal,” says Dr. Thomas O’Connor, aka the “Anabolic Doc,” who specializes in patients seeking recovery from anabolic-steroid use. However, O’Connor goes on to say that the bubble gut is a result of drug use—specifically insulin and Human Growth Hormone (HGH)—in tandem with a high-calorie, high-carb diet.

“It’s not steroids, per say,” O’Connor says. “Steroids have been used back in the ’70s, ’80s, and ’90s and you didn’t see the bubble guts. So, what happened? The bar rose. Competitors all take in more insulin [a substance used to increase bulk, which can cause bloating], HGH, and calories—upwards of 10,000 calories a day and 1,000 grams of carbohydrates.”

As for how much is too much, O’Connor says that competitors can take more than 10 IUs (International Unit) of HGH, which is five times more than the standard 1-2 IUs—or less—prescribed at anti-aging facilities.

A lot of spectators also refer to the gut as “HGH Belly,” a term coined based on the notion that HGH grows their innards, pushing out the gut. This is only partially true.

“It grows the mesentery, the gut tissue itself, and it grows the muscles in your abdomen,” says, O’Connor, who stresses that HGH by itself is not the cause.

“A lot of people think growth hormone is going to increase the size of your internal organs which bloats the waistline,” says Dorian Yates, a six-time Mr. Olympia (1992-97), in an interview with Joe Rogan in July 2017. “So I went and had a battery of tests where they actually measure all of your internal organs and mine were all normal.”

“[Gut growth] is multi-factorial,” O’Connor adds. Those factors being: genetics, increased calories, HGH and insulin, and water retention, as a result of the absurd carbohydrate intake.

Ok, but not all competitors have extreme guts—take this year’s Mr. Olympia, Shawn Rhoden as an example—so how can one prevent gut growth?

“It’s a dose-dependent phenomenon,” O’Connor says. “None of the classic physique guys have bubble guts. They may use a little HGH and insulin, but they’re not getting that big.”

Simply put: the more of something you do, the greater the effect will be. This means toning down the bulge is as simple as “tapering down your HGH and insulin use and the number of carbohydrates one is taking in, weeks before the show,” O’Connor adds.

There you have it. The bubble gut is likely a result of too many drugs, too much food, and too many carbs—all in the pursuit of more size. Hopefully, Shawn Rhoden’s win this year will change standards to reward tight, aesthetic physiques in the years to come. Hey, it may burst the other competitor’s bubble—but we’re not sure that’s such a bad thing.