Exogenous Insulin in Bodybuilding: Myths, Misapplications, and the Real Science

Insulin is often surrounded by hype and misinformation in the bodybuilding world. It's portrayed as a game-changer for muscle growth, feared for its supposed ability to make you fat, and misunderstood when paired with Human Growth Hormone (HGH). Many myths stem from a lack of understanding of basic endocrinology.

Myth: "Insulin Is the Key to Massive Muscle Growth"

Insulin is an anabolic hormone, meaning it fosters a growth environment by facilitating nutrient uptake into cells. However, it doesn’t exclusively shuttle nutrients to muscle—it also promotes fat storage.

Here’s how insulin works:

Insulin binds to its receptor, opening pathways for glucose and amino acids to enter cells.
This supports protein synthesis (building new muscle proteins) and reduces protein breakdown.

The critical question: Does exogenous insulin provide any real advantage for muscle growth if your pancreas already produces enough insulin?

Answer: No.

A systematic review by Trommelen in 2015, analyzing 40 studies, found that exogenous insulin doesn’t further increase muscle protein synthesis during high amino acid availability. Insulin plays a permissive role, meaning it sets the stage for muscle growth, but the real driver is amino acids.

Why Some Bodybuilders Think It Works

Many who report growth while using insulin fail to consider other variables:

They were likely eating more food and training harder at the same time.
The growth wasn’t due to insulin alone but from nailing the basics: high caloric intake and progressive overload in training.

Top coaches in bodybuilding are split on insulin use, and plenty of high-level athletes have achieved success without it.

Risks of Supraphysiological Insulin Dosing

Unlike anabolic steroids or HGH, you can’t simply increase insulin doses for better results. Insulin’s effects are tied directly to carbohydrate intake, and improper dosing can lead to hypoglycemia, which is dangerous and potentially fatal.

Here’s an example:

Eating 100 g of carbs might require your pancreas to release 10 units of insulin.
If you inject 15 units instead, without increasing carbs, you risk severe hypoglycemia.

This need to constantly match insulin with carb intake is why many bodybuilders get fat using it. They overeat to "cover" insulin doses instead of letting food intake guide their insulin needs.

When Might Exogenous Insulin Be Useful?

Exogenous insulin has a role in specific scenarios, particularly at the elite level:

HGH Use: High doses of HGH can create insulin resistance, increasing the body’s demand for insulin.
High Food Intake and PED Use: Combining large caloric intakes, higher body weights, and anabolic steroids can stress insulin production, pushing it to diabetic ranges.

Even in these cases, insulin should be part of a broader strategy:

Prioritize maintaining insulin sensitivity through diet, training, supplementation, and proper PED use.
View insulin as a tool to address a specific need, not a magic solution for growth.

For most bodybuilders, exogenous insulin offers little to no advantage over your body’s natural production. The best muscle-building strategies still boil down to eating enough, training progressively, and managing recovery.

Insulin’s role is highly contextual and mostly relevant for advanced users with unique physiological demands. If you’re not already maximizing the basics, insulin isn’t the missing piece of the puzzle—it’s just another way to complicate the process.

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