Even though sugar and alanine make insulin go up, that doesn’t stop your muscles from breaking down any more than protein alone does.

Adequate dietary protein intake stimulates sufficient insulin secretion to maximize suppression of muscle protein breakdown, rendering additional carbohydrate intake redundant for insulin-mediated anabolic signaling.

When carbohydrates are consumed, the body releases insulin, which lowers the rate at which muscle proteins are broken down and slightly raises the rate at which new muscle proteins are made.

Even if you pump insulin into a healthy young person’s body and boost certain amino acids by 150%, their muscles still won’t grow more—because insulin needs other amino acids too to make muscle.

When insulin is infused into healthy young adults without providing amino acids, the levels of key amino acids in the blood drop by 40–50% within 7 hours, and this is accompanied by a decrease in muscle protein synthesis and no activation of the mTOR signaling pathway.

In older adults with insulin resistance, consuming protein and doing resistance exercise causes a larger spike in insulin than in younger adults, but this higher insulin level does not lead to better use of amino acids or increased muscle-building signals.