Why does spaghetti turn sticky and limp when it keeps boiling past al dente?

Answer: Starch swells and leaks

Gluten becomes stronger — Not quite. Gluten can give pasta a skeleton, but extra boiling does not keep strengthening it like a tightening cable. As water keeps moving in, swollen starch and weakened structure dominate the bite. That is why overcooked spaghetti feels slack even though wheat protein is still present.

Salt pulls water out — No. Salted water mainly seasons pasta, and the cited salt sources treat boiling-point and texture effects as secondary. That does not explain why a noodle turns limp after too much time in hot water. The limpness comes from excess hydration and starch release, not salt pulling water out.

Starch swells and leaks ✓ — Right. Heat and water make starch granules hydrate, swell, and gelatinize; pushed too far, more starch escapes into the water and onto the surface. That makes noodles sticky while the internal network loses spring. It is the same starch that later helps sauce, but inside overcooked pasta it marks structural failure.