Starchy foods with intact cell walls and larger particle sizes significantly reduce postprandial glucose and insulin responses in healthy adults, with standardized mean differences of -0.43 mmol/L*min for glucose and -0.63 pmol/L*min for insulin, indicating that physical structure limits enzymatic access to starch.

When starchy foods have intact cell walls and large particles, the starch inside is trapped like a seed in a tough shell. Digestive enzymes cannot easily reach the starch, so it breaks down slowly. This means glucose enters the bloodstream gradually, so the pancreas doesn't need to release a big burst of insulin. The same thing happens when starch is in its natural crystalline form or has been cooled and re-formed into a hard structure — enzymes still can't break it down quickly.