Consider starch and fiber, both polysaccharides, both derived from plants, both composed of hundreds to thousands of monosaccharides joined together, but they're joined together differently, and that changes the effect  they have on your body.
Vejam os amidos e as fibras, ambos polissacarídeos, ambos derivados das plantas, ambos compostos por centenas de milhares de monossacarídeos unidos, mas unidos de formas diferentes. Isso altera o efeito que têm no nosso corpo.