If cell membranes are made up of lipids (fats), why do foods like lettuce have so few calories even though there are a lot of cells in it?

Question

If cell membranes are made up of lipids (fats), why do foods like lettuce have so few calories even though there are a lot of cells in it?

In: Biology

Answer 1

Plant cells have rigid cellulose walls that are largely indigestible to humans. What little nutritional value they do have is often inaccessible.

More generally, cell membranes are very thin comparatively. Think of a big bucket filled with water balloons. They fill the bucket, but there’s hardly any balloon rubber in there.