Fat-soluble absorption

Enough fat (avocado) to absorb the greens' fat-soluble vitamins.

Adding ~150 g of avocado to a vegetable meal raised absorption of fat-soluble carotenoids several-fold — β-carotene ~15×, α-carotene ~7×, lutein ~5× — by allowing them to form absorbable micelles. A greens-heavy shake specifically needs that fat to unlock the fat-soluble vitamins the greens provide.

Sources: 18