How Much of the Nutrients in Leafy Greens Does the Body Actually Absorb?

The short answer is: it depends - on the way its consumed, what its eaten with, and each individual's ability to absorb nutrients. 

Have you ever wondered if the high amount of nutrition touted for leafy greens is really getting absorbed by your body? Are you worried about oxylates, getting too much of a vitamins, like Vitamin A, or K, or a mineral like calcium? You might be surprised that each mineral and vitamin has a different set of absorption factors, based on how the food is processed, and the individual's current nutritional status. In this guide we'll cover the difference between chewing or blending greens in terms of nutrition, and the best ways of increasing absorption for specific nutrients. 

Vitamin Absorption

1. Vitamin A (as Beta-Carotene)

Leafy greens like spinach, kale, and collard greens contain beta-carotene, a precursor to Vitamin A. The absorption of beta-carotene depends on the plant cell walls being broken down properly. These cell walls are tough, and normal chewing may not break them down enough for efficient absorption.

• Absorption with Normal Chewing: When you chew leafy greens, only a small percentage of the beta-carotene is bioavailable because the cell walls remain largely intact. Some studies suggest that about 10-20% of the beta-carotene may be absorbed from raw, whole greens due to the limited breakdown of the plant material.

• Absorption with Blending: Blending breaks down the cell walls of the greens more effectively, making the beta-carotene more accessible for absorption. When the greens are blended, up to 30-50% of the beta-carotene is bioavailable, depending on the type of greens and whether the blend also includes healthy fats (since beta-carotene is fat-soluble and is absorbed better in the presence of fat).

• Summary for Vitamin A:

  • Normal Chewing: ~10-20% bioavailability.
  • Blending: ~30-50% bioavailability (better with fats like olive oil or avocado).

2. Vitamin C

• In Leafy Greens: Vitamin C (ascorbic acid) is abundant in leafy greens such as kale, spinach, and swiss chard. Unlike fat-soluble vitamins like Vitamin A, Vitamin C is water-soluble and does not require fats for absorption. However, it is sensitive to heat, light, and oxygen, and can degrade when exposed to these elements for long periods.

• Absorption with Normal Chewing: Normal chewing breaks down some of the leaf cells, but since Vitamin C is water-soluble, the absorption rate is generally not as restricted as fat-soluble vitamins. The bioavailability of Vitamin C from normal chewing can still be quite high, with studies showing that about 50-80% of Vitamin C can be absorbed if the greens are chewed and consumed raw.

• Absorption with Blending: Blending helps release more Vitamin C from the plant cells into the liquid. Since Vitamin C is water-soluble, it mixes into the juice when blended, potentially increasing its bioavailability. However, exposure to air and oxidation during blending might degrade some of the Vitamin C, but blending can still lead to slightly higher absorption compared to chewing. Some studies suggest that 90% or more of the Vitamin C may be absorbed from blended greens, especially if the blending process is quick and does not expose the mixture to air for too long.

• Summary for Vitamin C:

  • Normal Chewing: ~50-80% bioavailability.
  • Blending: ~90% bioavailability (with minimal exposure to air and light).

Factors That Affect Absorption:

Fiber Content: Leafy greens are high in fiber, which can bind to certain nutrients and reduce absorption. Blending breaks down the fiber, potentially making more nutrients available for absorption.

Fat Content: Both Vitamin A and Vitamin C absorption can be enhanced by adding healthy fats (like olive oil, avocado, or nuts) during blending. This is particularly important for Vitamin A (as beta-carotene) since it is fat-soluble, but it can also help with the absorption of Vitamin C to a lesser extent.

Oxidation: Both Vitamin A (as beta-carotene) and Vitamin C are sensitive to oxidation. Blending introduces more oxygen, which can cause some nutrient loss. However, blending usually still results in a higher bioavailability than chewing because of the enhanced breakdown of plant cell walls.

Conclusion:

For Vitamin A (Beta-Carotene): You will absorb more when blending leafy greens (30-50%) compared to chewing (10-20%).

For Vitamin C: While both methods offer high bioavailability, blending might slightly increase the absorption rate due to better nutrient release and less degradation than chewing (up to 90% vs 50-80%).

Mineral Absorption

The bioavailability of minerals in leafy greens can vary depending on the method of consumption, with factors like digestion, nutrient breakdown, and the form of the greens affecting how much the body can absorb.

Mastication (Chewing) vs. Blending:

Mastication (Chewing):

1. • When you chew leafy greens, the mechanical breakdown of the plant tissue is limited. The cell walls of greens are tough, which can make it harder for the body to access the minerals, particularly if the greens are consumed whole or in large chunks.
   • Bioavailability: Studies suggest that about 30-40% of the mineral content in raw leafy greens is bioavailable after normal chewing. However, this can vary based on the type of green, its preparation, and the presence of other foods that might aid or inhibit nutrient absorption.

      

     

     Liquefying in a Blender:

     • Blending greens in a high-speed blender breaks down the cell walls more thoroughly, leading to a greater surface area for digestive enzymes to act upon. This process essentially "pre-digests" the greens, making their nutrients, including minerals, more accessible to the body.
     • Bioavailability: When greens are blended, the bioavailability of minerals may increase by 50-70% compared to whole leaves that are simply chewed. This is because the blending process allows for better breakdown of cell walls, making it easier for the body to absorb the minerals.

Key Points:

• Blending generally makes nutrients more accessible because it mechanically breaks down the greens, aiding in the release and absorption of minerals. However, many naturopaths warn against consuming too much food processed in this way, as it creates fractured proteins that cause oxidative stress. 
• Mastication involves less breakdown of the plant's structural elements, meaning some minerals may remain trapped within the cell walls and be less available for absorption. However, it preserves fibers that are in turn used by good bacteria to populate the digestive tract. 

In summary, blending leafy greens increases the bioavailability of minerals by making them more accessible to the digestive system, whereas chewing results in less efficient absorption. However, the actual percentage varies depending on factors like the type of green and preparation method.

What about Oxylates in Spinach and Leafy Greens?

1. Effect of Cooking on Oxalates

• Boiling or steaming spinach can reduce soluble oxalate content because some oxalates leach into the cooking water.
  • Studies suggest that boiling can reduce soluble oxalates by 30–50%, depending on time and temperature.
  • Steaming or sautéing tends to reduce oxalates less because the water doesn’t carry them away.
• Total oxalates (soluble + insoluble) don’t change much; only the soluble fraction that binds minerals and is more easily absorbed decreases.

2. Effect of Chewing vs Blending

• Chewing cooked or raw spinach:
  • Breaks down some plant cell walls, but many oxalates remain trapped in the fibrous structure.
  • Mineral binding by oxalates still occurs, so absorption of calcium and magnesium is partially inhibited.
• Blending spinach into a smoothie:
  • Mechanically disrupts cell walls, releasing more oxalates into the liquid.
  • If the smoothie includes calcium-rich ingredients (like milk, yogurt, or fortified plant milk), more oxalates are free to bind calcium in the gut, potentially reducing calcium absorption more than if the spinach were eaten whole.