According to Mike Adams interview with Jameth Sheridan, iron will only be absorbed from plants if you need it. Once you no longer need it, the body will not absorb it. However, if you are deficient in iron, your body will absorb more iron from plants than from isolated iron and animal sources.
They also said you could take thousands of times more iron from plants, and it won't absorb more than it needs.

https://www.naturalnews.com/podcasts/...odcast2008.mp3

Carrot juice and beet juice are relatively high in sugar. There's about 15 grams of sugar in a cup of carrot juice.

I'm not buying that. A mineral is a mineral is a mineral. Just because it is organically sourced does not make it more or less absorbed. Zinc can be sourced from potato skins, and it is still zinc and should not exceed 50mg per day for more than a few days. Iodine can be sourced from kelp, and it's not any better than from any other source. Same for sodium. Sodium from celery. Sodium from the deep sea. Better? It may be true that if you take iron in the form of a supplement, the body will have more or better access to it, than if it came in with whole food. This would be true of iodine, if it came in kelp or rendered into the elemental. This is why it is OK to eat seaweed, which contains mercury as they all do. The whole food, seaweed, also contains other minerals that inhibit the bioavailability via chelation.

I know this when I eat beets, which I really love. Also spinach. I have to beware of constipation due to the iron. Iron will accumulate, but can be disposed of via blood letting or donating.

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- Jim
https://www.natmedtalk.com/blog.php?u=529