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I have been under word-of-mouth impression that while vitamin A is most replete in meats, a vegan who eats nutrient rich vegetables or sweet potatoes and carrots intakes their full share. However, the chemical reaction necessarily to create vitamin A in these vegetables requires cooking, which poses an additional challenge for raw vegans.

I was not easily able to validate these claims either direction from a few google searches. Do veggies fulfill vitamin A requirements, and does cooking impact this?

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Sources of Vitamin A

There are two dietary sources of vitamin A:

  • Taking up retinoids (vitamers of vitamin A) directly, which occurs in animal based, non-vegan food.
  • Converting a form of provitamin A into vitamin A. Provitamin A is abundant in lots of vegetables.

A quick note on supplements

Both forms can also be taken as a food supplement. Retinol overdose is harmful, especially during pregnancy. Provitamin A cannot be overdosed so easily since conversion to vitamin A stops with a high vitamin A blood level.

(Given the long discussion on the other answer I felt that this needed to be addressed, even if out of scope for the question.)

Provitamin A sources

The most common source of provitamin A is β-carotene. It occurs in all orange vegetables, such as carrots and sweet potatoes, but also in many others.

Other sources include α-carotene and γ-carotene. Not all carotenes are a source of provitamin A.

Provitamin A conversion

In a healthy human, provitamin A is converted into vitamin A. Conversion depends on the specific source of provitamin A, and other factors.

The actual question: Cooking and raw preparation

The bioavailable amount of vitamin A depends greatly on the preparation. In studies the following preparation methods of carrots improved β-carotene blood levels:

  • Slicing, ideally homogenizing (e.g. blending)
  • Cooking
  • Extracting juice
  • Preparation in fat

Effects of cooking

Cooking a carrot can have several effects:

  • The carrot is usually sliced in smaller pieces.
  • Fat is added.
  • Carrot cells break and release β-carotene.
  • The carrot is heated, and β-trans-carotene is converted to β-cis-carotene.

The first three of these increase the β-carotene blood level. The last one is potentially a problem, since β-cis-carotene is not converted to vitamin A as effectively as β-trans-carotene.

It seems like there is no decisive result yet whether the process of heating is beneficial or not. But certainly either option can provide you with sufficient amounts of provitamin A.

My recommendation: Grate your carrot and add some linseed oil for a great raw salad. Blend it for a great smoothie.

Main source: National Academies of Science - Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc, and the plentiful sources therein.

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  • "whether the process of heating is beneficial or not" -- Since you mention earlier there are multiple preparation methods that improved β-carotene blood levels, do you mean "whether heating is more beneficial than slicing, blending, or adding fat"? I hesitate to edit it myself because I'm not clear on your meaning :) – Erica Feb 7 '17 at 20:10
  • @Erica, no, I mean whether heating in itself is beneficial at all. As far as I know there is no study that blends carrots with some oil and then lets some people eat it raw and some people eat it cooked. It's only known that the combination of blending and cooking is beneficial. Please do edit if you see potential for clarification. – Turion Feb 8 '17 at 9:28

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