Vitamin A in its usable form, retinol, doesn't exist in plants
True, plants contain no retinol. They contain beta-carotene, which the body converts into it. A single sweet potato or a couple of carrots covers a day's needs, not six pounds of them.
Retinol, the form of vitamin A the body actually uses, comes only from animal foods. Plants supply beta-carotene, which has to be converted, and a large share of people carry genetic variants that make that conversion poor. A diet that relies entirely on conversion puts those people at real risk of falling short, without their knowing it.
Plants contain no preformed retinol. They supply vitamin A as carotenoids, mainly beta-carotene, which the body converts to retinol as needed. Dietary guidelines count both forms, which is why intake is measured in retinol activity equivalents rather than in retinol alone.
The quantities are where the claim goes wrong. Adult requirements are roughly 700 to 900 micrograms a day. A medium baked sweet potato provides more than that on its own. About 100 grams of raw carrot, one large carrot, comes close. Pumpkin, butternut squash, kale, spinach and red peppers are also rich sources. Six pounds of carrots would be many times the daily requirement.
The genetic point is real. Common variants of the BCMO1 gene reduce how efficiently some people convert beta-carotene. In one widely cited study, close to half of participants carried variants of this kind. The effect is reduced conversion, not none, and even a halved rate is covered by ordinary portions of these foods. Eating carotenoids with some fat and cooking them both improve absorption.
The outcome data match this. Clinical vitamin A deficiency is a problem of poverty and of diets low in both animal and plant sources. It is not a recognised problem among vegans in countries with varied food supplies. Conversion also has one advantage. The body converts less when its stores are full, so beta-carotene from food carries no risk of the toxicity that large amounts of liver or retinol supplements can cause.
Vitamin A is a nutrient worth knowing about on a vegan diet. It is not one that needs a supplement, or anything beyond orange and dark green vegetables most days.
- Some people convert beta-carotene poorly, so they can't get enough vitamin A without animal foods
Different wording, same argument. The response above answers all of them.