Question: Can frozen vegetables be trusted for folate?
You absolutely cannot trust frozen vegetables as a source of folate ever. That's because folate is extremely unstable in the freezer, and you have no idea how old the vegetables are. If they were fresh-frozen yesterday, they'd probably have plenty of folate. But if they were fresh-frozen three months ago, they may seem completely fresh and yet they don't have any folate in them.
I'm not a fan of frozen vegetables mainly on the folate issue, on the basis that many people believe they are getting folate from their vegetables. If they're eating frozen vegetables, they may not be. I'm very worried that there are a lot of people out there who believe that they are doing something good by cutting out refined flour from their diet and starting to eat lots of vegetables. But when they come as frozen vegetables, you may be cutting out a lot of folate from the form of synthetic folic acid added to the enriched flour that you had been eating and cut out of your diet and then not getting anything from the frozen vegetables, and that's a recipe for folate deficiency.
There are a lot of people out there who think folic acid is some kind of toxin. It's not a toxin. It's effective at treating folate deficiency. It is effective at preventing neural tube defects. That's why it's added to flour. It is not the ideal form of folate. There's no question about that. But this is like calcium. People are saying that calcium supplements are bad. Well, not as bad as not getting any calcium. It's the same thing with folic acid. Folic acid is not the ideal form of folate, but it's a lot better than a folate deficiency.
This Q&A can also be found as part of a much longer episode, here: https://chrismasterjohnphd.com/podcast/2019/03/30/ask-anything-nutrition-march-4-2019
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