Too much boiling (or frying) may destroy the necessary nutrients of vegetables. Is there any rule of thumb or guideline on how much time vegetables should be heated for?

  • I was told that my nudist, vegetarian great grandmother thought any cooking ruined the nutrition of vegetables and that most should be eaten as soon as they are picked. I will "Follow" this question. Commented Aug 31, 2021 at 2:02
  • @C.S.Cameron applicable to crucíferous vegetables known for anti-cancer properties. Better if eaten raw because anti-cancer compound is heat sensitive. Research says that steaming is best for them instead of boiling , frying etc.
    – ketanwip
    Commented Aug 31, 2021 at 3:15
  • 1
    Here is the link supporting my comment: cancer.gov/about-cancer/causes-prevention/risk/diet/…. And ncbi.nlm.nih.gov/pmc/articles/PMC5976619
    – ketanwip
    Commented Aug 31, 2021 at 3:17
  • ketanwip: Thank you. Commented Aug 31, 2021 at 3:28

2 Answers 2


Steaming works particularly well -- most of the flavors and nutritional values are not rinsed off in the cooking water. Also stir-frying over high heat works well too -- leaving the food with most of its moisture, without getting 'soggy'

  • Doesn't really answer the question that was asked, as you can steam vegetables for more or less time, too. Good point, though. Anyone else?
    – A. B.
    Commented Oct 18, 2021 at 23:08

A lot depends on which vegetables are being addressed. Root vegetables, in general, should be cooked. Most people would not relish eating a raw potato, for example, and its nutritional value would actually be less. Cooked carrots have more bio-available vitamin A than raw carrots.

But cooking vegetables will degrade their natural enzymes and most vitamins. For vegetables that can be eaten raw, the less they are cooked, the better. In order to cleanse the exterior surface of any bacteria, etc. that may be present, it is a good idea to blanch them. Blanching just means that the vegetables are cooked at high heat very briefly--enough to cook the outer layer of the vegetable without much warming to its core.

Another option, such as when frying vegetables, is to have a little water in the pan with them (be careful of hot splatter, though). The water will not allow the temperature to exceed water's boiling point (212˚F / 100˚C), as long as there is still enough water in the pan. This will slow the degradation of B-vitamins, vitamin C, etc. due to high heat.

  • 1
    +1 but there's one thing I'm always confused about - why would eating raw enzymes be beneficial? Enzymes are very likely to be denatured in the stomach anyway due to its high acidity... in the unlikely event that they aren't, are they supposed to do anything useful? Obviously enzymes are too big to be absorbed and would have to be broken down into amino acids (and potentially minerals). Kind of a side note here I guess...
    – Zanna
    Commented Dec 5, 2021 at 7:45

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