17

There are many people who cook vegetables without washing them (before cutting) because they think it removes important nutrients.

This claim is predominant in some Asian countries.

Is that true?

  • Is the claim "Wash vegetables BEFORE cutting them, to preserve nutrients"? In that, case your reference is fine, but the title is misleading. Or is the claim "Don't wash vegetables AT ALL before cooking them."? In which case your reference directly contradicts it, and you need to find someone else making this (IMHO, far-fetched) claim. – Oddthinking Jul 29 '12 at 18:24
  • @Oddthinking the claim is about do not wash vegetables at all. This claim is in asian countries where it is hard to find a reference for. – Believer Jul 29 '12 at 18:29
  • I removed the notability link that claimed the opposite to the key claim. Asia accounts for well over 50% of the population. Any chance you could narrow it down, and link to an Asian-language version of the claim? I don't think it is notable at the moment. – Oddthinking Jul 29 '12 at 19:08
  • Well it was practiced in my family and in many houses it still is. It is predominant in subcontinent (India, pak, bangladesh). – Believer Jul 29 '12 at 19:12
13

Yes, washing vegetables does remove some of the water soluble vitamins, specifically B-complex group, and vitamin C; however, in general, the health benefits of washing vegetables by avoiding pathogens as well as residual pesticides, herbicides, and other such residuals greatly outweighs the nutrient loss.

With regards to the nutrient loss, vitamin B-12 can be loss through the washing process; however, generally this is only a concern for vegans who are unable to get the vitamin through animal sources. For example, most of the nutritional value of rice is lost during milling which requires that it be enriched prior to sale. As the enrichment is on the surface of the rice, it can be lost if the water is discarded. Furthermore, the degree of vitamin loss can be mitigated by using proper washing and handling techniques and by limiting the washing of the vegetables until they are ready to be used and limiting the amount of washing that is needed (i.e. once washed, avoid contact with dirty vegetables; wash vegetables before they are chopped, etc.).

Barring the issue of vitamin B-12 and vegans who generally use supplements to resolve the problem; the nutrient losses are greatly offset by the risk of food poisoning caused by a not insignificant list of food-borne pathogens.

  • 1
    Can you provide a source for the fact that water soluble vitamins are washed away when washing vegetables, especially before cutting? The current link does not really address that, it merely explains what water soluble vitamins are. – nico Jul 30 '12 at 17:33
  • @nico Table 1 has a column titled "Stability in foods" that summarizes where some of the loss comes from. Most of the sources I've dug through indicate there is some loss due to washing, but doesn't break things down into numbers. I've been looking for a better one, but the better ones tend to be more specific to the type of vegetable or fruit as opposed to generics. – rjzii Jul 30 '12 at 17:41
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    sure, but it pretty much talks about loss during cooking, not during washing. – nico Jul 30 '12 at 18:59
  • @nico - Right, but most consider washing the vegetables to be part of the process of cooking them. The question itself is a bit of a catch-22 in my opinion as, unless you are using the vegetables raw (i.e. salads) then you are going to lose more nutrients during most cooking processes than during the initial preparation steps (i.e. washing). – rjzii Jul 30 '12 at 19:08
  • Strictly speaking washing that removes bacteria and related bugs will remove vitamin B12 as they produce it and plants don't. Plants don't make B12; only certain bacteria and archaea do it which is why it is a concern for vegans who wash their veg too thoroughly. – matt_black Jul 31 '12 at 15:32
8

Washing vegetables before you cut them wouldn't remove any nutrients since the skin of the vegetable protects it, just like in rain outside etc. Leaving vegetables soaked in water for to long and the protecting layer would disolve and the water get inside the vegetable though. Cutting the vegetables and then soaking them in water could also very likely, depending on the vegetable in question, remove nutrients.

U.S. Department of Agriculture recommends that you wash the vegetables to get rid of dirt and pathogenic microorganisms. I would find that a strong case to wash ;).

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    Do you have sources? – Flimzy Jul 31 '12 at 6:20
3

The claim appears to be "It is healthier not to wash vegetables at all, because washing may remove some of the nutrients."

This claim only considers one potential benefit of unwashed vegetables. It ignores a number of potential downsides, including potential leaving on the vegetables microorganisms known to be harmful (E. coli, Salmonella, Clostridium, Bacillus, Listeria), and also pesticide residues which are potentially harmful.

Even if it were true that some nutrients were lost, the risks of food poisoning and death outweigh the benefits.

In my searching, I found experts from the following science-based health organisations recommend washing your vegetables to remove microorganisms and contaminants:

I found more articles from the following non-peer-reviewed media organisations that also recommend washing your vegetables:

I found the following articles from any source at all recommending you not wash your vegetables to preserve nutrients:

  • -

Now, I wouldn't argue that the most popular point of view is necessarily the correct one, but the importance of washing vegetables compared to a claim about nutrients (an alleged claim, at that) isn't in the slightest bit controversial.

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    Right, but this still doesn't really answer the question, does washing vegetables actually remove any nutrients? Obviously even if that is the case the health benefits outweigh the nutrient loss, but this answer doesn't really answer the question. – rjzii Jul 30 '12 at 14:24
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    @Rob, Right, I agree, but this is an example of a How do I burn down my house? / Should I use a bottle or shoe to hammer a nail? question. The alleged claim isn't merely "Nutrients could leak out.", it is "It is better for your health not to wash the vegetables." That is a dangerous argument to fall for and we should step up to address it. – Oddthinking Jul 30 '12 at 15:41
  • I have edited to make that argument more explicitly. – Oddthinking Jul 30 '12 at 15:51
  • Bah, not sure the best way to reply, but philosophically, just be cause a question is bad one doesn't mean that it shouldn't be answered. Also, this is an easily addressable issue in this case since it can be answered (i.e. yes or no...) followed by why even if nutrients are washed away it is still worth doing. – rjzii Jul 30 '12 at 16:04
  • e.coli and salmonella isn't relevant if the situation is "prior to cooking" as in this question. Any salmonella on the surface of vegetables will die from cooking anyway. Washing is still helpful to get rid of, for example, traces of pesticide. – Agrajag Aug 3 '12 at 8:04

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