Quite often I can't 'stomach' veggies because I find them rather dull, but if I roast them (huge variety of types used) in oil and a pinch or three of sea salt, I can quite easily eat a very large portion of them.

But how for instance does potassium (veggies are a good source) get affected by roast heat?

How does roast heat affect their glycemix index?

Do any positive effects occur to vegetables' nutrition if exposed to high heat with oil?

After roasting, if I let them go cold in the fridge, does this increase their resistant starch? (Would it greatly depend on the type of veggie being roasted?) Thanks a lot for any thoughts.

  • As a personal comment, why do you care so much about the micro nutritional value differences? What is the link to health here?
    – John
    Commented Sep 28, 2016 at 15:40
  • Whoops I've asked this question in the wrong stack exchange group! I meant to ask in the "Seasoned Advice" group. However, as it's been answered, I'll leave it, unless a moderator wants to move it. Commented Sep 29, 2016 at 8:20
  • @JJosaur nutrition is off topic on this site.
    – Catija
    Commented Oct 4, 2016 at 10:00
  • I stand corrected. Nutrition appears to be off-topic on every SE site then.
    – John
    Commented Oct 4, 2016 at 10:06
  • 2
    @user2911290 If you need help figuring out whether a question is okay on a site, please ask on that site's meta. But nutrition/health things are definitely not on topic here. This one is veeery marginal - we'll talk about the chemistry of food, what's actually in it, including nutrients, but as soon as you start thinking about what effect it has on your body, that's out of scope.
    – Cascabel
    Commented Oct 10, 2016 at 18:25

1 Answer 1


1. The main nutrients destroyed by heating are vitamins from B complex and vitamin C (possible loss 50-70%). (NutritionData: Nutritional effects of food processing). The extent of this effect depends on the temperature, so roasting in oil can have more negative effect than cooking in water.

2. Minerals, such as potassium, are not destroyed by heating, but they can leak into the cooking water. So, boiled potatoes can have less potassium than roasted.

  • Boiled potatoes, in skin (1/2 cup, 78 g): 296 mg (USDA.gov)
  • Baked potatoes, in skin [should be similar to roasted, I couldn't find]: (80 g): 440 mg (USDA.gov)

A side note: sodium partially counteracts the effects of potassium in your body, so if you worry about potassium intake you may also worry about salt intake. (Advances in Nutrition)

3. Oil slows down stomach emptying thus slowing carbohydrate absorption and therefore lowering the glycemic index of a given roasted vegetable. Anyway, this sounds as overthinking to me. From the other viewpoint, roasted foods are heavier for the stomach, so they can increase the discomfort after meals.

4. Heating disinfects foods and makes them more digestible. I'm not aware that roasting in oil would be better in this regard than boiling in water. Roasted potatoes will retain more potassium than the boiled ones, but this alone is not already a "beneficial health effect." On the other hand you may consume more calories than intended vegetables roasted on oil.

5. Cooking, cooling and reheating can increase the amount of resistant starch in the food; this would, obviously, have a significant effect only in starchy vegetables (potatoes, red kidney beans, chickpeas) rather in greens (Nutrients Review). I have not found any reliable information about significant health benefits of resistant starches, anyway.

My conclusion:

I do not consider roasting healthier than cooking in water (boiling): more vitamins destroyed, heavier stomach after meals, greater unnecessary calorie intake from oil.


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