Food · 4 min read ·

Vegetables: how much, which and how to cook them

Raw or cooked? Frozen or from the market? And why don't potatoes count as vegetables?

In a nutshell

1How much

Strong evidence 800 g A summary of 95 studies: every 200 g of fruit and vegetables a day went with a 10% lower risk of premature death and a 16% lower risk of stroke. The benefit kept growing up to 800 g a day.4
Strong evidence 3 portions In a summary of studies with almost 1.9 million people, mortality was lowest at about 3 portions of vegetables and 2 portions of fruit a day. Starchy vegetables (peas, corn) and potatoes were not linked to lower mortality.1
WHO recommendation 400 g The WHO recommends at least 400 g of fruit and vegetables and at least 25 g of fibre a day for everyone older than 10.5

A portion of vegetables is about 80 g: three heaped tablespoons of cooked carrots or peas, one tomato, seven cherry tomatoes or a 5 cm piece of cucumber. Potatoes don't count as vegetables — in a meal they take the place of bread, rice or pasta.6

2Raw or cooked?

Lab measurement 0–91% How much vitamin C survives cooking ranged from 0 to 91% depending on the vegetable and the method. Most was kept after microwaving, least after boiling in water. Vitamin E and beta-carotene were sometimes even higher in cooked vegetables than in raw ones.2
Lab measurement In carrots, courgettes and broccoli, boiling and steaming preserved carotenoids better than frying. Cooked vegetables had a higher antioxidant capacity than raw ones — they soften and release their compounds more easily.7

3Frozen or fresh?

Lab measurement 8 kinds For eight kinds of fruit and vegetables, including peas, carrots, spinach and green beans, frozen samples had the same or more vitamin C than fresh ones kept in the fridge. Frozen peas, carrots and spinach had less beta-carotene.3

The WHO: frozen and canned vegetables are a good choice, provided they have no added salt or sugar.5

4Beetroot and blood pressure

Moderate evidence — short studies −4.4 mmHg Nitrate and beetroot juice lowered the upper, systolic blood pressure by 4.4 mmHg on average in small studies (254 people in total, two weeks at most).8

What to take from this

Sources

Written on , based on studies available at that date. Newer research may change the conclusions.

  1. Wang D. D. et al. (2021). Fruit and vegetable intake and mortality: results from 2 prospective cohort studies of US men and women and a meta-analysis of 26 cohort studies. Circulation 143:1642–1654. doi.org/10.1161/CIRCULATIONAHA.120.048996
  2. Lee S. et al. (2018). Effect of different cooking methods on the content of vitamins and true retention in selected vegetables. Food Sci Biotechnol 27:333–342. doi.org/10.1007/s10068-017-0281-1
  3. Bouzari A., Holstege D., Barrett D. M. (2015). Vitamin retention in eight fruits and vegetables: a comparison of refrigerated and frozen storage. J Agric Food Chem 63:957–962. doi.org/10.1021/jf5058793
  4. Aune D. et al. (2017). Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality — a systematic review and dose-response meta-analysis of prospective studies. Int J Epidemiol 46:1029–1056. doi.org/10.1093/ije/dyw319
  5. WHO (2026). Healthy diet — fact sheet. who.int
  6. NHS (2022). 5 A Day portion sizes. nhs.uk
  7. Miglio C. et al. (2008). Effects of different cooking methods on nutritional and physicochemical characteristics of selected vegetables. J Agric Food Chem 56:139–147. doi.org/10.1021/jf072304b
  8. Siervo M. et al. (2013). Inorganic nitrate and beetroot juice supplementation reduces blood pressure in adults: a systematic review and meta-analysis. J Nutr 143:818–826. doi.org/10.3945/jn.112.170233

This is general information and does not replace a doctor or dietitian. If you find a mistake or a newer study, let us know.