Raw or Cooked Vegetables: Which Is Better, and Does Cooking Change Cancer-Related Nutrients?

The short answer

Neither is simply "better." Cooking helps your body take in some plant compounds, like lycopene in tomatoes. It lowers others, like vitamin C and the sulforaphane that forms in broccoli. The size of the effect depends on the vegetable and how long and how you cook it.

Does that change cancer risk? We found no study that tested it directly. Observational studies hint that raw vegetables may be linked to lower risk for some cancers, but they cannot prove it.

The idea as it circulates

You may hear two opposite claims. One says raw vegetables are best because heat destroys the good parts, including "enzymes." The other says cooked vegetables are best because heat releases more nutrients. Each claim is partly true for some vegetables. Neither holds for all of them.

What the studies show: tomatoes and lycopene

Lycopene is the red plant pigment in tomatoes. In a 1998 study, ten healthy women ate tomato puree or fresh raw tomato with the same amount of lycopene, 16.5 milligrams. Blood lycopene was higher after the puree than after the raw tomato.

A 2005 study gave healthy adults 470 grams of diced tomatoes a day for five days, cooked with or without 25 milliliters of olive oil. Blood trans-lycopene rose 82% in the 11 people who ate the tomatoes cooked with olive oil. It did not change significantly in the 12 people who ate them cooked without oil. These studies were small, and they measured blood levels. They did not measure cancer.

What the studies show: broccoli and sulforaphane

Sulforaphane is a plant compound. The National Cancer Institute (NCI) says that during preparation, chewing and digestion, sulfur-containing chemicals called glucosinolates in vegetables like broccoli break down into active compounds, and sulforaphane is one of the most studied.

In a 2008 study, eight men ate 200 grams of crushed broccoli, raw or cooked. Absorption of sulforaphane was 37% from raw broccoli and 3.4% from cooked (p = 0.002). Peak blood levels came sooner after raw broccoli (1.6 hours) than after cooked (6 hours).

A 2007 study of 12 volunteers compared broccoli microwaved for 2 minutes with broccoli microwaved for 5.5 minutes. About three times more sulforaphane was made in the body after the lightly cooked broccoli. The authors said the way brassica vegetables are cooked had the main effect, more than the rest of the meal.

A 2017 lab test of digestion (not in people) found sulforaphane was up to 10 times higher in raw and 1-minute-steamed broccoli than in broccoli steamed longer.

So for broccoli, shorter cooking kept more sulforaphane in these studies. These were very small human studies, and they measured compounds in the body, not cancer.

What the studies show: vitamin C and other nutrients

Vitamin C is easily lost in water and heat. A lab study of frozen vegetables boiled in a stainless steel pan found these vitamin C losses: spinach 46.5%, peas 25.2%, green beans 18.2%, and okra 21.6%. Losses were higher in a glass pan.

But the picture is not all loss. A 2008 lab study cooked carrots, courgettes (zucchini) and broccoli by boiling, steaming and frying. Water cooking kept antioxidant compounds better than frying, especially carotenoids (orange and yellow plant pigments). Lab tests of "antioxidant capacity" went up in all the cooked vegetables. The authors think cooking softened the plant and made compounds easier to pull out. That is a test-tube measure. It does not show what happens inside a person.

What do studies of people and cancer show?

A 2004 review looked at 28 studies of raw and cooked vegetables and cancer risk. Most found that vegetables, raw or cooked, were linked to lower risk of several cancers. The links were more consistent for cancers of the mouth, throat, food pipe and stomach. In 11 studies that looked at both raw and cooked, 9 found a significant link between raw vegetables and lower risk, but only 4 found one for cooked vegetables. The review said these links "may be stronger" for raw vegetables.

One example is a German study of breast cancer with 310 women with cancer and 353 women without. Women who ate the most raw vegetables had about half the odds of breast cancer (odds ratio 0.51; 95% confidence interval 0.31 to 0.84). No significant link was seen for cooked vegetables.

These are observational studies. People who eat lots of raw vegetables may differ in other ways. NCI notes that in studies of food, participants may have trouble remembering exactly what they ate, and that people who eat certain vegetables may also have other healthy habits.

What about cruciferous vegetables and cancer?

NCI says compounds from cruciferous vegetables (broccoli, cabbage, kale and similar) have shown anticancer effects in cells and animals, but "studies in humans, however, have shown mixed results." For example, cohort studies found little or no link with prostate or colorectal cancer. A few found lower risk in certain groups: colon cancer in women (not men) in one Dutch study, and lung cancer in women who ate more than 5 servings a week in one US analysis. The NCI page we opened does not compare raw and cooked cruciferous vegetables.

Does cooking add any risk?

The NCI says acrylamide, a chemical formed when some vegetables such as potatoes are heated to high temperatures, raised cancer risk in animals. It also says there is no consistent evidence that acrylamide in food is linked to any cancer in humans. We did not find a source we could open that compared boiled or steamed vegetables with fried ones on this point. See also our page on microwaving food.

What official advice says

The Dietary Guidelines for Americans (2020 to 2025) say healthy eating patterns include a variety of vegetables from five subgroups. They count fresh, frozen, canned and dried vegetables, in cooked or raw forms. In the 2,000-calorie pattern they list 2½ cup-equivalents of vegetables a day. They do not tell people to prefer raw or cooked.

We could not open the American Cancer Society guideline page, so we do not cite it here.

What about cancer treatment?

Some people in treatment are told to avoid raw foods. We did not use a source on this topic for this story. Ask your care team what is safe for you. Our page on raw fruits and vegetables during chemo has more.

What this story cannot tell you

• It cannot tell you that raw or cooked vegetables will change your cancer risk. No trial tested that.
• The nutrient studies were small, often with fewer than 15 people. Several were lab tests, not human studies.
• A higher blood level of a plant compound is not the same as less cancer.
• Raw and cooked eaters differ in other ways. The cancer links could reflect that.
• The 2004 review is more than 20 years old. We did not find a newer review we could open that settles the question.
• We read most of these studies as abstracts only. We could not open the American Cancer Society page.

Sources

• Raw versus cooked vegetables and cancer risk, Cancer Epidemiology Biomarkers and Prevention 2004: https://doi.org/10.1158/1055-9965.1422.13.9
• Raw and cooked vegetables, fruits, micronutrients and breast cancer risk, Germany, Nutrition and Cancer 2003: https://doi.org/10.1207/s15327914nc4602_05
• Sulforaphane in humans after cooked versus raw broccoli, J Agric Food Chem 2008: https://doi.org/10.1021/jf801989e
• Meal composition, cooking duration and sulforaphane, British Journal of Nutrition 2007: https://doi.org/10.1017/s0007114507381403
• Sulforaphane formation and steaming time, Food Chemistry 2017: https://doi.org/10.1016/j.foodchem.2016.07.111
• Lycopene absorption from raw and processed tomato, British Journal of Nutrition 1998: https://doi.org/10.1079/096582198388300
• Plasma lycopene after tomatoes cooked with olive oil, Asia Pacific Journal of Clinical Nutrition 2005: https://europepmc.org/article/MED/15927929
• Vitamin C losses in frozen vegetables, Nahrung 2000: https://europepmc.org/article/MED/11190845
• Effects of cooking methods on selected vegetables, J Agric Food Chem 2008: https://doi.org/10.1021/jf072304b
• Dietary Guidelines for Americans 2020 to 2025: https://www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf
• National Cancer Institute, Cruciferous Vegetables and Cancer Prevention: https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/cruciferous-vegetables-fact-sheet
• National Cancer Institute, Risk Factors: Diet: https://www.cancer.gov/about-cancer/causes-prevention/risk/diet

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed. We opened the sources above, except where a limit is stated in the text.

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