{"url":"https://whatshealthyandwhy.com/cooking-methods/how-cooking-changes-nutrients","path":"/cooking-methods/how-cooking-changes-nutrients","alternates":{"json":"https://whatshealthyandwhy.com/api/articles/cooking-methods/how-cooking-changes-nutrients.json","markdown":"https://whatshealthyandwhy.com/cooking-methods/how-cooking-changes-nutrients.md"},"topic":{"slug":"cooking-methods","name":"Cooking Methods","url":"https://whatshealthyandwhy.com/cooking-methods"},"slug":"how-cooking-changes-nutrients","order":1,"title":"How Cooking Changes Nutrients","question":"Does cooking destroy nutrients: raw vs steamed vs fried?","answer":"Cooking probably cuts vitamin C and folate, especially when boiled, but it boosts lycopene and beta-carotene absorption; steaming keeps most nutrients.","description":"Boiling cuts vitamin C and folate, but heat frees lycopene and beta-carotene. How steaming, frying and raw eating compare, and how to keep the most nutrients.","confidence":4,"confidenceNote":"A review of 100+ studies and several small human crossover trials agree on the direction of change, but results vary by vegetable and method, and none measured disease outcomes.","evidenceSummary":{"rctCount":4,"observationalCount":0,"metaAnalysisCount":0,"totalParticipants":"About 40 across five small crossover trials","replicated":true,"newestStudyYear":2014},"category":{"categoryTitle":"What's Good For You","categorySlug":"good-for-you","subcategoryName":"Foods & Drinks","subcategorySlug":"foods","url":"https://whatshealthyandwhy.com/explore/good-for-you/foods"},"actions":["Steam vegetables lightly, or boil in little water and drink it as soup: boiled spinach and broccoli kept under half their folate, while steaming did not reduce it [1][2].","Cook tomatoes, carrots and other red and orange vegetables, and eat them with a little oil: heat released more lycopene, and fat is needed to absorb carotenoids [3][4].","Eat some broccoli, cabbage and other crucifers raw or only lightly steamed, because the enzyme that makes sulforaphane is destroyed by heat [5][6]."],"cautions":["Frequent high-heat dry cooking (grilling, frying, roasting) of meat and starches forms far more AGEs, linked to oxidative stress and inflammation; with diabetes or heart disease, favor moist heat [7].","Eat eggs cooked: in a small study of ileostomy patients, heating raised egg protein digestibility from about 51% to 91% [8]."],"simpleText":"Cooking is a trade-off, not a loss. Heat and water do cut vitamin C and folate, and boiling washes more of them into the pot [1][2]. But heat also breaks open plant cells, so you absorb more lycopene and beta-carotene [3][9]. Steaming or brief cooking keeps most nutrients, and a mix of raw and cooked vegetables covers both sides.","mediumText":"How it works\n\nHeat does two opposite things to plant foods. It breaks some compounds down, and it softens the plant's cell walls so other compounds are easier to release and absorb [9]. Which effect wins depends on the nutrient, the vegetable and the method.\n\nVitamin C and folate fall, mostly into the water. These water-soluble vitamins degrade with heat and leach into cooking water. Boiling kept only 49% of the folate in spinach and 44% in broccoli, while steaming caused no significant loss; grilling beef and boiling whole potatoes did not significantly change folate [1]. In broccoli, every cooking method except steaming caused significant losses of vitamin C, and stir-frying hurt glucosinolates most [2]. If you drink the cooking liquid, as in soup, you get back much of what leached out.\n\nCarotenoids rise. Heat frees lycopene and beta-carotene from tough cell structures. Tomatoes heated at 88 °C for 15 to 30 minutes held more than two and a half times the lycopene of raw tomatoes, even though vitamin C dropped [3]. Women who ate processed, pureed carrots and spinach had about three times the rise in blood beta-carotene of those who ate them raw, although that result was borderline [10]. Fat matters too: with a fat-free dressing, almost no carotenoids were absorbed from a salad [4].\n\nSulforaphane needs a raw or barely cooked crucifer. Broccoli's sulforaphane forms when the enzyme myrosinase, which heat destroys, meets its precursor. Sulforaphane bioavailability was 37% from raw broccoli and 3.4% from cooked in eight men [5], and steamed broccoli gave about a third of the urinary excretion of fresh in twelve men [6]. Very gentle heat (60 °C) actually raised sulforaphane in the lab by disabling a protein that diverts the reaction [11]. Our sulforaphane page has more.\n\nSome foods need cooking. Cooked egg protein was about 91% digested, against 51% for raw [8].\n\nHigh, dry heat makes new compounds. Dry-heat cooking raised AGEs 10- to 100-fold, while vegetables, fruit, whole grains and milk stayed low even when cooked. Moist heat, shorter times, lower temperatures and acidic ingredients such as lemon juice or vinegar all reduced AGE formation [7]. See dietary AGEs and acrylamide.\n\nPutting it together. Steaming comes out best for most vegetables [9][2]. Eat a mix of raw and cooked, cook tomatoes and carrots with oil, and go easy on charring and deep-frying.","deepText":"The evidence in detail\n\nThe big picture\n\nA 2014 review of more than 100 articles found great variability. Steaming generally preserved phenols and glucosinolates best, because the food does not touch water or oil and so loses less by leaching; carotenoids behaved differently, with severe processing increasing their extraction [9]. Italian researchers cooked carrots, zucchini and broccoli by boiling, steaming and frying. Water cooking preserved antioxidants better than frying, especially carotenoids (and ascorbic acid in carrots and zucchini), and antioxidant capacity rose in all cooked vegetables on three assays; steamed vegetables kept firmer texture than boiled ones [12].\n\nFolate and vitamin C\n\nIn the folate study, typical cooking habits were set by a survey of 100 shoppers, then folate was measured by microbiological assay. Spinach fell from 191.8 to 94.4 µg/100 g when boiled and broccoli from 177.1 to 77.0 µg/100 g. Steaming (up to 4.5 minutes for spinach, 15 for broccoli) caused no significant decrease. Grilled beef (54.3 to 51.5 µg/100 g) and potatoes boiled for 60 minutes (125.1 to 102.8 µg/100 g) did not change significantly [1]. A Chinese study compared steaming, microwaving, boiling, stir-frying and stir-frying followed by boiling in broccoli: all but steaming caused significant losses of chlorophyll and vitamin C, and all but steaming significantly changed glucosinolates, with stir-frying worst [2]. Not every study agrees. The Italian work found water cooking kept ascorbic acid in carrots and zucchini better than frying [12]. Different vegetables, times and assays give different answers, so no one method is best for every food.\n\nCarotenoids\n\nIn tomatoes, trans-lycopene rose from 2.01 mg/g raw to 5.45 mg/g after 15 minutes at 88 °C and 5.32 mg/g after 30 minutes, while vitamin C fell from 0.76 to 0.54 µmol/g and total antioxidant activity rose from 4.13 to 6.70 µmol vitamin C equivalents/g [3]. In a crossover study, eight women ate about 9.3 mg of beta-carotene a day from raw or thermally processed, pureed carrots and spinach for four weeks each. Blood beta-carotene rose significantly above baseline only with the processed vegetables, and the average response was three times larger, but the raw-versus-processed difference had P = 0.09 [10]. Seven people ate salads of spinach, romaine, cherry tomatoes and carrots with dressings containing 0, 6 or 28 g of canola oil. Absorption was negligible with no fat, higher with reduced fat, and highest with the full-fat dressing [4].\n\nSulforaphane\n\nEight men ate 200 g of crushed broccoli, raw or cooked, in a crossover trial. Sulforaphane peaked in plasma at about 1.6 hours after raw broccoli and about 6 hours after cooked, with 37% versus 3.4% bioavailability (P = 0.002) [5]. In twelve men eating 200 g of fresh or steamed broccoli, the isothiocyanate content after adding myrosinase was almost identical (1.1 vs 1.0 µmol/g), yet 24-hour urinary excretion was 32.3% of the dose after fresh broccoli and 10.2% after steamed [6]. Heating whole broccoli florets to 60 °C before crushing raised sulforaphane and lowered the inactive nitrile form, paralleling the loss of a heat-sensitive protein; at 70 °C and above, formation of both fell in florets [11].\n\nProtein and AGEs\n\nFive ileostomy patients ate 25 g of isotope-labeled egg protein, cooked and raw, on separate occasions. True ileal digestibility was 90.9% for cooked and 51.3% for raw [8]. A database of dietary AGEs found dry heat increased new AGE formation more than 10- to 100-fold above the uncooked state, mainly in animal foods high in fat and protein, and moist heat, short times, low temperatures and acidic ingredients cut it [7].\n\nWhere the studies leave gaps\n\nThe human trials are tiny (5 to 12 people), crossover in design, and measure blood or urine markers, not disease. The raw-versus-processed beta-carotene result was not statistically firm. The sulforaphane authors suggested cooking \"may markedly reduce\" broccoli's benefit [6], but we found no evidence that cooked rather than raw broccoli changes disease risk, and steaming keeps glucosinolates intact. Antioxidant-capacity assays rise after cooking, yet they are lab measures, not health outcomes [12].\n\nBottom line\n\nConfidence is 4 of 5. The direction of change is consistent across a large review and several independent trials: boiling costs water-soluble vitamins, heat improves carotenoid availability, and raw or barely cooked crucifers deliver more sulforaphane. The size of each effect varies by vegetable and method, and none of it has been tied to disease outcomes.","deepTruncated":false,"references":[{"id":"1","title":"The effect of different cooking methods on folate retention in various foods that are amongst the major contributors to folate intake in the UK diet","authors":"McKillop DJ, Pentieva K, Daly D, et al.","year":2002,"journal":"Br J Nutr","pmid":"12493090","url":"https://pubmed.ncbi.nlm.nih.gov/12493090/"},{"id":"2","title":"Effects of different cooking methods on health-promoting compounds of broccoli","authors":"Yuan GF, Sun B, Yuan J, et al.","year":2009,"journal":"J Zhejiang Univ Sci B","pmid":"19650196","url":"https://pubmed.ncbi.nlm.nih.gov/19650196/"},{"id":"3","title":"Thermal processing enhances the nutritional value of tomatoes by increasing total antioxidant activity","authors":"Dewanto V, Wu X, Adom KK, et al.","year":2002,"journal":"J Agric Food Chem","pmid":"11982434","url":"https://pubmed.ncbi.nlm.nih.gov/11982434/"},{"id":"4","title":"Carotenoid bioavailability is higher from salads ingested with full-fat than with fat-reduced salad dressings as measured with electrochemical detection","authors":"Brown MJ, Ferruzzi MG, Nguyen ML, et al.","year":2004,"journal":"Am J Clin Nutr","pmid":"15277161","url":"https://pubmed.ncbi.nlm.nih.gov/15277161/"},{"id":"5","title":"Bioavailability and kinetics of sulforaphane in humans after consumption of cooked versus raw broccoli","authors":"Vermeulen M, Klöpping-Ketelaars IW, van den Berg R, et al.","year":2008,"journal":"J Agric Food Chem","pmid":"18950181","url":"https://pubmed.ncbi.nlm.nih.gov/18950181/"},{"id":"6","title":"Disposition of glucosinolates and sulforaphane in humans after ingestion of steamed and fresh broccoli","authors":"Conaway CC, Getahun SM, Liebes LL, et al.","year":2000,"journal":"Nutr Cancer","pmid":"11525594","url":"https://pubmed.ncbi.nlm.nih.gov/11525594/"},{"id":"7","title":"Advanced glycation end products in foods and a practical guide to their reduction in the diet","authors":"Uribarri J, Woodruff S, Goodman S, et al.","year":2010,"journal":"J Am Diet Assoc","pmid":"20497781","url":"https://pubmed.ncbi.nlm.nih.gov/20497781/"},{"id":"8","title":"Digestibility of cooked and raw egg protein in humans as assessed by stable isotope techniques","authors":"Evenepoel P, Geypens B, Luypaerts A, et al.","year":1998,"journal":"J Nutr","pmid":"9772141","url":"https://pubmed.ncbi.nlm.nih.gov/9772141/"},{"id":"9","title":"The effect of cooking on the phytochemical content of vegetables","authors":"Palermo M, Pellegrini N, Fogliano V","year":2014,"journal":"J Sci Food Agric","pmid":"24227349","url":"https://pubmed.ncbi.nlm.nih.gov/24227349/"},{"id":"10","title":"Bioavailability of beta-carotene is lower in raw than in processed carrots and spinach in women","authors":"Rock CL, Lovalvo JL, Emenhiser C, et al.","year":1998,"journal":"J Nutr","pmid":"9567003","url":"https://pubmed.ncbi.nlm.nih.gov/9567003/"},{"id":"11","title":"Heating decreases epithiospecifier protein activity and increases sulforaphane formation in broccoli","authors":"Matusheski NV, Juvik JA, Jeffery EH","year":2004,"journal":"Phytochemistry","pmid":"15184012","url":"https://pubmed.ncbi.nlm.nih.gov/15184012/"},{"id":"12","title":"Effects of different cooking methods on nutritional and physicochemical characteristics of selected vegetables","authors":"Miglio C, Chiavaro E, Visconti A, et al.","year":2008,"journal":"J Agric Food Chem","pmid":"18069785","url":"https://pubmed.ncbi.nlm.nih.gov/18069785/"}],"wordCount":1172,"source":{"path":"src/content/topics/cooking-methods/how-cooking-changes-nutrients.md"},"citeAs":"“Does cooking destroy nutrients: raw vs steamed vs fried?.” What's Healthy and Why. https://whatshealthyandwhy.com/cooking-methods/how-cooking-changes-nutrients","notice":"General information backed by peer-reviewed research, not medical advice."}