How you cook changes what you eat, so steam more and char less

Key takeaways

• In a 1991 U.S. study, spaghetti sauce cooked in an iron pot held about 2.1 milligrams of iron per 100 grams, compared with 0.44 milligrams from a non-iron pot¹.
• In a 2009 broccoli study, steaming was the only one of five methods that didn’t cause a significant loss of vitamin C².
• The FDA says to fry potatoes to golden yellow rather than brown and to toast bread light brown, because darker browning means more acrylamide⁶.
• In one lab test, an air fryer used 10 grams of oil for 250 grams of potatoes while a deep fryer held 500 milliliters, but studies disagree on whether air fryers make less acrylamide⁷⁸.
• When you grill, the National Cancer Institute suggests microwaving meat first, turning it often and cutting off charred bits¹⁰.

Simmer spaghetti sauce in a cast-iron pot, and the pot becomes an ingredient.

In a 1991 U.S. study, sauce cooked in an iron pot held 2.10 milligrams of iron per 100 grams. The same sauce from a non-iron pot held 0.44 milligrams¹. That’s almost five times as much iron, and no one added a supplement.

Every cooking method makes trades like that. Water pulls some vitamins out of vegetables. Heat frees other nutrients. Browning starchy food and charring meat create compounds that scientists have studied for decades and still argue about.

People who cook from scratch already choose what goes in. This guide shows how the pot, the heat and the clock change what comes out.

Water and time pull vitamins out, and steam pulls out the least

Researchers in China cooked broccoli five ways for a study published in 2009 in the Journal of Zhejiang University SCIENCE B: steaming, microwaving, boiling, stir-frying, and stir-frying followed by boiling².

Every method except steaming caused a significant loss of vitamin C and chlorophyll, the green pigment². Steaming also left glucosinolates, natural sulfur compounds that scientists study for possible health effects, without a significant change². Stir-frying, alone or followed by boiling, caused the biggest glucosinolate losses².

The authors judged steaming best for keeping broccoli’s nutrients². It was one lab study of one vegetable, so treat it as a guide, not a rule. Steam green vegetables until bright and just tender. If you boil, use less water and less time, and save the water for soup.

Heat frees some nutrients, and a little fat helps you absorb them

Cooking doesn’t only take. In a 2013 study in the International Journal of Food Sciences and Nutrition, heating broccoli lowered its glucosinolates, and the losses grew with longer cooking³. Yet heating raised the measured levels of lutein and beta-carotene, plant pigments called carotenoids, along with two forms of vitamin E³. Longer heating made them easier to extract³.

That study measured what chemists could pull out of broccoli in a lab, not what people absorbed. Absorption is where fat comes in.

In a 2017 study in the American Journal of Clinical Nutrition, 12 healthy women ate salads with dressings holding anywhere from 0 to 32 grams of soybean oil, the top amount a bit over 2 tablespoons by our math⁴. More oil generally meant more carotenoids reached their blood. For beta-carotene, the steady rise held only up to about 8 grams⁴.

People varied widely⁴. Unilever funded the study and made the dressings; the authors said the company didn’t run the study or write the paper, though it hired a consultant for one analysis⁴.

The practical answer is a mix: some vegetables raw or lightly steamed for vitamin C, some cooked longer in soups and stews, and a little oil or other fat on the plate.

Heat does a safety job for dried beans, too. Beans contain lectins, natural proteins our legume guide explains in detail. In a small 2014 study from India, cooking cut the lectin activity of red kidney beans by about 91%, and pressure cooking soaked beans destroyed it completely⁵. It’s one small study, but it backs the pressure cooker as a good tool for soaked beans.

Browning potatoes and bread makes acrylamide. Aim for golden

Acrylamide is a chemical that can form when food is fried, roasted or baked. According to the Food and Drug Administration (FDA), it comes from natural sugars and an amino acid called asparagine in the food itself, not from packaging⁶.

Most of it comes from plant foods cooked hot and dry: potato products like fries and chips, coffee, and grain foods such as breakfast cereal, cookies and toast⁶. Meat, dairy and seafood aren’t usual sources, and raw, steamed or boiled foods don’t contain it⁶.

How worried should you be? The International Agency for Research on Cancer (IARC) classed acrylamide in 1994 as probably carcinogenic to humans⁷. In lab animals it caused cancer, but at doses far higher than people get from food, and the FDA is still studying whether food levels pose a risk to people⁶.

The FDA doesn’t tell people to stop eating these foods, and it specifically does not recommend cutting back on healthful grains such as whole-grain cereal⁶. Instead, it offers kitchen steps⁶:

• Fry or roast cut potatoes to golden yellow, not brown. Brown areas tend to hold more acrylamide.
• Toast bread light brown. Very brown spots hold the most.
• Soak raw potato slices in water for 15 to 30 minutes before frying or roasting, then drain and blot them dry.
• Store potatoes in a cool, dark place, not the fridge. Chilling raw potatoes can raise acrylamide when they’re cooked.

Longer and hotter cooking makes more, and the method matters a lot. In FDA’s ranking for potatoes, frying makes the most, roasting cut pieces less, and baking whole potatoes less still. Boiling potatoes, or microwaving them whole with the skin on, makes none⁶.

Air fryers cut the oil, but whether they cut acrylamide is unsettled

The oil savings from air fryers are real. In one 2024 test, cooks tossed 250 grams of potatoes with about 10 grams of oil for the air fryer, while the deep fryer held 500 milliliters⁷.

Acrylamide is murkier. Two lab studies in the journal Frontiers in Nutrition point different ways:

• Lower: A 2022 study found air frying cut acrylamide in fries by up to 47% compared with deep frying⁸. Levels climbed as air-frying temperature and time went up⁸.
• No difference: A 2024 study tested 24 samples of homemade potato sticks. Air-fried, deep-fried and oven-fried potatoes didn’t differ significantly in acrylamide⁷. A 10-minute soak sharply lowered acrylamide in the deep-fried batches⁷.

The 2024 team noted wide variation in its results⁷, and neither study looked at people’s health.

The fair reading: an air fryer is a good way to use less oil, not a pass to cook fries dark. The FDA’s golden-yellow rule and a quick soak apply whatever machine you use⁶⁷.

Grilled meat: the char is the part to cut

When muscle meat (beef, pork, poultry or fish) meets high heat, two families of compounds form, according to the National Cancer Institute (NCI)¹⁰. Heterocyclic amines, or HCAs, form when amino acids, sugars and creatine in muscle react at high temperatures¹⁰. Polycyclic aromatic hydrocarbons, or PAHs, form when fat and juices drip onto a flame or hot surface and smoke coats the meat; smoked meats get them too¹⁰.

Both are mutagenic in the lab, meaning they can change DNA in ways that may raise cancer risk¹⁰. Cooking above about 300°F, as in grilling and pan-frying, and cooking for a long time make more HCAs¹⁰. Well-done, grilled or barbecued chicken and steak carry high amounts¹⁰.

The human evidence is unsettled. Rodents fed HCAs developed tumors, but at doses thousands of times what a person eats¹⁰. Some population studies link lots of well-done, fried or barbecued meat to colorectal, pancreatic and prostate cancer, while others find no link¹⁰. NCI says no definitive link has been shown in people, and no federal guidelines limit HCA or PAH intake¹⁰.

That’s a reason to cook smarter, not to give up the grill. Undercooked meat can carry germs and overcooked meat carries more HCAs, so a thermometer lets you stop at the safe point.

A lower-risk grilling checklist

1. Precook in the microwave to cut the time meat spends over high heat¹⁰. Move it straight to the grill, since partly cooked raw meat shouldn’t sit and wait¹².
2. Keep meat off direct flame and avoid long cooking at very high heat¹⁰.
3. Turn it often. NCI says flipping meat again and again on high heat can substantially reduce HCAs¹⁰.
4. Try a marinade. In a 1997 Lawrence Livermore National Laboratory study, chicken breasts soaked for 4 hours in a mix of brown sugar, olive oil, cider vinegar, garlic, mustard, lemon juice and salt formed more than 87% less of two major HCAs on the grill than plain chicken¹¹. Store-bought marinades and single ingredients worked similarly¹¹.
5. Cut off charred pieces before serving, and skip gravy made from the drippings¹⁰.
6. Use a food thermometer instead of cooking until dark. Safe minimums: 145°F with a 3-minute rest for whole cuts of beef, pork and lamb; 160°F for ground meat; 165°F for poultry; 145°F for fish¹².
7. Fill half the grill with vegetables. NCI says HCAs aren’t found in significant amounts in foods other than meat cooked at high temperatures¹⁰.

Microwaves don’t make food radioactive. They do leave cold spots

Australia’s radiation safety agency, ARPANSA, explains that microwaves heat food by making its water molecules vibrate¹³. The waves stop the moment the power goes off, and they don’t make food or the oven radioactive¹³.

Microwaving can affect some nutrients in its own way, the agency says, but it has seen no sign that microwaved food harms health¹³.

The real microwave risk is uneven heating. Clemson University Cooperative Extension warns that microwaves leave cold spots where bacteria can survive¹². Cover the dish, stir or rotate it partway through, let it stand a few minutes, and check several spots with a thermometer¹².

Containers matter too. Glass, ceramic without metal trim and plastic labeled microwave-safe are fine¹². Margarine tubs, yogurt cups and whipped-topping bowls not labeled for microwave use can warp or melt and let chemicals move into food¹². Later articles on plastics go deeper.

Your pan is part of the recipe

Cast iron adds iron. The review behind the spaghetti sauce example gathered 13 studies from eight countries¹. Food cooked in iron pots picked up iron again and again, especially acidic and moist dishes like sauces, soups and pastes¹.

Whether that fixes anemia is less clear. In an Ethiopian trial of 407 young children, iron-deficiency anemia fell from 57% to 13% after a year of family meals cooked in iron pots¹.

But only four of nine trials found a significant rise in hemoglobin, the iron-carrying protein in blood¹. In Cambodian women, only one of three trials found a significant rise¹. The review’s authors called the research very limited¹.

If you’re short on iron, cast iron is a cheap, traditional helper, not a treatment. If a clinician has told you to limit iron, for example because of an iron-overload condition, ask before you switch all your cooking to iron.

Nonstick pans face a patchwork of new state laws. Many nonstick coatings are made with PFAS, “forever chemicals” that don’t break down in the environment or the body and have been tied to health harms¹⁴. Minnesota became the first state to ban PFAS in cookware, February 2025 reporting said¹⁵. By July 2026, Maine’s sales ban on many products with intentionally added PFAS, nonstick pans included, had taken effect; Colorado also had a ban, and Connecticut’s is set to begin in 2028¹⁴.

These laws are new, contested and changing, so check your state’s rules. In 2025, the Cookware Sustainability Alliance was suing Minnesota, arguing that PTFE, the type of PFAS in most nonstick cookware, is safe and approved by the FDA¹⁵. Ban supporters counter that fumes from an overheated pan can be harmful, and that the coating’s maker warns owners to keep pet birds out of the kitchen because of fumes¹⁵.

Anne Sedlack of the Maine Medical Association has said high heat, abrasive cleaners and chipped coatings can raise exposure¹⁴. So if you keep nonstick pans, use low to medium heat, don’t heat them empty, skip scouring pads and retire chipped ones. Lead in some imported cookware is a separate danger, covered in our article on cutting toxic exposures.

A method-by-method guide

Ratings use the library’s four-level evidence scale and describe the effect in the middle column.

Method	Good for	What it does to food	Safety tip	Evidence rating
Steaming	Green vegetables, fish	Kept vitamin C and glucosinolates best in broccoli2	Cook just until tender	Promising but early
Boiling	Potatoes, grains, beans	Vitamin C lost to water2; no acrylamide in potatoes6	Use less water; save it for soup	Promising but early
Microwaving	Vegetables, reheating, precooking meat	Lost vitamin C in broccoli2; no acrylamide in whole potatoes6	Cover, stir, let stand, check temperature12	Promising but early
Longer cooking of vegetables	Soups, stews	Raised extractable carotenoids and vitamin E3	Add a little fat4; pair with raw or steamed produce	Promising but early
Pressure cooking	Dried beans, stews	Destroyed bean lectin activity in one small study5	Soak beans first; follow the cooker’s directions	Promising but early
Roasting, baking, toasting	Potatoes, bread	Acrylamide rises as browning deepens6	Stop at golden; soak potatoes first6	Strong evidence
Deep frying	Occasional treats	Most acrylamide of any potato method6	Golden, not brown; retire oil that smokes or darkens69	Strong evidence
Air frying	Fries, crisp vegetables	Acrylamide results conflict78; uses far less oil7	Same golden rule	Not enough evidence
Grilling, pan-frying meat	Steaks, burgers, chicken	HCAs and PAHs form with high heat and smoke10	Precook, marinate, flip often, trim char1011	Strong evidence
Simmering in cast iron	Tomato sauce, stews, beans	Adds iron, most in acidic, moist dishes1	Ask a clinician if you must limit iron	Strong evidence

How strong is the evidence for the big claims?

Claim	Evidence level	What the research shows
Iron pots treat or prevent anemia	Promising but early	Four of nine trials found hemoglobin gains1
More oil in a salad dressing means more carotenoids absorbed	Promising but early	One small, company-funded dose study; people varied widely4
Marinating chicken before grilling cuts HCAs	Promising but early	Large drops in lab tests of grilled chicken11
Acrylamide at food levels causes cancer in people	Not enough evidence	Cancer seen in animals at far higher doses; FDA still studying6
Air frying makes less acrylamide than deep frying	Not enough evidence	Small lab studies disagree78
Charred, well-done meat causes cancer in people	Not enough evidence	Animal tumors at huge doses; human studies mixed10
Microwaved food becomes radioactive	Evidence says no, or unsafe	Microwaves stop when the power goes off13

Questions readers ask

The bottom line

How you cook is a set of trades. Steaming protects vitamin C, longer cooking frees carotenoids, a little fat helps you absorb them, and cast iron adds iron. Browned potatoes and bread and charred meat carry compounds worth limiting, even though harm at normal intakes isn’t proven.

You don’t need special gadgets. Steam more, stop at golden, marinate and flip the meat, trim the char, use a thermometer, and treat the air fryer and the cast-iron pan as useful tools rather than cures.

Related reading

• Frozen peas and candy bars are both processed, and the difference matters
• Cooked beans are cheap and well studied, and the lectin scare applies to raw ones
• A stockpot of chili took a day to cool, so batch cook the safer way
• Children’s blood lead levels fell 96% without help from any detox product
• Most adults eat too few vegetables, and five a day can cost under $3

Sources

1. Sharma S, Khandelwal R, Yadav K, Ramaswamy G, Vohra K. “Effect of Cooking Food in Iron-Containing Cookware on Increase in Blood Hemoglobin Level and Iron Content of the Food: A Systematic Review.” Nepal Journal of Epidemiology, 2021;11(2):994–1005. pmc.ncbi.nlm.nih.gov
2. Yuan G, Sun B, Yuan J, Wang Q. “Effects of Different Cooking Methods on Health-Promoting Compounds of Broccoli.” Journal of Zhejiang University SCIENCE B, 2009;10(8):580–588. zjujournals.com
3. “Effects of Various Heating Methods on Glucosinolate, Carotenoid and Tocopherol Concentrations in Broccoli.” International Journal of Food Sciences and Nutrition, 2013;64(1):103–111 (abstract on PubMed). pubmed.ncbi.nlm.nih.gov
4. White WS, Zhou Y, Crane A, Dixon P, Quadt F, Flendrig LM. “Modeling the Dose Effects of Soybean Oil in Salad Dressing on Carotenoid and Fat-Soluble Vitamin Bioavailability in Salad Vegetables.” American Journal of Clinical Nutrition, 2017;106(4):1041–1051. pmc.ncbi.nlm.nih.gov
5. Vasishtha H, Srivastava RP. “Effect of Soaking and Cooking on Dietary Fibre, Protein and Lectins of Rajmash (Phaseolus vulgaris) Beans.” Indian Journal of Agricultural Biochemistry, 2014;27(2):219–222 (abstract via FAO AGRIS). agris.fao.org
6. U.S. Food and Drug Administration. “Acrylamide and Diet, Food Storage, and Food Preparation.” FDA, content current as of March 5, 2024. fda.gov
7. Navruz-Varlı S, Mortaş H. “Acrylamide Formation in Air-Fried Versus Deep and Oven-Fried Potatoes.” Frontiers in Nutrition, 2024;10:1297069. frontiersin.org
8. Dong L, Qiu C, Wang R, et al. “Effects of Air Frying on French Fries: The Indication Role of Physicochemical Properties on the Formation of Maillard Hazards, and the Changes of Starch Digestibility.” Frontiers in Nutrition, 2022;9:889901. public-pages-files-2025.frontiersin.org
9. Food Safety and Standards Authority of India. “Handling and Disposal of Used Cooking Oil” (Guidance Note No. 06/2018). FSSAI, 2018. eastregion.fssai.gov.in
10. National Cancer Institute. “Chemicals in Meat Cooked at High Temperatures and Cancer Risk.” NCI, reviewed July 11, 2017. cancer.gov
11. Lawrence Livermore National Laboratory, Biology and Biotechnology Research Program. Research summary of Salmon CP, Knize MG, Felton JS, “Effects of Marinating on Heterocyclic Amine Carcinogen Formation in Grilled Chicken,” Food and Chemical Toxicology, 1997;35:433–441. LLNL web page, 1997 (archived copy). pubmed.ncbi.nlm.nih.gov
12. Clemson Cooperative Extension Home & Garden Information Center. “Microwave Food Safety” (HGIC 3586). Clemson University, updated June 30, 2026. hgic.clemson.edu
13. Australian Radiation Protection and Nuclear Safety Agency. “Microwave Ovens.” ARPANSA, undated. arpansa.gov.au
14. Budion K. “Want to Know if Your Nonstick Pan Contains PFAS? A New Searchable Database Has the Answer.” Maine Morning Star, republished by News From The States, July 24, 2026. newsfromthestates.com
15. ConsumerAffairs. “Minnesota Becomes First State to Ban PFAS in Cookware.” ConsumerAffairs, February 12, 2025. consumeraffairs.com