Friday Favorites: Are Aluminum, Stainless Steel, Cast Iron, and Teflon Safe?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

In this video I look at common cookware materials – aluminum, stainless steel, and cast iron. Watch the video to find out which might be best to use.

“Over the last decades, the toxicity of aluminum for humans has been heavily discussed and is still not completely clarified.” Those occupationally exposed to aluminum in, like, smelter plants suffer from oxidative stress (free radicals) that can damage their DNA. But what about just using aluminum cookware? Articles like this, suggesting an “unrecognized public health risk,” were limited to the developing world, where “cookware is made in informal shops by casting liquid aluminum melted from a collection of scrap metal,” including the likes of lead batteries, which is how you can get so much lead leaching into people’s food.

But then this study was published, suggesting the aluminum itself may be harmful. Most of our aluminum exposure comes from processed junk that contains aluminum-containing food additives, including those within some processed cheeses, baking powders, cake mixes, frozen dough, and pancake mixes. But approximately 20 percent of the daily intake of aluminum may come from aluminum cooking utensils, such as pans, pots, kettles, and trays. To see if this may be causing a problem, they took blood from consumers who used aluminum cookware versus those who did not, and found that not only were the aluminum users walking around with twice the level of aluminum in their blood, but they had more free radical damage of their body fats and proteins. And the total antioxidant capacity of their bloodstream was compromised; so, no surprise, they suffered significantly more DNA damage. And indeed, those with the highest levels of aluminum in their blood tended to suffer significantly more damage to their DNA. No surprise, since aluminum is considered to be a pro-oxidant agent.

These folks weren’t just casually using aluminum pots, though, but specifically using them daily to cook and store acidic foods, like yogurt and tomato sauce, which can leach out more aluminum. But even just a week using like camping dishes, which tend to be aluminum since it’s so light, if you were incorporating something acidic, like marinating a fresh catch in lemon juice, could greatly exceed the tolerable weekly intake guidelines, especially for children. Once in a while is not going to make much of a difference, but this suggests that you may not want to be cooking in aluminum day-in and day-out.

What about aluminum drinking bottles? They’re nice and light, but children drinking two cups of tea, or juice, a day from them could exceed the tolerable aluminum exposure limit. So, out of an abundance of caution, safety authorities, like the German Federal Institute for Risk Assessment, “recommend that consumers avoid the use of aluminum pots or dishes for acidic or salted foodstuffs such as apple sauce, rhubarb, tomato puree, or salt herring” to avoid any “unnecessary ingestion” of aluminum.

What about aluminum foil? “It’s a common culinary practice to wrap food in aluminum foil and bake it.” The concern is that this could potentially present “a hazardous source of aluminum in the human diet.” When put to the test, yes, there was leakage from the foil to the food, but the amount was so small that it would be more of an issue for small children, or those suffering from diminished kidney function.

What about just wrapping a food in foil to store it in the fridge? Only marginal increases in aluminum are seen— unless the food is in contact with both the foil and, at the same time, certain other types of metal, for example stainless steel, which is largely iron. And so that sets up a battery, and can lead to tremendous food aluminum concentrations. For example, here are the aluminum levels in a ham before and after a day covered in foil. But take that same ham and that same day of foil on top of a steel tray or serving plate, and the aluminum levels in the ham shoot up.

And finally, you know how there’s sometimes a glossy side of aluminum foil and then a dull side? Which would be worse? Fish fillets were baked and grilled both ways, wrapped in the glossy side versus wrapped in the dull side and…no significant difference was found.

In my last video, I expressed concerns about the use of aluminum cookware. So, what’s the best type of pots and pans to use? Stainless steel is an excellent option––the metal chosen in applications where safety and hygiene are considered to be of the utmost importance, such as kitchenware. But what about studies showing stainless steel can leach nickel and chromium into foods during cooking? (That’s what keeps the iron in the stainless steel unstained by rust.) The leaching is really only when they’re brand new. Metal leaching decreases with sequential cooking cycles and stabilizes after the sixth time you cook with it. Under more common day-to-day conditions, the use of stainless-steel pots is considered to be safe, even for most people who are acutely sensitive to those metals.

A little leaching metal can be a good thing in the case of straight iron, like a cast iron skillet, which can have the beneficial effect of helping to improve iron status, helping to potentially reduce the incidence of iron deficiency anemia among reproductive-age women and children. The only caveat is that you don’t want to be frying in cast iron. Frying isn’t healthy regardless, but at hot temperatures, vegetable oil can react with the iron to create trans fats.

What about using nonstick pans? Teflon, also known as polytetrafluoroethylene, is used as an inner coating material in nonstick cookware. Teflon’s dark history was the subject of a recent movie called Dark Waters, starring Mark Ruffalo and Anne Hathaway. Employees in DuPont’s Teflon division started giving birth to deformed babies before DuPont “removed all female staff” from the unit. Of course, they buried it all, hiding it from regulators and the public. Despite this significant history of industry knowledge about how toxic some of the chemicals used to make Teflon were, they were able to keep it all hidden. But eventually they were forced to settle for over a half a billion dollars after one of the chemicals was linked to kidney and testicular cancers, pregnancy-induced hypertension, ulcerative colitis, and high cholesterol.

“At normal cooking temperatures, [Teflon]-coated cookware releases various gases and chemicals that present mild to severe toxicity.” Here’s some of the different gases that are released at different temperatures, and the toxic effects that have been documented. You’ve heard of canaries in a coal mine? This is more like canaries in the kitchen, as cooking with Teflon cookware is well known to kill pet birds in the house; or Teflon-coated heat lamp bulbs wiping out half a chicken flock.

“Apart from the gases released during heating the cooking pans, the coating itself starts damaging after a certain period. It is normally advised to use slow heating when cooking in Teflon-coated pans,” but you can imagine how consumers might ignore that. And some of the Teflon can start chipping off if you’re not careful, and make its way into the food, though the effects of ingestion are unknown.

This is the only study I could find looking at the potential human health effects of cooking with nonstick pots and pans, and the use of nonstick cookware was associated with about a 50 percent increased risk of colorectal cancer. But that may be because of what they were cooking. Nonstick cookware is used in hazardous high-heat cooking methods, like broiling, frying, grilling, or barbecuing, mainly for meat, poultry, or fish, in which carcinogenic heterocyclic amines are formed from the animal protein. And then, the animal fat can produce another class of carcinogens, called polycyclic aromatic hydrocarbons––though it’s possible it was the Teflon itself, which contains suspected carcinogens like that C8 compound from the movie, also known as PFAO, perfluorooctanoic acid.

“Due to toxicity concerns, this chemical has been replaced with other chemicals such as GenX, but these new alternatives are also suspected to have similar toxicity.” But we’ve already so contaminated the Earth with it that now we can get it prepackaged in food before it’s even cooked––particularly in fish, dairy products, and meat, which is now the main source of human exposure to these toxic pollutants. Of those, seafood is the worst. In a study of diets from around the world, fish and seafood were major contributors of the perfluoroalkyl substances, as expected, given that everything eventually flows into the sea. Though the aquatic food chain is the primary transfer mechanism for these toxins into the human diet, “food stored or prepared in greaseproof packaging materials,” like microwave popcorn, may also be a source.

And in 2019, Oral-B Glide dental floss was tested. 6 out of 18 dental floss products they tested showed evidence of Teflon-type compounds. Here’s the list. So, did those who used those kinds of floss end up with higher levels in their bloodstream? Yes, apparently so. Higher levels of perfluorohexanesulfonic acid were found in Oral-B Glide flossers. There’s lots of environmental exposures in the modern world we can’t avoid, but we shouldn’t be making things worse by adding it to consumer products. But hey, at least it gives us some power to lower our personal exposure to these harmful chemicals.

Please consider volunteering to help out on the site.

• Ertl K, Goessler W. Aluminium in foodstuff and the influence of aluminium foil used for food preparation or short time storage. Food Addit Contam Part B Surveill. 2018;11(2):153-159.
• Samir AM, Rashed LA. Effects of occupational exposure to aluminium on some oxidative stress and DNA damage parameters. Hum Exp Toxicol. 2018;37(9):901-908.
• Weidenhamer JD, Fitzpatrick MP, Biro AM, et al. Metal exposures from aluminum cookware: An unrecognized public health risk in developing countries. Sci Total Environ. 2017;579:805-813.
• Celik H, Celik N, Kocyigit A, Dikilitas M. The relationship between plasma aluminum content, lymphocyte DNA damage, and oxidative status in persons using aluminum containers and utensils daily. Clin Biochem. 2012;45(18):1629-33.
• Stahl T, Falk S, Rohrbeck A, et al. Migration of aluminum from food contact materials to food-a health risk for consumers? Part III of III: migration of aluminum to food from camping dishes and utensils made of aluminum. Environ Sci Eur. 2017;29(1):17.
• Stahl T, Falk S, Rohrbeck A, et al. Migration of aluminum from food contact materials to food-a health risk for consumers? Part II of III: migration of aluminum from drinking bottles and moka pots made of aluminum to beverages. Environ Sci Eur. 2017;29(1):18.
• Dordevic D, Buchtova H, Jancikova S, et al. Aluminum contamination of food during culinary preparation: Case study with aluminum foil and consumers' preferences. Food Sci Nutr. 2019;7(10):3349-3360.
• Ranau R, Oehlenschläger J, Steinhart H. Aluminium levels of fish fillets baked and grilled in aluminium foil. Food Chem. 2001;73(1):1-6.
• Guarneri F, Costa C, Cannavò SP, et al. Release of nickel and chromium in common foods during cooking in 18/10 (grade 316) stainless steel pots. Contact Derm. 2017;76(1):40-48.
• Kamerud KL, Hobbie KA, Anderson KA. Stainless steel leaches nickel and chromium into foods during cooking. J Agric Food Chem. 2013;61(39):9495-501.
• Kulkarni SA, Ekbote VH, Sonawane A, Jeyakumar A, Chiplonkar SA, Khadilkar AV. Beneficial effect of iron pot cooking on iron status. Indian J Pediatr. 2013;80(12):985-9.
• Alves C, Saleh A, Alaofè H. Iron-containing cookware for the reduction of iron deficiency anemia among children and females of reproductive age in low- and middle-income countries: A systematic review. PLoS ONE. 2019;14(9):e0221094.
• Kala AL, Joshi V, Gurudutt KN. Effect of heating oils and fats in containers of different materials on their trans fatty acid content. J Sci Food Agric. 2012;92(11):2227-33.
• Sajid M, Ilyas M. PTFE-coated non-stick cookware and toxicity concerns: a perspective. Environ Sci Pollut Res Int. 2017;24(30):23436-23440.
• Richter L, Cordner A, Brown P. Non-stick science: Sixty years of research and (in)action on fluorinated compounds. Soc Stud Sci. 2018;48(5):691-714.
• Lim X. The fluorine detectives. Nature. February 13, 2019.
• Boucher M, Ehmler TJ, Bermudez AJ. Polytetrafluoroethylene gas intoxication in broiler chickens. Avian Dis. 2000;44(2):449-53.
• Kontou N, Psaltopoulou T, Soupos N, et al. The role of number of meals, coffee intake, salt and type of cookware on colorectal cancer development in the context of the Mediterranean diet. Public Health Nutr. 2013;16(5):928-35.
• Sznajder-Katarzyńska K, Surma M, Cieślik I. A Review of Perfluoroalkyl Acids (PFAAs) in terms of Sources, Applications, Human Exposure, Dietary Intake, Toxicity, Legal Regulation, and Methods of Determination. J Chem. 2019.
• Haug LS, Thomsen C, Brantsaeter AL, et al. Diet and particularly seafood are major sources of perfluorinated compounds in humans. Environ Int. 2010;36(7):772-8.
• Pérez F, Llorca M, Köck-schulmeyer M, et al. Assessment of perfluoroalkyl substances in food items at global scale. Environ Res. 2014;135:181-9.
• Vestergren R, Cousins IT. 12 - Human dietary exposure to per- and poly-fluoroalkyl substances (PFASs). In: Rose M, Fernandes A, eds. Persistent Organic Pollutants and Toxic Metals in Foods. Woodhead Publishing; 2013:279-307.
• Boronow KE, Brody JG, Schaider LA, Peaslee GF, Havas L, Cohn BA. Serum concentrations of PFASs and exposure-related behaviors in African American and non-Hispanic white women. J Expo Sci Environ Epidemiol. 2019;29(2):206-17.

Video production by Glass Entertainment

Motion graphics by Avocado Video