There's a concerning chemical in most canned goods.
And there's a good reason why we all stock up—canned foods are a staple for meal prep and cheap cooking, and they’re a super-simple way to get more produce and fish—foods all of us could stand to eat more of, says New York-based nutritionist Karen Ansel, R.D. “Canned tomatoes, beans, pumpkin, tuna, and salmon are incredibly healthy. And they’re super convenient because they have such a long shelf life,” she says.
What’s more, although it might seem like canned foods have less nutrients than their fresh counterparts, the canning process doesn’t affect foods’ protein, carbohydrate, and fat content, or the amount of minerals and fat-soluble vitamins (like A, D, E and K). But because canning involves high heat, some water-soluble vitamins (like C and B) can be damaged—although losses vary from food to food, says Ansel.
That said, there are some risks that come with consuming canned foods. Experts’ number-one concern: the cans themselves. “Many cans contain BPA, a chemical that can affect certain hormones and may potentially increase blood pressure, cancer risk, and lead to behavioral issues,” says Ansel.
An estrogen-mimicking chemical, BPA has been used since the 1960s in canned food coatings to keep the metal from rusting. Problem is, the chemical leaches into food and drinks. While the full effects of BPA are still unknown and most studies have been done on animals, many doctors and scientists are concerned that it can change the way the sex hormones estrogen and testosterone work in the body, which may affect the reproductive system and brain.
There is indeed evidence BPA can disrupt the brain and hormonal systems. A 2016 study in the journal Clinical Endocrinology found that BPA may be linked to insulin resistance and obesity in women. A 2017 study in rats found that low-level exposure to BPA during pregnancy might change the way the body processes signals from hunger hormones—which could mess with the brain’s ability to understand signals of hunger and satiety. Other researchhas even linked high levels of exposure to breast cancer and metabolic disorders including polycystic ovarian syndrome (PCOS).
The greatest concern, however, is about BPA exposure during pregnancy. “In humans, BPA exposure when the fetus is developing may increase the risk for behavior issues (like hyperactivity and aggression), later breast development during puberty, obesity, diabetes, heart disease, and changes in liver function,” says Maida P. Galvez, M.D. and associate professor at the Department of Environmental Medicine and Public Health & Pediatrics at the Icahn School of Medicine at Mount Sinai.
Although BPA is present in lots of places including dental sealants, medical equipment, consumer electronics, and cash-register receipts, our main source of exposure is the foods we eat, according to the National Institute of Environmental Health Sciences (NIEHS). A 2016 Johns Hopkins study found that people who ate just one canned food item in a day saw increased urinary concentrations of BPA by 24 percent compared with consuming no canned foods; two or more cans of food increased BPA concentrations by 54 percent.
The FDA’s last guidelines on BPA, published in 2008, put the daily upper limit of safe exposure at 50 micrograms of BPA per kilogram of body weight. But experts say those recommendations are outdated and should be much lower. Galvez points to a report from the EPA, which says that some animal studies have found that doses lower than 1 milligram and as low as 2 micrograms per kg of body weight per day can potentially have negative effects.
The FDA says it’s still investigating the risks and safety of BPA. It’s since banned BPA from baby bottles, sippy cups, and infant formula. In 2014, however, the FDA published a review of more than 300 studies that concluded no changes need to be made to its current recommendations. The Environmental Working Group, among others, is calling on the FDA to set a safe limit of exposure of no more than 1 part per billion (ppb). “Why do we continue to use a lining that poses potential concerns to human health? Pre-market safety testing, transparency in food labeling, and assurance that alternatives are in fact safer are critically needed,” says Galvez.
For now, BPA is still pervasive in canned foods. A 2016 report found two out of three cans tested in the U.S. contained BPA. So just about all of us are exposed: BPA is detectable in the urine of over 90 percent of Americans, according to research published in 2007 by the Centers for Disease Control and Prevention.
In an ideal world, it would be easy to avoid all BPA all the time—but unfortunately that’s just not possible given how prevalent it is. “Our general advice to families is to buy fresh or frozen fruits and vegetables when possible. Avoid canned and processed foods,” says Galvez. She points to research that’s found it’s possible to reduce BPA levels in the body by opting for fresh, non-processed foods over canned. Keep in mind that the amount of BPA you’re exposed to also varies quite a bit depending on the food. In 2009, Consumer Reports tested 19 brand-name foods including soups, juice, tuna, and veggies to determine their BPA levels. The worst offenders were canned green beans and canned soup.
Aside from the potential risks of BPA, Ansel notes that many canned foods are also high in sodium. Overconsumption of sodium of course comes with the side effects of bloating and water retention (although its link to high blood pressure and other scary health consequences is under debate). So read the nutrition label, compare brands, and choose no or low-sodium options when possible. If low-salt’s not available, many nutritionists recommend aiming to keep sodium to 500 mg per serving and rinsing canned foods like beans, which can reduce their sodium by 40 percent. And since tuna, specifically, contains some mercury, the FDA recommends keeping servings to three per week max of canned light tuna or one serving of canned albacore.
But while there are definitely downsides to canned foods, Ansel says they’re an easy, cheap way to get your greens. “I wouldn’t recommend eating a diet that’s entirely made of canned foods,” says Ansel. “But I wouldn’t be concerned about eating a serving of canned food a day if it helps you work in more healthy foods like beans and veggies, especially since few of us are eating enough of these foods to begin with.”
If you're truly concerned about BPA, look for BPA-free cans where possible and avoid canned goods otherwise. (Even BPA-free cans, according to the 2009 Consumer Reports paper, leached low levels of BPA into foods, but at much lower levels than other options—from 20 ppb in tuna in to 1 ppb in baked beans.) Check the label or the EWG’s searchable database, which notes whether products contain BPA in the packaging.