Many common foods contain hormones, either naturally produced by the animal or plant, added during production, or present as hormone-mimicking compounds. The main categories are dairy products, conventional beef, soy and other plant foods, and to a lesser extent, fish exposed to environmental contaminants. The amounts are generally small, and your body’s own hormone-regulation systems appear to keep dietary hormones from meaningfully shifting your blood levels.
Dairy Products
Cow’s milk naturally contains several hormones because it comes from a lactating animal. These include estrogen, progesterone, and insulin-like growth factor 1 (IGF-1), a protein hormone involved in growth. Surveys of bulk milk tanks from farms that don’t use any supplemental growth hormones have found IGF-1 concentrations averaging around 2.5 to 4.3 nanograms per milliliter. To put that in perspective, your body produces far more IGF-1 on its own than you’d ever get from a glass of milk, and IGF-1 is largely broken down during digestion.
Some dairy farms also use recombinant bovine growth hormone (rBGH), a synthetic version of a hormone cows produce naturally, to boost milk production. A 2014 USDA survey found that fewer than 1 in 6 cows in the U.S. were being injected with rBGH. The use has declined significantly as major retailers and dairy brands have moved away from it, and many milk labels now carry “rBGH-free” or “rBST-free” claims. Canada, the European Union, and several other countries have banned rBGH entirely.
Beef and Growth Hormones
Conventional beef production in the U.S. commonly uses hormone implants to help cattle grow faster. The FDA has approved both natural steroid hormones (estradiol, progesterone, and testosterone) and synthetic versions (trenbolone acetate and zeranol) for use in beef cattle. These small pellets are implanted under the skin of the ear, which is discarded at slaughter.
The FDA sets safe residue limits for these hormones in meat, based on the principle that the trace amounts remaining in beef at slaughter should have no harmful effect on people. A 3-ounce serving of beef from a treated animal contains only slightly more estrogen than the same cut from an untreated animal, and both contain far less estrogen than your body produces daily. Still, the European Union has banned imports of hormone-treated beef since the 1980s, citing a precautionary approach. A World Trade Organization panel ruled that the EU ban was not supported by the EU’s own risk assessments, but the ban remains in place.
If you want to avoid added hormones in beef, look for labels that say “no hormones administered.” USDA-certified organic beef also prohibits hormone use.
Chicken, Turkey, and Pork
Despite what many people assume, added hormones are not used in poultry production. Federal regulations prohibit giving hormones to chickens and turkeys, so any “hormone-free” label on poultry is technically true of all poultry. It’s a marketing distinction, not a meaningful one.
Pork has a slightly more complicated history. For years, the USDA required pork labels making “no hormone” claims to include a disclaimer stating that federal regulations prohibit hormones in swine. That disclaimer was updated in 2020 because there are now FDA-approved hormones for limited use in pigs during gestation. In practice, hormone use in pork production remains minimal compared to the beef industry, but it’s no longer accurate to say hormones are completely banned in swine.
Soy Foods and Phytoestrogens
Soy foods don’t contain animal hormones, but they do contain isoflavones, plant compounds that are structurally similar enough to estrogen to weakly interact with estrogen receptors in the body. These are often called phytoestrogens. The two main isoflavones in soy are genistein and daidzein.
The amounts vary dramatically depending on the food. According to the USDA’s isoflavone database, here’s what 100 grams (roughly 3.5 ounces) of common soy foods contain in combined isoflavones:
- Tempeh: about 59 mg total (22.7 mg daidzein, 36.2 mg genistein)
- Firm tofu: about 21 to 28 mg total, depending on preparation
- Silken tofu: about 17 to 29 mg total
- Soy milk: about 8 to 11 mg total for regular versions, dropping to under 2 mg for low-fat or nonfat varieties
Phytoestrogens are far weaker than human estrogen. They can bind to the same receptors but produce a much smaller effect, and in some tissues they may actually block stronger estrogens from binding. This is why soy research has produced mixed and sometimes contradictory findings. Eating normal amounts of soy foods is not the same as taking estrogen.
Flaxseeds, Sesame Seeds, and Other Plants
Soy gets the most attention, but other plant foods contain their own class of phytoestrogens called lignans. Flaxseeds are the richest dietary source by a wide margin. One ounce of flaxseeds contains about 85.5 mg of lignans. Sesame seeds come in a distant second at 11.2 mg per ounce. Most vegetables contain only trace amounts: half a cup of chopped curly kale, for example, has just 0.8 mg.
Lignans are converted by gut bacteria into compounds that can weakly mimic estrogen, similar to soy isoflavones. Crushing or milling flaxseeds improves how well your body can access these compounds. Whole flaxseeds often pass through the digestive tract intact.
Fish and Environmental Contaminants
Fish don’t naturally contain hormones in amounts relevant to human health, but wild-caught fish from contaminated waterways can accumulate hormone-mimicking chemicals from the environment. Aquatic environments act as reservoirs for endocrine disruptors, compounds that interfere with hormonal systems. Two of the most studied are BPA (from plastics manufacturing) and synthetic estrogen from oral contraceptives, which enters waterways through wastewater treatment plants. An estimated 16 to 68 percent of each dose of synthetic estrogen from birth control pills is excreted from the body and can end up in water systems.
U.S. Geological Survey research has shown that fish exposed to these chemicals can pass reproductive effects to offspring up to three generations later. For consumers, the concentrations in fish you’d buy at a grocery store are generally very low, but this is one reason health agencies monitor contaminant levels in commercial and recreational fisheries.
Do Food Hormones Affect Your Body?
The practical question behind this search is whether eating these foods will change your own hormone levels. The best available evidence suggests the answer is no, at least not in a meaningful way. A review of dietary intervention studies found that changes in food composition did not produce significant shifts in circulating sex hormone levels in men. Your body maintains hormone balance through a negative feedback system: when hormone levels drift slightly in one direction, your endocrine system compensates to bring them back to baseline.
Most hormones consumed through food are proteins or steroids that get broken down during digestion, reducing their biological activity well before they could reach your bloodstream in significant amounts. The research on phytoestrogens and human hormone levels is still limited, but routine consumption of soy foods in the amounts typical of Asian diets (which are far higher than the average Western diet) has not been linked to clinically significant hormonal disruption in large population studies.
The hormones naturally present in food exist in quantities that are tiny compared to what your own body produces every day. A adult man produces roughly 136,000 nanograms of estrogen daily, while a nonpregnant woman produces several hundred thousand. A glass of milk or a serving of beef contributes a fraction of a nanogram.