A look at nutrition and contamination in organic and conventional meat, milk, produce, eggs and fish. (Washington Post Photo Ilustration/Photo by Deb Lindsey for The Washington Post)

Organic or conventional? It’s a choice many grocery shoppers are faced with, over and over. The price difference is easy to see; it’s right there on the product. The quality difference is much harder. Is the organic milk better for your kids? Is the conventional lettuce more likely to carry pathogens?

Leave aside for the moment whether organic agriculture is better for the planet and whether organic livestock have better lives, although there’s a strong case for both of those arguments. Leave aside flavor, too, because it’s subjective and variable. What motivates many organic buyers, particularly the parents of small children, is health benefits, and there are two questions: Do organics do us more good (in the form of better nutrition), and do they do us less harm (in the form of fewer contaminants and pathogens)?

Because the risks and the benefits vary by product — meat is different from produce — it’s important to look at each category separately. While every category has the potential to harbor pathogens (such as E. coli in produce and salmonella in chicken), there are some product-specific concerns, including pesticide residue in produce and hormones in milk.

Here’s a rundown of the evidence on nutrition and contamination levels for organic and conventional products in five categories — milk, produce, meat, eggs and fish — to help you decide whether to buy organic or stick with conventional.


Nutrition: Compared with conventional milk, organic milk has higher levels of omega-3 fats, which protect against heart disease and may decrease the risk of depression, stroke, cancer and other diseases, but the quantities are too small to be very meaningful. (It takes 11 quarts of organic milk to equal the omega-3s in four ounces of salmon.) Milk’s omega-3 content is a function of the cow’s diet, and higher levels reflect more grass. (A few other nutritional differences between organic and conventional milk have been studied, but there isn’t enough research to draw conclusions.)

Contamination: Neither organic nor conventional milk contains antibiotics. By law, every truckload of milk, organic and conventional, is tested for veterinary drugs, including antibiotics, by trained dairy workers. Any load that tests positive is pulled out of the food supply. In 2012, that was one in 6,000 loads. Organic cows aren’t given antibiotics, and conventional ones are given them only for illness, and their milk isn’t used until after a withdrawal period.

The U.S. Department of Agriculture tests for pesticide levels and has found them to be “very low.” The main culprit is DDE, a remnant of the agricultural pesticide DDT.

DDT was banned years ago, but the USDA said it “is very persisten[t] and remains in many cropland soils. It is also in the body fat of all Americans and most farm animals and wildlife. Conventional and organic farmers can do little to avoid the DDE residues in milk. Over the next thirty to fifty years these residues will gradually decline below limits of detection.”

Pasteurization fails some of the time, allowing milk contaminated with bacteria to get into the food supply, but there are no reports comparing illnesses caused by organic vs. conventional milk.

Hormones: The issue with milk is that many conventionally raised dairy cows, unlike organic ones, are injected with bovine growth hormone (BGH, the synthetic version of which is called either recombinant bovine growth hormone, rBGH, or recombinant bovine somatotropin, rBST) to increase their milk production. The problem isn’t the hormone itself — it’s unlikely to survive pasteurization or human digestion and, even if it did, its mechanism doesn’t work in humans — but rather a compound called insulin-like growth factor (IGF-I).

Both organic and conventional cows have IGF-I in their milk, but cows that get hormone treatment may have more of it. Humans also produce IGF-I, and a recent review of many studies concluded that milk drinkers generally have higher IGF-I levels. But it may not be because of IGF-I in milk. Eating animal and soy protein can also increase IGF-I levels in our bodies. It’s not the IGF-I in foods, but how the body responds to other compounds, that increases human levels.

Some research has linked IGF-I to cancer. The American Cancer Society found that “some early studies found a relationship between blood levels of IGF-I and the development of prostate, breast, colorectal and other cancers, but later studies have failed to confirm these reports or have found weaker relationships.” The organization concluded in 2011 that “the evidence for potential harm to humans is inconclusive.” A 2009 FDA report says that IGF-I levels in rBGH milk are safe

The use of rBGH has fueled concerns among some parents about giving milk to children, but the FDA report concluded that “consumption by infants and children of milk and edible products from rBGH-treated cows is safe.”

Bottom line: Organic milk has higher omega-3 fat levels, but probably not enough to make a difference. Exposure to pesticides, contaminants or hormones is not a significant risk in either organic or conventional milk.


Nutrition: Many studies have compared the vitamins, minerals, macronutrients and other compounds in organic and conventional produce, and a 2012 review concluded that the results were all over the map. The one exception was that the phosphorus content of organic produce is higher, although the review, done by Stanford University scientists, calls that finding “not clinically significant.” Along with calcium, phosphorus helps build strong bones and teeth.

Contamination: There are two issues for foods that grow in the ground: pesticides and pathogens. There is widespread agreement that organic produce, while not pesticide-free, has lower residue levels and fewer pesticides. A study using USDA data found that 73 percent of conventional produce sampled had residue from at least one pesticide, compared with 23 percent of organic, though that study is more than 10 years old. There also isn’t agreement about whether that’s meaningful for human consumption.

Carl Winter, a toxicologist at the University of California at Davis, says that the Environmental Protection Agency, working from animal research and factoring in the special sensitivities of human subgroups such as babies and children, has found that lifetime risk of adverse health effects due to low-level exposure to pesticide residue through consumption of produce is “far below even minimal health concerns, even over a lifetime.”

Dana Barr, a research professor at Emory University’s Rollins School of Public Health, has less faith in the EPA standards. She points to one particular pesticide class, organophosphates, and notes evidence — including a 2013 review she co-authored — correlating exposure to possible neurological problems such as ADHD and lower IQ in children, which she says the EPA standards don’t adequately consider.

But another review last year by a different group of scientists found “the epidemiologic studies did not strongly implicate any particular pesticide as being causally related to adverse neurodevelopmental outcomes in infants and children.” As of December 2013, the position of the Centers for Disease Control and Prevention was that high levels of organophosphate exposure were associated with some neurobehavioral problems in farm communities with exposure higher than that in the general population.

An American Academy of Pediatrics 2012 report noted the correlation between organophosphate exposure and neurological issues that had been found in some studies but concluded that it was still “unclear” that reducing exposure by eating organic would be “clinically relevant.”

The EPA expects to have a new assessment of organophosphates in 2016. In the meantime, the agency has determined that certain foods —snap beans, watermelon, tomatoes and potatoes — are likely to have higher residues of the pesticide than other produce. If you’re pregnant or feeding small children, you may want to consider organic versions of those foods.

As for pathogens, the 2012 Stanford review found that E. coli contamination is slightly more likely in organic than conventional produce.

The best strategy to reduce risk from produce isn’t to buy either organic or conventional. Rather, it’s to cook your food. A CDC review notes that leafy vegetables, led by lettuce and spinach, are the No. 1 cause of food-borne illnesses, responsible for 22 percent of food-borne illnesses.

Bottom line: While there may be no significant nutritional difference between organic and conventional produce, organic does have lower levels of pesticide residue. However, there isn’t universal agreement on the risk those residues pose.


Nutrition: As with milk, the main issue here is omega-3 fats. Some organic meat and poultry have more of them than conventional products do. The reason is diet: Animals that eat more grass have lower fat levels overall and higher omega-3 levels than animals fed more grain.

Although measurements of omega-3 fats in beef vary, the numbers are low and substantially below what can be found in a serving of salmon.

Contaminants: The USDA randomly tests carcasses for residues of pesticides, contaminants and veterinary drugs including antibiotics. In 2011, it screened for 128 chemicals, and 99 percent of the tested carcasses were free of all of them.

It found a few with residue violations and a similar small number with residue within legal limits (mostly of arsenic and antibiotics). Although the USDA doesn’t report organic and conventional separately, contaminant risk overall is extremely low.

The bigger concern is pathogens. Studies of bacterial contamination levels of organic and conventional meat show widely varying results. These findings suggest that organic meat may be slightly more likely to be contaminated, possibly because no antibiotics are used. But conventional meat is more likely to be contaminated with antibiotic-resistant bacteria. The 2012 Stanford review found that slightly more organic chicken samples were contaminated with Campylobacter than conventional samples and that organic pork was more likely than conventional to harbor E. coli. But the risk in meat overall was essentially the same. And whether meat is conventional or organic, the solution is adequate cooking.

Bottom line: There doesn’t seem to be much difference, health-wise, between organic or conventional meats. Grass-fed beef has a slight edge over grain-fed because of higher omega-3 levels, but the amounts are probably too small to affect human health.


Nutrition: As with milk and meat, the omega-3 levels of eggs are affected by the hens’ diet and can be increased by pasturing or diet supplementation for either organic or conventional hens. Eggs high in omega-3s are generally labeled.

Contaminants: There’s very little research on contaminants in eggs. The USDA’s 2011 National Residue Program tested 497 egg samples and found no residues of pesticides, contaminants or veterinary drugs, including antibiotics. This isn’t surprising because, according to Pat Curtis, a poultry scientist at Auburn University, laying hens aren’t routinely given antibiotics, and there is a mandated withdrawal period after they do get the drugs (to treat illness) before their eggs can be sold. The 2012 Stanford review concluded that there is “no difference” in contamination risk between conventional and organic eggs.

Bottom line: There are no significant differences affecting health between organic and conventional eggs.


The USDA has not issued any organic standards for farmed fish or shellfish, but several overseas organizations have. (Because there’s no way to control the diet of wild fish, “organic” doesn’t apply.) Canadian standards prohibit antibiotics and hormones, restrict pesticides and set criteria for acceptable feed. There’s not enough research comparing organic and conventional fish to draw any conclusions about their health benefits.

Haspel writes regularly for The Post’s health and food sections. Follow her on Twitter: @TamarHaspel.