You may have heard claims that some common foods or ingredients are "toxic." Fortunately, most of these claims are not supported by science.
However, there are a few that may be harmful, particularly when consumed in large amounts.
Here is a list of 7 "toxins" in food that are actually concerning.
1. Refined Vegetable and Seed Oils
Refined vegetable- and seed oils include corn, sunflower, safflower, soybean and cottonseed oils.
Years ago, people were urged to replace saturated fats with vegetable oils to reduce their cholesterol levels and help prevent heart disease.
However, a lot of evidence suggests that these oils actually cause harm when consumed in excess (1).
Vegetable oils are highly refined products with no essential nutrients. In that respect, they are "empty" calories.
They're high in polyunsaturated omega-6 fats, which contain multiple double bonds that are prone to damage and rancidity when exposed to light or air.
These oils are particularly high in omega-6 linoleic acid. While you do need some linoleic acid, most people today are eating much more than they need.
On the other hand, most people don't consume enough omega-3 fatty acids to maintain a proper balance between these fats.
Observational studies found that women with the highest intakes of omega-6 fats and lowest intakes of omega-3 fats had an 87–92% greater risk of breast cancer than those with more balanced intakes (8, 9).
What's more, cooking with vegetable oils is even worse than using them at room temperature. When they're heated, they release harmful compounds that may further increase the risk of heart disease, cancer and inflammatory diseases (10, 11).
Although the evidence on vegetable oil is mixed, many controlled trials suggest that they are harmful.
Bottom Line: Processed vegetable and seed oils contain omega-6 fats. Most people are eating too much of these fats already, which may lead to several health problems.
Bisphenol-A (BPA) is a chemical found in the plastic containers of many common foods and beverages.
The main food sources are bottled water, packaged foods and canned items, such as fish, chicken, beans and vegetables.
Studies have shown that BPA can leech out of these containers and into the food or beverage (12).
Researchers have reported that food sources make the biggest contribution to BPA levels in the body, which can be determined by measuring BPA in urine (13).
One study found BPA in 63 of 105 samples of food, including fresh turkey and canned infant formula (14).
BPA is believed to mimic estrogen by binding to the receptor sites meant for the hormone. This can disrupt normal function (12).
The recommended daily limit of BPA is 23 mcg/lb (50 mcg/kg) of body weight. However, 40 independent studies have reported that negative effects have occurred at levels below this limit in animals (15).
What's more, while all 11 industry-funded studies found that BPA had no effects, more than 100 independent studies have found it to be harmful (15).
Results from one study suggest a connection between high BPA levels and polycystic ovarian syndrome (PCOS). PCOS is a disorder of insulin resistance characterized by elevated levels of androgens, such as testosterone (24).
Research has also linked high BPA levels to altered thyroid hormone production and function. This is attributed to the chemical binding to thyroid hormone receptors, which is similar to its interaction with estrogen receptors (25, 26).
You can reduce your BPA exposure by looking for BPA-free bottles and containers, as well as by eating mostly whole, unprocessed foods.
In one study, families who replaced packaged foods with fresh foods for 3 days experienced a 66% reduction in BPA levels in their urine, on average (27).
You can read more about BPA here: What is BPA and Why is it Bad for You?
Bottom Line: BPA is a chemical commonly found in plastic and canned items. It may increase the risk of infertility, insulin resistance and disease.
3. Trans Fats
Trans fats are the unhealthiest fats you can eat.
They're created by pumping hydrogen into unsaturated oils in order to turn them into solid fats.
Your body doesn't recognize or process trans fats in the same way as naturally occurring fats.
Not surprisingly, eating them can lead to a number of serious health problems (28).
Researchers who looked at data from 730 women found that inflammatory markers were highest in those who ate the most trans fats, including 73% higher levels of CRP, which is a strong risk factor for heart disease (31).
Controlled studies in humans have confirmed that trans fats lead to inflammation, which has profoundly negative effects on heart health. This includes impaired ability of arteries to properly dilate and keep blood circulating (32, 33, 34, 35).
In one study looking at the effects of several different fats in healthy men, only trans fats increased a marker known as e-selectin, which is activated by other inflammatory markers and causes damage to the cells lining your blood vessels (35).
The available evidence supports avoiding trans fats as much as possible and using healthier fats instead.
Bottom Line: Many studies have found that trans fats are highly inflammatory and increase the risk of heart disease and other conditions.
4. Polycyclic Aromatic Hydrocarbons (PAHs)
Red meat is a great source of protein, iron and several other important nutrients.
However, it can release toxic byproducts called polycyclic aromatic hydrocarbons (PAHs) during certain cooking methods.
When meat is grilled or smoked at high temperatures, fat drips onto hot cooking surfaces, which produces volatile PAHs that can seep into the meat. Incomplete burning of charcoal can also cause PAHs to form (40).
Additionally, researchers have reported that high intakes of PAHs from grilled meats may increase the risk of kidney cancer. Again, this appears to be partly dependent on genetics, as well as additional risk factors, such as smoking (48, 49).
It's important to note that this connection with colon cancer has only been seen in red meats, such as beef, pork, lamb and veal. Poultry, such as chicken, appear to have either a neutral or protective effect on colon cancer risk (52, 53, 54).
One study found that when calcium was added to diets high in cured meat, markers of cancer-causing compounds decreased in both animal and human feces (55).
Although it's best to use other methods of cooking, you can reduce PAHs by as much as 41–89% when grilling by minimizing smoke and quickly removing drippings (42).
Bottom Line: Grilling or smoking red meat produces PAHs, which have been linked to an increased risk of several cancers, especially colon cancer.
5. Coumarin in Cassia Cinnamon
However, cinnamon also contains a compound called coumarin, which is toxic when consumed in excess.
Two of the most common types of cinnamon are Cassia and Ceylon.
Ceylon cinnamon comes from the inner bark of a tree in Sri Lanka known as Cinnamomum zeylanicum. It is sometimes referred to as "true cinnamon."
Cassia cinnamon comes from the bark of a tree known as Cinnamomum cassia that grows in China. It is less expensive than Ceylon cinnamon and accounts for about 90% of the cinnamon imported into the US and Europe (57).
The safety limit for coumarin in food is 0.9 mg/lb (2 mg/kg) (59).
However, one investigation found cinnamon baked goods and cereals that contained an average of 4 mg/lb (9 mg/kg) of food, and one type of cinnamon cookies that contained a whopping 40 mg/lb (88 mg/kg) (59).
What's more, it's impossible to know how much coumarin is actually in a given amount of cinnamon without testing it.
German researchers who analyzed 47 different cassia cinnamon powders found that coumarin content varied dramatically among the samples (60).
The tolerable daily intake (TDI) of coumarin has been set at 0.45 mg/lb (1 mg/kg) of body weight and was based on animal studies of liver toxicity.
However, studies on coumarin in humans have found that certain people may be vulnerable to liver damage at even lower dosages (58).
While Ceylon cinnamon contains far less coumarin than cassia cinnamon and can be consumed liberally, it's not as widely available. Most of the cinnamon in supermarkets is the high-coumarin cassia variety.
That being said, most people can safely consume up to 2 grams (0.5-1 teaspoon) of cassia cinnamon per day. In fact, several studies have used three times this amount with no reported negative effects (61).
Bottom Line: Cassia cinnamon contains coumarin, which may increase the risk of liver damage or cancer if consumed in excess.
6. Added Sugar
Sugar is high in fructose, and excess fructose intake has been linked to many serious conditions, including obesity, type 2 diabetes, metabolic syndrome and fatty liver disease (62, 63, 64, 65, 66, 67).
One observational study of more than 35,000 women found that those with the highest sugar intakes had double the risk of developing colon cancer as those who consumed diets lower in sugar (70).
While small amounts of sugar are harmless for most people, some individuals are unable to stop after a small amount. In fact, they may be driven to consume sugar in the same way that addicts are compelled to drink alcohol or take drugs.
Bottom Line: A high intake of added sugars may increase the risk of several diseases, including obesity, heart disease, type 2 diabetes and cancer.
7. Mercury in Fish
Most types of fish are extremely healthy.
However, certain varieties contain high levels of mercury, a known toxin.
Seafood consumption is the largest contributor to mercury accumulation in humans.
This is a result of the chemical working its way up the food chain in the sea (74).
Plants that grow in mercury-contaminated waters are consumed by small fish, which are then consumed by larger fish. Over time, mercury accumulates in the bodies of those larger fish, which are eventually eaten by humans.
In the US and Europe, determining how much mercury people get from fish is difficult. This is due to the wide-ranging mercury content of different fish (75).
A 2014 analysis found that in several countries, mercury levels in the hair and blood of women and children were significantly higher than the World Health Organization recommends, particularly in coastal communities and near mines (78).
Another study found that the amount of mercury varied widely among different brands and types of canned tuna. It found that 55% of the samples were in excess of the EPA's 0.5 ppm (parts per million) safety limit (79).
Some fish, such as king mackerel and swordfish, are extremely high in mercury and should be avoided. However, eating other types of fish is still advised because they have many health benefits (80).
To limit your mercury exposure, choose seafood from the "lowest mercury" category on this list. Fortunately, the low-mercury category includes most of the fish highest in omega-3 fats, such as salmon, herring, sardines and anchovies.
The benefits of eating these omega-3 rich fish far outweigh the negative effects of small amounts of mercury.
Bottom Line: Certain fish contain high levels of mercury. However, the health benefits of eating low-mercury fish far outweigh the risks.
Take Home Message
Many claims about harmful effects of food "toxins" are not supported by science.
However, there are several that may actually be harmful, especially in high amounts.
That being said, minimizing your exposure to these harmful chemicals and ingredients is incredibly easy.
Simply limit your use of these products and stick to whole, single-ingredient foods as much as possible.