You’ve probably heard many claims that some common foods or food ingredients are toxic. Fortunately, most of these claims aren’t supported by science.

However, there are a few ingredients that may be harmful, particularly when consumed in large amounts.

Share on Pinterest
ben-bryant/Getty Images

Here are seven foods, ingredients, or compounds that are worth being concerned about.

1. Refined vegetable and seed oils

Refined vegetable and seed oils include corn, sunflower, safflower, soybean, and cottonseed oils.

Unlike oils that come from naturally oily foods — such as coconut oil, olive oil, and avocado oil — these oils must be extracted through a complicated process that involves using chemical compounds such as hexane to extract and purify them (1).

Therefore, these oils are highly processed.

Oils are also high in calories and fat. This is not generally an issue, because fat is a macronutrient that provides the body with energy. However, some oils are particularly high in omega-6 polyunsaturated fatty acids (2).

Omega-6 fats can be concerning if consumed in large amounts because they’re prone to damage and rancidity when exposed to light or air. They may also be pro-inflammatory if you don’t get enough omega-3 fatty acids (from foods like fatty fish or flaxseed) in your diet (3).

Additionally, one observational study 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 (4).

Still, new guidelines recommend replacing saturated fats with unsaturated fats such as omega-6s. In fact, the American Heart Association suggests getting 5–10% of your daily calories from omega-6 fats (5).

Finally, when these oils are heated, they can produce potentially cancer-causing aldehydes. The highest emissions can occur during deep-frying, while lower emissions occur from gentle cooking methods such as stir-frying.

You can reduce production of aldehydes by opting for oils low in unsaturated fatty acids, such as rapeseed oil (6).

Summary

Unlike oils from naturally oily foods, like coconut oil and olive oil, vegetable and seed oils may be refined. They can also produce potentially cancer-causing aldehydes, especially during deep-frying, but other cooking methods can reduce those emissions.

2. Bisphenol A and similar compounds

Bisphenol A (BPA) is a chemical that used to be found in the plastic containers of many common foods and beverages and in the lining inside metal cans (for instance, those used for canned tomatoes).

However, studies have shown that BPA can leach out of these containers and into the food or beverage inside (7).

BPA is believed to mimic estrogen by binding to the receptor sites meant for the hormone. This can disrupt typical hormone function (7).

What’s more, studies in pregnant animals have shown that BPA exposure leads to problems with reproduction and increases the future breast and prostate cancer risk of a developing fetus (8, 9).

Some observational studies have also found that high BPA levels are associated with insulin resistance, type 2 diabetes, and obesity (10, 11).

However, while animal studies have found an association between BPA and weight gain and insulin resistance, few human studies have studied the association between markers of BPA exposure and diabetes (10, 11).

Fortunately, most plastics and cans are now BPA-free. However, BPA has been replaced in many products with very similar compounds such as bisphenol S, which may have similar effects (12).

In fact, one review notes that BPS may be more toxic to the reproductive system than BPA (12).

To reduce your exposure to these potentially harmful compounds, avoid plastic dishware as much as possible — including bottled water. Use glass and stainless steel drinkware instead of plastic, and look for foods that are packaged in glass rather than aluminum cans.

Summary

BPA was once commonly found in plastic and the lining of aluminum cans, but it has since been mostly phased out because of links to negative health effects. However, replacements such as BPS may have similar drawbacks.

3. Artificial trans fats

Artificial trans fats are made by pumping hydrogen into unsaturated oils such as soybean and corn oils to turn them into solid fats. They used to be in many processed foods, such as margarine, snack foods, and packaged baked goods.

However, animal and observational studies have repeatedly shown that trans fat consumption causes inflammation and has negative effects on heart health (13, 14, 15).

For this reason, the use of artificial trans fats has been fully banned in the United States since January 2020 (16).

Some animal-based foods may contain some naturally occurring trans fats, but these don’t have the same negative health effects as industrial trans fats (15).

Summary

Artificial trans fats are highly inflammatory and may contribute to heart disease. They are now banned from being used in food in the United States, but if a serving of food contains less than 0.5 grams of trans fat, it can be labeled 0 grams.

4. Polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are considered environmental pollutants. They arise from burning organic material, but they’re also found in foods (17).

When meat is grilled or smoked at high temperatures, fat drips onto hot cooking surfaces, producing volatile PAHs that can seep into the meat.

Although red meat was once thought to be the main culprit, samples of grilled chicken and fish have been found to contain similar levels of PAHs (18, 19).

In fact, smoked and grilled meats are one of the primary sources of PAHs in food. But PAHs are also found in many types of processed foods (20, 21).

Unfortunately, researchers have found that PAHs are toxic and linked to an increased risk of breast, kidney, colon, and prostate cancer (22, 23, 24, 25).

Although it’s best to use other methods of cooking, such as braising or slow cooking, you can reduce PAHs by as much as 89% when grilling by minimizing smoke and quickly removing drippings (26).

Summary

Grilled and smoked meats are high in PAHs, which can increase the risk of cancer. Cooking methods such as braising and slow cooking can reduce the PAHs in meats.

5. Coumarin in cinnamon

Coumarin is a toxic compound found in C. cassia, C. loureiroi, and C. burmannii cinnamon. These types of cinnamon are commonly found in grocery stores (27).

At high doses, coumarin has been linked to an increased risk of cancer and liver damage. However, it’s impossible to know how much coumarin your cinnamon contains unless you have it tested (27).

One study found that children who regularly sprinkled cinnamon on their oatmeal could have unsafe levels of coumarin intake, so it’s something to be aware of if you consume cinnamon regularly (28).

If you want to avoid coumarin, look for a different type of cinnamon, called Ceylon cinnamon or “true cinnamon,” from the Cinnamomum verum plant. It’s harder to find in stores (you may have to order it online) and more expensive, but it contains much lower levels of coumarin (27).

Summary

Cassia cinnamon contains coumarin, which may increase your risk of liver damage or cancer if consumed in excess. Ceylon cinnamon is harder to find but contains much lower levels of coumarin.

6. Added sugars

Added sugars are often referred to as “empty calories.” However, the harmful effects of sugar go way beyond that.

Sugar is high in fructose, and excess fructose intake has been linked to many serious conditions, including obesity, type 2 diabetes, metabolic syndrome, fatty liver disease, and cancer (29, 30, 31).

Foods high in added sugars are also highly processed and may have addictive properties that make it hard for some people to regulate their intake of these foods (32).

Based on animal studies, some researchers have attributed this to sugar’s ability to cause the release of dopamine, a neurotransmitter in the brain that stimulates reward pathways (32, 33).

To lower your added sugar intake, limit sugar-sweetened beverages such as soda and fruit juices and eat processed snack foods and desserts only occasionally.

Summary

Added sugars, which are found in many foods, can contribute to unwanted weight gain and the development of type 2 diabetes, fatty liver disease, and a number of other chronic conditions.

7. Mercury in fish

Fish is an extremely healthy animal protein, but certain varieties of deep sea fish can contain high levels of mercury, a known toxin. This is a result of the pollutant working its way up the food chain in the sea (34).

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.

Mercury is a neurotoxin, meaning it can damage the brain and nerves. Research suggests that young children and pregnant and breastfeeding women are at particularly high risk, since mercury can affect fetal and infant brain and nervous system development (35).

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 (36).

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 (37).

To limit your mercury exposure, choose low mercury fish such as salmon, pollock, herring, and catfish (38).

Summary

Certain deep sea fish, like king mackerel and swordfish, contain high amounts of toxic mercury. However, other types of fish, such as salmon and herring, are safer to consume.

The bottom line

Many claims about harmful effects of food toxins aren’t supported by science, but some foods and food compounds do warrant concern.

To minimize your risk of harm, limit your consumption of processed foods, seed oils, processed meats, and added sugars as much as possible.

However, it’s also important to remember that many of these foods are harmful only with consistent regular or high intake, so you don’t have to give them up entirely — just limit them to occasional treats.