7 Foods You Should Never Eat. Ever.

Which diet foods are especially bad for you? (Photo: Courtesy of Mylan Torres)

Hard-and-fast food rules royally suck. But some foods can seriously mess with your health.

"It doesn’t mean you’ll get sick, get cancer, or die if you eat a dangerous food once," says Nneka Leiba, deputy director of research at the Environmental Working Group (EWG), which catalogs studies on potential toxins found in specific brand-name foods and ranks their safety in a massive database. "But there are certain foods you should avoid as much as possible if you have a choice."

Related: Your Favorite Wines Could Contain Toxic Amounts of Arsenic

The worst culprits are additives in highly processed foods. “We really don’t know what the long-term consequences of eating these science projects might be,” says Rachel Harvest, a registered dietitian affiliated with Tournesol Wellness in New York. With that in mind, do your best to steer clear of the foods that scare Leiba, Harvest, and other registered dietitians:

1. American Cheese: "The reality is that American cheese is not ‘cheese’ at all," says Beth Warren, a New York-based registered dietitian and the author of Living a Real Life With Real Food. Depending on the brand, "it’s a factory creation of a cheese-like food made from a blend of milk fats, solids, some whey protein, emulsifiers, and food coloring." It’s high in sodium, and so high in fat that one regular slice more closely resembles high-fat meat than anything considered dairy, Warren adds.

2. Margarine: Because margarine is made from vegetable oils and has less cholesterol and saturated fat than butter, it’s long been considered the healthier option. But now that experts say dietary cholesterol isn’t as harmful they thought, margarine, which is high in salt and contains artery-clogging trans fats, isn’t looking quite so healthy. “Trans fat, like saturated fat, increases blood cholesterol levels and the risk of heart disease,” explains Melissa Rifkin, a registered dietitian at Montefiore Medical Center in New York and a Rise nutrition coach. Margarines sold in tubs tend to contain less trans fat than margarine sticks — the softer the spread, the better for you — but olive oil (or another source of monosaturated fat) is still a better bet. Real butter is a close second, according to Rifkin.

Related: 15 Things Only Giant Hypochondriacs Will Understand

3. Regular Soda: Everyone knows that soda is Very Bad for your health. In case you missed the backstory: The average can contains about 10 teaspoons of sugar. When you consume that much, your body responds by creating excess insulin, which typically helps the body absorb sugar from the bloodstream and use it for energy. Over time, though, this over-the-top response can increase your risk of developing diabetes and some forms of cancer. If soda’s sugar content doesn’t still doesn’t scare you, its other ingredients might: The amount of caramel coloring you’d consume in one can of soda per day was recently linked to a 58 percent greater risk of cancer, according to a new study. AND Diet Soda: While there’s no straight-up sugar in this stuff, there are artificial sweeteners, and they’re not necessarily any better. Not all artificial sweeteners are equally offensive. However, most have a more intense flavor than plain old sugar. Over time, the extra-sweet sweeteners can dull your senses to naturally sweet foods like fruits, Rifkin says. So yes, your Diet Coke could, theoretically, make a perfectly sweet apple taste worse. Drinking diet soda has also been linked to depression, tooth decay, heightened risk of strokes and heart attacks, pancreatic cancer and premature birth.

4. “Sugar-Free” Candies: Sweets that are specifically advertised as “sugar-free” tend to contain artificial sweeteners too. (See no. 5 above.) Also: The digestive system doesn’t do a great job at breaking down sugar substitutes and sugar alcohols, Harvest says. When you overdo it (and the threshold is different for everyone) you could incur some serious stomach pains.

Related: 8 Things You Should Never Eat if You’re Trying to Lose Weight

5. Microwave Popcorn: “It’s not healthy eating out of a bag anymore,” Rifkin says. Microwave popcorn bags, in particular, are often lined with a chemical called perfluorooctane sulfonic acid (PFOS), which has been shown to affect fertility, cancer risk, and kidney functioning in animal and some human studies. Because microwave popcorn bags aren’t labeled “toxic,” it’s best to avoid them altogether. Another thing: Some brands of microwave popcorn add unhealthy trans fats to their products, and vaguely list “artificial flavors” or “natural flavors” on their labels — so there’s no way to know exactly what’s in there, Warren warns. In the worst case scenarios, the recipe could contain MSG, which can cause headaches or nausea, or diacetyl butter flavoring, which may cause respiratory damage when inhaled. (Air popped, anyone?)