If you’re trying to watch what you eat, and you’re obsessed with ridding your diet of unnecessary chemicals…well, good luck.

Eat a single tomato and you’ll ingest a number of aromatic compounds. Don’t worry, though—those make the suckers taste good. Crunch through an apple seed and you might consume a trace amount of amygdalin, a compound that produces extremely small amounts of cyanide. Don’t worry, though—you’d have to crunch through 150 seeds, or around 18 apples’ worth, before maybe going all Snow White on us.

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It’s true—even the simplest foods contain hundreds of chemical compounds. And while, yes, most of them are harmless in appropriate doses, some of those substances can have unintended side effects. Some are pretty obvious—by now, we all know that caffeine causes feelings of mild euphoria, for instance—but researchers are just starting to understand how some foods affect the human body.

Relax; it’s mostly good news until we get to the thing about butternut squash.

1. Tomatoes might help with depression.

The key word here is “might.” The information comes from a 2012 study that looked at the dietary habits of 986 geriatric Japanese people. Researchers found that participants who ate tomatoes regularly were 46 percent less likely to report symptoms of depression than participants who ate tomatoes less than once a week.

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Interestingly, no similar association was found for other vegetables (and yes, we know that tomatoes are technically fruits, but we’re using the researchers’ verbiage. They seemed to ignore the distinction when gathering their data).

The story quickly spread, likely thanks to the influence of the International Organization for Tomato Propagation, a trade association that we just made up. Publications like The Daily Mail picked up the story and ran with it, writing glowing stories with headlines like “Eating Tomatoes Could Ward Off Depression.”

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Unfortunately, the science isn’t completely solid—not yet. There are problems with the study, as the UK’s National Health Service pointed out later, and even the original researchers noted that further studies need to be completed in order to verify the findings.

With that said, if you’re looking for another reason to put tomatoes on your next sandwich, you’ve got one.

2. Beetroot juice might have an unexpected effect on athletic performance.

Ever chug a pint of beetroot juice and immediately go for a 5-mile run?

Yes, we know how awful that sounds. Beet juice is disgusting. That’s why you can’t buy it in most stores; to really enjoy an ice-cold glass of beets (yuck), you have to find your blender, hold your nose, and get to work.

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If you’re willing to drink a few beets, however, your lungs might thank you for your sacrifice. One study found that beetroot juice improves cardiovascular performance in athletes, potentially improving endurance. To get optimal effects, athletes should drink a moderate amount of beetroot juice within 90 minutes of performance, and they should add an extra serving if they’re performing tasks that involve their arms (for instance, rowing, swimming, or punching the guy who told them to drink beetroot juice).

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The bad news, according to that same study, is that caffeine might counteract the effects of beetroot juice. Other supplements might also disturb the juice’s magical endurance-boosting qualities, but there’s not much research on the subject (possibly because “I want to make marathon runners chug beet juice” isn’t a great pitch for research funding).

The takeaway: If you’re training for an endurance sport, go ahead and drink some beets, but lay off the coffee. We’re very, very sorry for delivering that news.

3. Coffee can reduce blood flow to your brain.

In fact, that’s a pretty well-established effect. Though coffee is often accepted as a vasodilator, meaning it increases blood flow throughout the body, several studies have shown that it is also vasoconstrictor, especially when it comes to the brain—it slows down cerebral blood flow by an average of 27 percent. That’s due to the presence of caffeine, of course.

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However, it doesn’t mean that you turn into a slobbering, simple-minded Michael Bay fan every time you drink an Americano. Your body can easily compensate to ensure that different parts of your brain receive enough oxygen to operate normally, provided that you’re not drinking an obscene amount of the stuff.

Besides, some research indicates that coffee can be beneficial for cognitive performance. In one study, researchers showed that coffee-supplemented diets could actually improve memory, motor function, and overall cognition in aging rats. The coffee itself seemed to be responsible for the effect—not caffeine—and researchers recommended about three cups per day.

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Of course, decaf coffee is a lot like an aging rat; we don’t really care about it one way or another. It’s still nice to know that our coffee habit isn’t severely restricting our ability to make words go good.

4. Carrots can change your skin color, and that’s actually a good thing.

Looking to get a healthy tan? Bad news: There’s no such thing, according to the American Academy of Dermatology.

When you tan, you’re bombarding your skin with UVA and UVB radiation, both of which can increase your chances of skin cancer. Still, about 58 percent of adults aged 18-29 believe that people look more attractive with tanned skin.

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That’s where the carrots come in. Eating enough carrots will, in fact, turn your skin slightly orange (or yellowish, depending on your complexion). That’s because our bodies store carotene—the stuff that turns carrots orange—causing a slight discoloration called carotenemia. It’s completely harmless, and it goes away over time. Tomatoes, by the way, can have a similar effect, as they contain a pigment called lycopene that can turn your skin yellowish-orange.

If you’re picturing yourself eating ridiculous amounts of produce to get unnaturally yellow skin, think again: Carrots and tomatoes can objectively improve your look. In 2012, a research team in Scotland found that six-week changes in fruit and vegetable consumption enhanced “apparent health and attractiveness.” Participants’ skin tone became more tanned over the trial period, and they were more likely to be rated as attractive by their peers.

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There are limits to the effect, but while chowing down on tons of vegetables might not get you the runway-ready tan of your dreams, it’s at least healthier than bombarding your skin with ionizing radiation.

5. Star fruit can cause mental confusion…and more serious issues.

We asked a few medical experts to weigh in on this piece, and while most of them provided fairly obvious advice (it turns out that it’s not a good idea to eat large amounts of cheese every day), one response caught our eye.

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“I don’t know why this always stuck with me since my internship 17 years ago,” says registered dietitian Lauren Manaker of Nutrition Now Consulting, “but many people don’t realize that star fruit can be toxic to people with chronic kidney disease. For those people, some side effects of eating star fruit can include vomiting, mental confusion, and seizures.”

Even if you don’t have chronic kidney disease, you might want to go easy on the star fruit. In one case study, a 56-year-old woman with normal renal function developed acute kidney injury after drinking “large amounts of star fruit juice at once.”

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“Over the next few days, she had felt weak and tired with loss of appetite,” the authors wrote. The patient was experiencing kidney failure—from consuming a mere 200 milliliters of juice, the equivalent of about six star fruits. Some researchers believe that only 25 milliliters of juice could cause toxicity.

That’s because star fruits are a rich source of oxalates, which can crystallize and impede kidney function in a matter of hours. Granted, if you only eat a single star fruit, you probably have nothing to worry about—provided your kidneys are healthy—but moderation is key. They should probably put some sort of a warning label on those things.

6. Butternut squash might cause your skin to peel off.

We warned you about butternut squash in the intro. Here’s the thing: Certain species of squash can cause severe allergic reactions, and…well, it’s not pretty.

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In one case study (link opens a PDF), a 30-year-old woman had no history of skin conditions whatsoever prior to an unfortunate “blistering eruption” that occurred when she prepared a single butternut squash. She experienced a localized reaction—in other words, she didn’t have the dangerous anaphylactic reaction that accompanies most serious allergies.

A quick Google search brings up dozens of similar stories, and we’ll warn you: They’re not fun. One home cook described her experience with butternut squash on cooking website Chowhound, describing it as “just like a chemical peel,” noting that the palm of her left hand (which had contacted the squash) “sort of shriveled and dried up.” Eventually, her skin began to crack and flake off.

Dermatologist Thomas S. Potter, the author of the aforementioned case study, believes that the hypersensitivity is caused by one of several chemicals created by certain species of squash, including the butternut squash, banana squash, and Kentucky field squash.

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If you don’t have the allergy, you’re not going to end up looking like Freddy Krueger after cutting up a few squashes. Still, it’s enough to make you think twice before preparing a fresh autumnal meal.