As the adage goes, the dose makes the poison. But the same can be said for our foods—a morbid morsel to chew on during your holiday noshing.

While still safe to eat, our favorite dishes have a dark side—a striking amount are laced with toxic and deadly substances. In fact, we flirt with intriguingly dangerous ingredients not just during the holidays, but daily. Potentially poisonous substances arrive in our foods through contamination and hazardous production conditions, and toxins are also naturally present in many plants. Nearly all are present at such low amounts that they pose little risk. But, in large enough quantities or if safety monitoring fails, some of our favorite dishes could easily turn against us.

This leaves the Food and Drug Administration with the tricky task of keeping our foods safe—and knowing when they slip into the realm of poisons.

Some contaminants and toxins are unavoidable in foods, FDA spokesperson Peter Cassell told Ars. “Since 1961, the FDA has monitored the levels of about 800 contaminants and nutrients in the US diet,” he said. The agency also keeps track of natural toxins in some produce. “Plants are known to produce, naturally, a number of toxicants and anti-nutritional factors.” These can include neurotoxins and chemicals that burst our blood cells (hemolytic agents). Plants can even contain substances called “anti-vitamins,” which block vitamins from doing their normal, helpful activities in the body. Several fruits and vegetables, including blueberries and Brussels sprouts, contain an anti-vitamin (called Thiaminase) that slashes vitamin B1, for instance.

“Many of these toxicants are present in today's foods at levels that do not cause acute toxicity,” Cassell said. But that’s not always the case.

For instance, the FDA likes to remind consumers each year around Halloween that black licorice contains hazardous amounts of glycyrrhizic acid. This natural toxin in licorice root can cause potassium levels in the body to fall. In people 40 years old and over, eating just two ounces of the candy a day for a couple of weeks can cause irregular heart rhythms.

Luckily, black licorice isn’t very popular, and the FDA notes that glycyrrhizic acid hasn’t been a significant menace to public health. In other words, they don’t see outbreaks of licorice intoxication among candy lovers every year. Still, the threat is real. Health researchers have recorded several cases where people became gravely ill from the treat. That includes a 1977 report of a 58-year-old woman who got into the habit of eating roughly 1.8 kilograms of black licorice each week and went into cardiac arrest. She recovered and her symptoms went away completely when doctors got her to stop eating licorice.

Of course, Halloween isn’t the only occasion to revel in all the different ways our delicious foods possibly could—but likely won’t—poison us. The end-of-year holidays are just as prime.

Based on information from the FDA and a 2010 review in the journal Toxins, here’s a quick look at a few of the delicious dangers you’re likely to encounter as you’re kicking back and celebrating:

Glycoalkaloids (solanine and chaconine) in potatoes

You might have heard that you should avoid eating the green bits of potatoes, but you may not know why. It’s because potatoes naturally produce toxic, defensive pesticides called glycoalkaloids α-solanine and α-chaconine.

These can exist throughout a potato tuber, but sprouts, peels, and sun-greened areas contain the highest levels. If eaten, glycoalkaloids can disrupt nerve signaling and the membranes around cells. At high enough doses, they cause gastric or neurologic problems, such as vomiting, diarrhea, abdominal cramping, fevers, headaches, weakness, hallucinations, and coma, Cassell said.

“Potato growers, packers, and commercial users have built safeguards through FDA’s current Good Manufacturing Practices to limit the concentration of glycoalkaloids,” he said.

The FDA considers the maximum acceptable content of glycoalkaloids in potatoes to be 20mg to 25mg per 100g of fresh potato weight. Ingesting doses of 1mg to 5mg per kilogram of body-weight is known to cause toxicity, and doses 3mg to 6mg per kilogram of weight can kill.

In 1993, the National Institute of Environmental Health Sciences found that the average person eats about 12.75mg glycoalkaloids per person per day from potatoes. That works out to about 0.18mg per kg of body weight based on a person weighing 70kg (154 pounds). In all, that dose is around a fifth of the lowest dose known to be toxic to humans (1mg per kg of weight).

So, second helpings of the mashed potatoes or latkes are OK—but maybe don’t eat five times the amount you usually eat.

Myristicin in nutmeg

What holiday isn’t more fun with hallucinogenic drugs? Myristicin is a natural insecticide in nutmeg that has a chemical structure similar to mescaline, a psychedelic alkaloid in peyote that has hallucinogenic effects akin to LSD.

At high enough doses—about 6mg to 7mgs per kilogram of body weight—myristicin also causes psychotropic effects, including feeling euphoric and free. That’s sometimes accompanied by nausea, tremors, rapid heartbeat, and anxiety. But, as Cassell notes, such high doses are “vastly greater than the usual levels of intake in the average diet.” Only about one to three percent of nutmeg’s content is myristicin, so this isn’t something anyone has to worry about while eating pumpkin pie or sprinkling the spice over their eggnog.

For the true thrill seekers, researchers have found that gulping down five grams of nutmeg straight (about 1mg to 2mg per kilogram of body weight of myristicin) can accomplish making you feel a little drunk. But the effects don’t last long. The FDA currently doesn’t have any guidelines or regulations about how much myristicin can be in food.

Cucurbitacins in zucchini, pumpkins, and squash

Produce in the Cucurbitaceae family (the gourd family, which includes zucchini, pumpkins, and squash, among others) can produce toxic steroids called cucurbitacins that protect the plants from herbivores. These toxins are among the most bitter tasting compounds identified by researchers.

There are a variety of cucurbitacins, which are designated by letters, i.e., cucurbitacin A and cucurbitacin B all the way to T. But, A, B, and C are the relatively toxic ones, Cassell said. At high enough doses, these cause lethal amounts of fluid to fill the lungs (pulmonary edema).

High levels of cucurbitacins can build up in zucchini and other plants if they’re grown in stressful conditions, such as in high temperatures or droughts. A signal that cucurbitacins are high is if your produce is excessively bitter. Eating extremely bitter zucchini has been linked to stomach cramps and diarrhea. During the 1980s, there were 22 recorded cases in Australia and the US of poisonings from bitter zucchini. The cases were all linked to specific species of zucchini called “Blackjack” and “Black Beauty.”

These are not common, Cassell said. “Most zucchini species commonly consumed either don’t contain cucurbitacins or do not contain enough of the compound to pose a health risk,” he said. “Like with potatoes, producers and growers take precautions to reduce the risk to consumers through FDA’s current Good Manufacturing Processes.”

Oxalic acid in rhubarb

If you’re a big rhubarb fan, you probably know not to eat the leaves. Unlike the stems and stalks, the leaves can contain oxalic acid. This is an organic acid that binds to calcium and other minerals, making them unavailable for normal use by the body. Some of the symptoms of oxalic acid poisoning include abdominal pain, vomiting, diarrhea, burning in the mouth and throat, seizures, weakness, and kidney stones, Cassell said.

The risks of oxalic acid is probably best exemplified by kidney stones. About 65 percent of stones are made up of calcium oxalate, formed by oxalic acid and calcium.

However unpleasant, eating rhubarb leaves is unlikely to be deadly. Researchers estimate that a person would have to eat about 4.5kg of leaves (nearly 10 pounds) to get a lethal dose.

Lectins in beans

Legumes (beans, chickpeas, lentils, peanuts, etc.) can contain high levels of lectins, a group of proteins that can reversibly bind to carbohydrates. Lectins can have a variety of roles, but some in beans are particularly dangerous. For instance, the biological warfare agent ricin is a lectin from castor beans.

Kidney beans contain a lectin called phytohaemagglutinin (PHA), which is less dangerous than ricin, but still a concern. PHA has a variety of effects on our bodies, including making red blood cells stick together, affecting how proteins move across cellular membranes, and even prompting cells to divide. Symptoms of PHA poisoning include nausea, vomiting, and diarrhea a few hours after eating.

Raw red kidney beans can contain toxic levels, and, as such, the FDA does provide recommended cooking methods to avoid risks, Cassell said. To cut down PHA levels to safe amounts, consumers have to cook the beans in moist—not dry—heat above 176 degrees Fahrenheit.

“Therefore, FDA recommends steaming or boiling legumes containing lectins, which process reduces significantly the concentration of lectins,” Cassell said. And, sad news for any slow-cookers: “Because cooking temperatures under 176 degrees Fahrenheit do not destroy lectin, use of slow cooking and/or a crockpot is not advised for cooking beans,” he added.

Glucosinolates in Brussels sprouts and broccoli

Raw members of the Brassica—a family of vegetables that includes Brussel sprouts, broccoli, turnips, watercress, and cauliflower, among others—contain glucosinolates. These substances interfere with thyroid function by blocking uptake of iodine, an essential nutrient for growth, efficient metabolism, hormone balances, and cognitive development. A shortage of iodine can cause the thyroid gland to enlarge, forming a goiter. For this reason, glucosinolates are also called goitrogens.

The FDA regulates the amount of glucosinolates in some foods, but generally, the agency says this isn’t a problem.

The extremely high levels that can impair thyroid function are not found in the average diet, Cassell said. Also, glucosinolates are rendered inactive by cooking. So, sadly, these toxins are not getting you out of eating your vegetable sides this year.

The Brassica family “provides important nutritional benefits,” Cassell added. “FDA recommends always eating a variety of produce.”