There are three constants in life—death, taxes, and that everyone’s shit stinks. Or does it? Though smelly poo has always seemed like a non-negotiable, there’s a chance that it may be more about diet than digestion.
And there’s no shortage of fad meal plans that promise to change your life. Most promote weight loss, heightened energy, and even better skin. Raw foodists and paleo practitioners believe their diets put them more in tune with natural eating patterns. Vegans have all the ethical and environmental arguments against eating animal products on their side. Though choosing a new diet is often more about health or weight loss than consideration for the person who uses the toilet after you, what if you could alter the odor of your poo by changing the way you eat?
In the list of health claims I’ve heard vegans make, the most memorable is that eliminating animal products has an odor-canceling side effect on their morning constitutionals. Or as one ex-vegan said in an interview, “I could definitely brag about how my poop didn’t smell, or that my urine was crystal clear!” Though no scientific studies have looked into this very important question, there are two main theories that explain the phenomenon.
One has to do with a compound traced to animal products and the other is all psychology.
“People have strongly held beliefs that don’t always hold up to the scrutiny of real science,” says Dr. Drew Schembre, a gastroenterologist at Swedish Hospital in Seattle. “They’re prone to a special type of magic thinking.” In short, if you think your diet is somehow more pure than others, you’ll find evidence to support it. Dr. Schembre, whose city is very close to Portlandia, is all too familiar with the phenomenon. “Virtually everyone here is celiac-sensitive and pseudo-vegan, except for bacon,” he says.
Yet others believe there could be something to the claim, believing that smelly stool is caused by an organic compound called a mercaptan. “Plant-based diets create less smelly flatulence and stool because they’re low in mercaptans,” says Dr. Anish Sheth, author of What’s Your Poo Telling You? These compounds are almost exclusively found in animal products and produce an odor that can only be described as a cross between boiled cabbage, sulfur, and garlic. If Dr. Sheth is right and you know someone on the paleo diet, watch out. Not only is the diet tough on your gut, it’s likely to be high in meats and therefore smelly mercaptans too. According to Heather Rasmussen of Rush University Medical Center, “The logic of paleo is a little misplaced.” Without whole grains or beans, it’s hard to get enough fiber, much less the recommended 25 grams a day.
“Everything else that causes foul-smelling stool is based on eating something your body is unable to digest,” Dr. Sheth says. People who have celiac disease or are lactose intolerant are excellent examples. One of the classic signals that you might be gluten intolerant is unusually putrid poo.
The idea that meat causes smells and sensations that are somehow unnatural has been around for 30 years, according to Dr. Schembre. “It’s largely not true.” On its way to the final destination, meat behaves like any other protein traveling through the gut. There are studies that link cancer, obesity, and other diseases to high animal fat diets, Dr. Schembre says. “But that’s a function of the variation of things you’re eating, not the absolute exclusion or inclusion of one type of food component.”
If changing your diet to experience odor-free poo is important to you, don’t expect your stool to smell like roses overnight. Your gut is typically only used to five grams of fiber per day, so suddenly revving up to the recommended 25 is a good way to throw your stomach off balance. “When people first introduce fiber they have side effects like gas and bloating and changes in stool,” says Rasmussen. “That doesn’t mean it’s a bad thing. It means you’re giving your stomach bacteria something to eat.”
The fact that “everybody poops” was well established in childhood. Yet many of us still have hang-ups over the smell of our stool. Last year, a product called Poo-Pourri appealed to many with the line, “Spritz the bowl before you go and no one else will ever know!”
But is odor-free poop really something to brag about? Whether it’s a figment of plant-based imaginations or a real phenomenon, it’s unlikely to have any health benefit. “The gut is complex and it’s a hot area right now,” Rasmussen says. “But we don’t know a lot about what’s the best bacteria and what’s the best diet.”
Dr. Schembre puts it a little more bluntly. “If your sole purpose in life is to make your poop smell less bad, then you probably need better things to do with your time.”