Medical Examiner

If You Could Eat Only One Thing …

You still wouldn’t want it to be Soylent.



Courtesy of Soylent Corporation

A friend admitted to me recently that she’d paid $65 into the crowdfunding campaign for Soylent, the “future of nutrition.” In August, she expects to receive a week’s worth of meals in the form of an unflavored beige powder. For her contribution she’ll also get a travel mug with a little wire ball inside, so that while reconstituting her meals in water she can more easily break up the chunks.

“Mostly it was curiosity,” said my friend, who asked me not to use her name. She learned about Soylent from a foodie listserv. “I wanted to see what quote-unquote pure nutrition tastes like.” She acknowledged that seven days’ supply will be more than enough to satisfy that curiosity.

According to the 24-year-old software engineer who dreamed up Soylent, the recipe for pure nutrition starts simply with the standard dietary recommendations from the Agriculture Department. Rob Rhinehart claims his powder includes “only the raw ingredients the body needs for energy,” as he wrote on his blog. (Those ingredients include maltodextrin and oat powder, but not people.) After testing the product on himself and others, he and a few business partners are raising money to mass-produce Soylent.

Rhinehart envisions Soylent as part of a future utopia in which no one has to grocery shop or scrub dishes, people spend less money and time on food, and everyone is healthy, having slurped down exactly the nutrients they need. It’s an engineer’s fantasy. Yet it neglects crucial details about the human machine: The body is not a computer in which a certain input guarantees a certain output. It’s not even a car engine, guzzling well-calibrated liquid fuel and returning energy. If you treat it like one, though, you may find your engine growling with hunger all the time.

We have evolved the ability to chomp and smash our food with our teeth and tongues, liquefy it in our stomachs, and wring the last bits of nutrition from it in our intestines. Our bodies are not adapted to suck food through a straw.

“There is very little that’s similar about how, physiologically, we handle beverages versus solid foods,” says Richard Mattes, a nutrition scientist at Purdue University. Chewing is the first difference, of course. And once swallowed, liquids drain from the stomach faster than solids. They slide through the intestine more quickly, and we absorb their nutrients more easily.

This matters because another machine the human body does not resemble is a coin counter. No mechanism inside us tallies up the calories we consume—tossed back in nickels or dimes or quarter-pounders—and reports the total. If it did, we would always feel hungry when we owed our body calories and full when we’d paid off our debt.

Instead, a complicated stew of hormones regulates the appetite. Various signals come from the pancreas, fatty tissues, or the stomach and intestine themselves. Some increase our appetite, and others decrease it; they may be triggered by a lack of food, by glucose in the bloodstream, or by physical stretching of the stomach. Meanwhile, the brain tries its best to make sense of all the signals.

People may think that a calorie is a calorie no matter what form we swallow it in, but in many studies over the past couple of decades, Mattes and other researchers have found that this isn’t the case. When we pipe in liquid calories—something that would have been rare for most of our evolutionary history—the system seems to lose count. Various studies have found that beverages, even when they provide as many calories as solid foods, don’t quell our appetites as well. This means the calories we drink tend to add to the total calories we consume in a day, rather than replacing solid ones.

It’s not clear exactly which mechanisms leave us unsatisfied after a liquid meal. A recent study by Mattes and his colleagues suggests that the power of expectation has a lot to do with it. They gave subjects a small meal of a cherry-flavored substance, as either a liquid or chewy gelatin cubes. Either way, the meal would rapidly dissolve in the stomach. But the researchers used visual demonstrations to make some subjects believe that the food would sit in their stomachs as a solid block, even if it started as a liquid. People who expected a solid in their stomachs felt fuller and ate less food later on—by about 400 calories—than people who ate the same food and expected it to liquefy.

Of course, if you commit to drinking the premeasured Soylent servings for all your meals, you don’t need to worry about overcompensating elsewhere. As long as you can ignore any cravings or stomach rumbles and stick to stirring up your powder, you’ll be guaranteed 1,800 calories a day with the women’s formula or 2,400 for the men’s. (These numbers are on the “sedentary” end of the USDA’s recommendations, so you may find them lacking if you exercise. Be glad Rhinehart abandoned his original “caloric restriction” recipe with only 1,550 calories a day.) Rhinehart plans to offer other options in the future. “As time goes on it will become more and more customizable and personalized,” he wrote in an email.

For now, Soylent treats the government’s dietary recommendations like a set of strict operating instructions. But they’re intended only to be an approximation of what keeps us healthy in a diet of actual food. “A basic premise of the Dietary Guidelines is that nutrient needs should be met primarily through consuming foods,” the USDA writes in its Dietary Guidelines for Americans 2010.

“Calorie and nutrient requirements may differ from person to person and can depend on factors such as age, gender, height, weight, physical activity level, medical conditions, etc.,” says Kim Croteau, a dietician with the USDA’s Food and Nutrition Information Center. Smokers, vegetarians, and anyone who is ill also have nonstandard needs, according to Dietary Reference Intakes, a book put out by the Institute of Medicine (on whose research the USDA bases its recommendations).

In fact, the Institute of Medicine says, “It is nearly impossible to determine what an individual’s exact requirement for a nutrient is.” Even when it comes to those numbers on the side of your cereal box, “It is important to keep in mind that … there is considerable uncertainty about these values.”

Rhinehart insists on his blog that Soylent has made him healthier in astonishing ways: “My physique has noticeably improved, my skin is clearer, my teeth whiter, my hair thicker and my dandruff gone.” He says the extra energy from Soylent lets him run miles and miles at the gym that he never could before—though he doesn’t address the possibility that he’s got it backward, that the added exercise accounts for his better health and energy (not to mention “physique”).

“My mental performance is also higher,” Rhinehart claims, adding that he can now navigate better without using GPS (he has not moved to a new city) and that he enjoys music more. Rhinehart is hardly an objective observer of his own behavior as a research subject. Expectations matter, even when it comes to cherry gelatin cubes. So does the more than $635,000 that Soylent’s crowdfunding campaign has raised as of June 17—more than six times the original goal. The campaign ends later this week.

When those thousands of backers get their first shipments of Soylent, they might provide new data about how well the substance meets people’s nutritional needs. But we will probably never find out how effective the food of the future is because people may not be able to stick with it.

“One of the best diets ever is the eat-all-you-want-of-one-food diet,” Mattes says. “It will work! For a short time. But due to the lack of sensory stimulation, the monotony of the single food, nobody can really follow it.” Soylent’s predecessors, the classic meal-replacement drinks like Slim-Fast, may help some people regulate their calorie intake—but they aren’t meant to be eaten full-time.

I asked Mattes whether people following any all-liquid regimen can expect to always feel a little hungry and unsatisfied. There’s not enough data to answer the question for sure, but as he said: “That would be my expectation.”

Even Rhinehart has left behind the strict Soylent diet that kicked off his experiment. “I still enjoy food,” he told me. “I just don’t crave it more often than the weekends.” My friend, despite the travel mug, doesn’t plan on drinking Soylent for more than three meals in a row.

Soylent backers may enjoy their beige shakes for a while, but they won’t become the fantasy diesel-engine bodies of the future. They’ll still be messy, expectation-ridden, variety-craving human machines.