“We, as humans, seem to have this need to chew,” Roach told me then. “Animals and humans like to chew; they like to destroy things with their mouths. It's kind of a basic pleasure.”
NASA discovered as much when it tested a milkshake-esque liquid diet at Wright-Patterson Air Force Base in 1964 (astronauts, presumably, being even more inconvenienced by food than Rhinehart). “The milkshake diet was unbelievably unpopular,” Roach said. “The subjects were emptying it under the floorboards of the space cabin simulator. It was that unappealing.”
Soylent is not entirely unlike a milkshake. Without added flavoring, the version I had tasted yeasty and chemically, like a vanilla milkshake that traveled through a wormhole and came out wrong. Its taste has also been described as “unsweetened custard,” “slightly sweet and earthy with a strong yeasty aftertaste,” and “chalky.” Rhinehart says it’s “more sweet than anything.”
Humans, generally, don’t like bland, monotonous food. “The mouth really does get bored,” Roach said. “I can’t think of anything more depressing than living on a milkshake texture.”
In a 2000 study on food cravings, Pelchat examined the effects of a “nutritionally adequate, liquid, sweet, monotonous diet” (hm, what does that sound like?) on young and elderly adults’ cravings. She found that while people’s liking for the diet didn’t change significantly over five days, the young adults did start to crave more savory foods, or entrees. Their cravings for sweet foods were the same both on and off the diet. Elderly adults seemed more okay with the monotony, and didn’t have significant changes in cravings.
“Older participants didn’t complain as much as the younger people did about a chemical or vitamin taste,” Pelchat adds. One danger of older adults’ willingness to go along with boring diets is that they might not get adequate nutrition—Soylent, in these cases, could be a boon.
“Society has been going in the direction of convenience foods and healthy meal substitutes, protein bars and things like that,” Pelchat says. “So I guess it’s not totally surprising that somebody would want to go one step further.” She notes that while she’s found in her studies that monotonous diets tend to induce cravings, it may be different if someone chooses to live on Soylent, as opposed to being told to drink the same beverage for five days for a study.
The monotony effect extends beyond just liquids—solid meal replacements tend to meet with similarly lukewarm responses. Pelchat says that servicemen eating the U.S. military’s “Meals Ready to Eat” (MRE) rations sometimes had trouble taking in enough calories because, even though there were different options, there wasn’t a large variety. Early this year, the Department of Defense awarded $16 million to Louisiana State University to support research to improve soldier health and make the MREs more palatable. A boring, non-military diet could have bring similar problems—a 2011 study published in The American Journal of Clinical Nutrition found that daily exposure to the same food caused women to eat fewer calories.