Liquid Meal Replacements: Can We Move Beyond Food?

Some powders and drinks boast all of the necessary nutrients a body needs — no grocery trips required. But it isn't clear how liquid meal replacements might affect our health.

By Molly Glick
Jan 19, 2023 5:30 PMJan 19, 2023 5:29 PM
Liquid Lunch (and dinner...)
(Credit: Halk-44/Shutterstock)


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This article was originally published on Feb. 19, 2022.

People have long sought out pre-prepared foods with a long shelf life; for example, Indigenous North Americans created pemmican, a mix of dried meat, tallow and berries, which settlers later found useful for long voyages and military expeditions. Quick eats looked pretty different by the 1990s, when millions of people were replacing meals with SlimFast drinks in hopes of quickly losing weight. Sales declined in the early 2000s as they were eclipsed by other diet options.

The latest iteration of convenient consumption: In 2014 and 2015, the companies Soylent and Huel introduced powdered drinks with Silicon Valley types in mind — people who want to extend their hacking beyond computers and into their diets, by consuming all of the necessary nutrients via multiple daily shakes, no grocery trips required.

Diet-oriented products like SlimFast preceded the craze for trendier, more millennial-friendly drinks like Soylent and Huel. (Credit: Diana Vucane/Shutterstock)

Online, you can find people who claim to have survived off of powder-based drinks such as Soylent and Huel for weeks (as Soylent’s founder, Rob Rhinehart, did) or even months and years on end. While neither company recommends this tactic, some social media users see liquid meal replacements as a welcome challenge and hope their personal experiments bring compelling results, including ramped-up physical fitness. 

That was the idea for Jason Hooper, a physical therapist and YouTuber who endured a 30-day Huel diet in which he got most of his calories by blending powder into drinks. He found it helpful for his busy schedule, which can include hours-long rock climbing sessions. “It kind of simplified what’s a huge part of our life … that very large factor became very simple, so that allowed me to focus energy elsewhere,” he says.

Regardless of one’s liquid of choice, decades of meal-drinking ushers us into unprecedented territory. Research shows that most people naturally desire a varied diet that provides a range of sensory experiences.

“It seems very hard. You will crave texture, basically,” says Paul Smeets, a senior researcher at Wageningen University in the Netherlands who studies eating behaviors. “Sure you can have all the nutrients that you need intubated or ingested, [but] that may not provide satisfaction.”

How Liquid Meal Replacements Affect Our Health

Scientists haven’t fully grasped how our diet evolved nor what exactly transpires in our bodies as we munch on burgers or pick through salads. But research has demonstrated that the diversity within one’s meals, including aspects like texture and taste, matters for our health. Experiments have demonstrated that we tire of specific foods and tend to move on to new ones shortly after — consider why you may have room for dessert after a heaping savory meal. Humans may have developed this behavior to ensure proper nutrient intake. 

Researchers have even observed this phenomenon, known as sensory specific satiety, among children (who haven’t exactly memorized the food pyramid) and animals. So choosing to turn entirely to liquid meal replacements when it isn’t otherwise necessary means overriding our hard-wired instincts. While meal replacement drinks may come in an increasing variety of flavors, you may encounter a relatively similar consistency and miss out on the crunch and flavors from a wider range of foods.

Eliminating that fundamental variety-seeking that we have is not a good thing,” says Barbara J. Rolls, a nutrition scientist at Penn State University who coined the term sensory specific satiety and has studied the process for over four decades. “It’s so ingrained across species and from a very young age.”

It has been found that liquids don’t make us feel as satisfied as solids do. One possible explanation: even “complex” liquids like smoothies and protein shakes leave the stomach more quickly than solids do — literal “fast food,” Smeets says. Meanwhile, protein- and fat-rich solid meals can linger twice as long, according to the Cleveland Clinic. 

Horace Fletcher (also known as "The Great Masticator") took the benefits of chewing to the extreme at the turn of the 20th century, when he advised dieters to munch on food until it reached a liquid consistency. (Source: Wikimedia Commons)

Exclusively slurping on SlimFast or Soylent also means that you’ll miss out on the joy of chewing. As it turns out, chewing is rewarding even when food is absent — consider why some people tear through packs of gum. Most importantly, munching signals the body to prepare for digestion, and longer chewing might even help us eat less.

Lindsey* experiences multiple chronic illnesses and disabilities, including gastroesophageal reflux disease (GERD), that can make eating and cooking difficult. They add supplements to protein shakes for most breakfasts and other occasional meals as they await treatment, and sometimes add ice cream or coffee to mix things up. But that doesn’t always make up for the lack of mastication. “It’s definitely not the most satisfying,” Lindsey says. “It’s not the same as sitting there and slowly chewing and eating.”

Do Liquid Meal Replacements Work?

Beyond feeling bored and perhaps hungry and disgruntled, what health effects come with exclusively drinking your meals? While weight-loss trials have deemed months-long liquid meal replacement plans as generally safe under medical supervision, there isn’t much data on the safety of a regimen filled with newer drinks like Soylent and Huel (apart from small trials carried out by the companies themselves).

Read More: Forget Dieting. Here’s What Really Works to Lose Weight

Another challenge with drinking most (or all) of your food: It may be difficult to get enough fiber, which helps regulate hunger and blood sugar levels. Brands vary on their fiber content. The powders from Huel and Soylent offer a considerable amount per serving, while Boost and Ensure drinks offer little to none. Meanwhile, drinks in the latter category can contain extremely high amounts of sugar, which add up if you’re throwing back multiple per day. Drinking your food can also affect drug absorption, since thick liquids may delay the dissolution of drugs.

Liquid diets are also ironically associated with dehydration, likely because people forget to drink enough water and aren’t getting much from food (which provides around 20 to 30 percent of the H2O we need). Hooper says he fared well except for a day of feeling “quite awful,” which he attributes to dehydration. A lab test revealed that he had elevated potassium levels, which can result from a lack of fluids. Additionally, he consumed more than the recommended daily amount of potassium via approximately 2,700 daily calories of Huel products.

(Credit: Dan Leveille/Wikimedia Commons)

And although some brands claim to stuff all of the necessary nutritional components into a bottle or powder, Rolls and Smeets say this feat may not actually be possible. We haven’t necessarily pinpointed all of the compounds that make certain foods healthy, and how they might work together to produce specific effects.

“As much progress as nutrition has made, we don’t understand all the complexities of what’s in different foods,” Rolls says. “Fruits and vegetables, for example, have all kinds of phytonutrients that aren’t necessarily even defined yet.”

Not to mention, the act of eating is inherently social. While his companions dug into Domino’s pizza one night, Victor Nevarez sat looking defeated with his bottle of strawberry Soylent. Nevarez, a video producer who makes cooking tutorials under the username Internet Shaquille, tried a weeklong diet composed exclusively of Soylent — he says he often felt exhausted, and may have suffered digestive issues from drinking so much fat at once (it is advised to sip slowly). 

He sees a willing departure from whole foods to Soylent as veering toward anti-social behavior. “For someone to say, ‘No thank you, I am not eating because I am consuming Soylent for all my meals,’ it’s not going to be an easy understanding,” he says. 

A Helpful Alternative

For the three months in 2019 when Bethany* was drinking all of her meals, she had little choice in her lack of participation in group dining. After catching a virus two years earlier, she had developed gastroparesis, a condition that causes partial paralysis of the stomach and can slow or stop the movement of food to the small intestine. This made it difficult to eat without throwing up, and she had few options while waiting to see a specialist. 

So she relied on Boost and Ensure drinks for sustenance, along with some Gatorade and saltines — all the while working toward her Ph.D. “I don’t recommend it,” she says, and the routine left her with “crap” energy levels and barely enough nutrition to survive.

Unlike the popular view of liquid meal replacement consumers as overzealous software engineers or fad dieters, these products may serve as a last resort for people who can’t eat solid foods for a variety of reasons. Nevarez says he was surprised to learn from the comments of his Soylent video that people have used it when recovering from surgery and eating disorders.

While more diverse options have cropped up in the past few years for liquid meal replacements, Lindsey and Bethany point to the fact that people with disabilities and chronic illnesses would benefit from more drinks free of common allergens like soy and dairy, which are prevalent in such products, along with reduced levels of sugar.

In the future, Bethany also hopes to see more rigorous evidence behind the various products that help bridge the gap when solid food isn’t an option. “You’re trying to get stuff for a medical reason but you end up having to step your foot into either toxic diet weight-loss culture or the wellness grift of pseudoscience,” she says.

*Certain sources’ last names have been omitted to provide anonymity.

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