soylent diet soylent cafe

Soylent Diet Study: Liquid Diet Might Affect Mood

Thryve Inside recently conducted an internal study about changes in the health of someone who consumes a Soylent drink meal replacement for their sole source of nutrition. Results found that Soylent nutrition, instead of solid food, may increase stomach bacteria that can affect your mood. While this liquid diet is rich in many beneficial nutrients, it doesn’t meet daily fiber recommendations per caloric intake. So, strict Soylent drinkers might not achieve optimal gut health. Let’s take a closer look at the benefits and drawbacks of consuming a Soylent bottle for each meal.


Soylent Diet Study Methodology

Our Thryve Inside Soylent diet study was conducted in three phases over an eight-day period. Phase A saw our volunteer consume a regular Western diet of solid food. They followed this protocol for two days.
In Phase B, the participant consumed Soylent for three days. During Phase B, Soylent nutrition was the test subject’s only source of nutrition.
Days six through eight were Phase C. During Phase C; our volunteer went back to the diet they followed in Phase A.
Every day of this Soylent diet study, we sampled the gut biome of our participant. Let’s take a look at the differences a diet of only Soylent nutrition can have on the human body when compared to regular eating habits.


What Are Soylent Products?

Soylent is a brand of products that are the brainchild of Silicon Valley software engineer Rob Rhinehart. Soylent products offer all the elements of a healthy diet in one convenient product. With the main ingredient being soy protein isolate, this liquid diet provides the human body with adequate nutrition without the calorie intake of consuming traditional food.
According to Soylent’s website,

“Soylent is engineered nutrition. We carefully and purposefully choose each ingredient to offer a complete meal in every bottle of Ready-to-Drink Soylent and each scoop of Soylent Powder [1].”

There are many types of Soylent products, including:
soylent diet study
• Soylent Drinks (Meal Replacement Drinks)
• Soylent Squared (100 Calorie Nutrition Bars)
• Soylent Cafe (Coffee and Nutrition Beverages)
• Soylent Powder (Shake and Smoothie Powders)
• Soylent Bridge (Heavy Nutrition Snack)
Out of the many Soylent products, only the meal replacement drink was consumed during Phase B of the Soylent diet study.
It’s hard to determine if Soylent diets can be a person’s sole source of nutrition forever. A long term liquid diet isn’t something with a ton of studies to read.
Our Soylent diet study just gives a small snapshot of changes the human body goes through when we trade in traditional food for a Soylent bottle. With that said, Soylent drinks have all the elements of a healthy diet in one meal replacement drink.


What is In A Soylent Drink?

Many of the ingredients comprising Soylent nutrition are also staples in the weightlifting community. Let’s take a look at the ingredients that lie within a Soylent bottle to see if they meet the elements of a healthy diet.


Soy Protein Isolate

Soy protein isolate is a complete protein and is one of the most nutrient-dense plant-based proteins in the world. One Soylent bottle contains 500mg of omega-3 fatty acids.
soy in soylent diet
Studies about adopting a soy protein liquid diet seem to indicate potential benefits. One study involving 77 volunteers found that switching to a soy protein meal replacement drink caused the average person to lose 4.4 pounds [2].
Furthermore, those who switched from a traditional food diet to one of liquid saw a 26.3% decrease in C-reactive protein in the system. Our liver secretes more of this protein when there is inflammation present in the microbiome [3]. Therefore, soy protein isolate might be an anti-inflammatory food.
There are many health benefits of soy. Unfortunately, it’s also a common allergen. So, not everyone can reap the benefits of this plant-based protein. Therefore, following a Soylent diet might actually cause them digestive issues.


Sunflower Oil

We’ve got the protein covered. Now, it’s time for the healthy fats. Sunflower oil is rich in oleic acid. Oleic acid is a monounsaturated fatty acid.
Therefore, it’s very efficient for our bodies to break down. So, these fatty acids are less likely to accumulate around your gut and cause weight gain.
You need fats for brain health, nutrient absorption, and repairing your gut lining.
However, most of us who eat traditional food tend to get a bit overboard with the fats. So, drinking a Soylent beverage is an easy way to monitor your fat intake.



The last primary ingredient in Soylent drinks is isomaltulose. Isomaltulose is a sugar alternative. Soylent products get this sweetener from beetroots.
Many who watch their sugar intake prefer isomaltulose. Our body metabolizes it slower. So, it is less likely to cause an increase in blood sugar levels.


Other Ingredients

There are other ingredients that round out this meal replacement drink. Some of them are beneficial, such as alkalized cocoa powder. However, there are many other potential red flags in this product.
Other ingredients in Soylent drinks include:
• Natural and Artificial Flavors
• Sucrose
• Cellulose
artificial flavors
When you see “natural” flavors, it can mean that the flavors are synthetically made to mimic flavors derived in nature. However, Soylent also admits to having “artificial” flavors in their beverage. We have no idea what these ingredients are and potential benefits or detriments they may bring.
Sucrose is a funny addition to Soylent drinks. After all, isomaltulose is usually used as a replacement for sucrose. So, the amount of sugar in the drink continues to add up.
Speaking of which, cellulose is also a polysaccharide. That’s more sugar. Not to mention, our bodies have trouble digesting these simple sugars.
Research published by Kahn Academy indicates,

“Cellulose, an important structural component of the plant cell wall, is a polysaccharide consisting of a linear chain of multiple β(1-41−41, minus, 4) linked glucose units. Cellulose is difficult for most animals to digest. Humans are unable to digest cellulose due to the lack of the enzyme needed to cleave its β(1-41−41, minus, 4) glycosidic bond [4].”

Kahn Academy
Based on our data and research, long-term use of Soylent drinks may cause some digestive issues. If you find following a Soylent diet works for you, try doing it intermittently with traditional food that is high in probiotics. That way, the bacteria can help your body break down this product and flush out the system.


Soylent Nutrition

Most Soylent products are enriched with:
• 26g of Protein
• 26+ Vitamins and Minerals
• 21g of Healthy Fats
• Complex Carbohydrates
According to Soylent’s website, the Soylent Diet bases their serving sizes on a 2,000 caloric intake [5]. To achieve this recommendation, you would have to consume a Soylent bottle five times per day.
The average male and female need between 46g to 56g of protein everyday [6]. Consuming just Soylent drinks as meal replacements would give you the averaged recommended protein intake. By rights, Soylent drinkers should be super-powered with Soylent nutrition. Did our study agree with this sentiment?


Soylent Diet Study Results

When we started our Thryve Inside internal studies, we looked at numerous dietary methods. Perhaps none saw as small of a change in gut bacteria than switching to a Soylent diet.
gut bacteria diversity thryve diet studies
Almost no change in gut bacteria from Phase A to B,
with a small drop off when switching to Phase C
Most of the changes to stomach bacteria had to do with microbes that influence the gut-brain-axis. Let’s take a closer look at our data.


Increases and Decreases Bacteria Associated With Irritable Bowel Disease (IBD)

Most of the side effects of a Soylent diet that our volunteer experienced weren’t gut-related. They were more mental. We saw an interesting development when we tested their gut biome. Bacteria associated with inflammation in the colon increased in some areas and decreased in others. Here’s what we found.


Increases Proteobacteria

The two major phyla of bacteria in the gut biome are Bacteroides and Firmicutes. They make up 90% of intestinal florae. Having Proteobacteria in the microbiome is indicative of a healthy gut. However, having too much can cause some digestive problems.
soylent data graphSwitching to a Soylent diet saw Proteobacteria levels jump
A meta-analysis about the influence Proteobacteria has on the gut stated,

“Overgrowth of Proteobacteria has been associated with metabolic syndrome and inflammatory bowel disease. Also, Proteobacteria can be selected (over Bacteroidetes and Firmicutes) by intestinal inflammation as tested by TLR5-knockout mice, and some Proteobacteria can induce colitis in this background, potentially leading to a feedback loop [7].” 

It should be noted that the volunteer already relatively high levels of Proteobacteria going into the study. Their presence already took up 7% of space. That would leave almost 3% for other bacteria if the test subject had a ratio of Bacteroides to Firmicutes that added up to 90%. After a Soylent diet, Proteobacteria was almost 10% of their gut bacteria.
Lack of Sufficient Fiber
gluten-free grains
We hypothesize that the reason for this growth of bacteria associated with IBD is that solely Soylent drinkers don’t get adequate dietary fiber. In Soylent drinks, there is just 2.83g of dietary fiber [8]. At five bottles, a Soylent diet provides 14.25g of total fiber. According to the American Heart Association (AHA), the average person should consume 25g of fiber per day [9].
Dietary fiber serves as nutrition for your probiotics. Fiber our body can’t consume provides food for probiotic growth. These energy sources are known as prebiotics. The more prebiotics we feed probiotics, the more beneficial short-chain fatty acids they will create.
When our probiotics have prebiotics, they provide our system with butyrate. Butyrate is essential for the strength of our colon cells. By consuming fiber, we help prevent instances of IBD.


Lowers Paraprevotella

While Soylent promotes the growth of bacteria associated with IB,  it reduces the presence of others related to gut inflammation. During the study, our test subject saw a 63% drop in Paraprevotella in the system.
soylent diet moodOur test subject felt down as the Soylent diet progressed
One analysis of this opportunistic bacteria stated,

“Studies indicate that Prevotella predominantly activate Toll‐like receptor 2, leading to production of Th17‐polarizing cytokines by antigen‐presenting cells, including interleukin‐23 (IL‐23) and IL‐1. Furthermore, Prevotella stimulate epithelial cells to produce IL‐8, IL‐6 and CCL20, which can promote mucosal Th17 immune responses and neutrophil recruitment [10].” 

The lowering of Paraprevotella may explain why the test subject didn’t experience severe gastro issues. It may have offset the increase in Proteobacteria.


Alters Bacteria Associated With Mood

Our test subject self-reported that they felt really depressed as the Soylent diet progressed. We noticed that these feelings correlated with a shift in balance between two types of gut bacteria associated with mental health.


Lowers Phascolarctobacterium

As our gut test indicates, their levels of Phascolarctobacterium plummeted during the second day of the Soylent diet.
soylent diet sadnessDay 2 of the Soylent diet was the hardest for our test subject
This genus is known to produce two beneficial short-chain fatty acids in acetate and propionate. These fatty acids help with everything from producing gut hormones to nutrient absorption [11]. Furthermore,
Phascolarctobacterium plays a vital role in mental health.
A study on the connection between Phascolarctobacterium and mood concluded,

Phascolarctobacterium was found to be positively correlated to the positive mood of the human (6). An increasing number of studies proposed that Phascolarctobacterium faecium (P. faecium) exerted beneficial effects on the host, including rat model of nonalcoholic fatty liver [12].”

Exp Ther Med
When our test subject entered Phase C, they noted positive changes in the demeanor. Our data shows that this change in perception correlates with a rise in Phascolarctobacterium in the gut biome.


Increases Sutterella

Additionally, our test subject saw a rise in Sutterella wadsworthensis in the system. For one, this bacteria is heavily associated with IBD. One study found that 83.8% of adults who have ulcerative colitis have an abundance of this bacteria [13].
Furthermore, this bacteria seems to be abundant in people diagnosed with autism. While autism isn’t the same as the depressive mood felt by the test subject, it does show there is a correlation between state of mind and Sutterella wadsworthensis.
With that said, levels of this bacteria remained higher in Phase C than they did Phase A. However, the volunteer self-reported they felt better emotionally during Phase C. So, these findings may infer that the presence of Sutterella has less influence on moods than the absence of Phascolarctobacterium.


Are Soylent Diets Healthy?

All-in-all, switching from traditional food to a liquid diet is stressful for the system. So, in the long term, it will probably be stressful for you. These unenviable effects were felt by our test subject during their Soylent diet.
Soylent diets seem to offer a lot of nutrition in one sitting. In the short term, it might not hurt to have a meal replacement drink instead of a complete meal. However, it shouldn’t be your permanent source of nutrition.
Our test subject didn’t see much change in their bacteria diversity overall. However, the alterations in the abundance of specific species led to a change in moods. We believe the reason for this is the lack of necessary dietary fiber present in Soylent drinks isn’t enough to sustain a diverse microbiome.


Click Here To View Resources



[1] “About Soylent: What’s in Soylent?” Soylent, 24 Mar. 2020,
[2] Li, Z, et al. “Long-Term Efficacy of Soy-Based Meal Replacements vs an Individualized Diet Plan in Obese Type II DM Patients: Relative Effects on Weight Loss, Metabolic Parameters, and C-Reactive Protein.” European Journal of Clinical Nutrition, U.S. National Library of Medicine, Mar. 2005,
[3] “C-Reactive Protein Test.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 21 Nov. 2017,
[4] “Why Rabbits Can Digest Cellulose (Practice).” Khan Academy, Khan Academy, 2 Apr. 2020,—passage-2.
[5] Labs, Rosa. “Soylent Serving Sizes.” Soylent FAQ, 2 Apr. 2020,
[6] “Protein Intake – How Much Protein Should You Eat Per Day?” Healthline, 24 Mar. 2020,
[7] Bradley, P. H., & Pollard, K. S. (2017). Proteobacteria explain significant functional variability in the human gut microbiome. Microbiome, 5(1), 36.
[8] Labs, Rosa. “Fiber and Digestion.” Soylent FAQ, 2 Apr. 2020,
[9] “Whole Grains, Refined Grains, and Dietary Fiber.”, 20 Sept. 2016,
[10] Larsen J. M. (2017). The immune response to Prevotella bacteria in chronic inflammatory disease. Immunology, 151(4), 363–374.
[11] Ríos-Covián, D., Ruas-Madiedo, P., Margolles, A., Gueimonde, M., de Los Reyes-Gavilán, C. G., & Salazar, N. (2016). Intestinal Short Chain Fatty Acids and their Link with Diet and Human Health. Frontiers in microbiology, 7, 185.
[12] Wu, F., Guo, X., Zhang, J., Zhang, M., Ou, Z., & Peng, Y. (2017). Phascolarctobacterium faecium abundant colonization in human gastrointestinal tract. Experimental and therapeutic medicine, 14(4), 3122–3126.
[13] Mukhopadhya, I., Hansen, R., Nicholl, C. E., Alhaidan, Y. A., Thomson, J. M., Berry, S. H., Pattinson, C., Stead, D. A., Russell, R. K., El-Omar, E. M., & Hold, G. L. (2011). A comprehensive evaluation of colonic mucosal isolates of Sutterella wadsworthensis from inflammatory bowel disease. PloS one, 6(10), e27076.

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