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What to Expect with Plenity

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Plenity is a pill approved by the FDA for weight loss. Interestingly, this is one of the few prescription weight loss tools that might have equally effective non-prescription alternatives.

But what are these alternatives?

To understand how to use Plenity and effectively use potential alternatives, we need to first understand how it works, and how effective it is. So here’s what to expect with Plenity.

What is Plenity?

Plenity was approved in April 2019, and is considered by most experts to be a weight loss device, rather than a weight loss medication, despite the fact that it’s taken as a pill. The reason for this is the way that Plenity works.

How does it work?

Plenity is a bulking agent. Bulking agents make us feel full by filling our stomach up without adding calories.

These agents kind of work more “naturally” with our bodies, by stimulating fullness, using the body’s own natural mechanisms, without becoming absorbed into our bodies and suppressing our hormones or nervous system.

With Plenity, it expands in the stomach into a gel when mixed with water and allows the expanding stomach itself to tell you it’s too full.

Plenity is not absorbed into the bloodstream and doesn’t interfere with any hormones or enzymes, so this is why we consider it a medical device, rather than a medication.

What’s inside Plenity?

Plenity is composed of a cellulose hydrogel and citric acid, this mixture, when combined with water, holds up to 100 times its weight.

It’s dosed at 3 pills before both lunch and dinner, and given that each pill contains 0.75 g of this stuff, 3 pills will expand from 2.25 g to around 225 g in the stomach. That’s the weight of a small orange.

For the average adult, this fills approximately a quarter of the stomach volume, effectively reducing the stomach size to around 75% at max dosage.

Comparisons with Plenity

Plenity vs Phentermine

This is in comparison to phentermine, which is a medication that directly suppresses appetite, stopping you from naturally wanting to eat.

Phentermine’s mechanism of action could be seen as more “unnatural”, and because phentermine is absorbed into your body, and stimulates your sympathetic nervous system, we consider it a medication.

The more “natural” way that Plenity works with your body generally means that Plenity will have less side effects and will be safer to take than phentermine, but is also quite a bit less effective than phentermine for weight loss.

Plenity vs Glucomannan (PGX)

Plenity vs glucomannan for weight loss
Plenity vs glucomannan for weight loss.

The bulk created by Plenity is described as a “three-dimensional hydrogel matrix”.

There is something else that creates a “three-dimensional hydrogel matrix” when mixed with water, that’s soluble fiber.

Many types of foodstuffs that, when mixed with water, can bulk out and fill the stomach, and many of these have been researched for weight loss in the past. These foodstuffs include things like guar gum, pectins, and of course soluble fiber.

One soluble fiber that shows the most promise in bulking the stomach for weight loss is glucomannan, a refined component of konjac fiber.

Glucomannan has an unusually high concentration of soluble fiber per weight, and can hold around 50 times its weight in water.

For comparison, chia seeds hold a mere 10 to 15 times its weight in water.

PGX is just a commercially marketed and refined form of glucomannan, and works pretty much exactly the same as any generic purified glucomannan.

We unfortunately don’t have any studies that actually compare Plenity with any other soluble fibers, however based on the way it works, glucomannan, and maybe even other soluble fibers supplements like Metamucil or psyllium husk, might be able to do similar to what Plenity does, but cheaper.

Plenity costs around $100 per month, whereas generic glucomannan costs around $25 per month.

Plenity also requires a prescription, whereas glucomannan can be easily obtained over the counter.

Now Plenity uses a purified form of cellulose, which is more “gut-neutral”, meaning your gut bacteria is less likely to create gas from it.

Glucomannan is a fermentable fiber, meaning gut bacteria can break it down and cause gas, bloating and constipation.

This means that Plenity may cause less digestive issues than glucomannan, although this may not always be the case.

Side effects

Plenity is usually pretty well tolerated, and most adverse effects will be limited to mild gastrointestinal issues. Things like gas, bloating, infrequent stools, and mild abdominal pain were the most common in studies.

Some people might become constipated, however this issue is likely due to not drinking enough water with Plenity, since you are required to drink around 2-3 glasses of water with the pills.

You may also notice that the quality of your poop changes, with some people noticing it for the better, like they become a lot more regular, or their poop becomes softer.

From research studies, an outline of the common and rare side effects associated with Plenity is as follows:

Common side effects (reported in more than 1% of patients):

  • Gastrointestinal disorders (31%)
  • Abdominal pain (16%)
  • Diarrhea (16%)
  • Flatulence (13%)
  • Constipation (11%)
  • Headache (8%)

Rare side effects (reported in less than 1% of patients):

  • Allergic reactions (frequency unknown)

It’s important to note that Plenity is made from plant-based substances and is generally well-tolerated. However, it’s not recommended for patients with a history of gastrointestinal obstruction, including bowel obstruction or stricture.

Plenity diet plan

Plenity, like any bulking agent, needs to be paired with a proper weight loss diet to work properly.

Diets high in protein and fat will help stimulate the release of fullness hormones, and will work well with the stomach bulking effects that Plenity provides.

You can consider a low-carbohydrate diet or a calorie controlled Mediterranean diet.

Diets that benefit the most from supplementing soluble fiber like psyllium husk, glucomannan, or Plenity, into your diet are ones that are low in fiber to begin with.

These are typically high protein or fat diets like the keto diet, and supplementing soluble fiber bulk into these diets can be quite helpful for some people.

Finally, if you have a tendency to snack, you’ll need different ways to keep your snacking under control. Plenity is not going to prevent you from snacking, so you’ll need separate strategies to address this.

How effective is Plenity?

There are a lot of people that don’t find it effective at all, but for those who do find it effective, it has to be used properly.

It’s supposed to be filling your stomach up, meaning it needs to be taken before your meals to effectively reduce your stomach size, causing you to eat less.

Plenity is not going to be nearly as effective as other weight loss medication, like orlistat or Saxenda. You’re looking at best, a modest 3-5% weight loss over 6 months.

However, Plenity is approved for those with a BMI of over 25, unlike the other medications which are usually only prescribed for those with a BMI over 30.

This means that your doctor will be much more willing to prescribe Plenity if you’re only slightly overweight, compared to other medication which is usually only considered if you’re much more heavily overweight.

Should you try it?

Plenity might be helpful if you find that having a full stomach helps you to eat less. This means that it should be used in combination with a proper weight loss diet, to manage hunger and help you to feel fuller quicker.

If you do decide to try it, keep in mind these few things:

  1. If you’re an emotional eater, and tend to snack out of boredom or stress, Plenity is not likely going to work at all, since you might be used to ignoring the fact that your stomach is already full. Plenity only works by simulating a slightly fuller stomach.
  2. I suggest taking it with your two largest meals, rather than just lunch and dinner.
  3. Plenity is kind of like a prescription form of soluble fiber, so you can consider trying another soluble fiber supplement like glucomannan or Metamucil first, since it won’t require a prescription, will be much cheaper, and will give you an idea of whether these bulking agents like Plenity will actually help you lose weight.

So if you do try it, don’t expect miracles. It’s not very effective by itself, and you should only use it to support a proper weight loss diet and lifestyle.

Learn more about

Citations

Das A. Advances in Chia Seed Research. Adv. Biotechnol. Microbiol. 2018;5:5–7. doi: 10.19080/AIBM.2017.05.555662.

De novo classification request for Plenity (FDA). https://www.accessdata.fda.gov/cdrh_docs/reviews/DEN180060.pdf

Doi K. Effect of konjac fibre (glucomannan) on glucose and lipids. European Journal of Clinical Nutrition. 1995;49(supplement 3):S190–S197.

Giruzzi N. Plenity (Oral Superabsorbent Hydrogel). Clin Diabetes. 2020;38(3):313-314. doi:10.2337/cd20-0032

Greenway FL, Aronne LJ, Raben A, et al. A Randomized, Double-Blind, Placebo-Controlled Study of Gelesis100: A Novel Nonsystemic Oral Hydrogel for Weight Loss [published correction appears in Obesity (Silver Spring). 2019 Apr;27(4):679] [published correction appears in Obesity (Silver Spring). 2019 Jul;27(7):1210]. Obesity (Silver Spring). 2019;27(2):205-216. doi:10.1002/oby.22347

How to Determine if Your Product is a Medical Device https://www.fda.gov/medical-devices/classify-your-medical-device/how-determine-if-your-product-medical-device

Keithley JK, Swanson B, Mikolaitis SL, et al. Safety and efficacy of glucomannan for weight loss in overweight and moderately obese adults. J Obes. 2013;2013:610908. doi:10.1155/2013/610908

Onakpoya I, Posadzki P, Ernst E. The efficacy of glucomannan supplementation in overweight and obesity: a systematic review and meta-analysis of randomized clinical trials. J Am Coll Nutr. 2014;33(1):70-78. doi:10.1080/07315724.2014.870013

Pass A, Bialonczyk D, Chiquette E, Goldman JD. Oral Superabsorbent Hydrogel (Plenity) for Weight Management. Ann Pharmacother. 2021;55(9):1146-1152. doi:10.1177/1060028020983046

PLENITY. https://www.rxlist.com/plenity-drug.htm#description

Plenity FDA Approval History. https://www.drugs.com/history/plenity.html

The Nutrition Source – Chia Seeds https://www.hsph.harvard.edu/nutritionsource/food-features/chia-seeds/

Ullah R, Nadeem M, Khalique A, et al. Nutritional and therapeutic perspectives of Chia (Salvia hispanica L.): a review. J Food Sci Technol. 2016;53(4):1750-1758. doi:10.1007/s13197-015-1967-0

Walsh DE, Yaghoubian V, Behforooz A. Effect of glucomannan on obese patients: a clinical study. Int J Obes. 1984;8(4):289-293.

Zalewski BM, Chmielewska A, Szajewska H. The effect of glucomannan on body weight in overweight or obese children and adults: a systematic review of randomized controlled trials. Nutrition. 2015;31(3):437-42.e2. doi:10.1016/j.nut.2014.09.004


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  • Bupropion vs Contrave vs Naltrexone
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  • New Obesity Drugs in 2024
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  • Mounjaro: Who Loses the Most Weight?
    White or Asian younger women who use metformin and have lower sugar and lipid levels tend to experience more weight loss with Mounjaro.

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4 thoughts on “What to Expect with Plenity”

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    1. I disagree. I am very constipated after 2 months of Plenity. I have pictures of my colon. There is so much crap inside my colon. It made me very sick. I had colitis (not actually confirmed) but the MRI and Cat scan showed why I was hunched over in pain. And my stomach felt like it was gonna fall down.

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