Achieving a healthy weight is definitely important—but we're not sure if any pill could replace eating healthier.

By Lisa Valente, M.S., R.D
Updated: April 17, 2019

When it comes to weight loss, it seems like most of us wish there was a magic bullet that could make the whole thing easier. So when it was announced the FDA had approved a new weight loss pill this week, I knew lots of people would be excited. As a registered dietitian, however, I had some questions—and a few concerns.

The new weight-management device is called Plenity, and is made by a biotechnology company in Boston called Gelesis. Now that it's cleared FDA approval, it is expected to launch later this year. You can read more about the device and how it works here, but there are a few key points I want to call out:

  • It’s approved for people with a body mass index (BMI) of 25 or more with no other health conditions.
  • Instead of increasing metabolism or suppressing appetite by altering brain chemistry (the way some weight-loss pills in the past have done), this capsule works by expanding in your stomach to help you feel more full.

Here are my questions so far:

How will it be prescribed?

Your body mass index, or BMI is calculated via your height and weight (learn more about how BMI is calculated). Because BMI only looks at height and weight it doesn’t necessarily offer a fully accurate picture of health. For instance, It doesn’t account for muscle mass or body fat percentage or weight distribution. It also doesn’t change based on sex, so the number ranges are the same for men and women. In short, It’s not the best measurement for assessing someone’s health.

Technically, a BMI of 25 or greater is considered overweight (30 or greater is considered obese). And Plenity is approved anyone whose BMI is at least 25. This means a woman who is 5’4’’ and weighs just 147 pounds (BMI = 25.2) or a 6' tall man who weighs 185 pounds (BMI = 25.1) would be able to take this device.

What does it do to your gut?

If you watch this video, which explains how Plenity works, you learn that particles made with cellulose from the pill expand in your stomach and small intestine, mixing with food "to increase the volume," and make you feel more full. Eventually they travel down to your large intestines, where they shrink back down.

We’re still learning a lot about gut health, including the importance of eating prebiotics and probiotics. Given how important gut bacteria are, and how much food absorption occurs in the intestines, I'm curious about how Plenity affects the gut microbiota. If it's degrading (or changing) the microbiome, this could be problematic.

Cellulose (what the pill is made of) is a non-digestible plant fiber. According to the press release, “the remaining cellulosic material is expelled in the feces.” That makes sense, as it's what happens with all non-digestible fiber. But it doesn’t tell us how much fiber is actually in the pill or the impact it has on our gut health.

Will it help people eat more healthy food?

Being healthy isn't just a matter of eating less, it's also about eating the right kinds of foods, and getting plenty of natural fiber, healthy fats, and protein. Choosing foods that contain these three nutrients generally help you stay satisfied for longer because they take longer to digest. And foods that contain these nutrients also contain other beneficial compounds. Vegetables and fruits have fiber and also deliver vitamins, minerals and antioxidants.

While PLENITY says it is meant to be used in combination with a healthy diet and exercise, I wonder if it will actually help people change their eating habits, or if it will make change harder, especially since becoming "full" from low-calorie foods can mess with hunger and fullness cues.  

Does the research really prove Plenity works?

The FDA approval was largely based off of this weight-loss study, which was sponsored by the manufacturer. The study looked at 324 people over 6 months (112 withdrew from the study for lifestyle or personal reasons). Participants ate a calorie-controlled diet and consumed 300 calories below than their baseline estimated energy needs. They were also advised to get some moderate exercise (for example, a 30-minute walk).

The group taking Plenity lost 6.4 percent of their body weight compared to 4.4 percent for people taking a placebo. There were no significant differences in heart-disease risk factors, such as cholesterol, or insulin resistance. The most common reported side effects were mild and GI-related: “diarrhea, abdominal distension, infrequent bowel movements, flatulence, constipation, nausea, and abdominal pain.”

The weight-loss difference is statistically significant, yes, but it’s not that different (6.4 percent compared to 4.4 percent). What's more, the study doesn’t touch on the types of foods people were instructed to eat or if people taking Plenity ate less food. In real life, outside of a research setting, most people are making their own food choices without nutrition counseling and support that the participants had in this study. It may be harder to make healthy food choices around different foods and portions without that support, even with Plenity. 

Do we really need a new weight-loss tool?

And my biggest question of all: do we really need this? The weight-loss industry is a 60 billion dollar force. Quick fixes, restrictive diets and weight-loss pills have never made us healthier. The solution to being healthier is simple, if it's not always easy: Eat more vegetables, don't stress too much, and find ways to move your body (walking, dancing, yoga, running, lifting weights—whatever makes you happy). Those things can all help us actually be healthier, and this pill doesn't seem to address any of them.

The FDA has made mistakes with weight-loss drug approval before (looking at you fen-phen) and there are plenty of unregulated weight-loss supplements and detox teas out there right now that at best give you mild GI symptoms and at worst can lead to serious health risks. Eating disorders are the most deadly mental health disorder. I’m curious to learn more about Plenity. And while it sounds safer than some of the previous weight-loss pills, I still remain skeptical.

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This story has been updated. The original version incorrectly called Plenity a weight-loss drug. It is actually classified by the FDA as a weight-management device. The participants in the weight-loss study were also not given meals to eat, as the original article stated, but rather counseled on their diets, and given a specific calorie goal.

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