Weight vest fat loss science
Why weighted vests and packs help us lose weight.
Post summary
We have an epic guest post from Dr. Nick Norwitz, PhD/MD, of Stay Curious Metabolism.
He’ll walk us through some fascinating new research suggesting that weight vests can help us lose weight—especially fat.
You’ll learn the fascinating science of “the gravitostat” and five ways you can use it to reach your goals.
Housekeeping
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Audio version
The post
Something funny happens when I do a lot of weighted walking—whether that’s a long backpacking trip, walking through my neighborhood with a weighted pack, or being a weirdo who vacuums while wearing a weight vest.
I lose weight. And that weight loss is mostly fat.
I’ve cited research that shows walking with weight seems to preferentially burn fat. I’ve had my theories about why.
Today, we have an epic guest post from Dr. Nicholas Norwitz explaining the science of the phenomenon.
Nick has a Ph.D. in Metabolism from Oxford and just earned his M.D. from a little-known institution named Harvard University. Nick also recently started a Substack that dives deep into health science in a fun and practical way. You can check it out here:
Here’s Nick …
Humor me for a moment and imagine a scenario: You’re gaining too much weight, and this annoys your skeleton because now it has to carry even more of you.
So your bones—cranky that your caloric excursions are forcing them to work extra hard against gravity—send a signal to your brain that says, “Hey, you’re getting too heavy. Ease off the snacking!” Then your brain listens to this message and decreases your appetite.
This may sound like science fiction—but new research suggests there is metabolism science in the madness.
It turns out that we may be able to use this to our advantage—and trick our bodies into losing weight with a weighted vest.
Remarkable research is showing how strategically loading your body with a weighted vest or pack can decrease your hunger. And if you’re less hungry, you’ll probably eat less—and lose some fat.
Today, we’ll:
Break down this fascinating work.
Leave you with five practical tips on how to use it.
Three studies with wild results
We’ll focus on three studies.
The first two are human randomized controlled trials (RCTs). RCTs are considered the "gold standard" in clinical research because they can establish a cause-and-effect relationship between an intervention and an outcome.
The third is an animal model study. Animal studies can help us understand why we see the results we do in human studies.
We’ll blaze through the human studies because, while they establish the human relevance of these findings, they merely set the stage for the remarkable “why it works” findings of the animal study.
Human RCT 1: short-term, big impact
In one RCT1, 72 participants with obesity were split into two groups.
The first group wore a weight vest that was equal to 11 percent of their bodyweight. That’s equal to 22 pounds for a 200-pound person.
The second group wore a non-weighted vest (1 percent of their body weight).
Both groups wore the vest eight hours per day for three weeks.
The findings: Wearing the weight vest led to statistically significant weight loss over only three weeks (just under four pounds of weight loss).
Remarkably, all of this weight was from fat (down ~4lbs), and the participants gained about half a pound of muscle.
Losing fat without losing (or maybe even gaining?) muscle over a short time period is impressive.
But this study was just three weeks. What happens if we wear a weighted vest for much longer?
Human RCT 2: long-term weight loss defense
In a 2025 RCT2, participants were again randomized to two groups. The first group wore a weighted vest (~13lbs for 6.6 hours per day). The second group didn’t wear a vest. The study lasted six months.
This study, however, came with two additional features.
First, during this six-month phase, both groups were placed on a strict, very low-calorie diet (1,100–1,300 calories a day).
Second, all participants were then followed for an additional 18 months after the intervention ended.
In sum: For 0–6 months people ate a very low-calorie diet with or without wearing a weighted vest. Then, for 6–24 months, people were left to live their lives freely without the weighted vest or a diet.
The findings:
Both groups lost the same amount of weight during the initial six-month intervention, likely because of the restrictive nature of the diet.
But what happened next was fascinating: while the control group gained all their weight back, the weighted vest group only gained half the weight back.
In other words, weight regain was twice as much in the control group compared to the weighted vest group after the intervention ended.
This suggests there was a ‘lingering’ metabolic effect of wearing the weighted vest. Weird? How? What’s going on?
Before I reveal the possible mechanism, try to generate your own hypothesis and—if you’re bold—share it in the comments.
Now, let’s reveal the metabolic secret. To do that, we have to look to animals since we can’t ethically tinker with human genetics to dissect mechanisms.
The animal study: lab rats, loaded vests, and a weighty discovery
The animal study3 set the foundation for the first human trial we discussed.
It was published by the same research group who, in 2018, developed the hypothesis of a “gravitostat.”
Gravitostat is an important idea we’ll be referencing often in the rest of this post.
Think of gravitostat as a weight sensor in your body that regulates fat mass.
In this brilliant study, the scientists loaded mice and rats with capsules equal to 15 percent of their body weight, the rodent equivalent of a weighted vest (hence, I’ll refer to weigh-loaded animals as the ‘weighted vest’ group).
Remarkably, compared to control animals that were loaded with empty capsules, the ‘weighted vest’ animals lost a tremendous amount of weight over just two weeks.
Interestingly, the ‘weighted vest’ animals lost about as much weight as the additional load they carried.
Gravity up, forks down
If we were thinking superficially about what drives weight vest weight loss, we might assume we’re just burning more calories.
We also might hypothesize that our appetite would increase or ‘at best’ remain the same (after all, we’re burning more calories, so we might want to eat more).
But that’s NOT what the researchers observed.
Instead, the ‘weighted vest’ animals ate less.
That’s what drove the loss, as demonstrated by the fact that when the control mice were restricted to a diet that matched the amount of food the ‘weighted vest’ animals were eating, they lost the same amount of weight. (This is called “pair feeding.”)
Pause and consider this: Increasing the gravitational load on these animals decreased their appetite.
Their bodies appeared to respond by adjusting their food intake until their total weight with the weighted capsules was equal to their starting weight without the weighted capsules.
This was the origin of the “gravitostat” hypothesis.
It’s the idea that the body, particularly the bones, senses an increased gravitational load and sends signals to the brain to curb food intake.
In short: The bones scream, “I’m overloaded,” and the brain says, “Ok, I’ll have this person eat less.”
The goal? To bring the organism (whether that’s Stuart ‘Not So’ Little or future you after an all-inclusive cruise) back to a movement-friendly body mass.
It works in many species
Before we dive into the mechanism, it’s worth highlighting that this phenomenon appears across species.
We've already observed similar responses in humans and rodents—but scientists always want to know if a system extends beyond mammals. If it does, it becomes more weighty.
Birds became the next logical group to study. After all, if a bird gets too heavy, it quite literally goes the way of the dodo.
The scientists found the phenomenon holds in birds.
When researchers4 attached small weights to the backs of homing pigeons, equal to roughly 5 percent of their body weight, the pigeons compensated by losing nearly the same amount of body mass.
When the load was removed, the birds regained the lost weight (blue in the graph below). They also lost it when the load was placed back on them (orange).
By adding or removing the weights, the researchers could toggle the pigeons’ body weight almost like flicking a switch.
The takeaway: The gravitostat may be a deeply rooted, evolutionarily conserved system—one that helps animals, feathered or otherwise, maintain their optimal size.
What drives the weight loss
Now, let’s return to rats and mice.
Researchers wanted to know why this happens—the mechanism.
So they tinkered with different hormone systems to figure out what might be mediating the weight-loss and appetite-curbing effects of loading the body.
They thought the appetite-regulating hormone leptin might be at play. It wasn’t.
When the same experiment was performed on leptin-deficient (Ob/Ob) mice, the results were the same. This suggests the mechanism was independent of leptin.
What about the weight-loss hormone GLP-1? Nope. It wasn’t GLP-1 either.
What about ghrelin? αMSH? ERα? Sclerostin? FGF-23? Osteocalcin? Lipocalin?
Nope. Nope. Nope. Nope. Nope. Nope. Nope.
With enough tinkering, the researchers found what was going on …
Your bones speak up: “Put down that donut!”
When scientists knocked out the function of osteocytes—which are cells in bones that sense mechanical load and coordinate bone remodeling—the weight-loss effect was completely abolished.
You don’t need a fancy degree to see this phenomenon in the graph below.
Left, normal osteocytes: Animals lose weight.
Right, osteocyte knockout: Animals don’t lose weight.
In animals without functional osteocytes in their bones, adding a load does ‘diddly squat’ for weight loss. (That’s a highly-technical scientific term.)
It’s like this: Extra weight annoys your bones. Your bones, upset they need to carry extra load, signal to your brain to curb your appetite. That’s what the research suggests, anyway.
Leptin and gravity act as weight “guardrails”
Before we dive into practical ways to apply this science, let’s zoom out and connect the dots between the “gravitostat” and what we already know about weight regulation—especially the role of the hormone leptin.
First, consider that each of us has a natural range of comfortable body weights.
Sure, weight fluctuates from day to day and week to week, but most of us hover within a familiar zone.
From an evolutionary perspective, this makes perfect sense. Small shifts in weight don’t threaten survival.
But if your weight drops too low, it signals starvation and frailty.
Too high, and mobility and agility suffer.
It follows that our bodies have built-in tricks designed to nudge us back into a healthy range—whether too high or too low.
When weight gets too low, your body’s trick is to decrease leptin—a hormone released by fat tissue.
Leptin levels fall when your fat stores get too low. This drop signals your brain to conserve energy and find something to eat. That helps restore the lost weight.
You can think of leptin as a “bottom guardrail,” pushing weight back up when it falls too low (blue in the graph below).
But when you get too heavy, the gravitostat comes into play.
This gravitostat system senses the increase in your body weight—essentially, through increased loading on your bones/skeleton. It then pushes your weight back down when it creeps too high. In other words, gravity acts as the “top guardrail” (purple).
Interestingly, these two systems appear to complement each other.
The body’s response to leptin is strongest in leaner organisms, while the gravitostat’s weight-reducing effect becomes more pronounced in those with obesity.
Of course, it’s not quite that simple.
Factors like central leptin resistance and other hormonal signals can shift your weight set point or make it harder to return to your natural range.
Still, this “dual mechanism” model—with leptin at the bottom and gravity at the top—helps us understand how biology works to keep your weight within optimal boundaries.
Nuance note: It’s important to acknowledge Gravity and Leptin are just two levers among many. Obesity and metabolism are complex. However, the fact that among calories, sugar, hormones, and sociocultural factors, gravity may also be a lever against obesity is in and of itself remarkable and doesn’t need any further sensationalism. It’s not about revealing the complete puzzle but adding a noteworthy piece that has fallen under the couch and been overlooked.
Read this footnote5 if you’re wondering, “If I’m already heavy, will that make me lose weight?”
How to use it
Now that we understand the science, let’s benefit from it.
Here’s how you can apply this research to your own life:
1. Consider a weighted vest
Start light—around 5 to 10 percent of your body weight—and wear it during daily tasks like walking, working, or chores.
Start with short bouts. Gradually build up to longer durations and/or greater weights as tolerated. For safety, keep it below 30 percent of your body weight.
2. Focus on consistency, not extreme efforts
Wearing the vest should not be a hard workout. It should feel like a slight addition to your body. Aim for subtle, consistent loading over the day.
3. Add loading to your life
The magic comes from your bones sensing extra weight.
Figure out ways to load your skeletal system in everyday life. At the grocery store, use the basket. Carry your kid more often. Get creative.
Little swaps like these can accumulate to build your muscles and bones and—like I said in the opening—decrease your appetite so you lose weight.
4. Pair it with healthy habits
A weighted vest isn’t magic, but it may complement good nutrition and regular activity by naturally reducing your appetite.
Think of it as another weapon in your health arsenal. There are no nuclear bombs in health—just lots of useful weapons.
5. Listen to your body
If you start wearing a vest, pay attention to how your body responds.
Watch your appetite, energy, and comfort levels. Adjust over time.
Here’s Michael again. Thanks to Nick for the deep dive.
Go deeper: For more practical advice on weighted walking, read this post.
And Remember, you can subscribe to Nick’s newsletter here:
Have fun, don’t die, go load yourself.
-Michael
Increased weight loading reduces body weight and body fat in obese subjects – A proof of concept randomized clinical trial, Ohlsson, Claes et al., eClinicalMedicine, Volume 22, 100338
DeLong, C., Nicklas, B.J., Beavers, D.P. et al. Does weighted vest use during weight loss influence long-term weight loss maintenance? A pilot study in older adults living with obesity and osteoarthritis. Int J Obes (2025). https://doi.org/10.1038/s41366-025-01795-5
J. Jansson, et al., Body weight homeostat that regulates fat mass independently of leptin in rats and mice,Proc. Natl. Acad. Sci. U.S.A.115 (2) 427-432,https://doi.org/10.1073/pnas.1715687114(2018).
Jansson, J.-O., Anesten, F., Hägg, D., Zlatkovic, J., Dickson, S. L., Jansson, P.-A., Schéle, E., Bellman, J. & Ohlsson, C. (2023). The dual hypothesis of homeostatic body weight regulation, including gravity‑dependent and leptin‑dependent actions. Philosophical Transactions of the Royal Society B: Biological Sciences, 378(1888), 20220219. https://doi.org/10.1098/rstb.2022.0219
Some people may be wondering, "If I’m already heavy, won’t that make me lose weight?" or, "Why hasn’t it?" Of course, if the gravitostat were all-powerful, obesity wouldn’t exist. The answer is simple: Obesity is complex. There aren't just one or two levers that determine whether someone develops obesity. Multiple genetic, epigenetic, environmental, and behavioral factors all interact to influence the comfortable weight range for a given body. To be clear, that doesn’t mean the optimal weight range—but rather the range of weights to which a particular body is attracted within the framework of genetics and almost always suboptimal environmental and dietary factors. Shifting that range—which absolutely can be done—requires intentional use of the many tools at our disposal, many of which involve diet and lifestyle. But the fact that gravity may be one of those tools is truly remarkable.
This is so cool! Great article Michael!
Haha, footnote 5 came in exactly at the time I was wondering that very thing! Wondering how this works for maybe not so much weight, but a slight paunch. I guess if the fat is what gets lost, that could work.