When we talk about weight loss, we tend to focus on the number on the scale. How much weight did you lose? How quickly did you lose it? What size are you now?
But there is another part of the weight-loss conversation that deserves attention: What is actually happening to your bones?
A question I get often is, “Can losing weight cause bone loss?” Or, “Are GLP-1 medications such as semaglutide and tirzepatide harmful to your bones?”
Today, we’re going to focus on who is most at risk for bone loss during weight loss and, most importantly, what you can do to protect your bones while losing weight.
Why Can Weight Loss Affect Bone Health?
Your bones are living tissue. They’re constantly being broken down and rebuilt in a process called bone remodeling. This process responds to several factors, including hormones, nutrition, physical activity, and the mechanical forces placed on your skeleton.
When you lose a significant amount of weight, several of these factors can change.
One is mechanical loading. Imagine someone who weighs 250 pounds and loses 75 pounds. Every time that person stands, walks, or climbs stairs, their skeleton is now carrying substantially less weight.
Bones respond to mechanical forces. When that stimulus decreases, there may be less signal to maintain the same amount of bone mass.
But there is another important connection here: muscle and bone work together.
When your muscles contract, they pull against your bones and create mechanical stress that helps stimulate bone. So if you lose muscle or become less physically active during weight loss, your bones may receive less of that important stimulus.
This is one reason resistance and strength training are so important. You’re not just building or maintaining muscle—you’re also providing your skeleton with the mechanical stimulus it needs to stay strong.
What About Hormones?
Hormones are another major piece of the bone-health equation.
For women, estrogen is particularly important. During perimenopause and menopause, estrogen levels decline, which can accelerate bone loss.
So imagine someone going through menopause who is also losing a significant amount of weight. Their bones may be dealing with several factors at the same time: lower estrogen, less mechanical loading, changes in body composition, and potentially lower nutritional intake.
That’s why bone-loss risk isn’t the same for everyone.
A younger person with healthy bone density may tolerate significant weight loss differently than a postmenopausal woman who already has osteopenia.
Do GLP-1 Medications Cause Bone Loss?
A question I get quite often is, “do GLP-1 medications cause bone loss?”
This is where the conversation online can become misleading.
Someone may start semaglutide or tirzepatide, lose a significant amount of weight, and then learn that bone density can decrease during substantial weight loss. The immediate assumption is, “The medication is damaging my bones.”
But we don’t know that that’s necessarily the case.
Weight loss itself can reduce the mechanical load on your skeleton. You may also lose some lean tissue, become less physically active, and eat substantially less because of reduced appetite. All of these factors can influence bone health.
So when we see changes in bone density during GLP-1-assisted weight loss, we have to ask: How much is related to the medication itself, and how much is related to the weight loss and other lifestyle changes that accompany it?
Researchers are still studying this question. And there is promising laboratory and preclinical research suggesting that GLP-1 signaling may interact with osteoblasts, which are cells involved in bone formation. But this doesn’t mean we can conclude that GLP-1 medications strengthen bones in humans.
The important takeaway is that the independent effects of GLP-1 medications on human bone health are still being studied. In the meantime, we can focus on the things we can control.
Protein, Muscle, and Bone
One of those very things we can control is protein.
Protein isn’t important for bone health simply because it helps you build bigger muscles. Bone itself contains a protein framework, primarily collagen, which provides its structure. Protein also supports the muscle tissue that places mechanical force on your bones.
So if you’re losing weight and eating significantly less food, inadequate protein can contribute to muscle loss. And losing muscle means losing some of the mechanical stimulation that helps support your skeleton.
Now, there is a difference between the minimum amount of protein you need for basic nutritional requirements and the amount that may be useful during weight loss or strength training.
As a simple guide for:
- Basic needs: about 0.4 grams per pound of body weight per day
- Maintaining muscle during weight loss: about 0.6–0.7 grams per pound
- Building muscle with regular strength training: about 0.8–1 gram per pound
For example, someone weighing 150 pounds would need approximately 60 grams for basic needs, 90–105 grams for muscle maintenance during weight loss, or 120–150 grams when actively trying to build muscle.
Now, these are general guidelines, and individual needs can vary based on things like age, body size, activity level, kidney function, and overall health.
Good protein sources include eggs, fish, chicken and other lean meats, Greek yogurt, cottage cheese, tofu, beans, and lentils. If your appetite is significantly reduced, a protein shake can also be a practical way to increase protein intake.
Resistance Training: One of the Best Things You Can Do for Your Bones
Another thing we can control is physical activity. If you’re trying to protect your bones during weight loss, resistance training deserves some serious attention.
When you lift weights, use resistance bands, perform bodyweight exercises, or work against another form of resistance, your muscles generate force that is transmitted to your bones.
You don’t need to become a bodybuilder or lift extremely heavy weights. The goal is regular, progressive resistance training that’s appropriate for your age, fitness level, and physical abilities.
That might include squats, lunges, rows, presses, step-ups, resistance-band exercises, or weight machines.
Weight-bearing activities such as walking and climbing stairs can also help.
So during weight loss, don’t think of exercise only as a way to burn calories. Think of it as a way to tell your skeleton, “I still need you to be strong.”
Calcium: An Essential Building Block
Another thing we can control is nutrient intake. Remember, mechanical stimulation isn’t enough if your body doesn’t have the nutrients it needs.
Calcium is one of the most important minerals for bone health. Your body also needs calcium for functions such as muscle contraction and nerve signaling, so it works hard to maintain calcium levels in your blood.
If your dietary calcium intake is chronically inadequate, your body can pull calcium from your bones to help maintain normal blood levels. Over time, inadequate calcium intake can contribute to poor bone health.
Good sources include milk, yogurt, cheese, calcium-fortified plant milks, calcium-set tofu, sardines or canned salmon with bones, bok choy, kale, and collard greens.
Many adults need approximately 1,000 mg of calcium per day, while some groups need 1,200 mg, including women 51 and older and men 71 and older.
Food is generally a great place to start. If you can’t meet your needs through food alone, supplementation may be appropriate—but more isn’t always better.
And if you have a history of kidney stones or certain kidney conditions, talk with your healthcare professional before starting a high-dose calcium supplement.
Vitamin D: Helping Your Body Absorb Calcium
And speaking of calcium, we can’t forget to mention Vitamin D. Vitamin D works closely with calcium and helps your body absorb calcium from the digestive tract.
Sources include fatty fish, egg yolks, fortified milk, fortified plant-based milks, and fortified cereals. Sun exposure can also contribute to vitamin D production, although the amount varies based on factors such as location, season, skin pigmentation, age, and sun exposure.
The recommended daily intake is 600 IU for most adults and 800 IU for adults over 70.
If there is concern about vitamin D status, your healthcare professional can check a blood test called 25-hydroxy vitamin D.
Who Is at Higher Risk?
The bottom line is that not everyone begins weight loss with the same bone-health risk.
You should be particularly proactive about bone health if you:
- Already have osteopenia or osteoporosis or a strong family historyÂ
- Have had a previous fragility fracture
- Are postmenopausal or older
- Have a low body weight
- Are experiencing significant or rapid weight loss
- Have undergone bariatric surgery
- Take medications that can affect bone health
Long-term glucocorticoid use, including medications such as prednisone, prednisolone, and dexamethasone, is one important example. Certain cancer treatments and medications that affect sex hormones can also contribute to bone loss.
This doesn’t mean you should stop any medication on your own. It simply means your medication history should be part of your overall bone-health discussion with your healthcare professional.
Do You Need a DEXA Scan?
Lastly, I want to touch on DEXA Scans. For people at increased bone health risk, medical monitoring can be an important part of protecting bone health.
A DEXA scan measures bone mineral density, typically at the hip and spine. It can identify osteopenia or osteoporosis and can be used to monitor bone density over time.
Not everyone taking a GLP-1 medication needs a DEXA scan.
But if you’re at a higher risk for bone loss it’s worth asking your healthcare professional whether bone-density testing is appropriate for you.
Thanks again for listening to The Peptide Podcast.
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