You’re standing in front of the mirror, maybe adjusting your shirt or getting ready for a shower, and there it is. The bone right in the center of your chest. It’s prominent. It sticks out. You start wondering: am i too skinny if i can see my sternum? It’s a question that sends thousands of people to search engines every month, usually fueled by a mix of body dysmorphia, genuine health concerns, or just plain curiosity about how human anatomy is supposed to look.
The short answer? Not necessarily.
Honestly, the visibility of your sternum—that flat bone that connects your ribs—isn't a definitive diagnostic tool for being underweight. Bodies are weird. Some people have very little subcutaneous fat on their chest even at a healthy weight. Others might have a high Body Mass Index (BMI) but still show a bit of bone because of their skeletal structure. But let’s be real: if you can see every single rib and your breastbone is jutting out like a shelf, it might be time to look at the bigger picture of your health.
Understanding the anatomy of the chest wall
The sternum consists of three parts: the manubrium, the body, and the xiphoid process. It sits right under a very thin layer of skin and fascia. Unlike your thighs or your belly, the chest doesn't naturally store a massive amount of fat for most people.
Think about it.
Even elite athletes—people with incredible muscle mass—often have visible sternums. Take a look at marathon runners or rock climbers. They are incredibly fit, yet their chest bones are often quite prominent because their body fat percentage is low. This doesn't mean they are "too skinny" in a clinical sense; it means they have low adipose tissue covering that specific bone.
However, there is a condition called Pectus Carinatum, often nicknamed "pigeon chest." This is where the sternum protrudes outward due to an overgrowth of cartilage. If you’ve always noticed your sternum sticking out, even when you were at a heavier weight, it’s possible your bone structure is just built that way. Genetics plays a massive role here. If your parents have a "bony" look to their upper torso, you likely will too.
The difference between "lean" and "underweight"
We need to talk about the distinction between being lean and being clinically underweight.
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Being underweight is usually defined by a BMI of less than 18.5. But BMI is a blunt instrument. It doesn't know the difference between muscle and fat. It doesn't know if you have a wide ribcage or a narrow one. A person with a narrow frame might see their sternum even at a BMI of 20. Conversely, someone with a very broad frame might only see it when they hit a BMI of 17.
Am i too skinny if i can see my sternum? Well, you have to look at secondary symptoms. Are you tired all the time? Is your hair thinning? Do you feel cold even when it’s 75 degrees out? If you're seeing your sternum and also feeling like a zombie, that’s a red flag. Dr. Jennifer Gaudiani, an eating disorder expert and author of Sick Enough, often points out that the body will start "eating" its own muscle and fat stores when it’s in a calorie deficit. The chest is one of the first places where fat disappears, making the bone structure more obvious.
Why body fat distribution matters
Everyone stores fat differently. It’s called adipose distribution.
Some folks are "pear-shaped," storing most of their weight in their hips and thighs. These individuals might have a very skeletal-looking upper body, including a visible sternum and collarbones, while still having plenty of energy stores lower down. Then you have "apple-shaped" individuals who store fat in the midsection but have thin limbs.
If you're a "pear," you might see your sternum even if you are technically overweight. It’s just how your DNA decided to map out your fat cells. You can't really change where your body puts fat through diet alone. You can gain weight overall, but your body will still prioritize the hips over the chest.
What the medical community says
If you visit a GP and ask about your chest bones, they aren't going to just look at you and say "yep, too thin." They’re going to look at your bloodwork. They want to see your electrolytes, your iron levels, and your thyroid function.
A visible sternum can sometimes be a sign of "wasting" or sarcopenia, but that usually happens in older adults or people with chronic illnesses. For a young, healthy person, it's often just a matter of low body fat or high muscle definition.
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When you should actually worry
Let's get into the nitty-gritty. There are times when a visible sternum is a sign that something is wrong.
If you’ve recently lost a lot of weight without trying, that’s a problem. Unintentional weight loss that makes your bones pop out can be a sign of hyperthyroidism, Type 1 diabetes, or even digestive issues like Celiac disease where you aren't absorbing nutrients.
Also, look at your ribs. If your sternum is visible and your ribs look like a xylophone from the front and the back, you might be dipping into a dangerously low weight. This is often accompanied by "lanugo"—fine, downy hair that grows on the body to try and keep it warm when there isn't enough fat to do the job.
The psychological aspect
Sometimes the "am i too skinny" question isn't about health at all. It's about body image. We live in a world of filters and "thirst traps" where everyone looks perfectly contoured. This can skew our perception of what a normal human chest looks like.
Take a look at Renaissance paintings. Or old photographs from the 1920s. You’ll see plenty of healthy people with visible chest structures. It’s only recently that we’ve become obsessed with a specific "buffered" look where every bone is covered by either thick muscle or a layer of soft fat.
Muscle mass vs. body fat
If you're unhappy with seeing your sternum because you feel you look "scrawny," the answer usually isn't just "eat more donuts." It's often "build more muscle."
The pectoralis major muscles sit right on either side of the sternum. If these muscles are underdeveloped, the "valley" in the middle of your chest—where the sternum is—looks much deeper and more prominent. By doing chest presses, push-ups, or dips, you build up the muscle meat on either side. This fills out the chest area.
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Interestingly, as you build muscle, your sternum might actually become more defined in a "ripped" way rather than a "skinny" way. There is a huge aesthetic difference between a sternum visible due to malnutrition and one visible because of low body fat and high muscularity.
Practical steps to take right now
If you are genuinely concerned that you are too thin, stop staring at the mirror and start tracking data.
- Check your BMI just as a baseline, but don't treat it as gospel.
- Monitor your energy levels. If you’re too thin to support your organs, you’ll feel it in your brain first—brain fog is real.
- Evaluate your diet. Are you getting enough protein and healthy fats? Sometimes people "see their bones" because they are "skinny fat"—low muscle mass combined with low-ish body fat.
- See a doctor if you’re experiencing heart palpitations, dizziness when standing up, or if your periods have stopped (for women). These are much better indicators of being "too skinny" than the visibility of a bone.
- Strength train. If the look of your chest bothers you, focus on hypertrophy in the pectoral region.
The verdict on the visible sternum
So, am i too skinny if i can see my sternum?
Probably not, provided you feel good and eat well. The sternum is a superficial bone. It’s supposed to be there. In many body types, it's one of the first landmarks to appear. Unless it’s accompanied by a laundry list of physical exhaustion symptoms or a sudden, unexplained drop in weight, it’s usually just a quirk of your personal anatomy.
Every body has a "set point" weight where it functions best. For some, that set point includes a bit of chest bone. For others, it doesn't. Stop comparing your "middle" to someone else’s "chest" and focus on how your body actually performs during the day.
If you're eating enough calories to fuel your life and your doctor says your bloodwork is clean, then your visible sternum is just a part of your frame. It’s not a defect. It’s just how you’re built.
Actionable takeaways for moving forward
- Audit your caloric intake. Use a TDEE (Total Daily Energy Expenditure) calculator to ensure you aren't accidentally undereating for your activity level.
- Focus on "The Big Three" for chest growth. Bench press, incline press, and weighted dips will thicken the muscle fibers around the sternum.
- Check for Pectus Excavatum or Carinatum. If the bone shape seems truly unusual, a quick physical with a doctor can rule out structural ribcage issues that have nothing to do with weight.
- Assess your relationship with the mirror. If you find yourself obsessively checking for bone visibility, it might be more of a mental health check-in that's needed rather than a sandwich.
Focus on strength and vitality. The bones will take care of themselves.