Why Am I Underweight but Look Fat?: 5 Reasons

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Why Am I Underweight but Look Fat

Bodies come in all shapes and sizes. While having standards when it comes to things like body composition helps doctors identify health risks, often, these standards don’t take things like a person’s skeletal frame or the unique build of their body into account.

With that being said, you can’t always use weight as a benchmark for health. Some people that appear overweight are actually healthy and it’s also possible to be underweight and still look fat.

This can leave a person wondering, “Why am I underweight but look fat?”

A person can be overweight but still look fat because of their body composition, or their body’s muscle-to-fat ratio. Problems with your perception of your body or body dysmorphia can also make you think you look fat. Finally, some people may be underweight but look fat because of excess skin or bloating. 

Below, we’ll take a closer look at these five reasons that you might look fat even if you are underweight. We’ll also talk more about what it means to be skinny fat and why your weight doesn’t always give an accurate picture of your health.

Why Am I Underweight but Look Fat?

There are several reasons that you might be underweight but still look fat, including body composition, your perception of your body, body dysmorphia, excess skin, and bloating. Let’s take a closer look at these reasons below.

Body Composition

Body composition includes things like your overall weight, how much fat you actually have on your body, and your muscle mass. Basically, it’s all the things that make up your total weight and your body.

Using a chart or having your BMI checked by the doctor isn’t really a good measure of your body composition. Since a person can be thin without having a lot of muscle mass, it’s very possible to be fat even with a BMI that says you are underweight.

There are several more accurate ways to get an idea of your body composition. Doctors might use a variety of tools, including the skin-fold test,

Here’s a look at the average fat percentages for men and women. These changes are based on things like level of fitness, which I’ve included in this chart.

Healthy Body Fat Percentages

Fitness Level Men Women
Average 18-24% 25-31%
Above Average 25% and up 32% and up
Physically Fit 14-17% 21-24%
Athlete 6-13% 14-20%

While you can learn a lot from knowing the percentage of fat in your body, keep in mind that the amount of muscle mass you have matters, too. Muscles play a big role in your life and make it easier to meet physical demands and keep energy levels up for different activities, whether you’re out walking your dog, helping a friend move, or swimming.

Your Perception of Your Body

Your attitudes and the way you generally feel about your body play a pretty big role in the image that you see when looking in the mirror. For example, if you put on an outfit and are worried about your tummy, odds are you are going to focus on your tummy in the mirror and think it looks bigger than it does.

In addition to considering things like your own perception, it’s also important to keep in mind that any time you look at a picture or your reflection, it’s possible that there is some distortion. This is the reason that people look fatter in pictures sometimes and why you may notice you look different in different mirrors.

Body Dysmorphia

Body dysmorphia gets its own category because while it technically has to do with the perception of your body, body dysmorphia is often more serious than just problems with your perception. People with body dysmorphia are at high risk for eating disorders because no matter how much weight they lose, they still see themselves as fat.

If you do believe that body dysmorphia is the reason that you look fat in the mirror but still have a high BMI, it’s important to seek help. People with body dysmorphia often don’t get help for a long time because they are ashamed of their bodies.

Often, one of the most notable symptoms is that you never seem to be happy with your appearance. People with this condition often fixate on one area of their body for some time, though their fixation might change occasionally.

Body dysmorphia goes beyond a lack of confidence and often causes people to do drastic things like starve themselves or undergo plastic surgery to “fix the problem”. Even after drastic measures, however, they still see their body as the same and continue to be unhappy with themselves when they look in the mirror.

Excess Skin

For people who have successfully lost a significant amount of weight or even lost muscle mass, a fatter appearance could be caused by excess skin. You see, while skin has collagen that allows it to stretch as you gain weight or muscle mass, it often stays stretched after you lose weight too.

This doesn’t mean that your skin won’t ever bounce back, but I’ll be honest in saying that many people who lose a LOT of weight do have excess skin. This extra skin is one of the few reasons you might look fat even after losing weight.

The good news is that if you have excess skin from weight loss that makes you look fatter than you are, there are actually quite a few things you can do about it. We’ve actually talked about some of those things like using sculpt your body using shapewear, hiding belly fat in your jeans, and even dressing to hide back fat in a dress or even tight clothing.


Bloating is another reason that you might look fat even if you are underweight. There are so many different things that cause bloating, including water weight, eating a meal too late, your digestive tract being backed up, inflammation from your diet, poor sleep habits, and several others. These reasons can even make you look fatter on some days than others.

If you’ve been working out recently, your body also might look swollen or bloated. This happens because of the microtears in your muscles that go along with a tough workout. As water and nutrients rush to repair these microtears, the added water weight can make you look puffy.

Why Is My BMI Underweight but I Look Fat?

When it comes down to it, there are two basic reasons that you might look fat even though your BMI is underweight. The first reason essentially comes down to body composition, as in where fat accumulates on your body and how muscular you are.

The second general reason a person believes they are fat even with an underweight BMI is that their mind makes them see fat, even if it isn’t there. This could be something to do with perception, but in some cases, the disconnect between your body image and what you actually look like is caused by body dysmorphia.

Why Your BMI Isn’t Always an Accurate Measurement of Weight or Health

At one time, a person’s BMI was considered the benchmark for whether they are considered underweight, average weight, overweight, obese, or even morbidly obese. While there are times when a person’s BMI does accurately reflect their weight, there are other better ways to find out how fat you actually are.

You see, your BMI doesn’t really tell you a whole lot about your overall health. It’s calculated by considering the ratio of your total weight to your total height. This is done without considering things like the muscle-to-fat ratio of your body.

People who appear thin but don’t have a lot of muscle are the perfect example of this. Being “skinny fat” isn’t really healthy, but someone who is skinny fat often has a BMI that reflects them being average or underweight.

What Does it Mean to Be Skinny Fat?

Basically, skinny fat means that while your body looks “normal” according to society’s standards, you actually have a higher fat level for your body than recommended. People who are skinny fat also don’t usually have a lot of muscles.

Skinny Doesn’t Always Mean Healthy

While people generally associate being overweight or having a higher BMI with being unhealthy, the truth is that you can’t always tell about a person’s health just by looking at them. There are people out there that are fat and healthy, just like it’s possible to be thin and unhealthy. There is more to health than just your weight.

How Do I Know if I’m Skinny Fat?

People who are skinny fat are usually thin and appear healthy. However, they might not be able to tolerate long periods of physical exertion and might get tired easily when being physically active. There are also some other symptoms that might indicate you are skinny fat, even if you haven’t had your body composition tested by the doctor.

In addition to being tired after physical exertion, people who are skinny fat might feel light-headed or dizzy after working out. Their muscles might appear weak, so areas like their arms and stomach appear flabby instead of having muscle tone underneath.

You can also take a look at your day-to-day habits to get an idea if you may be skinny fat. If you don’t eat healthily but don’t gain weight or if you’re skinny but have a sedentary lifestyle, then your low BMI may not be an indication of health.

Finally, family history can give clues about whether you are at risk for being skinny fat. People with a family history of obesity, heart disease, type 2 diabetes, or high blood pressure are more likely to become skinny fat if they don’t exercise or eat right.

Final Word

Hopefully, this article has answered your questions about, “Why am I underweight but look fat?” It could be your body composition, your perception of your body, or even that you have body dysmorphia. Bloating and excess skin can also make you look fatter than you are, even with a low BMI.

It’s important to remember that your BMI and the number on the scale don’t always accurately reflect your health. People’s body types are different and your BMI doesn’t necessarily account for this.

If you are worried that you are underweight but still feel fat, talk to your doctor about having your body composition tested. Starting to build muscle mass can help you look leaner and thinner, as well as become healthier.

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