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What Causes a Person to Be Underweight?

While there is a considerable amount of concern in society regarding issues of body image and weight, most of that attention is focused on those who are perceived to be overweight or obese; relatively little time is spent discussing those at the other end of the spectrum. Being underweight is a legitimate health issue affecting many thousands of people, and it can occur for a variety of reasons. There are even many circumstances in which having too little body weight can present a risk to a person’s life; this is especially true of situations in which a major illness, such as cancer or cystic fibrosis, threatens a patient’s well-being. However, the lack of general discussion on this topic in health and fitness media has left many questions unanswered for those who are underweight. For instance, what causes a person to be underweight, and can I use nutrition shakes for weight management to combat this? To find out, keep reading as the people at ENU explain.

When Is a Person Considered Underweight?

Though there is plenty of room to debate what constitutes being “underweight,” the Centers for Disease Control and Prevention (CDC) offers a solid definition based on a person’s body mass index (BMI). This number is based on a person’s height and weight; to find yours, take your weight (in pounds) and multiply it by 703, then divide by your height (in inches) squared.

A person is considered underweight if their BMI is below 18.5. Those with a BMI of between 18.5 and 24.9 are considered to be at a “normal” weight, while those with a BMI greater than 25 but less than 30 are deemed “overweight.” A BMI of greater than 30 is considered obese.

Determining your BMI can be useful, but keep in mind that it’s a fairly simplistic tool that fails to distinguish between fat and muscle; for example, those who work out frequently may have a high BMI thanks to their muscle mass but still be perfectly healthy. The best way to determine whether you are at a healthy weight is to talk to your doctor and solicit a professional opinion.

Why a Person Might Be Underweight

Many things can cause a person to be underweight, including genetics, illnesses, and various environmental factors. Below, we’ll cover each of these scenarios in some detail.


Although what we eat and how we live can certainly affect our weight, there’s no denying that genes play a big role as well. If your parents passed on a thin frame as part of your genetic profile, you might be naturally predisposed to have a lower body weight. For those with this trait, you may be technically considered underweight while still being healthy; if you’re concerned that you may be underweight, it may be best to contact a physician.


There are many ailments that can cause a person to become underweight; if this is true for you, addressing the underlying condition might help to restore your proper body weight. Some illnesses, such as cystic fibrosis, can make it more difficult for your body to absorb nutrients or increase your body’s energy expenditure – either of which can cause you to become underweight.

Those battling a life-threatening sickness, such as cancer, may also have to use up the resources their bodies have stored, such as visceral fat and the protein in muscles, to heal, which can cause extreme weight loss, though protein shakes for cancer patients can be helpful. It is also possible for a mental illness to cause unwanted weight loss; for example, people suffering from an eating disorder are often underweight and may require the use of weight gain shakes for anorexia. Depression can cause a person to stop eating as well.


Even if you typically hover around a normal BMI, circumstances in your life could easily impact your weight. Extreme stress tends to cause people to eat either more or less than they usually do, depending on the person. And because eating habits vary based on the availability of food and the way in which a person was raised, you might tend to simply eat less than others, which could also cause you to be underweight.

How Can I Change My Weight?

There are a number of factors that can contribute to a change in a person’s weight, and these factors are essentially the same whether the change involves adding or losing body mass. Perhaps the easiest way to think about how a person’s weight can change is to remember this fundamental equation: Take the number of calories you consume in a day and subtract the number of calories your body uses. If the result is positive, then you’ve gained weight, and if it’s negative, you’ve lost weight. If this calculation seems oversimplified somewhat, that’s because it is, but the basic principle applies to virtually all issues of weight.

That said, the hidden complexities of this formula become clear as soon as you try to determine exactly how many calories your body uses. For most people, it’s pretty much impossible to nail down the exact number of calories used in a day. A much more useful method is to weigh yourself each day and look for trends; if your weight is dropping, increase your calorie intake until the trend stops to maintain your current weight, and vice versa if you’re gaining weight.

Nutritional Shakes for Healthy Weight Gain Available from ENU

If you struggle with being underweight or need to put on a few pounds to improve your health, know that meal replacement shakes from ENU could be the solution you’re looking for. Each ENU shake contains 400 calories derived from nutritional ingredients, offering a healthy mix of fats, carbs, and protein along with a blend of 24 vitamins and minerals. Try an ENU protein shake for weight gain between meals or after eating to boost your calorie intake and increase your weight in a safe and effective way. To learn more, visit ENU online or call (855) 266-6733 today.

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