Weight gain comes down to consistently taking in more calories than you burn, either by eating more or moving less — right? Actually, sometimes it's more complicated than that. And if you feel like you can't gain weight no matter how much you eat, there could be other factors at play.
Each person's metabolism functions at a slightly different rate, and some people gain or lose weight more easily than others. But if you're consistently unable to gain weight, you could have an underlying health problem that isn't being addressed.
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"There can be medical as well as non-medical reasons, and getting to the bottom of the cause could require detective work," says Louis Morledge, MD, an internist at Lenox Hill Hospital in New York.
Figuring out what could be going on starts with paying attention to your symptoms. Here are some of the most common medical reasons behind an inability to gain weight and what you may be able to do to get the number on the scale into a healthier range.
Hyperthyroidism is among the more common diseases that cause an inability to gain weight, or at least make weight gain more difficult, Dr. Morledge says. This condition causes the body to overproduce thyroid hormone, which speeds up the body's metabolism.
"This can result in weight loss, hand tremors and rapid or irregular heartbeat," Dr. Morledge says.
You might also notice you feel hungrier, more anxious or irritable and warmer or sweatier than normal.
Anyone can develop an overactive thyroid, but you may be more prone if thyroid problems run in your family. Some people also develop hyperthyroidism after being pregnant, according to the Mayo Clinic.
Medications are often the first-line fix for hyperthyroidism. Anti-thyroid hormone drugs or radioiodine therapy prevent the thyroid from making too much thyroid hormone, per the Mayo Clinic.
"Surgery can also be implemented to remove all or part of the thyroid gland," Dr. Morledge says.
2. Inflammatory Bowel Disease
IBD can cause the following symptoms, which may come and go:
- Severe abdominal pain
- Diarrhea (sometimes with blood)
- Urgent need to have a bowel movement
- Rectal bleeding
- Anxiety and depression
Over time, IBD can also lead to weight loss or trouble gaining weight, notes Dr. Morledge, as well as damage to the intestines if it's not well managed.
Doctors don't know why some people develop IBD, per Johns Hopkins Medicine, but you may be at higher risk if you have a family member with the condition.
Prescription medications like corticosteroids, immunomodulators or biologics are typically needed to get IBD under control and keep symptoms in check, per the Cleveland Clinic. Sometimes surgery is necessary as well.
3. Celiac Disease
A chronic digestive and immune disorder, celiac disease is marked by an intolerance to gluten, a protein found in wheat, barley and rye.
For people with celiac, "eating gluten triggers an immune response in the small intestine, over time damaging the intestinal lining and causing diarrhea, fatigue, bloating, weight loss and anemia," Dr. Morledge says.
Some people with celiac disease also develop lactose intolerance, or an intolerance to eating dairy products made with cow's milk.
Managing celiac disease means following a gluten-free diet, per the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
Working with a registered dietitian can help you get started: They can tell you more about the foods you'll need to avoid and how to carefully read food labels. You can also come up with a plan together for maintaining a balanced, nutritious diet while eating gluten-free.
Trouble gaining weight isn't always a side effect of diabetes, a condition that affects how the body uses blood sugar for energy.
People with type 1 diabetes, whose symptoms tend to come on more quickly and severely compared to those with type 2 diabetes, are more likely to be affected, Dr. Morledge says.
In addition to unexplained weight loss or an inability to gain weight, symptoms may include:
- Feeling thirstier than usual
- Needing to urinate more often
- Itchy skin
- Dark patches around the neck or armpits
- Slow wound healing
Type 1 diabetes is thought to be caused by an autoimmune reaction in the body, per the Centers for Disease Control and Prevention, which destroys the cells in the pancreas that make insulin. This can happen at any age.
It's not clear what triggers this reaction, although you may be at higher risk if you have a family history of the condition. (Unlike type 2 diabetes, diet and lifestyle habits don't play a role.)
Managing diabetes means keeping your blood sugar levels in a healthy range. For people with type 1 diabetes, that typically requires taking insulin or other prescription diabetes medications several times per day, per the NIDDK.
Being unable to gain weight can sometimes be an early sign of cancer. Sometimes cancer increases the body's metabolism and causes muscle loss and diminished appetite, according to the American Society of Clinical Oncology. A person might also feel weak or fatigued and have less energy to do their everyday activities.
It's important to keep in mind that while cancer can cause a person to lose weight unexpectedly or trouble with gaining weight, the disease isn't always the culprit.
"Patients should not jump to assuming the most severe outcome before consulting with their primary care physician and exploring all possible reasons for unexplained weight loss," Dr. Morledge says.
Cancer is among the rarest reasons for not gaining weight. Still, if you suspect for any reason that you may have cancer, make an appointment with your doctor ASAP, who can run the appropriate tests, determine your diagnosis and get you on a treatment plan.
Tips for Gaining Weight the Healthy Way
If you're eating more but not gaining weight and you're concerned your weight isn't in the healthy range, start by seeing your doctor, who can help you get to the root cause.
If there's an disease or health condition at play, treating the underlying problem may be the starting point for getting your weight back up, Dr. Morledge says. Once you and your doctor have a handle on your overall health, you can put together a plan for gaining weight.
While simply eating more high-calorie foods might do the trick, this approach may not give your body the nutrition it needs and could have a negative effect on your health, according to the American Academy of Family Physicians.
Instead, it's important to focus on finding ways to get more calories along with more nutrients. Some ways to do that include:
- Eat smaller, more frequent meals. If you struggle to finish your three squares a day, try breaking things up into smaller mini meals or hearty snacks, Dr. Morledge recommends.
- Go for wholesome, calorie-dense foods. Find ways to sneak more healthy calories into your meals. Top your plate with nuts or seeds, a drizzle of olive oil or pesto, diced avocado or guacamole, or some shredded cheese, for instance.
- Try a shake or smoothie. Supplemental meal-replacement shakes are a nutritionally balanced way to pack in extra calories. Plus, it can sometimes be easier to sip a smoothie or shake rather than eat a solid meal when you don't have much of an appetite.
- Limit liquids before a meal. Filling up on fluids leaves less room in your stomach for food, which can cause you to eat less at mealtime, per the Cleveland Clinic. Sip your drink with your food, but if you want to guzzle a big glass, do so in between meals instead.
When to See a Doctor if You Can't Put on Weight
You should let your doctor know if you notice you've lost more than a few pounds without trying. While small weight fluctuations can be normal, sustained, unexplainable weight loss may be a sign of a health problem.
"A conversation with your primary care physician is a good place to start and begin the process of better understanding if the decline in weight is the result of a physical ailment," Dr. Morledge says.
You should also see a doctor if you can't gain weight and have other concerning symptoms such as abdominal pain, frequent diarrhea, fatigue, frequent urination or an irregular heartbeat.
- Mayo Clinic: "Hyperthyroidism (overactive thyroid)"
- Cleveland Clinic: "Inflammatory Bowel Disease (Overview)"
- National Institute of Diabetes and Digestive and Kidney Diseases: "Treatment for Celiac Disease"
- National Institute of Diabetes and Digestive and Kidney Diseases: "Insulin, Medicines, & Other Diabetes Treatments"
- American Society of Clinical Oncology: "Weight Loss"
- Cleveland Clinic: "How To Gain Weight Safely"
- Johns Hopkins Medicine: "Inflammatory Bowel Disease (IBD)"
- Centers for Disease Control and Prevention: "What Is Type 1 Diabetes?"
- American Academy of Family Physicians: "Healthy Ways to Gain Weight If You’re Underweight"