Weight & Metabolic Health
Weight Gain & Underweight — When Your Weight Is Telling You Something
Unexpected weight changes — gaining without trying, or struggling to reach or maintain a healthy weight — are often signs that something else is going on. A licensed provider can help figure out what, and what to do about it.
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About weight changes
⚖️ Weight changes are often a symptom, not just a number
Most conversations about weight focus on people trying to lose it. But unexplained weight gain and difficulty maintaining a healthy weight in either direction are both legitimate medical concerns that deserve clinical attention. The number on the scale is rarely the whole story — it is often a signal worth understanding.
This page covers two distinct situations: weight gain that is unexpected, unexplained, or seems unrelated to diet and activity; and being underweight or having difficulty gaining enough weight to support good health. Both can have medical causes — and both are worth talking to a provider about.
⚠️ Sudden or unintentional weight changes deserve attention
Unintentional loss of about 5% of your usual body weight over 6 to 12 months — or any faster, substantial loss — should be evaluated by a provider. Rapid weight gain over days or weeks may reflect fluid accumulation or another medical issue, particularly when it occurs with swelling. Call 911 for chest pain, severe breathing difficulty, fainting, confusion, or blue or gray lips. Seek urgent same-day evaluation for rapid gain with new leg or abdominal swelling, worsening shortness of breath, or difficulty breathing while lying flat. Fluid-related weight changes can involve heart, kidney, liver, or other medical causes.
Unexplained weight gain
📈 When weight increases without an obvious reason
If you are gaining weight without a clear change in how you eat or move — or if weight that used to be manageable has become much harder to control — there may be a medical explanation worth exploring. Weight is influenced by more than calories in and calories out. Note also that eating disorders including binge eating disorder can occur at any body size and may contribute to weight-related concerns regardless of a person's BMI.
Common medical contributors to unexplained weight gain:
- →Thyroid dysfunction — Hypothyroidism can contribute to fatigue, cold intolerance, constipation, and modest weight gain. Because these symptoms have many possible causes, diagnosis requires appropriate thyroid testing rather than symptoms alone.
- →Prediabetes and insulin resistance — These conditions commonly occur alongside abdominal weight gain and other metabolic risk factors. Sleep, activity, diet, genetics, medications, and body composition may all contribute. Blood-sugar testing can help determine whether metabolic changes are present.
- →Medication side effects — Many common medications contribute to weight gain, including antidepressants (especially SSRIs and mirtazapine), antipsychotics, corticosteroids, beta blockers, and certain diabetes medications. This is not a reason to stop medication — but it is worth discussing with a provider.
- →Hormonal and reproductive-health factors — Menopause may change fat distribution and body composition, while PCOS may be associated with insulin resistance and weight-related concerns. Low testosterone can affect muscle mass and body composition in some men. Symptoms and weight change alone do not establish any of these diagnoses — testing when clinically indicated is needed.
- →Fluid retention — Swelling and fluid accumulation from heart, kidney, liver, or other medical conditions can register as weight gain. Rapid fluid-related weight gain, particularly with swelling or breathing difficulty, requires prompt medical evaluation.
- →Sleep disruption — Poor sleep may affect appetite, energy, and metabolic health, making weight management more difficult. Poor sleep and obstructive sleep apnea are associated with appetite and metabolic changes — weight can worsen sleep apnea, while untreated sleep apnea may make weight management harder. Signs that may suggest sleep apnea include loud snoring, witnessed pauses in breathing, gasping at night, morning headaches, or excessive daytime sleepiness.
- →Chronic stress — Stress may affect sleep, appetite, eating patterns, alcohol use, and physical activity, all of which can influence weight. Rarely, true cortisol excess (as in Cushing syndrome) causes a distinct pattern of symptoms that requires medical evaluation.
Weight change is often multifactorial
Weight change often reflects several interacting factors — diet, activity, sleep, medications, stress, genetics, and environment — rather than one hidden medical condition. The purpose of evaluation is to identify any concerning causes, review medication effects, and determine which factors are most relevant for your situation.
Looking for support with gradual weight management?
If your goal is structured, provider-guided weight support rather than evaluation of unexplained weight gain, our Medical Weight Support page covers the full range of options — including GLP-1 medications, clinical assessment, and ongoing provider support.
Gaining weight without a clear reason? A provider can help identify what is driving it.
Start a VisitBeing underweight
📉 When weight is too low — and why it matters
Being underweight is less talked about than obesity, but it carries its own significant health risks. A low body weight can sometimes be associated with inadequate nutrition, loss of muscle or bone, hormonal changes, or an underlying condition. Some people are naturally at a lower weight and remain healthy — so the full clinical picture matters, not a single number.
For most nonpregnant adults, a BMI below 18.5 is considered underweight — though BMI has limitations and a provider will consider the full clinical picture alongside it. A clinical evaluation can help determine whether low weight is associated with nutritional deficiency, muscle loss, medical symptoms, or another concern.
Symptoms that may occur alongside low weight or nutritional deficiency:
These symptoms have many possible causes and do not prove that low weight is responsible. A clinical evaluation helps determine what is driving them.
- →Persistent fatigue, weakness, or dizziness not explained by other causes
- →Hair thinning or hair loss
- →Getting sick frequently or taking longer than usual to recover
- →Irregular or absent menstrual periods
- →Difficulty getting pregnant
- →Feeling cold all the time
- →Loss of bone density (which may show up as stress fractures or be detected on a bone density scan)
- →Visible loss of muscle mass
Common reasons people are underweight:
- →Constitutionally low weight or family pattern — Some people have a naturally lower stable weight without symptoms or nutritional deficiencies. However, new weight loss, declining muscle, fatigue, or other symptoms still warrant evaluation regardless of baseline build.
- →Chronic illness — Cancer, inflammatory bowel disease, hyperthyroidism, celiac disease, COPD, and other conditions can all lead to unintentional weight loss or difficulty maintaining weight.
- →Digestive and absorption issues — Conditions like EPI (exocrine pancreatic insufficiency), Crohn's disease, or chronic diarrhea can prevent adequate calorie and nutrient absorption even when food intake is normal.
- →Medication effects — Some medications reduce appetite, cause nausea, or affect taste in ways that reduce food intake.
- →Mental health factors — Depression, anxiety, and eating disorders can all reduce appetite or food intake. If you think an eating disorder may be a factor in your weight, specialist support is available and effective.
- →Increased caloric need — Very high physical activity levels or recovery from illness can increase caloric needs beyond what a person is consuming. Pregnancy and breastfeeding change energy and nutrient needs significantly — inadequate gain, weight loss, or rapid gain during pregnancy should be coordinated with an obstetric clinician rather than evaluated through a general weight visit.
- →Other contributing factors — Difficulty chewing or swallowing, dental problems, food insecurity, substance use, chronic infection, grief, social isolation, and cognitive decline in older adults can all reduce food intake or increase nutritional needs. Hyperthyroidism may cause weight loss despite increased appetite. Type 1 diabetes can produce weight loss when glucose cannot be used normally.
A note about eating disorders
Eating disorders can occur at any body size — a person does not need to be underweight or to look a certain way to have a serious eating disorder. Restricted eating, bingeing, purging, intense fear of weight change, compulsive exercise, or significant distress around food deserves compassionate, specialized care — not judgment. A telehealth visit may help begin the evaluation, but medical examination and eating-disorder specialty treatment may be needed.
⚠️ Seek urgent or emergency care for:
Fainting or near-fainting, chest pain, severe weakness, breathing difficulty, confusion, inability to keep down food or fluids, vomiting blood, severe dehydration, a very slow or irregular heartbeat, or suicidal thoughts. Eating disorders and severe undernutrition can affect the heart, electrolytes, and other organs even when a person does not appear extremely thin. These symptoms require urgent in-person medical assessment — not telehealth. For eating-disorder support and treatment referrals, contact the National Alliance for Eating Disorders at 1-866-662-1235 during published helpline hours (Monday–Friday). Call or text 988 for suicidal or emotional crisis support. Call 911 for immediate danger or a medical emergency.
Concerned about being underweight or struggling to gain? A provider can help evaluate what is going on.
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💻 What a provider can do for weight concerns
Whether you are dealing with unexpected weight gain or struggling to maintain a healthy weight, the right starting point is understanding why — not simply being told to eat more or less. A licensed provider can evaluate the clinical picture and help you find the right path forward.
For unexplained weight gain
Finding the underlying cause
Your provider can review your health history, symptoms, and current medications, order relevant labs — which may include blood count, blood sugar, thyroid testing, kidney and liver function, electrolytes, and other tests when clinically indicated — and help determine whether a medical condition is contributing. When a contributing medical condition or medication effect is identified, addressing it can be an important part of the plan alongside nutrition, activity, sleep, and other individualized recommendations.
For underweight
Evaluation and safe next steps
Your provider can assess whether your weight is affecting your health, check for nutritional deficiencies and complications (such as anemia or bone loss), evaluate for underlying medical or digestive causes, and help connect you with appropriate specialist care — including a registered dietitian nutritionist — when needed. Some situations require in-person evaluation or specialist management.
What telehealth can and cannot do for weight concerns
A telehealth visit is well-suited for reviewing your history and symptoms, ordering labs, evaluating medication contributions, and discussing next steps. In-person examination may be necessary to assess vital signs, hydration, swelling, muscle loss, heart rhythm, orthostatic blood pressure, dental or swallowing problems, abdominal findings, or signs of severe malnutrition — laboratory testing alone does not determine nutritional status. Situations involving eating disorders, severe undernutrition, rapid unexplained loss, or fluid-related weight gain may require in-person or specialist evaluation. Your provider will let you know when in-person care is the more appropriate first step.
Care that follows through
🩺 A provider visit is just the beginning
Understanding why your weight is changing is the starting point. From there, a provider can initiate treatment for underlying conditions, review medications that may be contributing and, when appropriate, discuss changes or coordinate recommendations with the original prescribing clinician, refer you to a registered dietitian nutritionist for individualized nutritional support, or connect you to medical weight support if that is the appropriate next step.
- ✓A visit may result in laboratory orders, prescription treatment when appropriate, or recommendations for in-person and specialist follow-up
- ✓When prescription treatment is appropriate, it may be sent electronically to your selected pharmacy
- ✓No required memberships to access our telehealth services
- ✓If we cannot treat you online, you will not be charged
Your weight is trying to tell you something. Let's find out what.
A licensed provider can help you understand what is driving unexpected weight changes — and what the right next step looks like for your situation. No judgment. No required membership. No charge if we can't help online.
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Medical disclaimer: The information on this page is for general educational purposes only and does not constitute medical advice. Unexplained or rapid weight changes require evaluation by a licensed provider. Rapid weight gain with swelling or shortness of breath may indicate a medical emergency. Underweight with severe nutritional deficiency, eating disorders, or complex medical causes may require in-person evaluation and specialist management. Eating disorders can occur at any body size. For eating-disorder support and treatment referrals, contact the National Alliance for Eating Disorders at 1-866-662-1235 during published helpline hours (Monday–Friday). Call or text 988 for suicidal or emotional crisis support. A licensed MyPhysician360 provider will review your complete health history before making any recommendations or prescribing any medication. MyPhysician360 services are available in most states. Services are not currently available in Mississippi or Alaska.