How to Gain Weight? Here Is What the Evidence Says

How to gain weight safely usually means eating more energy-dense, nutritious foods, increasing protein, and doing resistance exercise so the added weight is more likely to be muscle as well as body fat. In many people, being naturally slim is harmless, but unexplained weight loss, poor appetite, digestive symptoms, or fatigue should be reviewed by a doctor.

Overview: what the evidence suggests

For most adults asking how to gain weight, the safest evidence-based approach is straightforward: eat more calories than the body uses, make sure meals contain enough protein, and add resistance exercise so some of the gain supports muscle. Weight gain does not need to rely on junk food or extreme diets. In many cases, small, consistent changes work better than trying to eat very large meals.

It is also reassuring that some people are simply naturally slim because of genetics, appetite patterns, activity level, or a high metabolic rate. If body weight has been stable for a long time, energy levels are good, and there are no other symptoms, low weight is not always a sign of illness.

At the same time, not all low weight is harmless. If there has been unintentional weight loss, trouble eating, diarrhea, vomiting, abdominal pain, fever, sweating at night, palpitations, low mood, or marked tiredness, a medical review is important. Before focusing only on diet, it helps to know whether there is an underlying reason the body is not maintaining weight.

When low weight may need medical review

Medical care is especially important if weight has dropped without trying, clothing suddenly becomes loose, or appetite has changed for no clear reason. A person should also seek medical advice if weight loss is accompanied by digestive symptoms, repeated infections, weakness, menstrual changes, poor wound healing, or signs of nutrient deficiency such as hair thinning or dizziness.

Certain symptoms deserve more urgent attention. These include blood in the stool, persistent vomiting, trouble swallowing, severe abdominal pain, chest symptoms, fainting, confusion, or rapid weight loss over a short period. In children, older adults, and people with chronic illness, undernutrition can affect recovery and day-to-day functioning more quickly.

People may also benefit from assessment if gaining weight has been difficult despite trying consistently for several weeks. A clinician can help decide whether the issue is low intake, increased calorie needs, poor absorption, a hormonal condition, medication effects, or another medical problem.

Possible causes of being underweight or not gaining weight

There are many possible reasons why someone may struggle to gain weight. Some people have a naturally smaller body frame or a family tendency to be thin. Others burn large amounts of energy through physically demanding work, endurance exercise, or simply high day-to-day activity. Stress can also reduce appetite and make regular eating difficult.

Medical causes are important to consider when weight is low or falling. These can include overactive thyroid disease, diabetes, long-term infections, digestive disorders that reduce nutrient absorption, food-related symptoms, and chronic inflammatory conditions. Problems such as Crohn’s disease or celiac disease can make it harder for the body to absorb calories and nutrients properly.

Mental health can play a major role as well. Anxiety, depression, grief, substance use, and eating disorders may all reduce food intake or change weight over time. Certain medicines can also suppress appetite or cause nausea. In older adults, dental problems, swallowing difficulty, isolation, memory changes, and reduced sense of taste may contribute.

Because the causes vary, the goal is not to assume the reason. It is to identify whether low body weight is a normal body pattern or a sign that the body needs medical support.

How a doctor evaluates unexplained low weight

When someone seeks help for low weight or difficulty gaining, the first step is usually a careful history. The doctor may ask whether weight loss was intentional, how long it has been happening, what appetite is like, whether there are bowel symptoms, and if there have been changes in mood, sleep, exercise, medications, or major life stressors. Reviewing a typical day of eating can also be useful.

A physical examination may include measuring weight and height, checking pulse and blood pressure, and looking for signs of anemia, dehydration, thyroid problems, muscle loss, or vitamin deficiency. Depending on the symptoms, a doctor may examine the abdomen, mouth, skin, lymph nodes, and heart and lungs.

Tests are guided by the person’s situation rather than done in the same way for everyone. They may include blood tests for blood count, iron levels, thyroid function, blood sugar, liver and kidney function, inflammation markers, and vitamin levels. If symptoms suggest digestive disease, stool tests, imaging, or endoscopy may be considered, sometimes through gastroenterology evaluation. If hormone-related causes are suspected, assessment through endocrinology care may help.

This step matters because the best answer to how to gain weight depends on the cause. If a medical problem is driving weight loss, treating that problem is often just as important as increasing calorie intake.

Nutrition strategies that support healthy weight gain

The most reliable nutrition strategy is a modest calorie surplus built from regular meals and snacks. Many people do better with three meals plus two to three snacks rather than trying to force very large portions. Eating every few hours can be especially helpful for people who fill up quickly.

Protein is important because it helps the body build and maintain muscle. Good options include eggs, dairy foods, yogurt, cheese, beans, lentils, soy foods, fish, poultry, and lean meats. Pairing protein with carbohydrate and healthy fats can raise the calorie content of meals without making the portion size too large.

Energy-dense foods can help when appetite is low. Examples include nut butters, nuts, seeds, avocado, olive oil, full-fat dairy foods if tolerated, hummus, granola, dried fruit, and smoothies made with milk or yogurt. Adding extras such as cheese, olive oil, powdered milk, nut butter, or seeds to usual meals can increase calories quietly and consistently.

Some practical ideas include:

• Choose snacks such as yogurt with granola, toast with peanut butter, trail mix, or cheese and crackers.
• Drink calories between meals rather than before meals if liquids reduce appetite.
• Keep easy foods available for low-energy days, such as smoothies, soups, or sandwiches.
• Avoid relying mainly on sugary or highly processed foods, which may add calories without supporting overall nutrition.

People with digestive symptoms, diabetes, kidney disease, or food intolerances may need an individualized plan. In those situations, support from a doctor or dietitian is especially helpful.

Exercise, routine, and other lifestyle factors

Exercise may seem surprising in an article about how to gain weight, but it often helps. Resistance training encourages the body to use extra calories to build muscle rather than gaining only body fat. This can improve strength, appetite, posture, and confidence. Simple programs using body weight, resistance bands, or weights can all be effective when done regularly.

Very high volumes of endurance exercise can make gaining weight more difficult in some people by increasing calorie needs and suppressing appetite after training. This does not mean stopping activity altogether. It means balancing training with nutrition and, if needed, adjusting exercise patterns while trying to gain.

Routine also matters. Skipping meals, sleeping poorly, and eating irregularly can make it harder to maintain a calorie surplus. Some people benefit from setting reminders to eat, planning snacks in advance, or having a bedtime snack. If chewing or swallowing is difficult, softer meals and calorie-rich drinks may be easier than solid foods.

For people recovering from illness, surgery, or frailty, rehabilitation and nutrition support may overlap. In selected cases, clinicians may recommend tailored exercise and nutrition planning through services such as physical therapy and rehabilitation.

What usually does not help

Many people are told to simply eat anything and everything. While weight may increase that way, the approach is often uncomfortable and may not support long-term health. Large amounts of fast food, sweets, or sugary drinks can leave a person feeling sluggish, worsen blood sugar control, and provide fewer vitamins, minerals, and protein than the body needs.

Supplements marketed for rapid weight gain are not always necessary, and some are poorly regulated. Protein powders or oral nutrition drinks can be useful for some people, but they should complement meals rather than replace balanced eating unless a clinician advises otherwise. Products promising dramatic results should be viewed cautiously.

It is also common to become discouraged if the scale does not change quickly. Healthy weight gain is usually gradual. Day-to-day fluctuations in weight can reflect fluid changes more than true progress, so trends over several weeks are more meaningful than single measurements.

When to seek medical care and where specialist support fits in

A doctor should be consulted if weight is falling without trying, if there is ongoing poor appetite, or if weight does not improve despite a reasonable nutrition plan. Medical review is also important when there are digestive complaints, menstrual changes, persistent fatigue, fevers, palpitations, or concerns about an eating disorder. Early assessment can help prevent nutritional deficiencies and identify problems that are easier to treat when found sooner.

If symptoms point to a digestive disorder, specialist review may include endoscopy or other targeted testing. If the main issue appears to be emotional distress, anxiety, depression, or disordered eating, mental health support is an important part of care, not a separate issue from physical health.

In complex cases, a multidisciplinary approach may be most helpful. Acibadem International’s multidisciplinary specialists and JCI-accredited hospitals evaluate and treat causes of low weight and unexplained weight loss for international patients, coordinating care across nutrition, internal medicine, gastroenterology, endocrinology, and rehabilitation when needed.

For many people, the answer to how to gain weight is not extreme eating. It is a steady, personalized plan that first rules out underlying illness, then builds weight with nourishing food, adequate protein, and appropriate exercise.

Frequently asked questions

How can a person gain weight in a healthy way?

Healthy weight gain usually comes from eating slightly more calories than the body uses, choosing nutritious foods, getting enough protein, and adding strength training. This helps support muscle as well as body fat. If weight is low because of illness or poor absorption, medical treatment may be needed too.

Is being underweight always a problem?

Not always. Some people are naturally slim and remain healthy, energetic, and well nourished at a lower body weight. It becomes more concerning when weight is dropping unexpectedly or is linked with fatigue, digestive symptoms, weakness, or missed periods.

What foods are best for gaining weight?

Foods that combine calories with protein and healthy fats are often most helpful. Examples include dairy foods, eggs, nuts, nut butters, seeds, avocado, beans, fish, poultry, olive oil, whole grains, and smoothies. Eating these regularly in meals and snacks can be easier than trying to eat huge portions.

Should someone exercise while trying to gain weight?

Yes, especially resistance exercise such as weight training or body-weight strengthening. It can improve appetite and help the body build muscle rather than gaining only fat. Very high amounts of endurance exercise may need to be balanced with higher calorie intake.

When should unexplained weight loss be checked by a doctor?

A doctor should evaluate weight loss that happens without trying, continues over time, or comes with symptoms such as diarrhea, vomiting, pain, fever, palpitations, low mood, or marked tiredness. More urgent review is needed for red flags such as blood in the stool, trouble swallowing, or severe weakness.

Can stress or anxiety make it hard to gain weight?

Yes. Stress and anxiety can reduce appetite, cause nausea, disturb sleep, and make meal routines irregular. When emotional health is part of the problem, addressing it can be just as important as changing the diet.

References

• World Health Organization
• National Institute of Diabetes and Digestive and Kidney Diseases
• Centers for Disease Control and Prevention
• Academy of Nutrition and Dietetics
• National Health Service

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.