Should you eat more calories if you're underweight for healthy weight gain?

December 19, 2025 •

4 min read

According to the Centers for Disease Control and Prevention, a Body Mass Index (BMI) below 18.5 is generally considered underweight, which can pose serious health risks if not addressed. For those in this category, strategic and healthy weight gain is often recommended by medical professionals.

Quick Summary

Underweight individuals should increase their intake of nutrient-dense calories to promote healthy weight gain. This requires a balanced diet of proteins, healthy fats, and complex carbs, often coupled with exercise to build muscle mass safely.

Key Points

Nutrient-Dense Calories: It's crucial to increase intake of healthy, nutrient-dense calories, not empty ones, to gain weight healthily.
Caloric Surplus is Key: For weight gain, you must consume more calories than your body expends. A gradual increase of 300-500 extra calories per day is a good starting point for most adults.
Focus on Protein and Strength Training: Combining increased calorie intake with strength training helps build muscle mass rather than unhealthy fat.
Frequent, Smaller Meals: Eating 5-6 smaller, balanced meals and snacks throughout the day can be more manageable and effective than large, infrequent meals.
Consult a Professional: If you have unexplained weight loss or struggle to gain weight, a doctor can identify any underlying medical issues, and a dietitian can create a personalized plan.
Be Mindful of Liquids: Healthy smoothies and high-calorie shakes can boost your intake, but avoid filling up on low-nutrient beverages before meals.

Why Being Underweight Can Be a Health Concern

While societal focus often centers on weight loss, being underweight can have significant health implications. A consistently low body mass can lead to a range of issues, from weakened immunity to long-term chronic conditions. Undernutrition, often a cause of being underweight, can affect crucial bodily functions.

Symptoms related to being underweight and undernourished can include:

Chronic fatigue and low energy levels
A weakened immune system, leading to frequent illnesses
Nutritional deficiencies, causing hair loss and brittle nails
Irregular or absent menstrual cycles in women
Increased risk of bone mass loss (osteoporosis)
Dizziness or lightheadedness
Delayed or slow growth in children and adolescents

The Core Principle: A Healthy Caloric Surplus

To gain weight, you must create a caloric surplus, meaning you consume more calories than your body burns. However, the quality of these calories is paramount. Simply eating junk food can lead to unhealthy fat gain, similar to health risks seen in obesity, but without the benefit of muscle mass. Experts recommend focusing on nutrient-dense foods to ensure the weight gained is healthy and supports overall well-being. For a gradual, steady increase, adults can aim for an extra 300–500 calories per day, while those seeking faster gains might target 700–1000 extra calories. The specific number can vary based on metabolism, activity level, and other individual factors, making consultation with a healthcare provider beneficial.

Strategic Eating Tips for Healthy Weight Gain

Instead of feeling overwhelmed by the prospect of eating larger meals, strategic adjustments to your eating habits can make the process manageable and effective. The key is to increase your intake gradually with the right foods.

Here are some tips to help you increase your caloric intake healthily:

Eat More Frequently: Instead of three large meals, try eating five to six smaller, nutrient-dense meals throughout the day. This can prevent the discomfort of overeating at one sitting.
Add Calorie-Dense Toppings: Incorporate nuts, seeds, grated cheese, or nut butter into your meals and snacks. For example, add slivered almonds to your yogurt or sprinkle cheese on a baked potato.
Enjoy Healthy Drinks: Drink calorie-rich beverages like smoothies, full-fat milk, or milkshakes made with fruit, nut butter, and yogurt. These can add calories without making you feel too full to eat solid food.
Choose Whole Grains: Opt for whole-grain bread and pasta over refined versions, as they offer more nutrients and calories.
Focus on Healthy Fats: Incorporate healthy fats from sources like avocados, olive oil, and nuts. These are very calorie-dense and provide essential nutrients.

Calorie-Dense vs. Empty-Calorie Foods

Choosing the right types of food is crucial for healthy weight gain. The table below compares healthy, nutrient-rich calorie sources with empty-calorie options that offer little nutritional value.


Food Type	Healthy Calorie Source	Empty Calorie Source
Fats	Avocado, extra virgin olive oil, nuts, seeds	Fried foods, highly processed oils, hydrogenated fats
Carbohydrates	Whole grains (oats, brown rice), sweet potatoes, bananas	Cakes, cookies, sugary cereals, white bread
Protein	Lean meats, eggs, fish, legumes, full-fat dairy	Processed meats, excess red meat
Beverages	Smoothies with fruit and protein powder, full-fat milk	Soda, sweetened juices, alcoholic beverages

The Role of Protein and Strength Training

Simply eating more won't guarantee healthy weight gain. The type of weight you gain—muscle mass versus fat—is important for long-term health. A caloric surplus combined with regular strength training directs extra calories toward building muscle tissue instead of just fat stores. Protein is the building block for muscle and is essential for this process. Ensuring adequate protein intake, particularly after workouts, helps maximize muscle repair and growth. Strength training also has the added benefit of potentially increasing your appetite.

How to Build a Weight-Gain Meal Plan

Creating a structured meal plan can ensure you consistently meet your caloric goals. Here is a sample approach based on strategies recommended by health professionals:

Start the day right: A hearty breakfast with eggs, avocado, and whole-grain toast can provide a solid foundation of protein and healthy fats.
Meal prep nutrient-dense snacks: Prepare small, portable snacks like trail mix, nuts, or a peanut butter and jelly sandwich on whole-grain bread.
Include a protein source in every meal: Integrate protein from sources like lean meats, beans, or dairy into your lunch and dinner.
Maximize liquids: Have a high-calorie shake or smoothie between meals. Consider a pre-made weight-gainer shake or make your own with whole milk, protein powder, and fruit.
Add a bedtime snack: A protein-rich snack before bed, such as Greek yogurt with honey and fruit, can provide extra calories and support muscle recovery while you sleep.

When to Consult a Professional

While a strategic diet can help many, it's vital to consult a healthcare provider, especially if your weight loss is unexplained or sudden. A doctor can rule out underlying medical conditions that may be hindering weight gain, such as thyroid disorders or malabsorption issues. A registered dietitian can also provide a personalized diet plan tailored to your specific needs and goals. For those struggling with eating disorders, professional help is essential.

Conclusion: Gaining Weight Healthily

Eating more calories is a necessary component for underweight individuals seeking to gain weight, but it must be done in a strategic and healthy manner. Prioritizing nutrient-dense foods, incorporating strength training, and eating more frequently are key strategies. By focusing on quality calories and building muscle mass, you can achieve healthy weight gain that supports your body's overall health and well-being. Always consult a healthcare professional to ensure your approach is safe and effective for your unique circumstances.

Frequently Asked Questions

Using the Body Mass Index (BMI) as a screening tool, a BMI below 18.5 is generally classified as underweight. However, a healthcare professional should provide a proper assessment based on individual health factors.

For gradual and healthy weight gain, adults can aim to add around 300 to 500 extra calories per day. For faster gain, a target of 700 to 1000 calories above maintenance might be suitable, but individual needs vary.

Excellent choices include nuts, avocados, whole milk and dairy products, lean meats, fatty fish like salmon, eggs, complex carbohydrates such as whole grains, and dried fruits.

No, relying on junk food can lead to unhealthy fat gain and other health issues, like heart disease or type 2 diabetes. The goal should be healthy weight gain through nutrient-dense foods.

Strength training, such as lifting weights, helps build muscle mass. This ensures that the extra calories you consume are used for muscle growth rather than being stored as fat. It can also help increase your appetite.

Some people have a naturally fast metabolism or genetic predisposition to being underweight. Consistently consuming more nutrient-dense calories than you burn, along with strength training, is still the most effective strategy. If it persists, a doctor can rule out underlying issues.

Yes, protein shakes and other supplements can help add extra calories and protein to your diet, especially if you struggle with eating large volumes of food. However, they should complement a balanced diet, not replace nutrient-rich meals.