Should you eat more if you're underweight? A guide to healthy weight gain

December 24, 2025 •

4 min read

According to the Cleveland Clinic, being underweight can lead to serious health risks including malnutrition, a weakened immune system, and fertility issues. So, should you eat more if you're underweight? Yes, but focusing on nutritious, calorie-dense foods is crucial for safe and sustainable gain.

Quick Summary

Gaining weight healthily requires a calorie surplus from nutrient-rich foods, not junk food. Strategies include eating frequent, smaller meals, choosing high-calorie snacks, and incorporating strength training to build muscle mass.

Key Points

Assess Underlying Issues: Consult a doctor to rule out medical conditions, such as a thyroid disorder or an eating disorder, contributing to being underweight.
Create a Calorie Surplus: To gain weight, consistently consume more calories than your body expends, typically an extra 300 to 500 per day for a steady pace.
Prioritize Nutrient-Dense Foods: Focus on whole foods like nuts, seeds, healthy oils, and full-fat dairy to ensure you gain weight in a healthy way, not just from empty calories.
Eat More Frequently: Try consuming five to six smaller, nutrient-rich meals and snacks throughout the day, which can be easier for those with a small appetite.
Incorporate Strength Training: Combine a high-calorie diet with resistance exercises to build lean muscle mass, promoting healthy weight gain and a stronger body.
Choose Smart Snacks and Beverages: Add calorie-dense snacks like nuts and dried fruits, and opt for high-calorie drinks like milk and homemade smoothies over water with meals.

Understanding the Risks of Being Underweight

While much public health focus is on the risks of being overweight, being underweight also carries significant health risks. A low body mass index (BMI) can indicate inadequate nutrition and lead to various problems. Being underweight can weaken the immune system, leaving you more susceptible to infections and illnesses. It can also result in nutrient deficiencies, potentially causing issues like anemia, fatigue, and hair loss. Women who are underweight may experience irregular periods or infertility due to hormonal imbalances. Furthermore, it can increase the risk of developing osteoporosis, as the body may lack the necessary nutrients like calcium and vitamin D for strong bones. For healthy growth in younger individuals and for recovery in older adults or those with illness, maintaining a proper weight is essential.

The Fundamental Rule: Achieving a Calorie Surplus

The core principle of gaining weight is consuming more calories than your body burns, a state known as a calorie surplus. Your body needs this extra energy to build new tissue, whether that's muscle or healthy fat. For gradual and sustainable weight gain, experts suggest increasing your daily intake by 300 to 500 calories. A more rapid increase of up to 1,000 calories per day is possible but should be monitored closely to ensure it doesn't result in excessive, unhealthy fat gain. The quality of these extra calories is just as important as the quantity.

The Importance of Nutrient-Dense Calories

Not all calories are created equal. Eating junk food high in sugar and unhealthy fats is an easy way to boost calorie intake but can lead to metabolic issues and health problems down the line. For healthy weight gain, the focus should be on nutrient-dense foods—those that provide substantial calories along with essential vitamins, minerals, and protein. This helps build healthy body tissue rather than just accumulating unhealthy fat.

Strategic Eating for Healthy Weight Gain

To increase your calorie intake effectively, it's often more manageable to eat more frequently rather than trying to consume larger meals. This approach is particularly helpful for those with a low appetite.

Eat smaller, more frequent meals: Aim for five to six smaller meals throughout the day instead of three large ones.
Incorporate healthy snacks: Nutrient-dense snacks between meals can significantly increase your daily calorie count. Good options include trail mix, nuts, protein bars, and Greek yogurt.
Add extra calories to your meals: Find simple ways to boost calories. Add cheese to casseroles, sprinkle nuts on oatmeal, or drizzle olive oil over vegetables.
Drink your calories: High-calorie, nutritious beverages can be a great supplement. Think whole milk, protein shakes, or homemade smoothies with fruits, nuts, and yogurt.

The Role of Strength Training in Healthy Weight Gain

While increasing calorie intake is the primary driver for weight gain, incorporating strength training is crucial. Strength training, such as weightlifting or bodyweight exercises, helps ensure that the extra calories are converted into muscle mass rather than unhealthy fat. This builds a healthier, stronger body composition. Exercise can also help stimulate your appetite, making it easier to consume the necessary calories. Consistency is key; a regular resistance training program is far more effective than sporadic workouts.

A Balanced Approach to Weight Gain

Healthy weight gain requires patience. Gaining weight slowly and steadily is the most sustainable approach. Listen to your body and make gradual changes. If you struggle with a poor appetite, don't force-feed yourself. Instead, use strategies like smaller, frequent meals and calorie-dense liquids to make the process more manageable. In cases where a medical condition is suspected, consulting a healthcare provider is essential.

Comparison Table: Nutrient-Dense vs. Empty Calories


Feature	Nutrient-Dense Calories	Empty Calories
Source	Whole foods like nuts, seeds, whole grains, avocados, eggs, lean meats, and full-fat dairy.	Processed foods like candy, sugary drinks, cakes, fried snacks, and excessive fast food.
Nutritional Value	High in protein, healthy fats, fiber, vitamins, and minerals.	Low in essential nutrients; provides energy but little else of value.
Health Impact	Promotes building healthy muscle tissue and body fat, strengthening bones and immune function.	Can contribute to unhealthy fat accumulation, inflammation, and increased risk of metabolic diseases.
Satiety	More filling and satisfying due to fiber and protein content.	Less filling, often leading to overconsumption without feeling full.
Primary Goal	Supports overall health, muscle growth, and a balanced body composition.	Primarily focuses on quick calorie intake, often at the expense of long-term health.

Conclusion

Should you eat more if you're underweight? Yes, but with a deliberate, informed approach that prioritizes nutrient-dense foods over empty calories. Combining a strategic eating plan that includes frequent, calorie-dense meals and snacks with a consistent strength training routine will help you gain weight healthily and build a stronger body. By focusing on quality over quantity and being patient with the process, you can achieve a healthy weight and improve your overall well-being. Always consult a healthcare professional to address any underlying medical concerns and to develop a personalized plan.

For more detailed advice on integrating strength training into your routine, you can visit the Healthline guide on how to gain weight.

Frequently Asked Questions

Being underweight can lead to numerous health issues, including a weakened immune system, nutritional deficiencies, low bone density (osteoporosis), and hormonal imbalances that can affect fertility.

For gradual weight gain, aim for a surplus of 300 to 500 extra calories per day, focusing on nutrient-dense foods. More rapid gain might require a higher surplus but should be done with care.

No, relying on junk food can lead to unhealthy fat gain and an increased risk of conditions like type 2 diabetes. The focus should be on gaining weight healthily with nutrient-rich sources.

Excellent options include nuts and nut butters, avocados, full-fat dairy products, eggs, red meat, and healthy grains like rice and oats.

High-calorie beverages like whole milk and homemade protein smoothies can be an easy way to increase intake, especially if you have a poor appetite. It’s best to drink these between meals to avoid feeling too full to eat.

Strength training, such as weightlifting, helps build muscle mass. This ensures the weight you gain is healthy muscle, not just excess body fat, leading to a stronger physique.

Light exercise, eating smaller and more frequent meals, and incorporating flavorful foods can all help stimulate a poor appetite. Avoid drinking large amounts of water before meals.