A Comprehensive Look at What do underweight people eat in a day?

October 8, 2025 •

4 min read

For some individuals, gaining weight or building muscle can be just as challenging as losing it. A sustainable and healthy approach requires a focus on a balanced, high-calorie diet featuring nutrient-dense foods, which often begs the question: What do underweight people eat in a day?

Quick Summary

Underweight individuals should consume more calories than they burn by prioritizing nutrient-dense, high-calorie foods across frequent meals and snacks. The diet must balance protein, healthy fats, and complex carbohydrates to promote healthy weight gain and muscle development.

Key Points

Prioritize Nutrient-Dense Foods: Focus on calorie-rich foods that are also packed with vitamins and minerals, such as avocados, nuts, and whole-fat dairy.
Eat Frequently: Consume 5-6 smaller meals and snacks throughout the day to maintain a consistent calorie intake and avoid feeling overwhelmed by large portions.
Boost Calories with Healthy Fats: Add calorie-dense sources like nut butters, olive oil, and seeds to meals and smoothies to easily increase intake.
Don't Forget Protein: Incorporate high-quality protein from sources like eggs, lean meats, and legumes into every meal to support muscle growth.
Combine Diet with Strength Training: Incorporate resistance exercise to promote muscle mass gain, ensuring weight gain is healthy and not just fat.
Avoid Junk Food for Calorie Surplus: Steer clear of relying on sugary drinks and processed foods, which offer empty calories and can lead to unhealthy weight gain.

The Importance of Healthy Weight Gain

While societal focus often leans towards weight loss, being underweight can present its own set of health risks, including a weakened immune system, bone density issues, and nutrient deficiencies. Gaining weight healthily means building a balanced combination of muscle mass and subcutaneous fat, not just gaining unhealthy belly fat through junk food. The secret to a successful weight-gain strategy lies in consuming a calorie surplus from nutrient-dense foods, ensuring every calorie counts towards overall health and strength.

Key Components of a Weight-Gain Diet

To effectively gain weight in a healthy manner, the diet must be rich in protein, healthy fats, and complex carbohydrates. Instead of relying on empty-calorie junk food, focusing on these macronutrients from whole-food sources is crucial.

Prioritizing Protein

Protein is the building block of muscle tissue and is essential for repairing and rebuilding muscle fibers, especially when combined with resistance training. Consuming protein with every meal helps ensure a steady supply of amino acids in the blood, which supports muscle growth. Aim for about 1.6 to 2.2 grams of protein per kilogram of body weight daily.

High-Protein Foods:

Meats and poultry: Lean cuts of beef, pork, chicken, and lamb.
Fish and seafood: Fatty fish like salmon and mackerel, as well as shellfish.
Eggs: The yolk is particularly nutrient-dense.
Dairy products: Milk, cottage cheese, Greek yogurt, and cheese.
Legumes: Lentils, beans, and peas.
Nuts and seeds: Almonds, walnuts, peanuts, and nut butters.
Soy products: Tofu, tempeh, and fortified soy beverages.

Embracing Healthy Fats

Healthy fats are a concentrated source of energy, containing 9 calories per gram, making them an efficient way to boost calorie intake without consuming large volumes of food. They also play a role in hormone production and vitamin absorption.

Examples of Healthy Fat Sources:

Avocados: A single large avocado can provide over 300 calories.
Nuts and nut butters: Calorie-dense and easy to add to meals or snacks.
Seeds: Flax, chia, and sunflower seeds can be sprinkled on many dishes.
Oils: Olive oil and avocado oil.
Full-fat dairy: Whole milk, cheese, and yogurt.
Oily fish: Salmon, sardines, and mackerel are rich in Omega-3s.

Integrating Complex Carbohydrates

Carbohydrates are the body's primary energy source, essential for fueling workouts and supporting muscle growth. Choose whole-food sources over refined and sugary options.

Complex Carb Choices:

Whole Grains: Oats, quinoa, brown rice, whole-grain bread, and pasta.
Starchy Vegetables: Potatoes and sweet potatoes.
Fruits: Bananas, mangoes, and dried fruits like dates and raisins.
Legumes: Beans and lentils.

Sample Daily Meal Plan: What Underweight People Eat in a Day

To demonstrate how these foods come together, here is a sample day focusing on six smaller, high-calorie, nutrient-dense meals.

Breakfast (8:00 AM): Whole-grain oatmeal made with full-fat milk, topped with a handful of mixed nuts, dried fruits, and a drizzle of honey.

Mid-Morning Snack (11:00 AM): A homemade protein smoothie with whole milk, a scoop of protein powder, a banana, a tablespoon of peanut butter, and a handful of spinach.

Lunch (1:30 PM): A large bowl of brown rice with grilled chicken or chickpeas, mixed with avocado chunks, olives, and a side of steamed vegetables dressed in olive oil.

Afternoon Snack (4:00 PM): Full-fat Greek yogurt mixed with granola, berries, and a sprinkle of seeds.

Dinner (7:00 PM): Baked salmon served with a large baked sweet potato topped with butter and a side of roasted broccoli with grated cheese.

Evening Snack (9:30 PM): Whole-grain toast with a generous spread of nut butter and a glass of warm whole milk.

Comparison Table: Healthy vs. Unhealthy High-Calorie Choices


Feature	Healthy High-Calorie Choice	Unhealthy High-Calorie Choice
Nutrient Density	High (vitamins, minerals, fiber)	Low (empty calories, trans fats)
Protein Quality	High (lean meat, eggs, dairy)	Often low or processed (e.g., some fast food)
Fat Source	Healthy unsaturated fats (avocado, nuts)	Unhealthy saturated and trans fats (fried foods, processed snacks)
Carbohydrate Source	Complex carbs (whole grains, sweet potatoes)	Simple and added sugars (soda, candy)
Overall Health Impact	Supports muscle growth, bone density, and immunity	Can lead to high cholesterol, type 2 diabetes, and heart problems

Common Mistakes to Avoid When Gaining Weight

To ensure your weight gain journey is a healthy one, steer clear of these common pitfalls:

Relying on Junk Food: While high in calories, junk food lacks essential nutrients and can cause unhealthy fat gain and related health issues.
Skipping Meals: Inconsistent eating patterns make it difficult to achieve a calorie surplus. Establish a routine of frequent, smaller meals and snacks.
Ignoring Strength Training: Without resistance exercise, extra calories are more likely to be stored as fat rather than building muscle mass.
Overdoing Cardio: Excessive cardiovascular exercise can burn a significant amount of calories, hindering weight gain efforts. A balanced routine is best.
Impatience: Healthy weight gain takes time. Consistency is more important than rapid, unsustainable gains.

The Role of Exercise

For an underweight person, incorporating regular exercise is crucial for ensuring that the increased calorie intake translates into lean muscle mass instead of just fat. Strength training, such as weightlifting or bodyweight exercises, stimulates muscle growth and can also help increase appetite. A routine that targets major muscle groups at least twice a week is recommended, alongside limited, moderate cardiovascular exercise for heart health.

Conclusion

By focusing on a nutrient-dense, high-calorie diet and implementing a structured eating schedule, underweight individuals can achieve healthy and sustainable weight gain. The core principle lies in consuming more calories than you burn, sourcing those calories from quality protein, healthy fats, and complex carbohydrates. Combined with a consistent strength training routine, this approach promotes muscle development and improves overall health. Always consult with a healthcare provider or a registered dietitian to tailor a plan that fits your specific needs and monitor your progress safely.

For more expert guidance on healthy weight gain, consider visiting the official Mayo Clinic resources on the topic.(https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/underweight/faq-20058429)

Frequently Asked Questions

Ideal snacks include trail mix with nuts and dried fruit, cheese and crackers, full-fat yogurt with granola, peanut butter on toast or fruit slices, and hard-boiled eggs.

Mass gainer supplements can be a helpful addition, particularly for those with a low appetite, as they provide a concentrated source of calories, protein, and carbohydrates. However, they should complement, not replace, a diet rich in whole foods.

Eating smaller, more frequent meals can be less overwhelming than large ones. Light exercise, particularly strength training, is also known to help improve appetite.

If you struggle with a low appetite, it's often recommended to drink high-calorie beverages like smoothies or shakes between meals to avoid feeling full too quickly and leaving less room for solid food.

Include a protein source in every meal and snack, such as eggs, dairy products, nuts, legumes, and lean meats. A supplement like whey protein can also help meet higher daily protein needs.

Factors like genetics, a fast metabolism, high physical activity levels, or an underlying health condition can make it difficult to gain weight. Stress and poor sleep can also play a role.

Incorporate calorie-dense ingredients such as cheese in sauces, add nut butters to oatmeal and smoothies, use healthy oils like olive oil when cooking, and sprinkle seeds or nuts over salads and yogurt.