How to Increase BMI Safely: Healthy Weight Gain Guide

Being underweight can be just as concerning for your health as being overweight. If your BMI is below 18.5, or if you've been told by a doctor that you need to gain weight, this guide will help you do it safely and effectively. The goal isn't just to increase the number on the scale - it's to build healthy muscle and tissue while supporting your overall wellbeing.

When Should You Increase Your BMI?

Not everyone with a low BMI needs to gain weight, but you should consider it if:

Your BMI is below 18.5 (underweight category)
You've lost weight unintentionally
Your doctor has recommended weight gain
You're experiencing symptoms like fatigue, weakness, or frequent illness
You're recovering from illness or an eating disorder
You're struggling to build muscle despite training

Use our BMI calculator to see where you currently stand and track your progress as you work toward a healthier weight.

Health Risks of Being Underweight

A BMI below 18.5 can carry several health risks:

Weakened immune system - More frequent infections and longer recovery times
Nutritional deficiencies - Lack of essential vitamins and minerals
Bone health issues - Increased risk of osteoporosis and fractures
Fertility problems - Difficulty conceiving for both men and women
Muscle loss - Weakness and reduced physical function
Anaemia - Fatigue and weakness from low iron
Growth problems - Particularly concerning for children and teenagers

Gaining weight to reach a healthy BMI can significantly reduce these risks and improve your quality of life.

Safe Rate of Weight Gain

Just as rapid weight loss isn't healthy, neither is gaining too quickly. Aim for a gradual increase of 0.25 to 0.5 kilograms (0.5-1 pound) per week. This allows you to build muscle and healthy tissue rather than just adding fat.

At this pace, you could move from underweight (BMI 18) to the healthy range (BMI 19-20) in about two to four months, depending on your height. Patience is key - this is a marathon, not a sprint.

Nutrition Strategies for Healthy Weight Gain

The foundation of healthy weight gain is eating more calories than you burn, but the quality of those calories matters enormously.

Create a Calorie Surplus

You need to consume 300-500 calories above your maintenance level to gain weight at a healthy pace. But don't do this by eating junk food - focus on nutrient-dense options that support muscle growth and overall health.

Eat More Frequently

If you struggle to eat large meals, try eating smaller amounts more often throughout the day:

Aim for three main meals plus two to three snacks
Set reminders to eat if you forget when you're busy
Don't skip breakfast - it's an opportunity for extra calories
Have a snack before bed to support overnight recovery

Choose Nutrient-Dense, Calorie-Rich Foods

Focus on foods that pack lots of nutrition and calories into smaller volumes:

Nuts and nut butters - Almonds, peanut butter, cashews are calorie-dense and healthy
Avocados - Packed with healthy fats and calories
Whole grains - Brown rice, quinoa, whole grain bread, oats
Dried fruits - Dates, raisins, apricots provide concentrated calories
Healthy oils - Olive oil, coconut oil for cooking and drizzling
Full-fat dairy - Whole milk, yogurt, cheese (if tolerated)
Oily fish - Salmon, mackerel, sardines for protein and healthy fats
Eggs - Versatile, protein-rich, and nutrient-packed

Prioritize Protein

Protein is essential for building muscle mass. Aim for 1.6-2.2 grams of protein per kilogram of body weight daily. Good sources include:

Lean meats (chicken, turkey, beef)
Fish and seafood
Eggs
Greek yogurt and cottage cheese
Beans, lentils, and tofu
Protein smoothies and shakes

Try Calorie-Dense Smoothies

Smoothies are an excellent way to pack in calories without feeling overly full. Try blending:

Banana, oats, peanut butter, whole milk, and protein powder
Avocado, spinach, mango, coconut oil, and Greek yogurt
Berries, nuts, dates, and full-fat milk

A well-made smoothie can provide 500-700 calories in an easy-to-consume form.

Exercise for Healthy Weight Gain

Exercise might seem counterintuitive when you're trying to gain weight, but the right type of training ensures you're building muscle, not just adding fat.

Focus on Strength Training

Resistance training is essential for healthy weight gain. It signals your body to use those extra calories to build muscle rather than store fat. Aim for:

3-4 strength sessions per week - Full-body workouts or split routines
Compound exercises - Squats, deadlifts, bench press, rows work multiple muscles
Progressive overload - Gradually increase weight or reps over time
8-12 repetitions per set - This range is optimal for muscle growth

You don't need expensive equipment - bodyweight exercises, resistance bands, and dumbbells work brilliantly for beginners.

Limit Excessive Cardio

While some cardio is good for heart health, too much burns calories you need for weight gain. If you enjoy running or cycling, keep it moderate (2-3 sessions per week for 20-30 minutes) and compensate by eating extra calories.

Rest and Recovery

Muscle grows during rest, not during workouts. Ensure you:

Get 7-9 hours of sleep per night
Take at least one full rest day per week
Don't train the same muscle groups on consecutive days
Listen to your body and rest when needed

Sample Daily Meal Plan for Weight Gain

Here's an example of what a weight-gain day might look like (approximately 2,800 calories):

Breakfast: Porridge made with whole milk, topped with banana, honey, and a handful of almonds

Mid-morning snack: Smoothie with banana, peanut butter, oats, protein powder, and milk

Lunch: Chicken and avocado sandwich on whole grain bread, with a side of hummus and vegetable sticks

Afternoon snack: Greek yogurt with granola and dried fruit

Dinner: Salmon fillet with quinoa and roasted vegetables drizzled with olive oil

Evening snack: Handful of mixed nuts and a piece of cheese

Adjust portions based on your individual calorie needs and preferences. This is just a template to show what balanced, calorie-dense eating looks like.

When to Seek Medical Help

Consult a healthcare professional if:

You've lost weight unintentionally or rapidly
You can't gain weight despite trying
You have digestive problems or food intolerances
You're recovering from an eating disorder
You have other health conditions that might affect weight
You're experiencing concerning symptoms alongside low weight

Your doctor can rule out underlying medical conditions (like hyperthyroidism, diabetes, or digestive disorders) and may refer you to a registered dietitian for personalized nutrition advice.

Understanding Your Target BMI

As you work on increasing your BMI, it helps to understand what you're aiming for. Read our article on understanding BMI categories to learn about the healthy weight range and what it means for your health.

For most adults, a BMI between 18.5 and 24.9 is considered healthy, but your doctor can provide personalized guidance based on your individual circumstances.

Medical Disclaimer

This article provides general information and is not a substitute for professional medical advice. Always consult your doctor or a registered dietitian before starting a weight gain programme, especially if you have underlying health conditions or a history of eating disorders. If you're experiencing unintended weight loss or other concerning symptoms, seek medical attention promptly.