BlogHealthHow to Gain Weight with a Fast Metabolism?

How to Gain Weight with a Fast Metabolism?

Mariia Roza
Written by Mariia Roza on November 05, 2021
Dr. Olena Avdiievska
Medically reviewed by Dr. Olena Avdiievska
Ievgeniia Dobrynina
Fact checked by Ievgeniia Dobrynina

According to the National Center for Health Statistics, 1.7% of US adults are underweight. You're not alone in your struggle to gain weight, and there are working techniques that will help you achieve your goal!

Table of contents

We understand that for some people it is very hard to gain weight. Your weight might result from your genetics; it can be explained by fast metabolism, and it can be due to the small amount of food you eat. Whatever the reasons are, you can challenge them. It’s not going to be an overnight change. Achieving your goal weight might take you some time. However, by eating in a surplus and working out, you will get there. Just stay consistent in your endeavors.

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Why are some people underweight?

The main reason behind being underweight is eating fewer calories than you burn. There are two parts to this equation. 

On the one side, you might have a too fast metabolism, which means you’re fidgeting all the time, you do a lot of exercises, your work is connected with walking or riding a bike, or doing other physical activities. Your body can also spend a lot of energy on functioning. For example, you might be warm all the time (even when it’s cold outside), which means that your body spends a lot of energy to warm you up. Overall, when you have a fast metabolism, your body consumes too much energy to keep you going.

On the other side, you might eat in a calorie deficit. This means you don’t get enough energy from food and cannot get to the anabolic state1 when your body builds new muscles or fat tissue.

1.7% of adult Americans are underweight | Unsplash
1.7% of adult Americans are underweight | Unsplash

Being underweight is not always a decision of a person. There are health conditions that can lead to extreme weight loss or appetite imbalance. If you have always been at a normal weight and started to lose weight all of a sudden without any effort on your behalf, you should immediately see your doctor. Unhealthy weight loss might be caused by diabetes, infections, cancer, and thyroid misfunction.

What are the threats of being underweight?

Health providers determine whether someone’s underweight or not by indicating the body mass index. If a person’s BMI is below 18.5, he or she will be considered underweight. Though not that frequent as obesity, this condition can have the same health risk factors2. If you feel good, have no health issues, and love the way you look with a BMI lower than 18.5, there is no need to worry. Body mass index is just a number, it doesn't consider your muscle mass, your age, and other important factors.

However, underweight people might have greater risks of bone fractures due to the lower bone mineral density3, they might have lower fertility4, and even have greater chances of developing dementia5

Summing up: Being underweight is not only a question of aesthetics. Having too low a body mass might lead to multiple health problems. However, health condition is connected with weight in both directions. Meaning, if you’ve lost a lot of weight without trying to do so, you should see your doctor, as this weight loss might be a sign of some health problems.

What is metabolism, and how does it affect your weight?

Metabolism is a sum of chemical reactions that take place in your body. It determines how food transforms into energy and how your body uses this energy for living. When we talk about metabolism in terms of weight loss or weight gain, most frequently, we refer to the total daily energy expenditure, which is the sum of your physical activity, non-exercise thermogenesis, the energy your body needs to digest food, and the basal metabolic rate, which is the energy your body uses to fuel the brain, muscle tissue, and other organs.

If you have a slow metabolism, your body needs less energy to function. You will need less food to maintain your weight. If your metabolism is very slow, you might have trouble losing weight.

If you have a fast metabolism, this means your body needs a lot of energy for living. In other words, you will need more food to maintain weight. If the amount of calories you should be eating is more extensive than you actually eat, you can discover trouble gaining weight.

Can we say that your genetics determines your metabolism? In some way, yes, it does. For example, if both your parents are endomorphs, which means they both have narrow body frames and are pretty skinny, the chances are, you will inherit it and will look leaner than your peers, having more struggle gaining fat and muscle. If both your parents are ectomorphs, meaning they have a wider frame and bigger bodies, you will probably gain weight (both fat and muscles) easier than your peers and face difficulties losing it.

How does gaining weight for men and women differ?

As a rule, men have more insecurities with being too skinny because of the beauty standards of the modern world. When you look at all the Gymshark athletes and all the magical transformations of Hollywood actors into superheroes, you feel like it should be so easy to gain all that muscle! In reality, gaining muscle is much more complicated. It is for sure much harder than gaining fat tissue. It’s not only about eating in a surplus. It’s also about getting the proper workout routine that you should be doing for months and years! 

What makes gaining weight even more challenging for men is that men tend to have more muscles than women, which increases their metabolism. The thing is, you need more energy to maintain your muscles than fat, so when you become bigger, you need to increase your calorie intake even more.

According to Men’s Health, new lifters can gain one to four pounds of muscle in a month. So, the process of transformation is neither easy nor fast. And because of the changes between men and women, it is even harder to build muscle as a female.

As women on average have a bit slower metabolism than men, gaining weight might be easier for them. On the other hand, getting new pounds from muscle and not fat tissue will be more challenging for women.

Healthy and unhealthy weight gain

To gain weight, be it from muscles or fat, you have to be in a calorie surplus. There is no need to increase your calorie intake drastically! Adding 300 to 500 calories to your daily consumption will be enough if you want to bulk up.

However, not all calorie sources are the same! For example, if your goal is to build muscle, you have to pay particular attention to the amount of protein you consume. According to a large meta-analysis6, to maximize your muscle gain, you have to consume 1,6 to 2,2 grams of protein per one kilogram of your body mass daily. In other words, you will have to get almost 30% of your calories from protein.

The challenging part is that protein is a very satiating macronutrient, and it is not that easy to eat more of it.

Of course, you can pile more calories by eating fast food, sugary snacks, and drinking soft drinks and alcohol, but your health will not benefit from this type of nutrition. Even underweight people can develop diabetes and cardiovascular diseases due to unbalanced eating. This is why we recommend eating healthier energy-dense food to gain weight.

A plate of well-balanced food for weight gain | Unsplash
A plate of well-balanced food for weight gain | Unsplash

Nutrition rules for weight gain

The only way to gain weight is to eat more calories than you burn. See what you can do to make the first part of the equation easier.

  • Don’t skip meals. Many busy people have this habit. Have at least three square meals a day or add more calorie-dense snacks.
  • Drink your calories. Add creamer to your coffee, have the whole and not skim milk, drink juices and smoothies. They all contain calories but don’t make you feel stuffed or bloated.
  • Try post-workout shakes. These are weight gainers that contain proteins and carbs. 
  • Choose whole-fat versions of products. If you were buying fat-free products just out of a habit, stop it right now. Eat whole eggs and not egg whites from a bottle, buy 50% fat cheese instead of low-fat versions, cook an entire chicken and not chicken breasts, etc.
  • Add more oil to your salad. When increasing your fat consumption, remember that there are fat sources that are beneficial for your health (like olive oil, fish, and nuts) and not that healthy trans fat and saturated fats.
  • Eat nuts and nut butter. They are very dense in calories and taste good. So, you can quickly eat a lot of additional calories with no effort.
  • Try creatine. There are few supplements for muscle growth that are safe for your health and show science-based7 efficiency. Creatine is one of them. It can help you improve your strength and power and assist with muscle growth and recovery.

If you’re a healthy person with no critical health conditions, you will quickly gain weight using these tips. However, if you want the biggest part of your weight gain to come from muscles and not fat tissue, you will have to add workouts with progressive overload to your routine.

Workout tips to gain weight

If you have a fast metabolism, you need to decrease the amount of cardio you do. 

If you’re prone to fidgeting and moving your body a lot, try to stay calm and rest most of the day.

Choose low reps with high weights. Do three to four sets with a maximum of eight reps of each exercise to maximize muscle hypertrophy. Another way to gain muscle faster is to do compound movements instead of isolated exercises.

The most important part about working out for muscle build is to stay consistent. To stay on track, you need a workout plan. There are multiple online programs, and you can choose whatever fits you, from three times a week push-pull-leg slits to more coherent 5-day split workouts. 

By the way, lifting weights can increase your appetite too. So, if you’re struggling to eat extra calories, you should definitely try heavy lifting!

Two men in a gym after a workout | Unsplash
Two men in a gym after a workout | Unsplash

Summing up

  • Being underweight can be dangerous to your health in many respects.
  • Even underweight people can develop health problems if they have an unbalanced, unhealthy diet.
  • The main rule of gaining weight is by consuming more calories than you burn.
  • To gain muscle, you have to lift weights and use progressive overload.

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By choosing high-quality sources, we make sure that all articles on the Unimeal blog are reliable and trustworthy

McCarthy J. J., Esser K. A. (2010, May). Anabolic and Catabolic Pathways Regulating Skeletal Muscle Mass. Current Opinion in Clinical Nutrition and Metabolic Care. DOI:
Ringback Weitoft G., Eliasson M., Rosen M. (2008, March). Underweight, Overweight, and Obesity as Risk Factors for Mortality and Hospitalization. Scandinavian Journal of Public Health. DOI:
Coin A., Sergi G., Beninca P., et al. (2000). Bone Mineral Density and Body Composition in Underweight and Normal Elderly Subjects. Osteoporosis International. DOI:
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