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How to Gain Weight With a Fast Metabolism

Written by Dr. Michael Ruscio, DC on November 15, 2024

Written by Dr. Michael Ruscio, DC on November 15, 2024 — Reviewed by Hilary Watts

• Deconstructing Metabolism|
• Strategies for Healthy Weight Gain|
• Increasing Protein|
• Focusing on Strength Training|
• Taking Control of Gut Health|
• Relaxing and Enjoying Meals|

Are you struggling to gain weight with a “fast metabolism”? The idea that some people have a naturally faster metabolism than others isn’t entirely false, but as with most ideas around your health, it’s a little more complex than we’ve been led to believe. Although we can assume genetic factors contribute something to our weight and metabolic rate, we still have yet to understand how or to what extent 1. 

Instead of hyperfocusing on the metabolism aspect, it’s much more productive to look at calorie intake and macronutrient distribution, stress levels, gut health, exercise, and other factors when achieving weight gain goals. 

For most people, intentional weight gain is about building muscle as opposed to body fat. Here are some practical strategies for how to gain body mass in a healthy, sustainable way (i.e. not overdoing the junk food!).

Deconstructing the Concept of “Metabolism

It turns out that what we think of as having a “fast” or “slow” metabolism is a bit of an oversimplification in terms of what causes people to lose or gain weight. 

Metabolism is technically defined as, “the whole sum of reactions that occur through the body within each cell and that provide the body with energy.”

The rate at which the body makes energy (i.e., burns calories) is called its basal metabolic rate (BMR), and it is influenced by factors such as your hormone levels, exercise, diet, age, and any diseases present 1. The problem is the basal metabolic rate is pretty difficult to measure scientifically, so we typically look at a similar measurement called the resting metabolic rate (RMR) 2. Resting metabolic rate is exactly what it sounds like: the rate at which the body burns calories at rest. 

The most common way to measure the resting metabolic rate is an equation called the Mifflin-St Jeor Equation: 

• Men: (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5
• Women: (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161

You can use an online calculator to easily find your RMR. From there, you can find your total daily energy expenditure (TDEE) based on how much activity you regularly do. Your TDEE will then give you an idea of how many calories you should consume in a day. Many people who struggle to gain weight simply do not realize that they should be consuming a lot more calories than they think they should. 

If your goal is to gain weight, you should be consuming more calories than you burn in a day. For most people, this doesn’t have to be a ton of added calories; simply bulking up meals a little should do the trick. If your goal is to build lean muscle, simply increasing protein consumption and keeping healthy fat and carbohydrates the same can be enough. 

What Else Can Impact the Ability to Gain Weight?

As we mentioned earlier, the metabolism can be affected by several factors: 

• Diet 
• Age 
• Exercise 
• Hormone levels/imbalance
• Disease states
• Stress levels

Let’s look at a few different examples here. Say we’ve got a 20-year-old man looking to gain weight. He’s in good health but currently undereating for his total daily energy expenditure. In this case, increasing his calorie intake with healthy protein sources would likely be enough for him to put on weight. 

However, now let’s take the same man, but say he has IBS. He doesn’t digest his meals well, so his body isn’t optimally converting his food into energy. As a result, he can’t seem to gain weight no matter what he eats or how much exercise he does. In this case, there is an underlying cause—gut health—that needs to be addressed before his body can put on weight. 

A body under high stress may also resist weight gain, whether or not the stress makes it difficult to eat more calories. As much as possible, it’s important to return the body to a state of calm in order to increase calories and facilitate healthy weight gain. This might mean a regular meditation practice, EFT tapping exercises, or simply taking several deep breaths before sitting down to a meal. Whatever the weight goal is, the body needs to feel safe in order for the metabolism to work properly. 

Strategies for Healthy Weight Gain

Now that we’ve shown that changing your weight is not as simple as having a “fast” or “slow” metabolism, let’s outline a few practical strategies for healthy weight gain. 

Increasing Protein Intake

One reason many people might be unable to put on weight—and especially lean muscle—is that they’re undereating protein. Aiming to increase protein to at least 1.3 grams per kilogram (2.2 lbs) of body weight can help 3. Under this rule, a 150-lb man should aim for at least 89 grams of protein per day, and likely more depending on his daily energy expenditure and a goal to increase muscle mass. 

A gram of protein per pound of body weight per day would be perfectly within reasonable protein intake and contribute toward increasing muscle mass, with the appropriate amount of strength training to support it. When struggling to eat enough protein, a high-quality protein powder can help fill in the gaps, especially  after workouts. 

Once protein intake is dialed in, additional calories from fat and carbohydrates may be necessary to gain weight and support energy. These calories should come from whole, nutrient-dense foods, such as regular and sweet potatoes, grains, nuts and seeds, dairy as tolerated, and colorful fruits and vegetables 4. Keeping added sugars low is important for protecting the liver and cholesterol levels 5.

Focusing More On Strength Training Over Cardio

Research shows that prioritizing strength training over aerobic exercise can help to increase lean muscle mass 6 7 8. It may be more ideal to have more sessions per week (2–3 per muscle group) with fewer sets per session as opposed to hitting a max number of sets in one or two longer sessions 6. For each set, it’s key to use just enough weight to make the last few reps challenging. 

This isn’t to say that cardio exercise is bad, or that we shouldn’t do fun cardio-based activities like biking or recreational sports. But if the goal is to to gain weight, strength training should be the primary focus 8. 

Taking Control of Gut Health

No matter what your health or metabolism goals are, your gut health is going to have an impact. If you have issues with digesting your food, it’s going to be harder for your body to fully utilize the proteins, carbs, and healthy fats you’re eating for sustainable weight gain. Unwanted guests, like parasites, can even steal nutrients from your food that should be going to your cells. 

For our clients with gut issues, we work on resolving them so that their metabolism can operate efficiently and their body has the energy to build muscle mass in a sustainable way 9. For some individuals, repairing the gut may be as simple as eating a healthy anti-inflammatory diet and getting regular exercise alongside stress management. Others may need additional tools like probiotics for balancing gut microbes, antimicrobials for treating gut infections, or other strategies to reduce inflammation and regulate motility. 

Relaxing and Enjoying Meals

Oftentimes, stress is the biggest factor in unintentional weight loss or being unable to gain weight. We can intentionally counteract this by making each meal an enjoyable, relaxing experience. For example, I recommend the following guidelines to my clients: Cook and eat meals with family and friends, and make conversation fun and light. Eat at the dinner table instead of in front of your TV, and maybe even light a candle for some warm ambiance. Practice gratitude and take a few deep breaths before your meal. It really does make a difference for both mindset and digestion!

Leave the Idea of a High Metabolism Behind and Focus on What You Can Control

For my underweight clients who want to gain weight fast (the healthy way), we focus on first getting enough calories according to their resting metabolic rate and total daily energy expenditure. We then increase their caloric intake with nutrient-dense foods and additional protein to support muscle growth. When paired with a consistent strength training routine, these steps can help underweight people achieve their weight goals. 

Learn more about diet, healthy exercise, macronutrients, and gut health in my book Healthy Gut, Healthy You and on my YouTube channel.

The Ruscio Institute has developed a range of high-quality formulations to help our clients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you. The information on DrRuscio.com is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.