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How to Gain Weight With a Fast Metabolism

And Other Factors to Consider for Healthy Weight Gain

Key Takeaways:
  • While some people are technically genetically predisposed to a “fast metabolism,” it isn’t as black and white as we might think.
  • Many other factors, such as stress levels, gut health, exercise, and macronutrient distribution affect how we gain or lose weight. 
  • A few strategies for healthy weight gain include focusing on protein intake, choosing strength training more than cardio, and correcting any gut health issues that may be impacting nutrient absorption. 
  • You’re not powerless against a fast metabolism if you’re trying to gain weight/muscle mass — focus on the factors you can control and you’ll see positive results.

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 it comes to achieving your weight gain goals (which for most people is probably a goal to gain 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 you may have going on [1]. The problem is your basal metabolic rate is pretty difficult to measure scientifically, so we typically look at a similar measurement called your resting metabolic rate (RMR) [2]. Resting metabolic rate is exactly what it sounds like: the rate at which your body burns calories at rest. 

The most common way to measure your 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, and that will give you an idea of how many calories you should really 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 your meals slightly should do the trick. If your goal is to build lean muscle, simply increasing your protein consumption and keeping your healthy fat and carbohydrates the same can be enough. 

What Else Can Impact Your Ability to Gain Weight?

As we mentioned earlier, your 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 you’re a 20-year-old man looking to gain weight, in good health but currently undereating for your total daily energy expenditure. In this case, increasing your calorie intake with healthy protein sources would likely be enough to put weight on. 

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, not to mention the person may simply find it difficult to eat a higher amount of calories under a lot of stress. As much as possible, we want to focus on returning 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 you sit down to a meal. Whatever your weight goal is, your body needs to feel safe in order for your 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. 

Increase your Protein Intake

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

A gram 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. If you’re struggling to eat enough protein, a high-quality protein powder can help fill in the gaps and keep you satisfied post-workouts. 

Once you have your protein intake dialed in, you may find you still need additional calories from fat and carbohydrates to gain weight and keep your energy up. These calories should come from whole food, nutrient-dense sources such as regular and sweet potatoes, whole grains, nuts and seeds or nut butter such as peanut butter, dairy if you can tolerate it, and colorful fruits and vegetables [4]. Keep your intake of added sugars low to protect your liver and cholesterol levels [5].

Focus More On Strength Training Over Cardio

Research shows that prioritizing strength training over cardio exercise helps 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 trying to do your max number of sets in one or two longer sessions [6]. For each set, you want to push your muscles with just enough weight to make the last few reps challenging. 

This isn’t to say that cardio exercise is bad, or that you can’t do fun cardio-based activities like biking or recreational sports. But if you want to gain weight, strength training should be your primary focus [8]. 

Take Control of Your 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. 

If you have gut issues, work on resolving them so that your metabolism can operate efficiently and your body has the energy to build muscle mass in a sustainable way [9]. For some individuals, repairing the gut may be as simple as a healthy anti-inflammatory diet and regular exercise alongside stress management. Others may need additional tools like probiotics, antimicrobials for gut infections, or other tools to reduce inflammation and regulate motility

Relax and Enjoy Your Meals

Oftentimes, stress is the biggest factor in unintentional weight loss or being unable to gain weight. We can intentionally counteract this by making meals an enjoyable, relaxing experience. 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, in both your mindset and your digestion!

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

If you’re underweight and want to gain weight fast (the healthy way), focus on first getting enough calories according to your TDEE and then increasing your caloric intake with nutrient-dense foods and especially additional protein to support muscle growth. Alongside a consistent strength training routine, you’ll be well on your way to achieving your 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 patients 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.

➕ References

  1. Qasim A, Turcotte M, de Souza RJ, Samaan MC, Champredon D, Dushoff J, et al. On the origin of obesity: identifying the biological, environmental and cultural drivers of genetic risk among human populations. Obes Rev. 2018 Feb;19(2):121–49. DOI: 10.1111/obr.12625. PMID: 29144594.
  2. Resting Metabolic Rate: How to Calculate and Improve Yours – NASM [Internet]. [cited 2023 Sep 11]. Available from: https://blog.nasm.org/nutrition/resting-metabolic-rate-how-to-calculate-and-improve-yours
  3. Hudson JL, Wang Y, Bergia Iii RE, Campbell WW. Protein Intake Greater than the RDA Differentially Influences Whole-Body Lean Mass Responses to Purposeful Catabolic and Anabolic Stressors: A Systematic Review and Meta-analysis. Adv Nutr. 2020 May 1;11(3):548–58. DOI: 10.1093/advances/nmz106. PMID: 31794597. PMCID: PMC7231581.
  4. Quatela A, Callister R, Patterson A, MacDonald-Wicks L. The Energy Content and Composition of Meals Consumed after an Overnight Fast and Their Effects on Diet Induced Thermogenesis: A Systematic Review, Meta-Analyses and Meta-Regressions. Nutrients. 2016 Oct 25;8(11). DOI: 10.3390/nu8110670. PMID: 27792142. PMCID: PMC5133058.
  5. Bray GA, Bouchard C. The biology of human overfeeding: A systematic review. Obes Rev. 2020 Sep;21(9):e13040. DOI: 10.1111/obr.13040. PMID: 32515127.
  6. Benito PJ, Cupeiro R, Ramos-Campo DJ, Alcaraz PE, Rubio-Arias JÁ. A Systematic Review with Meta-Analysis of the Effect of Resistance Training on Whole-Body Muscle Growth in Healthy Adult Males. Int J Environ Res Public Health. 2020 Feb 17;17(4). DOI: 10.3390/ijerph17041285. PMID: 32079265. PMCID: PMC7068252.
  7. Grgic J, Mcllvenna LC, Fyfe JJ, Sabol F, Bishop DJ, Schoenfeld BJ, et al. Does Aerobic Training Promote the Same Skeletal Muscle Hypertrophy as Resistance Training? A Systematic Review and Meta-Analysis. Sports Med. 2019 Feb;49(2):233–54. DOI: 10.1007/s40279-018-1008-z. PMID: 30341595.
  8. Lundberg TR, Feuerbacher JF, Sünkeler M, Schumann M. The Effects of Concurrent Aerobic and Strength Training on Muscle Fiber Hypertrophy: A Systematic Review and Meta-Analysis. Sports Med. 2022 Oct;52(10):2391–403. DOI: 10.1007/s40279-022-01688-x. PMID: 35476184. PMCID: PMC9474354.
  9. Montenegro J, Armet AM, Willing BP, Deehan EC, Fassini PG, Mota JF, et al. Exploring the influence of gut microbiome on energy metabolism in humans. Adv Nutr. 2023 Jul;14(4):840–57. DOI: 10.1016/j.advnut.2023.03.015. PMID: 37031749. PMCID: PMC10334151.

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