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Understanding Metabolism: How Undereating Hinders Results

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There are so many questions out there about metabolism and weight loss: What is metabolism? How do you get faster metabolism? What causes your metabolism to slow down? How does your metabolism impact your weight and does what you eat impact how many calories you burn each day?

Fast metabolism, slow metabolism, broken metabolism and increased metabolism are all buzz phrases in the fitness and nutrition industry and these are just a few of the metabolism questions we get at WAG Nutrition.

What is Metabolism?

Your metabolism is the combination of processes that turn your food into energy. The calories you consume fuel the buildup and breakdown of the nutrients necessary for optimal health and performance. Your metabolism has a direct impact on weight loss, weight gain and long-term health. 

Ultimately, your body needs adequate energy intake to stay active, support day-to-day activity, maintain (or grow!) muscle and keep you from experiencing fat gain or weight plateaus.

How Does Metabolism Affect Weight Loss?

Someone with a higher metabolism usually has an easier time losing weight. Why? Their body quickly breaks down and utilizes the food they eat and harnesses it for fuel instead of storing it as fat.

That being said, the energy in/energy out equation still stands in a majority of cases. Even someone with a fast metabolism will gain weight if they’re eating more energy (food) than they expend on a regular basis.

Is It Possible to Speed up Your Metabolism?

The quick answer is yes! There are things you can do to speed up your metabolism. 

We’ll dig into more specifics in a second. Before we get into it, you need to understand the different components of metabolism, how they work and how what (and how much) you eat impacts your metabolism.

What Are the Components of Metabolism

There are five main components that make up your metabolism. They’re impacted by how much you eat, your movement, body type and more. The components of metabolism are:

  1. BMR (Basal Metabolic Rate)
  2. RMR (Resting Metabolic Rate)
  3. TEF (Thermic Effect of Food)
  4. EA (Exercise Activity) 
  5. NEAT (Non-exercise Activity Thermogenesis).

Let’s dig into each.

What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR) includes the very minimum energy needed to keep vital bodily functions fueled. Think: heartbeat and breathing.

What Impacts Basal Metabolic Rate?

Your BMR is influenced by age, body composition, body size, climate, gender and hormone status. Generally, a larger, younger individual with more muscle will have a higher BMR. Men also tend to have higher BMRs than women [1].

How Does BMR Impact Weight Loss?

Because people with a higher BMR burn fat more readily, a higher Basal Metabolic Rate usually indicates that an individual will have a quicker, easier time dropping fat and are more likely to keep it off long term.

What is Resting Metabolic Rate (RMR)

Resting Metabolic Rate is pretty similar to your BMR in that it is still measuring minimal functioning in your body. RMR extends to respiration, circulation, synthesis of organic compounds (like building muscle!) and basic cellular functioning. 

There is usually about a 10% difference between your BMR and your RMR and it accounts for about 60-75% of your total energy you expend each day [2].

Resting Metabolism and Weight Loss

Just like BMR, age, body composition, body size, climate, gender and hormone status can all impact your Resting Metabolic Rate. People with more lean body mass (aka more muscle!) have an RMR that is about 5% higher than non-athletic individuals [3].

Those with a higher RMR tend to lose weight and keep it off more easily.

How Undereating Impacts BMR and RMR

If you’re not eating enough to support healthy muscles, your RMR will be lower and you will burn fewer calories at rest. Undereating can also cause hormone imbalances, which can cause water retention and unwanted fat storage.

How to Calculate Your Resting Metabolic Rate

There are many ways to calculate your Resting Metabolic Rate. The two most popular are the Harris and Benedict Equation and the Mifflin-St Jeor Formula developed in 1918 and 1990, respectively [4,5].

Calculating BMR with the Harris and Benedict Equation

  • Men: 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) - (5.677 × age in years)
  • Women: 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) - (4.330 × age in years)

Calculating BMR with the Mifflin-St Jeor Formula

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

The Problem with These Equations (and a Better Way to Do It)

No two people are the same and although these formulas account for gender, age, height and weight, they do not take lean body mass or genetics into account. After more research, scientists learned that muscle mass plays a huge role in RMR and fat loss.

So, is there a better way to get an accurate look at how much you burn in a day?

Determining Your Energy Needs

Equations are great, but as we chatted about, they’re pretty general and aren’t specific to your body.

The best way to know how many calories you’re burning is to track your macros and measure the many aspects of progress that come along with a shift in diet and lifestyle.

At WAG Nutrition, our experienced coaches and comprehensive platform, Seismic, can analyze weight trends, give you tips to help you hit your targets and guide you towards your dream body composition.

Here are a few quick tips to help you determine your energy needs:

  1. Review the basics of tracking macros and download our Macro Calculator.
  2. Download our favorite food tracking app, MacrosFirst.
  3. Weigh yourself every morning before eating/drinking anything, without your clothes on (or with minimal, consistent clothing).
  4. On the same day each week, average out your daily weights.
  5. Compare your average weekly weight from one week to the next to assess progress.
  6. Hire a coach who can help you determine what macro changes need to happen to keep you tracking towards your goals.

What is the Thermic Effect of Food?

The Thermic Effect of food is the energy expended in the digestion, breakdown, and absorption of the foods you eat [6]. It accounts for around 10% of your calorie intake but much like BMR and RMR, TEF is impacted by other factors. Age, genetics, meal timing, and meal composition all impact TEF [7].

Foods With a High Thermic Effect

Wondering what foods have the highest thermic effect? Here is a macronutrient breakdown [8]:

  • Thermic effect of fats: 0–3%.
  • Thermic effect of carbohydrates: 5–10%.
  • Thermic effect of protein: 20–30%

Right off the bat, you can see that protein is a game-changer when it comes to keeping your metabolism strong. Not only does protein have the highest Thermic Effect of Food but it also supports healthy lean muscle maintenance which helps keep BMR and RMR strong.

How Does TEF Impact Weight Loss?

Because TEF is highest after a large meal, you may think that eating one or two big meals will increase TEF. That could be true but isn’t always the case. A lesser TEF after smaller, frequent meals could still add to the same overall daily TEF if you eat frequently enough. Thus, there is generally little-to-no thermogenic benefit of eating smaller, more frequent meals vs. larger, less frequent ones if overall calories are controlled [9,10,11].

H3: How Undereating Impacts TEF

Eating food takes energy. Chewing, swallowing, digesting, creating the enzymes that break down your food — these things all cost you calories.

Protein especially has a high thermic effect, which means it takes your body extra energy to digest, process and store protein. Fat has the lowest thermic effect out of the three macronutrients. When you undereat, you are decreasing this overall calorie output.

Exercise and Metabolism (EA)

I bet you can guess what this includes! Your exercise activity includes deliberate exercise like going for a run, doing hot yoga or hitting a CrossFit class. If you exercised on purpose, that is EA!

Exercise Activity varies drastically from one person to another, accounting for anywhere between 10% (or less) to 30% (or more) of total daily energy expenditure [12].

How Does Exercise Affect Metabolism?

Even though RMR and BMR account for a majority of metabolic output, Exercise Activity still plays a really important role in overall health. After a tough workout, your body continues burning calories as your muscles recover so metabolism stays high for a larger portion of your day. In fact, high-intensity exercise (shorter, more intense bursts) can help increase RMR [12]. Pair that with resistance training to build muscle and you have the recipe for higher metabolism and a much easier time keeping weight and body composition where you want it. 

That being said, if you’re already participating in regular exercise, more isn’t always better. Here’s why!

How Undereating Impacts EA

Have you ever had a day in the gym when your energy was through the roof and you felt like you could go forever? Have you ever had a day when you were dragging and headed home feeling like you didn’t accomplish much because you didn’t have enough energy?

Getting adequate calories allows you to push hard in the gym, build and maintain muscle and get stronger. Sufficient nutrients also support quick recovery so you can hit it hard again tomorrow.

In other words, undereating can cause your EA to decrease enough that it wasn’t worth the calorie loss in the first place. If you eat less but can’t burn as much at the gym because of it, it evens out, right?

Eating a bit more, feeling fueled and recovering adequately can cause more muscle gain and/or fat loss over time. 

But, what about all your other movements that aren't organized exercise?

Non-Exercise Activity Thermogenesis (NEAT)

Non-exercise activity thermogenesis (NEAT) is the most variable part of energy expenditure from person to person. So, if you’ve ever wondered, “Why does metabolism change so much from person to person?” NEAT is the first place to look!

Non-exercise activity thermogenesis includes all energy expended for the activities you do that aren’t eating, sleeping, breathing or exercising on purpose. NEAT includes things like walking your dog, doing yard work, standing instead of sitting at work, fidgeting, walking around the grocery store, meal prepping, taking the stairs, etc.

How Does Non-Exercise Activity Thermogenesis Affect Metabolism?

In extreme cases, NEAT can differ by 2,000 calories a day between individuals [13]. In simple terms, the more you move, the more calories you’ll burn. If you want to make some drastic changes in fat loss without feeling like you live in the gym, focus on your NEAT. 

How to Increase Your NEAT

Here are some quick ideas to help you increase your Non-Exercise Activity Thermogenesis:

  • Make it measurable. Wear a watch and set a movement or step goal.
  • No more princess parking — pick a spot farther away from the door.
  • Put yourself on a clock, set a timer and make sure you get up every 20-30 minutes to walk, stretch or knock out some air squats.
  • Stand — at work, in the coffee shop, while you’re chatting at a get-together — any chance you get! If you’re stuck at a desk all day, check out these Stretches You Can Do at Your Desk to keep yourself moving and mobile.
  • Take the stairs or the long way to your office instead of jumping on the elevator

How Undereating Impacts NEAT

When you are under-fueled, your body will automatically start down-regulating your NEAT to conserve as much energy as possible. This means you will naturally stop moving around, you’ll opt for the closest parking spot, you’ll avoid taking your dog for a walk, you’ll sit instead of stand at your desk, etc. Eating less means less energy and less overall movement which decreases calorie expenditure.

Can I Change My Metabolism?

Great (and popular) question! 

Although there are some things you can’t change like age or genetics, there are many things you do have control over that can impact whether you have a fast or slow metabolism. Let’s review what can cause slow metabolism and how to increase your metabolism.

What Causes Slow Metabolism?

Thinking back to everything we chatted about, here are a few things that you have control over that could contribute to a slower metabolism:

  1. Limited daily movement 
  2. Not engaging in regular, purposeful exercise 
  3. Skipping weight training days
  4. Undereating - especially protein

If you’re afraid you may be undereating, check out this guide to rebuild your metabolism after dieting. Hiring a coach to help you slowly increase food intake while minimizing fat gain is also a great option!

How to Increase Your Metabolism

Wondering how you can get a faster metabolism? Here are some of the things you have control over:

  • Increase NEAT: Review the list above and think about ways you can add more movement in your day outside of your hour (maybe two) at the gym.
  • Eat more protein: Here are some ideas!
  • Strength train and participate in high intensity exercise: This will help you build and hold onto more lean muscle mass.
  • Sleep: Sleep has a direct impact on your energy levels and hormone balance. Healthy hormones and high energy levels will keep your metabolism strong.
  • Maintain a healthy body weight: Keeping body fat in a healthy range and holding onto lean muscle can increase BMR and RMR.

We get it — there are a lot of pieces to this puzzle. When you sign up for Working Against Gravity, we’ll pair you with your own personal nutrition coach. You’ll have formal weekly check-ins with your coach, plus the ability to message them 24/7 anytime you need to chat.

Together, you’ll decide the steps to take to reach your goals and master healthy habits. You’ll also join our exclusive online community, where you’ll find additional accountability and support.

Get a Taste of WAG

The WAG Crash Course is OPEN for enrollment. This 30-day course will teach you the ins and outs of macro tracking, building healthy lifestyle habits and sustaining results without restricting the foods you love. Get personalized macros from a WAG Coach, join the members-only Facebook Group and participate in quarterly Live Q&A sessions with WAG Coaches.

  1. Mayo Foundation for Medical Education and Research. (2020, November 10). Can you boost your metabolism? Mayo Clinic. Retrieved from https://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/metabolism/art-20046508 
  2. Bean, A. (2013). The complete guide to sports nutrition (7th ed.). London: Bloomsbury. 
  3. Helms, E., Valdez, A., & Morgan, A. (2015). The muscle and strength pyramid: Nutrition. Eric Helms.
  4. Harris, J. A. & Benedict, F. G. (1918). A biometric study of human basal metabolism. Proc Natl Acad Sci USA, 4(12), 370-373. doi: 10.1073/pnas.4.12.370
  5. Mifflin, M. D., St Jeor, S. T., Hill, L. A., Scott, B. J., Daugherty, S. A., Koh, Y. O. (1990). A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 51(2), 241-247. doi: 10.1093/ajcn/51.2.241.
  6. Reed, G. W., & Hill, J. O. (1996). Measuring the thermic effect of food. Am J Clin Nutr, 63(2), 164-169. Doi: 10.1093/ajcn/63.2.164
  7. de Jonge, L., & Bray, G. (1997). The thermic effect of food and obesity: a critical review. Obes Res, 5(6), 622-631. doi: 10.1002/j.1550-8528.1997.tb00584.
  8. Tappy, L. (1996). Thermic effect of food and sympathetic nervous system activity in humans. Reprod Nutr Dev, 36(4), 391-397. doi: 10.1051/rnd:19960405.
  9. Kinabo, J. L., & Druin, J. V. (1990). Effect of meal frequency on the thermic effect of food in women. Eur J Clin Nutr, 44(5), 389-395. https://pubmed.ncbi.nlm.nih.gov/2387273/
  10. Smees, A. J., & Westerterp-Plantenga, M. S. (2008). Acute effects on metabolism and appetite profile of one meal difference in the lower range of meal frequency. Br J Nutr. 99(6), 1316-1321. doi: 10.1017/S0007114507877646.
  11. Verboeket-van de venne, W. P., & Westerterp, K. R. (1991). Influence of the feeding frequency on nutrient utilization in man: Consequences for energy metabolism. Eur J Clin Nutr 45(3), 161-169. https://pubmed.ncbi.nlm.nih.gov/1905998/
  12. Berardi, J., Scott-Dixon, K., Kollias, H., DePutter, C., St. Pierre, B., & Andrews, R. (2018). The essentials of sport and exercise nutrition. Precision Nutrition.
  13. Levine, J. A. (2004). Nonexercise activity thermogenesis (NEAT): Environment and biology. Am J Physiol Endocrinol Metab. 286(5), 675-685. doi: 10.1152/ajpendo.00562.2003.
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Posted by Ali Macy
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Ali is a born and bred Vermonter who fell in love with nutrition and fitness in her early 20’s and never looked back. She is a coach, blog editor and Program Lead for WAG with a BA in English Literature and a Master's in Nutrition and Human Performance.

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