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Fitness, Fat Loss

How Do I Know if my Metabolism is Slow?

By Blaide Woodburn on Jun 27, 2019 9:15:00 AM
6 Minutes Reading Time

The term “slow metabolism” is thrown around a lot in health and fitness and often carries a negative connotation, but what exactly is a slow metabolism? When someone says “I have a slow metabolism” what they are actually saying is that their body burns calories very slowly, and this is why it may be difficult for them to burn fat. Another way to look at it as that their body is very efficient with calories, which throughout evolution where food was scarce would have been an advantage. But in a society where food is plentiful and the challenge is to abstain from food rather than find it, an efficient, or slow, metabolism has actually become a disadvantage because it increases the propensity to store fat and all the negative side effects that come with that. So, how can you tell if you have a slow metabolism?

A tell-tale sign of a slow metabolism is gaining weight on a relatively low caloric intake i.e. not eating that much food and still gaining weight consistently. However, there are numerous variables involved in weight gain, so to take out some of the guesswork, I think using a tracking-centric framework is the best way to determine if you have a slow metabolism (or are experiencing negative metabolic adaptation). A slow metabolism can be loosely defined as a maintenance calorie set point that is lower than what would be expected given your height, weight, and biological sex. Consequently, this makes it much easier to exceed maintenance calories and increases the probability that those excess calories will be stored as fat. To understand where your maintenance calories should be, you can use a equations such as the Katch-McArdle or Muller to establish Basal Metabolic Rate (I usually use both then average the BMR), then calculate your maintenance calories by multiplying your BMR by your activity factor (which can be found using a quick Google search). After establishing your predicted maintenance calories, you should then compare them to your “real-world” maintenance calories (the number of calories you can eat/day and not gain or lose any weight). This can be achieved through tracking calories and recording the number of calories needed to maintain weight over a ~2 week period. Once you have both your predicted maintenance calories and your real-world maintenance calories, you should be able to determine how your metabolism stacks up to what would be expected given your biology. Take make things simpler, here’s an example:

Name: Jane Doe                                                  

Biological Sex: Female                                        

Height: 5’7’’                                                                                         

Weight: (61.4 kg) 135 lbs                                                                 

Lean Body Mass: (54 kg) 118.8                       

Activity Factor: 1.55 (Moderate Activity)                                              

Predicted Maintenance Calories              

Katch-McArdle: BMR= 21.6 x LBM (kg) + 370

BMR= 21.6 x 54 kg + 370

BMR= 1,536 kcals       

Maintenance Calories= BMR x Activity Factor

= 1,536 kcals x 1.55                                                                     

= 2,381 kcals

Real-World Maintenance Calories

Jane began tracking her calories and observed that to maintain a constant 135lb over two weeks she had to eat ~1,600 calories, which is about 800 calories less than her predicted maintenance calories and could be considered a slow (or really efficient) metabolism. To make weight loss/weight gain more manageable, Jane can slowly introduce more calories to bring her maintenance calorie set point to a more desirable number i.e. what is feasible for her to eat regularly and fits her fitness/body comp goals.

It’s worth stating that any given person’s metabolism isn’t fixed for their entire lifetime. You’re not born with a fast or slow metabolism then destined to be underweight or overweight, respectively, for the rest of your life, although genetic predisposition does play a large part in body composition. Your metabolism can be shaped to become slower (more efficient with calories) or faster (less efficient with calories) if the proper principles are applied. Specifically, my article “What Is Metabolic Adaptation?” (found via the Mind Pump Blog and PassioInventa) provides a detailed blueprint for how to slow down or speed up your metabolism by re-establishing maintenance calories.

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Blaide Woodburn

Blaide graduated from Eckerd College in 2017 with a B.S. in Molecular Biology. From 2013-2017 he participated in multiple diverse research projects at different institutions across the United States. This included conducting cancer research at Harvard Medical school, investigating the role of oxidative stress in Duchenne Muscular Dystrophy at the Baylor College of Medicine, and culminated with an undergraduate thesis at Eckerd, exploring the role of oxidative stress in Parkinson’s Disease. Blaide is currently a second year PhD student at the University of North Carolina Chapel Hill where he conducts research on the molecular mechanisms giving rise to HIV infection of the brain. Outside the lab, Blaide has a passion for evidence-based fitness and nutrition and science communication. He has worked as a personal trainer and still creates pro bono fitness and nutrition plans for a diverse set of clients. Blaide also writes for multiple graduate blogs, including one sponsored by the National Institute of Health, and co-created a diverse science communication website called PassioInventa (piphd.com). In the future, Blaide hopes to use his strong foundation across scientific disciplines to work at the interface of science and business as a Life Science Consultant or Medical Science Liaison.

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