What Happens To The Body When We Lose Fat & Gain Muscles

How fat loss and muscle gain occur in the body.

Fat Loss
When it comes to fat loss, there is a lot to go over. I’ll do my best to keep it simple, short, and sweet. Let’s start with metabolism, which is the energy your body uses to stay alive. This often-used excuse for gaining fat, or as a sales tool, is almost always overstated. In reality, 96% of us will stay within 200-300 calories of the average person’s metabolic rate (2). While doing things to raise your metabolism may seem like a great way to lose fat, in reality, those efforts may largely be meaningless. This is because our body knows that when metabolism is higher, we will need to eat more to recover the calories burned. And that’s why we get hungrier after we go for a run or swim (3). This can be counteracted by having a steady and healthy diet/lifestyle, instead of “going on a diet” for a particular period of time (4).
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Fat loss and weight loss are two completely different things. To lose weight, simply go to the bathroom. To lose fat, you will need to metabolize fat. To accomplish this, an activated fatty acid is oxidized to introduce a double bond; the double bond is hydrated to introduce an oxygen; the alcohol is oxidized to a ketone; and, finally, the four carbon fragment is cleaved by coenzyme A to yield acetyl CoA and a fatty acid chain two carbons shorter (5). Yes, that’s a lot of technical terms. However, what I wanted to demonstrate is that burning fat is not just as simple as applying a magic wrap or using lasers to liquidate the fat. There are a lot of things that need to happen for your body to use stored fat. A combination of diet, training, sleep, stress management, hormones, and other lifestyle factors play an integral part in how much body fat one has (6). 
Most people workout, in part, to look fit. Your aesthetics are mostly determined by how long your bones are, the length relationship between muscle bellies and tendons, and insertion points. Muscle growth is essential for all sorts of things like bone health, fat loss, and looking great naked. Muscle growth occurs, in part, by resistance training-induced release of inflammatory agents, activation of satellite cells, and upregulation of the IGF-1 system, or at least setting in motion the signaling pathways that lead to hypertrophy (7). Despite what you may hear, everyone is capable of building substantial amounts of muscle (8). I have found that the people who have done the best at gaining muscle:
1. have trained with intensity (adding weight to the bar, increasing total volume, and approaching failure with their training).
2. were very consistent and made training a lifestyle (years of consistent training, not a few months here and there).
3. varied their training over time to help induce new muscle growth stimulus and avoid adaptation and injuries.
4. and were methodical in their approach, meaning they paid attention to rep schemes, tracked their progress, and aimed to improve over and over again.
And while I can go on for days about the nuances of exercise and resistance training, I’ll boil it all down to consistency. As long as you are weight training each muscle group at least once per week, you will see improvements. Just lift heavy things, and lift them often, because there is a dose-response relationship (9). So what I am saying is, take the “at least” advice literally and shoot for more. At the end of the day, if you want to gain muscle there are no legitimate “get ripped quick” plans. 

  1. Klein, A. V., & Kiat, H. (2015). Detox diets for toxin elimination and weight management: A critical review of the evidence. Journal of Human Nutrition and Dietetics, 28(6), 675-686. doi:10.1111/jhn.12286
  2. Donahoo, W. T., Levine, J. A., & Melanson, E. L. (2004). Variability in energy expenditure and its components. Current Opinion in Clinical Nutrition & Metabolic Care, 7(6), 599-605.
  3. Weise, C. M., Thiyyagura, P., Reiman, E. M., Chen, K., & Krakoff, J. (2015). A potential role for the midbrain in integrating fat‐free mass determined energy needs: An H215O PET study. Human brain mapping, 36(6), 2406-2415.
  4. Dulloo, A. G. (2017). Collateral fattening: When a deficit in lean body mass drives overeating. Obesity.
  5. Berg, J. M., Tymoczko, J. L., & Stryer, L. (2002). Lipids and cell membranes. Biochemistry, fifth edition. New York: WH Freeman, 1050.
  6. Müller, M. J., Enderle, J., & Bosy-Westphal, A. (2016). Changes in energy expenditure with weight gain and weight loss in humans. Current Obesity Reports, 5(4), 413-423.
  7. Schoenfeld, B. J. (2012). Does exercise-induced muscle damage play a role in skeletal muscle hypertrophy?. The Journal of Strength & Conditioning Research, 26(5), 1441-1453.
  8. Montero, D., & Lundby, C. (2017). Refuting the myth of non-response to exercise training: ‘non-responders’ do respond to higher dose of training. The Journal of Physiology, doi:10.1113/JP273480
  9. Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2016). Dose-response relationship between weekly resistance training volume and increases in muscle mass: A systematic review and meta-analysis. Journal of Sports Sciences, 1-10.

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