Shocking Facts About Metabolism (That You Never Knew)

July 10, 2014

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Human metabolism really blows my mind.

I’m at the tail end of my advanced macronutrients class and this past week has been eye-opening. The research that was presented goes against pretty much everything that I’ve learned when it comes to health.

Throw everything you’ve ever learned about weight and metabolism out the door. Prepare to change the way you think about calories, weight, and health from here on out.


(Fact #1)- Carbohydrates are not converted to fat if you overeat 

Contrary to what your sorority sister told you back in the day, carbs are not the devil. Under normal circumstances, carbohydrates are not converted to fat if you overeat. I say “normal circumstances” because it can happen, but it’s extremely rare. The process of converting ingredients from other sources into fat is known as de novo lipogenesis, which very rarely happens in human metabolism.

This makes perfect sense if you think about it in a practical way…

Why would your body do more work than it has to? It’s incredibly inefficient for your body to convert something that “isn’t fat” (such as carbs, protein, or alcohol) into fat to be stored. It’s much easier for your body to take fat from the food you eat and store that instead.

There’s no point in running a bunch of unnecessary metabolic pathways that are huge energy hogs. Converting and storing carbs as fat is like driving a metabolic Hummer. On the contrary, storing fat from your food is the equivalent to driving a metabolic Prius (much cheaper).

The underling message is that it’s possible to eat large amounts of carbohydrates and not gain weight. Excessive carb intake causes your body to increase carbohydrate oxidation and you burn right that huge bowl of pasta you just ate. Sound too good to be true? It’s not! The good news is you will burn all the extra carbs you eat, the bad news is this doesn’t apply to other nutrients. Bummer.


(Fact #2)- Eating too much fat is the culprit of weight gain

Eating more fat than you need (whether it’s “good” or “bad” fat) will easily be stored in the body. Remember what I said earlier? It’s easy to store fat as fat! Before you panic about your chronic avocado habit, take comfort in the fact you still need a daily dose of some healthy fats for optimal function. Just don’t go overboard!

This brings the so-called ‘obesity epidemic’ into play as well. It’s easy to jump to the conclusion that Americans eat too much, contributing to increased rates of obesity and chronic diseases.

The issue may not be that Americans are “eating too much”, but simply that we are consuming excessive carbohydrates without lowering the amount of fat we eat.

Maybe that low-fat diet trend back in the 90s wasn’t so bad after all?


(Fact #3)- Weight loss may actually be impossible for some people

Adaptive thermogenesis is the ultimate enemy for losing weight (and keeping it off).  The concept of adaptive thermogenesis means when you decrease the calories you eat, your body becomes more efficient at using whatever it has left to survive. You become better at storing energy and your metabolism learns to function with less calories. Therefore, to sustain weight loss in the long run you will have to continue eating a low-calorie diet for life.

Yes, for life. Adaptive thermogenesis does not go away and can’t be reversed. If the low-calorie diet isn’t maintained, you’ll gain all the weight back. This is just one of the many factors that make some people genetically resistant to losing weight. Society needs to shift it’s focus away from weight and move to overall health and disease prevention. Weight is a lousy indicator of health, which I mentioned in this post about BMI

Think about it this way:

Dogs come in all shapes and sizes. Would you say to a St. Bernard: “Just keep exercising and eating healthy and one day you’ll look like a Chihuahua.” I know, it’s a crazy analogy. Humans accept different body types in other species of animals, except when it comes to our own. We think everyone should fit into the same mold, but it’s not biologically possible.


Ponder that!


  • Jordan

    Ahhh i love this post! So it’s so easy to get confused with all the diet, weight, calorie mumbo jumbo out there. I’ve done a ton of research and started upping my carbs/decreasing my fats in February. I’ve seen a HUGE change in my energy and my cravings! Thanks for the info!!

    • Kathryn

      I was initially skeptical when I heard this information, but then our teacher presented the research studies and science doesn’t lie! I typically eat a high-carb diet anyway (I’m always concerned about getting enough fiber), so this was beneficial information for me too. I’m glad your energy and cravings have normalized!

  • Melissa @ Nourish By Melissa

    Wow! This was super informational…I had no idea! Glad to hear I can enjoy that pasta without second thoughts though hahah ;)

  • Nicole @ Fitful Focus

    Great post! I love the analogy to dogs – so funny and so true!

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