For some fucked-up reason (thank you, keto zealots) people believe this is what happens when they eat carbohydrates:

Bread —> Glucose —> Adipose tissue aka body fat

This is some mega bullshit. Here’s what really happens when you eat carbs — from now on it’s “carbs” because “carbohydrates” is a long word to type and my fingers are already sore. So, here’s the chain of events after you eat carbs:

Bread —> Glucose —> Carbs are rarely converted to fat under normal dietary conditions

The pathway for converting dietary carbs into fat is called de novo lipogenesis and I used to believe too many carbs would be stored as body fat. Because, well, it made complete sense. Also, the guy who told me this on Twitter seemed like a legit source of information. 

Truth is, de novo lipogenesis rarely occurs. ​​Small spoiler warning: usually, it’s a dietary fat that’s stored in adipose tissue.

A tightly controlled metabolic ward study (food was provided by the researchers) overfed subjects by 50% above their maintenance calories. Predominantly from carbs. Through scientific methods I don’t really understand, they determined where the stored body fat came from — carbs or fat:

 The subject on average, stored a total of 282 grams of fat per day in adipose due to excess calories. A measly 4 grams of that fat resulted from de novo lipogenesis, and 278 grams came from dietary fat.

How about that? Only 1.4% of fat the subjects gained was directly from carbs while 98.6% came from dietary fat

And it’s not just one study. Multiple studies (study 1, 2, 3) have shown de novo lipogenesis is inefficient for the body and carbs rarely contribute to fat gain (they contribute indirectly, though, and I’ll get to it later in the article):

1) De novo lipogenesis is not the pathway of first resort for added dietary carbohydrate in humans, at least on Western (high-fat) diets. De novo lipogenesis can occur, but it generally does not. 
2) Most experimental data in humans, however, contradict this view of the function of de novo lipogenesis. Initial studies in which indirect calorimetry was used showed little or no net de novo lipogenesis after short-term carbohydrate overfeeding. 
3) De novo lipogenesis increases after overfeeding with glucose and sucrose to the same extent in lean and obese women but does not contribute greatly to total fat balance.

If you’re not a diehard low-carb lover and you’re still reading, you may be wondering why carbs are rarely converted and stored as body fat?

Broderick Chavez, a sports performance expert, biologist, and chemist has a cool analogy that he stole from his college professor and now I’m stealing it from Broderick and as far as I’m concerned, if you steal a previously stolen idea, it’s not really stealing. Is it? Anyway…

Think of your metabolism as a pair of pants with a number of pockets. Carbohydrate aka glucose metabolism is like wearing cargo pants — you have heaps of pockets. You eat carbs and they can be burned for energy right away, stored in the liver and muscles in a form of glycogen, and in the blood in a form of blood sugar.

So you have four main places that your body can store glucose before it says enough is enough, de novo lipogenesis is in full swing, I’m shifting carbs into the adipose tissue, muthafucka.

An average person can store about 600 grams of glycogen before de novo lipogenesis kicks in:

~80 grams can be stored in the liver and ~500 grams in the muscles. (It varies widely based on body mass, diet, exercise, etc.)

Protein is irrelevant for this topic so let’s give a massive fuck you to protein and move on to the fat metabolism. 

You eat fat above the momentary requirement (which is like a spoon) and the rest of it has nowhere to go except your hips and waist. Fat goes to body fat. There are no other pockets for fat. Fat goes to fat. That’s how human metabolism works.

Now, cast your mind 654 words back where I said carbs don’t contribute to fat storage much, however, they contribute indirectly. While carbs are rarely converted to fat, higher carb intake equals more glucose and less fat used for energy. Your body gives a massive fuck you to dietary fat and stores more of it as body fat.

In a way, you could rationalize it’s a problem — more carbs consumed = more dietary fat stored as body fat. But it’s only a problem if you consume too many calories. This is why a 500 calorie surplus of carbs and a 500 calorie surplus of fat will both make you gain fat equally. Just via different mechanisms.

So don’t fear carbs. They don’t single-handedly make you gain body fat nor do they prevent body fat loss (remember “the rice study”?). Fat loss comes down to being in a calorie deficit. The carb to fat ratio doesn’t make much of a difference.

I’ll leave you with what the recent review by Koliaki et al. concluded:

<…> the most effective strategy to achieve long-term weight loss and good cardiometabolic health is shifting to a healthy dietary pattern, compatible with individual food preferences and lifestyle habits.”

The translation: if you prefer carbs, eat more carbs and if you prefer fat, eat more fat. Don’t limit yourself to eating 50 grams of carbs just because some low-carb zealot of simian stupidity mentioned ketosis or insulin (insulin isn’t an issue either, btw).


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Originally published by me on Medium on February 23, 2022

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