Where Does Body Fat Actually Come From?
Most people don’t realize that the bulk of what we call “body fat” – about 90% of it – isn’t created from fat we eat.
It’s actually produced from sugar.
But not in the way you might think.
The key lies in how sugar interacts with your hormones – those chemical messengers that decide how your body uses incoming nutrients.
Ultimately, your hormonal response determines whether sugar gets burned for energy or stored as fat.
So let’s break down what really happens when you eat carbohydrates – and why this matters for anyone trying to lose fat.
Not All Fat Is the Same
Let’s be clear: Not all body fat is bad.
Every cell in your body has a membrane made from fatty acids. You literally couldn’t survive without it.
But when we talk about “getting rid of fat” or “being overweight,” we’re referring to something else entirely – the fat that accumulates under the skin and around organs.
This is the excess fat that’s stored in specialized cells called adipocytes – and it makes up about 90–95% of the fat we typically see and feel.
And this fat isn’t just random fat from your diet – it’s a very specific type: the triglyceride.
Triglycerides look a bit like a tadpole – they have a sugar-based “head” (called glycerol) and three fatty acid “tails.”
The name says it all: “Tri” for three fatty acids, and “-glyceride” for the glycerol (sugar) component.
This is the form your body stores fat in – both in fat cells and sometimes, dangerously, in blood vessels or internal organs.
How Are Triglycerides Made?
When you eat carbohydrates – from bread, pasta, rice, fruit, beans, snacks, or sweets – your body eventually breaks them all down into glucose, or blood sugar.
Once sugar enters the bloodstream, it needs to be dealt with quickly:
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To provide energy to your cells
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To protect your blood vessels, since high sugar levels can damage them
Your body responds by releasing insulin, a hormone that directs the sugar out of your blood and into storage or use.
Here’s what insulin does, in order:
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It tells your cells to absorb the sugar and use it to create energy (ATP).
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If your cells are full, insulin tells the liver and muscles to store the excess sugar as glycogen – short chains of sugar for quick energy later.
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If those stores are also full, insulin gives the signal to convert the leftover sugar into triglycerides, pairing it with fatty acids and storing it in your fat cells.
In other words: Excess sugar = stored body fat.
How the Body Burns Fat
When your body runs low on blood sugar – for example, between meals or while fasting – it releases another hormone: glucagon.
Glucagon breaks down stored glycogen in your liver and muscles, releasing sugar back into the bloodstream for energy.
Once glycogen stores are empty, your body goes one step further.
It activates an enzyme called lipase, which breaks down your stored triglycerides – the fat in your fat cells.
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The glycerol (sugar head) is used for energy
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The fatty acid “tails” are converted into ketones, an alternative fuel source for the brain and muscles
This process happens regularly – but only when your body has a reason to tap into its fat stores.
What Does This Mean in Practice?
If you consume more carbs than you can burn or store, your body will store the excess as fat.
And if you want your body to burn fat, you need to limit sugar intake enough that it starts accessing its long-term energy reserves.
Here’s the key point:
As long as insulin is present in your bloodstream – because sugar is still being processed – your body’s fat-burning machinery is shut down.
That means:
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Glucagon (the fat-accessing hormone) is suppressed
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Lipase (the fat-burning enzyme) is turned off
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And fat loss is minimal, even if you’re working out
That’s why snacking on carbs all day – even healthy ones – can keep your insulin levels elevated and block fat burning entirely.
It also explains why some people cut calories but still don’t lose fat –
if the calories they keep are mostly carbs, insulin remains high, and glucagon stays suppressed.
What’s the Solution?
That’s where strategies like intermittent fasting or fasted workouts come in:
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For example, eating dinner around 6 p.m.
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Then not eating again until late morning or noon the next day
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In between: optionally doing a workout
By then, your body will have used up the sugar in your bloodstream and burned through glycogen –
and will finally tap into your fat stores for fuel.
During this window, glucagon and lipase are active, and fat loss can occur efficiently.
Summary So Far:
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When sugar is in your blood, your body is storing fat and blocking fat loss
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When sugar has been gone for a while, your body starts using stored fat for energy
But that’s just the start.
You might be wondering:
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Why can’t some people lose fat even after cutting sugar?
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What types of sugar are the most problematic?
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How long does it take for fat-burning to really begin – hours, days, or weeks?
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What about insulin resistance and the role of cortisol?
No worries – we’ll dive into all of that in the next articles.