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What Do Fat Burners Do? (Science-Based)

Connor Sellers
Published by Connor Sellers
Fact checked by Donald Christman, BHSc FACT CHECKED
Last updated: April 13, 2023
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You only need to spend a few minutes in Facebook groups or forums to figure out that so many people have a complete misunderstanding of what fat-burning supplements do.

As a personal fitness coach, I recommend these products for people with an established exercise routine to help them with weight loss.

And I totally get that many people are skeptical that a few pills might help change their body composition.

So, to help you better understand what these supplements do, I did some research into the science with my dietitian.

Quick Summary

  • Fat burners promote a weight loss journey by triggering fat metabolism that specifically targets fat reserves in the body.
  • The common ingredients in fat burners are caffeine, green tea extract, L-Carnitine, and conjugated linoleic acid (CLA).
  • A fat burner will stay in your system for up to 10 hours before wearing down.

What Happens To Your Body When You Take Fat Burners?

person drinking a capsule

Fat burners work on the principle of triggering natural processes in your body that specifically target fat reserves. It's a way to trick your body into fat metabolism.

And even with just a small effect, a few grams of fat loss each day will add up over the days and months.

Here's how they generally aim to trigger body fat reduction.


Thermogenesis is a metabolic process where the primary output is heat. That means that the process consumes calories from food and body fat and then releases that energy by slightly raising your body temperature [1].

Our experience with client testing and research is that this fat oxidation process may be the most effective way to get through a weight loss plateau and fat loss stalling.

With the right thermogenic fat burner ingredients, this is something you can trigger several times a day.


This is a different metabolic process where stored fat reserves are broken down through hydrolysis into smaller molecules [2].

The end result is similar in that it may help you lose weight, but the released energy is then available for other parts of your body, including muscles.

This metabolic process seems to be more difficult to trigger with supplements and is mainly the result of exercise [3].

Do Fat Burners Have Side Effects?

man with insomnia

No, generally speaking, most natural fat burners won't trigger severe side effects, with only a few of them causing minor side effects [4].

They mostly contain amino acids, minerals, herbs, and other common substances like caffeine.

And these are all a common part of your regular diet anyway.

But, you still need to always double-check the ingredients list of dietary supplements for anything that you might have known allergies to.

And despite caffeine having a positive effect on your body weight, it's still a dietary stimulant and could cause jitters and sleepless nights [5].

So always be careful how much coffee you drink and what time of day you take a supplement to support fat loss.

How To Get The Most Out Of Fat Burners?

The first thing you need to get out of your mind is that fat-burning pills will promote weight loss while you binge-watch Selling Sunset with a box of donuts.

That's just not going to happen.

To lose fat, you will need to eat fewer calories, especially from carbs, and have a regular exercise routine. That will kickstart your metabolism and impair fat absorption.

When you add a fat-burning dietary supplement, you can burn off more calories to bring you into a calorie deficit mode [6].

"The optimal calorie deficit is large enough to stimulate steady fat loss, but not so large that you're always hungry and lethargic. Avoiding a calorie deficit that is too large is even more important for athletes, who need to keep their muscles well-fueled for training."

- Matt Fitzgerald, Writer at

4 Common Fat Burner Ingredients

stack of coffee beans and a glass of green tea

There are a few effective supplements that we have researched and tested for clients. And the ones that help you lose weight the best tend to include a few ingredients with scientific evidence.

Green Tea Extract

If you don't like drinking green tea, then a green tea extract is an ideal solution for weight loss. Several studies have shown a link to burning fat at rest and during exercise [7].


L-carnitine is produced by your brain and stimulates the body to burn fat reserves. One study has shown a moderate impact from supplementation trials, especially with obese people [8].


Yes, that morning coffee could actually trigger thermogenesis and burn off some extra fat [9]. Just be careful with the dose, as your body can only process so much before becoming jittery.

Conjugated Linoleic Acid (CLA)

There's an interesting study that looked at supplementing CLA for a year, with results showing that it may help burn fat more effectively [10].


Are Thermogenic Fat Burners the Safest?

Yes, thermogenic fat burners tend to be the safest due to natural ingredients like caffeine. Thermogenesis is a completely natural metabolic process that you won’t even notice it going on [1].

How Long Does a Fat Burner Stay In Your System?

A fat burner will only stay in your system for up to 10 hours. This is mainly down to caffeine, which takes about 10 hours to fully flush out [11].

Do You Know What To Expect With Fat Burners?

A fat burner can be a great asset for your weight loss journey as long as you combine it with a balanced diet and a regular exercise routine.

If you've struggled with that yo-yo effect of weight gain and loss, then see if a thermogenic supplement could help you gain more control.


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