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How Long After Eating Does Your Body Start To Burn Fat?

Anthony Diaz
Published by Anthony Diaz
Last updated: March 28, 2023

I advise many of my clients to keep a careful food journal along with the exact times that they are eating. As a personal trainer, that’s a key piece of information that I need to understand how quickly people can lose weight.

And since the matter is not exactly universal, I decided to dive into research a bit deeper.

So, to better understand how the body reacts to food and exercise and when it actually starts burning fat, I got together with my dietitian and nutrition specialist, and we discussed some relevant literature together.

Here’s what I learned.

Quick Summary

  • The body begins burning body fat when it has exhausted glycogen stores and blood glucose.
  • To lose weight, you need to make sure that your last meal is not too close to your workout, as that’s when your blood glucose peaks.
  • By adjusting your meal and exercise timing, you can speed up your weight loss journey significantly.

How Long After Your Last Meal Does Your Body Start Burning Fat?

Eating a sandwich

Your body will start burning fat about 12 hours after your last meal [1]. That’s typically how long your glycogen and blood sugar levels will last before your metabolism is forced to look for energy from other places.

When your stomach is full, the body will send signals so that the pancreas releases insulin.

And insulin then escorts the glucose into cells and eventually causes your body to store excess energy as fat [2].

It’s a clever process that has helped humans avoid starvation, but it’s also the main reason people find losing weight to be so difficult.

So, if it takes 12 hours to start burning fat, then how is it possible to not gain weight?

This is where eating less and exercising at the right time comes into play. You can significantly reduce your blood glucose levels by being physically active after eating. And if you then add a workout routine several hours after a meal, you can boost fat loss significantly.

More on this weight loss approach shortly.

Does It Make A Difference What You Eat?

Yes, it matters what you eat when it comes to triggering weight loss through fat metabolism.

If you eat a lot of calorie-dense food, like saturated fat, and particularly processed carbs, then your blood glucose will spike, and you’ll gain more weight [3].

Not only that, but it will increase your blood pressure and significantly increase your risk of heart disease.

To help with weight loss efforts, aim for a low-carb diet with more healthy fats and lean proteins. These take longer to digest, break down and transform into glucose and ketone bodies.

And don’t forget to count calories in a food journaling app like Noom. You’ll be surprised how much all those small snacks add up to over 24 hours.

Nutritionist Amy Beney of My Nutrition Insights shares that when we eat also has an impact on weight.

If a person does not eat on a regular basis (e.g. 3 meals a day with or without snacks) or ignores hunger cues, he may overcompensate by overeating when there is food available.

This can lead to unintended weight gain.

Beney adds that this does not mean fasting is bad as there are researches which indicate that some types of fasting are beneficial for weight loss and other health conditions.

Will Intermittent Fasting Hasten Fat Burning?

A concept of intermittent fasting

Yes, intermittent fasting will hasten fat burning, especially if you extend the time and introduce fasted training.

Once the system has used up all the easily accessible glucose and glycogen stores, it has to get energy from the body fat [4].

Ultimately, when you can keep up that process on a regular basis, you’ll speed up your weight loss.

And from my experience with clients, it’s also one of the best ways to make sure the lost weight doesn't find its way back.

And the more stable you can keep your glucose levels through a low-carb diet, the more effective your diet will become.

“Insulin levels drop when a person is not consuming food. During a period of fasting, decreasing insulin levels cause cells to release stored glucose as energy. Repeating this process regularly, as with intermittent fasting, leads to weight loss.”

- Jane Racey Gleeson, Member of University of Michigan Frankel Cardiovascular Center

Tips For More Effective Fat Burning

Beyond reducing calories to tackle fat stores for weight loss, there’s also the option of spending several weeks on a low-carb and high-protein diet.

You don’t have to go to the extremes of keto diet, but by limiting your intake of carbs and focusing on complex ones like whole grains and raw vegetables, you can have a big impact on your insulin production [5].

The higher protein intake will also have an impact on your metabolism and can help to build up more muscle tissue.

And the more muscle you have, the higher your basal metabolic rate will be [6].


Do You Have To Fast To Burn More Fat?

No, you don’t have to fast to burn more fat. But you do have to eat less and consume fewer calories than you need in a day. When you have excess energy, that excess is stored, and that will be reflected in your BMI.

Does Eating Late In The Evening Limit Fat Burning?

Yes, eating late in the evening can limit fat burning. Your metabolic rate slows down while you sleep, and the excess energy will add to your body mass.

Plan Your Meals For More Effective Weight Loss

What you eat in any 24 hours and when you eat those meals will have a significant impact on your weight loss.

By having your last food intake of the day before 7 pm and waiting until after 10 am for your breakfast, you can make a big difference in your total body weight.

And if you want to speed things up a bit more, consider adding the next fat burners to your stack:

These are based on natural ingredients that can slightly boost your basal metabolic rate and get you to your goals a bit faster.


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