How Do We Get Energy From Food?

Estimated reading time: 3.5 min

How Do We Get Energy from Food?

Sugar is very important in the weight loss management equation. I am writing a series of posts about it, and the first step is to learn how do we get energy from food, so you understand that by sugar I mean more than that honey that you add to your coffee.

How does your body digest food?

After each meal, ingested food is digested in the intestines where they are transformed into energy: simple sugars, protein, carbohydrates or fats.

This is how it works.

Simple carbohydrates (sugars) - table sugars, candies - are absorbed from the intestine into the blood stream very quickly, as simple glucose.

More complex carbohydrates - wheat, rice, etc - take longer as they need to be modified into simpler sugars (glucose) first.

And “very complex carbohydrates” - whole grains, some vegetables - not only take even longer, but part of those sugars may not be absorbed at all after being retained between the fiber that makes up whole grains and vegetables.

Fats break into simple forms (fatty acids) and are absorbed like that.

Proteins are transformed into amino acids before being absorbed. Both protein and fat slow the absorption of glucose into the bloodstream.

How do the cells in your body get energy?

Glucose will move rapidly to the bloodstream, from where it is removed by insulin to feed first the main glucose-consuming organ, our brain, and then all cells in our organism.

When there is more glucose than needed, insulin removes the excess and brings it to the liver were it is transformed temporarily into glycogen until needed. If it is not needed because we have fulfilled our requirements with basic glucose, or the liver has reached its capacity to store more quantity, glycogen is transformed into triglycerides (a type of fat) and it is deposited as fatty tissue in different parts of the body.  

On the other hand, when glucose runs too low to be able to fulfill the requirements of different organs, another important hormone, glucagon, which is also secreted by the pancreas, in this case by the alpha cells, transforms glycogen into glucose to be directly used. If there is still not enough glucose, it will reach the fat deposits to transform fat into triglycerides and then into glucose.

Our body organs, especially our brain, which can’t use any other source of energy, always use sugars as a primary source of energy. Fats will only be used once sugars and glycogen have been consumed. This is especially the case with our muscles when exercising.


Amino acids from proteins are building blocks for our body, especially for our muscles, and are only used as a source of energy as a very last resource, basically, when fasting.

How to trick our body to burn more fat?

That’s why, when planning our exercise routine, it is recommended we first do anaerobic exercise (weight lifting or similar exercise) to consume all the glucose and glycogen easily available and then go for an aerobic exercise (run or similar).

In this way, the body accesses fat deposits, as a source of energy during aerobic exercise (running), once glucose and glycogen are all consumed during the anaerobic exercise (weight lifting).

Some authors recommend the inverse routine, and it can be a controversial argument, but the most important fact is to exercise long enough to consume glucose and glycogen (better by anaerobic exercise), and to keep exercising when they are not available anymore so the body needs to reach the fat storage to burn fat to be used as an energy fuel. Medium-intensity aerobic exercise (medium-intensity running) seems favors fat burning. 

Why do we lose weight fast when following a very low carb diet?

By the way, for each gram of glycogen stored, the body stores 3 grams of water too. This is one of the reasons why when you follow one of the multiple diets that restrict carbohydrates and you lose weight so quickly: You are basically losing all the water attached to glycogen.

The reason is that because there is no glucose available (no hydrocarbons in the diet), the body is forced to burn all the glycogen available, and therefore the water associated to the glycogen is lost.

You will recover that water again as soon as you eat carbohydrates again and restore your glycogen deposits.

What no to eat to lose weight

If you ask me what not to eat to lose weight I would tell you to avoid simple sugars and to eat complex sugars in moderation and always respecting the portion sizes. If you don’t know how the healthy portion sizes look like, you can download a pdf here your free guide to healthy portion sizes.    

Over to You!

Was this information new to you or did you know this already? 

I'd appreciate your feedback!

About the Author

Arantxa Mateo

Arantxa is a trained biologist, nutrition specialist and weight management coach. Born in Spain, she spent 5 years in Australia before moving to the US. Her motto is "Food is a pleasure. Nobody deserves to be on a diet."

Find out more about Arantxa and 32 Mondays >>

Write a comment

Comments: 2
  • #1

    top essay writing service (Friday, 16 June 2017 23:55)

    Our main source of energy in body is digested food.Wonderful post.This is nice post and provides full information. i prefer to browse this post as a result of I met such a lot of new facts concerning it really.Thanks loads. I bookmark your web log as a result of I found superb info on your web log, Thanks for sharing.

  • #2

    Mattress Sales Gilbert (Thursday, 09 January 2020 06:28)

    Would love to always get updated outstanding blog !<a href="">Mattress Sales Gilbert</a>