Ab wann baut der Körper beim Fasten Fett ab?

Ein kleiner Teil der Energie kommt immer aus Fett. Deutlich steigt der Anteil nach etwa 12 bis 24 Stunden, wenn die Glykogenspeicher in der Leber zur Neige gehen.

Was passiert nach 12, 16, 24 und 36 Stunden Fasten?

Nach 12 Stunden werden die Glykogenspeicher zunehmend genutzt, nach 16 Stunden werden Fettsäuren verstärkt als Energiequelle genutzt, nach 24 Stunden kommt ein großer Teil der Energie aus Fett und die Ketonkörperbildung beginnt, nach 36 bis 48 Stunden steigen die Ketonkörper deutlich an.

Ab wann nimmt man Fett ab statt Wasser?

Fett wird ab Beginn eines Defizits mit abgebaut. In den ersten Tagen zeigt die Waage aber vor allem Wasser, weil jedes Gramm Glykogen rund drei bis vier Gramm Wasser bindet. Nach einigen Tagen wird der Anteil von Fett größer.

Ist Fasten für jeden geeignet?

Nein. Schwangere, Stillende, Kinder und Menschen mit bestimmten Erkrankungen oder Essstörungen sollten nicht ohne ärztliche Rücksprache fasten.

Kann ich während des Fastens Sport machen?

Leichte Bewegung wie Spaziergänge oder Yoga passt gut. Intensives Training ist während längerer Fastenphasen eher nicht zu empfehlen.

Fasting: When does your body start burning fat?

Fasten und auch Fasten ist in den letzten Jahren immer populärer geworden – und das nicht ohne Grund! Es gibt viele spannende Gründe, warum Menschen eine Zeit auf feste Nahrung verzichten und fasten: um abzunehmen, den Geist zu klären oder einfach, um sich fitter zu fühlen. Aber eine der häufigsten Fragen, die uns immer wieder gestellt wird, ist:

Highlights

When fasting, the body first uses its glycogen stores. After about 12 to 24 hours, the share of fat burning rises clearly.
Your previous diet, activity and metabolism influence how quickly the switch happens.
From about 24 hours, the liver produces ketone bodies as an alternative energy source.
In the first days, the scales mainly show water, because glycogen binds water.
Good preparation, enough fluids and light exercise make your fasting period more relaxed.

When does my body actually start to burn fat?

Today we take you on a journey through the processes you go through during fasting, explain when and how fat burning starts and give you valuable tips on how to get the most out of your fasting time.

What happens in the body during fasting?

When you are fasting, this primarily means: no or hardly any calorie intake. Without new energy from outside, your body has to fall back on its reserves. But it doesn't do this immediately from fat deposits - there are other sources of energy that it prefers to use first.

The first source of energy: glycogen stores
Immediately after your last meal, your body has enough energy from the carbohydrates you have eaten. These are stored as Glycogen stored in the liver and muscles. As long as these stores are full, this energy is used first.
What happens after 12-24 hours?
When your glycogen stores start to run low, your system has to get creative. Now it starts to fall back on other sources of energy - and here comes the Fat comes into play. Your body starts the so-called Lipolysisin which fat cells are broken down into fatty acids and glycerol to produce energy.
The role of ketone bodies
In addition to direct fat burning, you start to burn so-called Ketone bodies to produce. These are produced in the liver from fatty acids and serve as a source of energy for your brain when carbohydrates are no longer available. This process is a sign that you have completely switched to fat metabolism.

When exactly does fat loss begin?

When your body starts breaking down fat depends on several factors. For most people, the share of fat burning rises clearly after about 12 to 24 hours, when glycogen stores run low. How fast this happens varies from person to person:

Your diet before fasting: if you ate a lot of carbohydrates beforehand, it takes longer for glycogen stores to empty.
Your activity level: movement uses up glycogen faster, so the share of fat burning rises sooner.
Your metabolism: age, muscle mass and habits influence how quickly the switch happens.

A popular way to build longer eating breaks into everyday life is intermittent fasting, especially the 16:8 method. During the 16-hour break, insulin levels fall and the body draws more on its fat reserves. Many people find it a practical routine because it fits well around work and family.

Buchinger fasting is a longer form of fasting in which only liquids such as vegetable broth, tea and juices are consumed for several days. Prepare well for longer fasts and check with your doctor first if you have health conditions or take medication.

What switching to fat metabolism means

When your body switches to fat metabolism, this is what happens:

Fat reserves become an energy source
Without new energy coming in, the body draws on stored energy. Fat cells are broken down into fatty acids and glycerol and used for energy.
Ketone bodies are produced
During longer fasts, the liver produces ketone bodies from fatty acids. Among other things, they serve the brain as an alternative energy source when few carbohydrates are available.
A conscious break in everyday life
Many people also use fasting days to rethink their eating habits and start new routines. If you have a health condition, please check with your doctor before fasting.

Typical myths about fat burning and fasting

When it comes to fasting, there are many persistent myths. We clear up the most common misconceptions:

"You only lose water weight."
This is partly true for the first few days because glycogen binds water. But as soon as fat burning starts, you actually lose body fat.
"Fasting slows down the metabolism."
The opposite is the case: during short periods of fasting, your Basal metabolic rate even increases slightly. The metabolism only slows down with longer periods of fasting or too few calories over weeks.
"Fat loss only starts after several days."
This is not correct. Fat burning starts after about a day, as soon as the glycogen stores are empty.

Tips for your fasting period

How to make your fasting period more relaxed:

Preparation is everything
Eat light meals with plenty of vegetables and fewer carbohydrates in the days before. The lower carb high protein ready meals from LiveFresh are a practical option.
Drink enough
Drink plenty of water or unsweetened tea throughout the day.
Light exercise
Walks, yoga or gentle workouts suit fasting days well.
Fasting is not a competition
Listen to yourself. If you feel dizzy or weak, take a break or have a clear broth.
Start slowly after fasting
Begin with small, light meals such as steamed vegetables or soup. More on breaking a fast.

FAQ: Your questions about fasting and fat loss

When does the body start burning fat during fasting?

A small share of energy always comes from fat. It rises clearly after about 12 to 24 hours, when the glycogen stores in the liver run low. How fast this happens depends on your last meal, your activity and your metabolism.

What happens after 12, 16, 24 and 36 hours of fasting?

As a rough guide, individual results may vary:

Up to about 8 hours: the body mainly uses energy from your last meal.
12 hours: glycogen stores are increasingly used and the share of fat burning rises.
16 hours: fatty acids are used more as an energy source. This is the typical break in 16:8 intermittent fasting.
24 hours: liver glycogen is largely used up. A large share of energy now comes from fat and ketone production begins.
36 to 48 hours: ketone levels in the blood rise significantly.
From 3 to 5 days: metabolism has largely switched to fat and ketones. Prepare well for fasts this long and get medical support if you have health conditions.

When do you lose fat instead of water?

Fat is broken down from the start of a deficit. In the first days, however, the scales mainly show water, because each gram of glycogen binds around three to four grams of water. After a few days, the share of fat in the weight lost becomes larger.

How many hours after eating does your body start burning fat?

The body burns some fat all the time. The share rises noticeably after about 12 hours without food and becomes dominant after about 24 hours, once liver glycogen is largely used up.

Is fasting suitable for everyone?

No. Pregnant or breastfeeding women, children and people with certain medical conditions or eating disorders should not fast without consulting a doctor.

Can I exercise while fasting?

Light movement such as walking or yoga works well. Intense training during longer fasts is not recommended.

Is fasting the best way to lose weight?

Fasting is one of several ways to create a calorie deficit. What matters is finding an approach you can stick to. A balanced diet and exercise are always part of it.

Conclusion

When fasting, your body first uses its glycogen stores and, after about 12 to 24 hours, increasingly switches to fat as an energy source. How fast this happens depends on diet, activity and metabolism. What matters is shaping your fast so it suits you and your everyday life, and preparing well for longer fasting periods.

Nutritionist

Developed on a scientific basis by Dr. Ulrike Fischer, who holds a doctorate in nutritional science.

Highlights

When fasting, the body first uses its glycogen stores. After about 12 to 24 hours, the share of fat burning rises clearly.
Your previous diet, activity and metabolism influence how quickly the switch happens.
From about 24 hours, the liver produces ketone bodies as an alternative energy source.
In the first days, the scales mainly show water, because glycogen binds water.
Good preparation, enough fluids and light exercise make your fasting period more relaxed.

Our recommendation for you

Fasting: When does your body start to break down fat?

When does my body actually start to burn fat?

What happens in the body during fasting?

When exactly does fat loss begin?

What switching to fat metabolism means

Typical myths about fat burning and fasting

Tips for your fasting period

FAQ: Your questions about fasting and fat loss

When does the body start burning fat during fasting?

What happens after 12, 16, 24 and 36 hours of fasting?

When do you lose fat instead of water?

How many hours after eating does your body start burning fat?

Is fasting suitable for everyone?

Can I exercise while fasting?

Is fasting the best way to lose weight?

Conclusion

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