Have you ever attempted to eat while exercising? Or workout on a full stomach? If you have, then you’ve probably felt uncomfortable, or worse, you’ve felt nauseous! In one sense, I guess you could say that fasting while we exercise is preferred – though there are occasions when you should eat (e.g. those crazy people who run marathons). However, if you’ve ever attempted to battle through a workout with a growling stomach, then you know that exercising on empty can be just as miserable. For most of us, the issue is not whether we should fast during exercise, but rather the duration of that fast. And more significantly, will exercise while fasting be a safe, beneficial, or a healthy option.

Maintaining a consistent exercise routine is critical. Everyone knows that if you break stride it can be difficult to get back on track. But not everyone does well with fasting. Actually, not everyone does well with a consistent exercise routine for that matter. If you add ‘exercise’ and ‘fasting’ together, it sounds almost impossible to say ‘yes’ to exercise while simultaneously saying ‘no’ to food.

First, lets learn a little about what happens when you fast, including the many benefits from fasting. And then, Second, lets learn about one of the best approaches to exercise and fasting.


People all over the world fast regularly for a variety of religious reasons (e.g. Ramadan, Lent, Yom Kippur). What happens during those religious fasts can produce significant spiritual benefits. But you may not know that fasting has many remarkable health benefits too! 

When you fast, your body begins by burning your stored sugar, and then it burns your stored fat. In essence, during feasting you burn food for energy, and during fasting you burn energy from your stored food. When you fast, you deplete much of your stored sugar. Your muscles then become much more efficient at using fat for energy. This happens because your muscles learn how to use the fat for energy by increasing the amount of proteins that metabolize that fat. In other words, your muscles learn to burn fat, not sugar.

A particular method of fasting, known as “intermittent fasting,” has steadily gained attention because it shows tremendous promise for fat loss, cancer prevention, muscle building, and increased resilience. The basic idea behind intermittent fasting is to eat all of your daily food in a brief period (e.g. eight hours) and fast the rest of the time. This tells your body to simultaneously build muscle and burn fat. 

This particular method of fasting has been known to extend your life, improve brain function, and makes you more resilient on all levels. Once you start intermittent fasting, you will have gained an advantage on your peers in health, longevity, and performance. Here are just few of the other benefits:

(1) Burn Fat

Intermittent fasting helps you enter ketosis (fat burning mode). Using MCT oil in your coffee increases the speed at which you go into ketosis, so it fuels your brain, and it helps you stay in ketosis even in the presence of some carbs in your diet.

When fasting, your body is forced to find (and burn) other energy sources, such as fat. That’s why, in one study, men who ran before eating breakfast burned up to 20% more fat than those who fueled up before their run.1

(2) Build Muscle

mTOR is a major mechanism that increases protein synthesis in your muscles. Exercise, coffee & intermittent fasting inhibit your muscle building for a brief period, ultimately causing you to bounce back and build even more muscle as soon as you eat.

(3) Reduce LDL

Intermittent fasting has shown to produce significant improvements in several markers such as LDL cholesterol in as little as eight weeks.2

(4) Reduce Chronic Disease & Inflammation

There are numerous regulated risk factors associated with chronic disease, which suggests that intermittent fasting impacts chronic disease itself.3

In addition to these benefits, some intermittent fasting methods claim to help regulate blood sugar, prevent diabetes, lower the risk of heart disease and slow the aging process4 and even improve memory.5


While you are exercising in the fasted state, you train your muscles to burn fat, similar to the way you can train your body to burn fat by following a very low carbohydrate diet (e.g. ketogenic diet). Instead of relying on easily accessible glycogen, you are powered by an almost unlimited energy drawn directly from your fat storage.

During the period when you begin to exercise while fasting, you will likely notice a decrease in performance. This lasts approximately two weeks as your body adjusts to this change. As you deplete the body of sugar, your muscles need time to adapt to using fat for energy. Your energy, muscle strength, and overall capacity, will decline, but will eventually recover.

When you fast, here is a helpful way to structure your workouts so you can still get great results:

1. Finish dinner approximately 2 hours before bed.

2. Drink one cup of coffee in the morning (w/grass-fed butter & MCT oil).

Brewed coffee with unsalted grass-fed butter (or grass-fed ghee), and MCT oil (I love to use Brain Octane Oil). You can find the complete recipe here. The healthy fats from grass-fed butter and MCT oil give you a stable current of energy that sustains you through the day. This drink is so filling, I’ve had clients who drank one cup (8-12oz) in the morning and didn’t feel like eating until mid afternoon.

3. Workout.

Exercise is not necessary to gain muscle and lose fat, but it helps. If you’re going to workout during your fast, I recommend high intensity integrated strength training. Shorter and harder is better than longer exercise.

A good gauge of intensity is your breathing. You should be able to carry on a conversation relatively easy. If you are going out for a light jog or brief burst on the elliptical, you probably aren’t going to have an issue. It is important to listen to your body, and stop exercising, if you feel light-headed or dizzy. If you push your exercise intensity or duration too high, your workout will become a struggle.

4. Do not eat until late afternoon.

This means you’ve not had anything to eat except coffee for almost 20 hours! This should occur from the time you wake, through the morning, and into the afternoon. If this feels too long, start with a shorter fast and then increase over time.

5. Eat as much as you want up until 2 hours before bed.

The number of meals you eat during this time is irrelevant, as is the amount of calories. Follow the Mosaic Health Simple Guide to Eating and Food List.

*Please keep in mind that this article is not medical advice and is not intended to be a substitute for professional medical advice, diagnosis, or treatment. As always, please use common sense and speak with your healthcare provider if you have a medical condition that might contraindicate intermittent fasting or any other lifestyle change. Please see my full disclaimer here.

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