Zwift How-To: Burning Fat on Zwift

on December 13, 2017

Ask 10 athletes about their nutrition regimens during training, and you’ll likely get 100 answers. Everyone maintains their engine differently, because everyone is different. But there are principles to put your body in a specific mode for that day’s workout. In this series, our resident sports scientist covers the basics and biology for fat burning.

Fat burning exercises can improve the way muscles use fuel. Targeted workouts train your body to use more fat, and save carbohydrates for the essential parts in a race. Note that there’s a difference between burning fat and burning calories, and these guidelines gear towards the former.

The fundamentals of fat burning

  1. Don’t eat carbohydrates before exercise
  2. Aim for longer durations of training
  3. Train at a moderate intensity – not low, not high

Fat BurnNo carbs before you workout

When carbohydrates and even some proteins are ingested, insulin spikes to remove glucose from the blood and store it throughout the body. This is a good thing, but high levels of insulin will also focus your body on storing, not burning fat. Say you have a meal an hour before exercise, and insulin levels are very high at the start. Fat burning is reduced by 30%.

Even small amounts of insulin can reduce fat burning. So if fat burning is your goal, training on an empty stomach is ideal, because even a small snack can make insulin levels rise.

Aim for longer durations

The time you spend working out matters too. As you train, your body depletes its carbohydrate stores, and turn to another source to stay charged. Most people store about 500 grams of carbohydrate in muscle, but will break this down during physical activity. After 2 hours, fat becomes the go-to fuel. So longer workouts are preferred, if fat burning is the goal.

Train at a moderate intensity

Many people believe that in order to burn fat you need to exercise at a low intensity. This is not true. If the intensity is too high, your body will have to rely on carbohydrates and fat burning shuts down. Too low, and you’ll decrease your calorie expenditure. Like most things, aim for moderation.

What exactly does moderation mean? Well, although fat burning is highly individual and not easy to measure (I don’t trust smartwatches or treadmills to do this), a general guideline is this: the pace is not entirely comfortable, but you’re still able to have a conversation without heavy breathing. Such as, sharing some of your fat burning wisdom with a friend as you work up a sweat.


Asker Jeukendrup is one of the world’s leading sports nutrition scientists, who’s worked with many Olympic champions and weekend warriors. Asker is also a keen cyclist, runner and triathlete himself. Read more at or chat up Asker while he’s riding in Watopia.

Zwift How-To: Reading a Ride Report over 4 years ago