I was recently asked by a client what she should eat before a 6 am CrossFit class

I asked her if she had thought about doing it fasted?

So are there benefits to exercising first thing in the morning, and more so doing it before breakfast?


I  love to do my gym sessions first thing in the morning for two reasons:

  • It gets it done. Despite my best intentions, any number of things can crop up as the day goes on, meaning the exercise gets skipped due to lack of time/ finding something else to do. Like today: things I’d ordered on Amazon all arrived and needed unpacking and sorting; I decided to write this; I had to speak make a couple of phone calls. And the time ran away…
  • There are additional health benefits to exercising before consuming your first meal of the day

Sadly my work schedule does not allow me to do fasted workouts for the most part, though I have enjoyed a couple of 6.45am gym sessions with my 15-year-old son in recent weeks, as he has figured this is the best time for him to go.

Some people find an early morning run exhilarating

Benefits of Fasted Workouts

Research has shown that exercising in the morning, before eating, can significantly lessen the ill effects of a poor diet. The study recruited healthy young men who were all fed a high calorie and high-fat diet. They were split into three groups:

  1. Non- exercisers
  2. Ate breakfast before exercise
  3. Exercised before breakfast

After 6 weeks both groups 1 and 2 put on 2-4kg weight and showed signs of insulin resistance; the precursor to type 2 diabetes

However, group 3 gained almost no weight AND showed no signs of insulin resistance.

fasted workouts

One benefit is that there are fewer people about

The study concluded that……

‘fasted training is more potent to fed training to facilitate adaptations to muscle  and to improve whole body glucose tolerance and insulin sensitivity during a hyper-caloric fat -diet’

How does it work?

One of the explanations for how fasted workouts can prevent weight gain and insulin resistance, is that the body’s fat burning processes are controlled by the sympathetic nervous system (SNS), and the SNS is activated by lack of food.

A combination of fasting and exercise maximises the impact of cellular factors and catalysts (cyclic AMP and AMP kinases) which force the breakdown of fat and glycogen for energy.

fasted workouts

Make sure to stretch if exercising outside on a cold morning



Hence training on an empty stomach will effectively force your body to burn fat.

On the contrary, eating a meal with lots of carbohydrates before exercising will inhibit the SN and reduce the fat burning effects thereof. Consuming carbohydrates activates the parasympathetic nervous system, which promotes energy storage.

Insulin Resistance

Insulin resistance is the root cause of most chronic diseases; maintaining good insulin regulation is a primary factor of good health, which can be done by

  • Exercising regularly
  • Avoiding excess sugar/ fructose/ grains

Exercising on an Empty Stomach

Most of the fuel used in exercise is not coming from the food you have just eaten. If working at a moderate to high intensity level you will be using glycogen and fat that is stored in the muscles, liver and fat cells. Typically there is enough stored to fuel two hours of intense work, or three to four hours of moderate intensity work.

Hence if you are eating a nutritious diet you may not need to eat anything before exercise.

Fasted weight training has been shown to increase insulin sensitivity and improve nutrient partitioning. This means that your body will be more efficient at directing nutrients into muscle cells and away from fat stores. Thus training in the fasted state makes the subsequent meals more anabolic.

Are fasted workouts for me?

Some people do find it difficult to exercise on an empty stomach. Generally, these people will be more sensitive to changes in their blood sugar levels, which can decline 20-25 minutes into the workout. It is this that causes dizziness, faintness, nausea and lightheadedness, especially first thing in the morning.

Combine a morning workout with your daily commute…


A number of factors can play a role in how you will feel exercising on an empty stomach. Age, when you last ate, pregnancy, medication, medical history, fitness level and type of workout should all be considered in deciding if this is a suitable approach for you.

Exercising on empty stomach may not suit a high-level athlete, as it can reduce overall sports performance.

So you need to use common sense, listen to your body, and take into account your goals.

Whey  protein

There is another even more efficient way to boost fat burning without fasting, according to a study in Medical and Science in Sports and Exercise.  They showed that eating whey protein  30 minutes before resistance training boosts the body’s metabolism for as much as 24 hours post workout.

It seems that the amino acids found in high-quality whey protein activate certain cellular mechanisms, which in turn promote protein synthesis, boost thyroid function and protect against declining testosterone levels after exercise.

Whey protein is also known for its ability to help insulin work more effectively,  which as discussed is one of the benefits of fasted exercise.

So if you do need to eat prior to working out in the morning, consider 20g of whey protein instead of your normal breakfast.