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Does fasted weight training accelerate fat loss?

The last few years have seen the health and fitness landscape evolve in leaps and bounds.

We have seen heavy strength training (and the many health benefits associated) introduced to the masses. We have realized that low-intensity cardio may not be the most effective option to boost health and enhance fat loss. And we have concluded that a diet high in carbohydrates may not be the best option for promoting health and longevity.

Within this, we have also seen the rise in several unique dietary strategies used to boost health and improve function. Intermittent fasting is arguably the most popular.

There is a growing body of evidence demonstrating that intermittent fasting is a valuable tool. It can be used to improve health in a big way. It has also been shown to assist in weight management and to help promote fat loss.

In short, its use has been overwhelmingly positive.

However, what has remained unclear is what happens to the body when we perform our heavy strength training in a fasted state – which is what we are exploring in today’s article.

What is intermittent fasting?

Intermittent fasting simply describes a dietary strategy that consists of adhering to small periods of eating, separated by longer periods of not eating (AKA fasting).

Although ‘not eating’ might sound like an odd dietary concept, try and remember that every single night we fast during sleep. During this time, we don’t eat at all. Then we break our fast with the first thing we choose to eat the following morning.

It is important to note that in the research world, the term ‘intermittent fasting’ can be used to describe several fasting related eating patterns. Although, it most commonly describes a style of fasting known as ‘time-restricted feeding’ – which simply has you extend your nightly fast by a few hours every day.

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Athletic young man doing battling with ropes.

How does intermittent fasting work?

The primary goal of intermittent fasting is to capitalize and enhance the hormonal changes that occur in the body when you are in a fasted state.

When fasting, you will see a significant decline in the secretion of the hormone insulin, combined with a significant increase in the secretion of human growth hormone (Ho, 1988; Heilbronn, 2005).

And this is where its key health benefits are derived.What are the benefits of intermittent fasting?

As I have already alluded to, by enhancing the hormonal changes that occur when maintaining a fasted state, intermittent fasting has been shown to have some pretty significant benefits. These include:

  • Enhanced ability to breakdown and use fats for energy, which in turn improves your capacity for fat specific weight loss (Blackman, 2002; Byrne, 2018).
  • Marked improvements in insulin sensitivity, which comes with chronic reductions in resting blood sugar levels (Arnason, 2017).
  • Large reductions in blood pressure (Moro, 2016).
  • Significant improvements in blood cholesterol profiles, derived from an increase in HDL cholesterol, and an associated reduction in LDL cholesterol (Sutton, 2018).
  • Through the above interaction, it can reduce your risk of developing both cardiovascular disease and diabetes.
  • Improvements in cognitive function and brain health, a reduced risk of age-related declines in cognition, and a decline in dementia risk (Mattson, 2018).

Taking all of this into consideration, there is a very good reason as to why intermittent fasting has become so popular.

What is fasted weight training?

Fasted weight training is exactly what it sounds like – undertaking weight training in a fasted state.

For example, if you are undertaking an intermittent fasting protocol where you try and abstain from eating for 5-6 hours after you wake, and then decide to do your gym session before you have your first meal, that would qualify as fasted training.

Now, for the longest time it was through that you needed to eat something before you train. It was said that if you didn’t, then you would not have the adequate nutrients available to recover from your training and that you wouldn’t progress in any manner.

In fact, some people would go as far as to suggest that it would even increase your risk of overtraining.

But is this really the case?

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Group of young people after sports.

What does the research say about fasted weight training?

While there is very limited research in the area, a recent study has aimed to look at the question in detail. It was essentially analyzing how the body responds to fasted training in comparison to normal (or fed) training states (Frawley, 2018).

And the results were interesting to say the least.

First and foremost, they found that when exercising in a fasted state, the individuals did not perceive the exercise to be any more challenging than normal – which is of interest, as under normal circumstances, the athletes in this study would perform an exercise in a fed state.

This means that despite not consuming any food prior to training, their energy levels were still high, and they were able to complete their session in full.

Secondly, despite doing the same amount of physical training in a fasted state as they did in a fed state, they did it at a significantly lower respiratory exchange ratio (or RER). RER is a measure that gives an indication of what type of fuel an individual is burning. The lower the RER, the more energy is being derived from fats.

This indicates that during a fasted state, the individuals simply derived more energy from fat to meet their required energy demands.

Pretty cool right?

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Food or food-less before your workout. What do you prefer?

Fasted weight training pros

So, we can easily draw some pros out of this study.

Firstly, fasted training does not appear to impact your gym performance. You should be able to lift the exact same amount as you would in a fed state, and it will not feel any more challenging than normal. This means that it should not impact your progress in any manner.

Secondly, in a fasted state you will not have carbohydrates as readily available for energy as you would under non-fasted circumstances. However, your body will simply increase its metabolism of fats to meet the energy requirements.

This explains why your performance will not suffer. It also suggests that training in a fasted state may enhance your ability to lose fat, which is an obvious positive. So fasted weight training for weight loss could be a very viable option.

Fasted weight training cons

While there are some definite positives associated with fasted weight training, there is actually no long-term research on the prolonged effects of using a fasted weight training program. This means we don’t really know whether it offers any real benefit over fed training in the long run, or not.

Due to the fact that intermittent fasting tends to be associated with lower daily energy intakes, we could assume that it may actually result in less muscle growth than we would see under normal circumstances.

As a result, if your goal strictly revolves around maximizing muscle size, fasted training might not be your best option.front squat

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Male versus female fasted weight training

With all this in mind, it is important to touch on evidence to suggests that the sharp calorie restriction associated with intermittent fasting may have a somewhat negative impact on some females (De Souza, 2004).

In this scenario, it may result in a disruption to the menstrual cycle, and associated feelings of lethargy. As a result, we often recommend females start with a 12-14 hour fasting window to reduce the risk of any negative effects occurring.

Considering this, if intending to train in a fasted state, it would be advisable for females to commence their training session around 12 hours into their fast. Alternatively, males might be able to get away with training between 14 and 16 hours into their fasting period.

Post workout nutrition and fasted weight training
Last but not least, I wanted to describe the importance of post-workout nutrition when choosing to use fasted weight training.

When training in a fasted state, you are going to see two significant differences that are worthy of mention:Your carbohydrate stores are going to be depleted (hence the observed increase in fat metabolism). You are going to have significantly less amino acids available for muscle repair and recovery.

As a result, it is in your best interest to consume a meal high in both protein and carbohydrates around an hour after your training session is completed. This provides you with the means to refuel your muscle carbohydrate stores. Additionally, it ensures that you have adequate amino acid molecules available for muscle recovery.

This will not only enhance the results of your session but also ensure that you have the energy available for your next fasted training session.

Take Home Message

With the rising popularity of intermittent fasting, we are seeing some interesting research providing insight into the intricacies of its application. Fasted weight training is of particular interest.

Evidence suggests that fasted weight training may have benefits for fat loss and has no impact on performance. It could be a valuable training tool we can implement to make fast changes in body composition.

If you have used fasted weight training in the past, then we would love to hear about it. So drop us a comment and we will get back to you ASAP.


Heilbronn, Leonie K., et al. “Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism.”. The American journal of clinical nutrition 81.1 (2005): 69-73.

Ho, Klan Y., et al. “Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man.”. The Journal of clinical investigation 81.4 (1988): 968-975.

Blackman, Marc R., et al. “Growth hormone and sex steroid administration in healthy aged women and men: a randomized controlled trial.”. Jama 288.18 (2002): 2282-2292.

Byrne, Nuala M., et al. “Intermittent energy restriction improves weight loss efficiency in obese men: the MATADOR study.”. International journal of obesity 42.2 (2018): 129.

Arnason, Terra G., Matthew W. Bowen, and Kerry D. Mansell. “Effects of intermittent fasting on health markers in those with type 2 diabetes: A pilot study.”. World journal of diabetes 8.4 (2017): 154.

Sutton, Elizabeth F., et al. “Early time-restricted feeding improves insulin sensitivity, blood pressure. And oxidative stress even without weight loss in men with prediabetes.”. Cell metabolism 27.6 (2018): 1212-1221.

Mattson, Mark P., et al. “Intermittent metabolic switching, neuroplasticity and brain health.” Nature Reviews Neuroscience 19.2 (2018): 63.

Frawley, Kendall, et al. “Effects of prior fasting on fat oxidation during resistance exercise.” International journal of exercise science 11.2 (2018): 827.

De Souza, Mary Jane, et al. “Fasting ghrelin levels in physically active women: relationship with menstrual disturbances and metabolic hormones.” The Journal of Clinical Endocrinology & Metabolism 89.7 (2004): 3536-3542.

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