From intermittent fasting to fasted cardio, we’ve all heard the advocates for limiting the hours in which you eat or manipulating your training around your meals. But, for every advocate, there are those who strongly argue that fasting is not necessary, or may even have detrimental effects. We’re here to give our view on the question, “Should I train fasted?” to help you make the right decision for you and your goals.
Why do people fast?
Fasting is an ancient practice that has been used to develop spiritual strength, enhance prayer, and focus on and connect with God, but the first records of fasting date back to the 5th century, starting with Hippocrates, who recommended fasting as a means of dealing with obesity.
While this is a commonly publicised approach to weight loss even now, his exact recommendations were:
“Obese people and those desiring to lose weight should perform hard work before food. Meals should be taken after exertion and while still panting from fatigue. They should, moreover, only eat once per day and take no baths and sleep on a hard bed and walk naked as long as possible.”
Not quite in line with current guidance.
Regardless, fasting is used now, alongside religious reasoning, to try to manipulate weight, with popular approaches such as 5:2, 16:8, or intermittent fasting.
But is fasting really the weight loss solution it’s made out to be?
While some research shows that fasting can aid with weight loss, and even has other potential health benefits, other research shows that it may be harmful to us, especially for women. So what’s the truth here? Let’s start by looking at what happens when we don’t eat.
What happens if we don’t eat?
When fasted, our bodies rely on fat stores to support our energy requirements, breaking down fat to provide an energy source.
In the fasted state our bodies will rely on their fat stores to support the ongoing need for energy, therefore you’d be burning fat.
If there’s no food to be digested, glucose and insulin in your blood will be low. Low insulin levels will cause an increase in the production of stress hormones.
Since there is no glucose to be taken up, glucose will be synthesised from protein (muscle and other tissues) and converted from stored glycogen under the influence of glucagon – a hormone.
When this happens, our bodies try to mitigate the damage by reducing our metabolic rate and the production of our growth hormones – it anticipates the reduction in food and tries to conserve energy instead. Note, this is normally an impact of fasting and restriction overall (i.e. eating far too few calories to maintain normal functioning – eating below your BMR).
Research in animals has shown that calorie restriction extends their life. Digesting food is a form of stress on the body and even though this is normal, it creates free radicals in the process: reactive particles that can damage body tissues if they build up too much. Fasting reduces the production of free radicals and combined with the reduced metabolic rate this may prolong life.
Fasting is found to have positive effects on disease prevention of diabetes, cardiovascular disease, some cancers and strokes, but also neurological diseases. The idea is that if our bodies don’t need to deal with the stress of digestion, it allows them to focus on repairs. However, most of this research is done on animals and the exact mechanisms are unknown.
What happens when you train fasted?
When training fasted, our bodies rely on fat for fuel instead of glucose or converting stored glycogen to glucose. While this does utilise fat via a process called fat oxidation, this does not directly correspond to fat loss or an increase in performance.
Reduction in fat is not immediate – it just means that our bodies are working a bit less efficiently throughout our sessions, and we still need to be in a deficit overall to ensure that we are able to lose fat.
However, if fat loss is your aim, it’s worth considering the impact of not eating on your workout itself. If you’re not fuelled properly, you won’t be able to perform as well as if you were fuelled and energised, meaning you’ll get less from the workout, and burn fewer calories overall.
In its most simplified form, fat loss occurs when consuming fewer calories than you’re expending, and while fasting may somewhat limit your overall intake, it will also limit your overall expenditure.
It’s a fine balance between eating enough to maximise performance, and consuming slightly under maintenance to create a deficit.
If you’re currently struggling through your workouts because you’re fasting, try eating something easy like a banana for a quick energy release, and see if it improves your performance at all!
Things to note
Fasting can cause great stress on the body, including, but not limited to the following:
- Increase your risk of injury
- Weaken your immune system
- Play havoc with your hormones – particularly in women
- Lead to unhealthy eating behaviours – if you are restricting yourself to the point of being ravenous, it can lead to a sense of loss of control around food, and binge-like behaviours, which can often be associated with guilt and feelings of hopelessness. This can impact any goals that you are working towards as well, as people often eat more in these periods of extreme hunger, as their hunger levels are not being properly regulated, eating more than they perhaps would have had they just eaten breakfast, or prior to a training session.
So, should I train fasted?
To conclude, if fasting is something that does not impact your performance, and helps you maintain a healthy calorie deficit (i.e. without any feelings of restriction, extreme hunger, or binge-like behaviours), then carry on as you are. However, if you’re really struggling through your workouts, feeling lethargic, and find fasting a challenge overall, you may benefit from more conventional meal timings.
Remember, nutrition is very personal and individual to you – just because fasting works for someone else, it doesn’t mean that it is the best option for you, and just because you benefit from it, it doesn’t mean it’s the best option for someone else – it can take trial and error, and patience to unearth what is best for you and your body.
