Exercising and Intermittent Fasting: Yes or No?

Exercising and Intermittent Fasting: Yes or No?

Probably you’re one of the types who wakes up and gets ready for an early morning jog or a light stretch. Or maybe you’re a late gymmer who sweats out all the toxins on exercise machines. In both cases, you win. In the morning you boost yourself with good energy and have plenty of endorphins and strength throughout the day. In the evening you release the stress, warm up your body before the night’s rest. But is there any difference in exercising if you’re fasting?

While naturally intermittent fasting was mainly used for cultural and religious purposes, nowadays it evolved a new trend for not only cleansing your body but also for losing weight. For diabetes, obesity, and people who have chronic heart disease, this eating pattern showed some major health results.

A well-balanced diet and eating regime is a good strategy when losing weight. Combine it with some physical activity and you’re earning the double – burning calories even more. With intermittent fasting, it’s a little bit tricky and confusing. Some find it unnecessary to exercise after a night’s fast when your body is tired and not woken up. Others tend to believe that it will triple the effect and you’ll lose weight faster.

Recent studies showed controversial results of exercising + fasting. The goal of the research was to check if physical activity in the morning would promote better fat loss. Based on two hypotheses:

  • that exercise uses predominantly fat in relation to the carbohydrates as an energy substrate
  • that the fasting condition increases fat oxidation rates

But for some people who performed a low-intensity aerobic exercise (it could be pilates, callanetics, yoga) after an overnight fast, symptoms such as fatigue and dizziness occurred, mainly because of low blood sugar levels. Also, the cortisol levels are on a high edge in the morning, promoting muscle mass loss. So for those who seek to stay in sharp and toned shape, losing muscle mass may negatively affect the general weight loss.

If you have obesity, then working out during your fast is O.K. – at the end, you will still burn fat. But if you’re a slimmer guy who wants to get muscles toned – it’s better to choose light cardio just before eating breakfast. If you want to lift weights or do other high-intensity exercises, the best option would be to squeeze your workout into your eating window.

Fasting and/or physical exercise is often used to investigate the regulation of intermediary metabolism. A couple of studies indicate a wider impact of fasting on metabolism with effects on protein and glucose metabolism in sedentary and untrained subjects. However, there are conflicting data on fasting metabolism in highly trained athletes. Some saw decreased performance while others didn’t have any significant changes. Done on many athletes of different levels of sport and physical fitness, the results vary. Possible, that the key factors of inconsistent research were respondents’ characteristics: sex, genes, the intensity of the workouts, their length.

What if: My goal is to shed some pounds

Then, you shouldn’t be worried about including exercise during intermittent fasting. The main key point of this eating pattern is weight-loss, so eventually, you will lose fat mass and lean mass. 

What if: I want to slim down but keep my muscle

It’s important to understand that while fasting, you consume fewer calories. For muscle growth you need to eat a lot of protein and to squeeze it into your eating window might not be the best idea. Additionally, based on Cortisol (C) levels, we also concluded that if a primary goal is to burn fat while, simultaneously, maintaining muscle mass, performing a low-intensity aerobic exercise under a fasting condition might not be the best choice. But if your diet consists of balanced nutrient-rich foods loaded with vitamins and minerals – having a workout during your fasting period or after will do no harm to your muscles.

Note that these results imply for people with identical characteristics. Still, more research is needed, but the point being, it is very important to listen to your body and detect what’s best for you.

In conclusion, compared to the exercise done after the feeding state, performing a low-intensity aerobic exercise in a fasting state doesn’t seem to make drastic changes. Whether you want to lose weight or maybe at the same time gain muscle or just stay toned and lean – everything is possible, it just depends on your body’s stamina and capability to react.

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