It’s early in the morning, and you would like to hit the gym. Should you skip breakfast and perform some fasted cardio? Or maybe you do some kind of time-restricted restricted-eating such as intermittent fasting. But are these options better than eating breakfast and then hitting the gym?
That’s a question many people ask themselves (including yours truly). It is a popular thought that fasted cardio will boost your metabolism and therefore help you burn more fat. The counter-argument is that eating before the gym will give you the energy to perform high-intensity workouts and thus help you burn more calories. So which one is better?
Let’s answer this question once and for all.
In this post, we’ll look into:
- Why do some people fast?
- Fasted activities versus fed activities, such as cardio and weight lifting.
- Whether fasting burns more calories and fat than calorie restriction diets, regardless if we workout or not.
- Whether fasting boosts our metabolism.
Some reasons why people fast regardless if they work out or not:
After waking up, our insulin levels are low (due to not eating for a few hours). Insulin suppresses lipolysis (the breakdown of fat to be used as fuel). Hence performing cardio (or any other activity) while insulin levels are low should allow you to use fat as fuel (instead of carbs) while exercising.
Also, after waking up, our glycogen levels (carbs stored in the muscles and liver) are low. Therefore the body will use fat to fuel our workouts.
Fed Cardio vs. Fasted Cardio
In a recent study by Ediburgh et al. (2019), participants did one of three things (1):
- Ate breakfast and rested
- Ate breakfast and exercised
- Skipped breakfast and exercised
The workout consisted of 60 minutes of cycling at 50% of peak power output.
Their Energy expenditure (the number of calories a person burns) during exercise and throughout the day was measured. The researchers also tracked the foods the participants ate and how many calories they consumed.
- Both groups burned the same amount of calories during exercise and throughout the day.
- The fasted group was able to be in a more significant caloric deficit due to skipping breakfast and therefore eating fewer calories during the day.
This research demonstrates that fasting should be used as a tool to consume fewer calories, but it does not provide a metabolic advantage compared to fed-state exercise.
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Breakfast and Lifting Weights vs. FAsted Weight Lifting
Another recent study compared the effects of fasted resistance training on 16 fasted men. After an overnight fast, the men would either have breakfast or drink water (every man would perform a fasted workout and a fed workout). Two hours later, they would complete a set of squats and bench press to failure (with 90% of their ten rep max) (1).
- The total reps for the squats were 15% lower compared to when they had breakfast before the workout.
- Total reps for the bench press were 6% lower compared to when they had breakfast before training.
This research confirmed that skipping breakfast is detrimental to your performance in the gym, especially when it comes to high-intensity workouts.
Does Skipping Breakfast Mean you Burn More Fat?
Researchers investigated the effects of eating breakfast versus fasting on the subject’s metabolic rate and substrate oxidation (a fancy way of saying if they burned fat or carbs).
The researchers found:
- When the participants fasted, they burned more fat in the morning. But also, more carbs in the evening.
- When participants ate breakfast, they burned more carbs in the morning. But, also more fat in the evening.
- Over 24 hours, the subjects burned the same total of carbs and fat, and their metabolic rates were similar.
This study proves that there’s no metabolic advantage to fasting (or eating breakfast). And that total fat oxidation (burning fat) isn’t affected whether you fast or eat breakfast (1).
A study looked at participants during Ramadan fasting to evaluate how I.F. affects metabolism. Ramadan fasting has a similar feeding window as the popular 16:8 intermittent fasting protocol (1).
Researchers found that fasting did not increase how many calories the participants burned. However, the study did find that participants weren’t as active as if they weren’t fasting.
Intermittent fasting is an excellent tool for those who do not like to eat breakfast and would want to lose weight. But it has to FIT your lifestyle.
If you believe intermittent fasting is some magical pill that will supercharge your metabolism, that’s just not the case. Intermittent fasting only works as a tool to restrict how much you can eat by giving you a feeding window. But, doing this does not mean you can binge eat to your heart’s desires. The rules of “calories in vs. calories out” also apply to intermittent fasting.
Alternate-Day Fasting vs. Calorie Restriction
A study by Trepanski et al. compared the results of alternate-day fasting versus a daily calorie restriction on (1):
- Weight loss
- Weight maintenance
- Risk indicators for cardiovascular illness
Researchers randomly assigned 100 Participants into three groups:
- 34 people to alternate-day fasting group
- 35 people to the calorie restriction group
- 31 people as the control group
The study found that there was no significant difference in weight loss between the calorie restriction group and the alternate-day fasting group as both had similar weight loss.
Nevertheless, of the three groups, the alternate-day fasting group had the highest dropout (13 of 34 or 45%), the calorie restriction group had a dropout of 10 of 35 (29%), and the control group had a dropout of 8 of 31 (26%).
Also, the alternate-day fasting group had a higher dropout due to dissatisfaction with their diet (5) compared to the calorie-restricted group (none).
The researcher’s conclusion: “Alternate-day fasting did not produce superior adherence, weight loss, weight maintenance, or cardioprotection vs. daily calorie restriction.”
Sustainability is one of the essential rules for weight loss. Unfortunately, not only isn’t fasting superior to good old calorie restriction, but it’s also harder to adhere to for some people.
Cortisol, the “stress” hormone
Research shows that continued elevation of cortisol levels has been linked with a higher level of muscle atrophy and strength deficiencies (3).
Therefore, we recommend that you eat something before working out as eating would lower levels of cortisol and so enhancing muscle growth (4).
What does this mean?
Even if you do burn more fat as a result of skipping breakfast, it doesn’t mean you will burn more fat overall. Regardless if you perform fasted cardio or not.
If you skip breakfast, be aware that your performance might suffer if you hit the gym, especially if you are lifting weights or performing an intense workout.
Fasting seems to be harder to adhere to than typical calorie restriction diets. Fasting doesn’t result in more weight loss compared to calorie restriction diets when calories are equal.
Habitual fasting could lead to muscle loss and loss of strength.
Should you fast?
If, after seeing all this research, you still would like to skip breakfast and do some form of fasting, these are the two questions you should ask yourself:
- Is it sustainable?
- Will I be in a caloric deficit?
- Intermittent fasting is an excellent tool for those who do not like to eat breakfast and would like to create a calorie deficit. But it has to fit your lifestyle. If you love eating breakfast, I would advise against adapting this weight loss strategy. Think about it this way, if five months from now you don’t see yourself doing some form of time restrictive eating, then don’t waste your time.
- Fasting isn’t magic. If you eat more calories than you burn, you will gain weight, regardless of if you are fasting or not.
Hopefully, this article helps you decide whether you should fast or not.
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