What does the research say surrounding intermittent fasting and athletic performance? Plus, a look at the various types of intermittent fasting and who it is recommended for (and who it is NOT). This post is much more than just Intermittent Fasting for Athletes, but for everyone!
What is intermittent fasting?
Simply put, intermittent fasting (IF) is cycling between eating and refraining from food intakes for a period of time.
Depending on the type of fasting you’re doing (more on the various options below), this could be for a few hours or up to a day.
Fasting has actually been around for thousands of years but as with most things (I see you Paleo or Caveman diet) it comes around again in a new hip, trendy form.
People fast for a variety of reasons.
In the past, it was largely due to an inadequate food supply (aka people didn’t have access to food) or for religious and cultural reasons (as often done today for Lent and Ramadan.)
Motivations have changed and people are fasting for a variety of health reasons, be it to lose weight and/or body fat, to control insulin, to promote longevity, to protect against diseases, or frankly whatever else the media or research says that week.
Regardless of the reason or motivation behind the interest in intermittent fasting, I want to share with you the full picture (research based of course) so you can make the most informed, educated decision for yourself.
What types of intermittent fasting are there?
If you were to ask Dr.Google, I’m fairly certain you would have more than 10 varieties of fasts populate, meaning there are countless options available for people to try.
But, for brevity’s sake (and to educate you on the types you’ve most likely heard of) we’ll discuss the most popular types of intermittent fasting below.
(aka Circadian Rhythm Fasting, 16/8, 14/10 or 12/12)
Seriously, I’m not kidding when I put the “also known as” up there because this method of fasting has various forms in and of itself.
Simply put, this method of fasting is when an individual fasts for a set hours of the day, limiting their food intakes to the other remaining hours.
The timing of whatever fasting protocol you try is completely up to you.
For instance, the 14/10 means you fast 14 hours and can consume food 10 hours. This can mean you eat between 8 am and 6 pm or 10 am to 8 pm.
The reason this is often referred to as circadian rhythm fasting is that it can often be in sync with your normal sleep-wake cycle.
Without putting a label on this, some individuals I’ve counseled who are very in touch with their own internal hunger cues eat within 2 hours after waking up and stop eating about 2 hours before going to bed. (Take note, many of these individuals aren’t engaging in high-intensity exercise.)
If you’ve been a nighttime eater it may take some time to break that cycle. And, if you rely on a bedtime snack, especially for medical reasons, then fasting is not likely for you then.
That’s ok. You can ABSOLUTELY still meet your healthy goals without fasting but you will need to figure out what style of eating works best for you.
Bottom line: Many people regularly engage in this method of fasting without calling it a fast. Extending your fasting period (moving from 12 hours of fasting to 16) may not always be the best idea depending on what your health goals are as well as how active you are.
5:2 Fasting Method
(aka the Alternate Day Fasting)
Eat “normal” and balanced for 5 days, then restrict calories 2 days during the week to 500 calories if you’re female, 600 calories if you’re male.
This method actually has no specific research conducted on it, but rather the anecdotal stories of people who’ve purchased the book and shared their results.
Following this diet may mean on Tuesday and Thursday you limit your intakes to just two small meals that equate to around 200 to 300 calories. This would look like a slice of bread with 1 tbsp of peanut butter to paint a picture here.
Truthfully, I’m hungry just thinking about this diet!
Bottom line: there’s not much evidence to support this way of eating, so let’s not starve ourselves and consider another method if you really want to try fasting.
(aka Eat-Stop-Eat Fasting)
In this method, there’s really no rhyme or reason to it that I’ve been able to find.
You simply eat normally most days of the week, then fast for 24 hours one to two days a week.
So, you may eat lunch on Sunday then fast from dinner to dinner Monday, breaking the fast with your dinner meal Monday night.
Bottom line: this may be challenging for many who are active and those who, well, like to eat!
What are the benefits of intermittent fasting?
There’s a reason fasting is so popular – studies have shown the benefits of fasting for a variety of health conditions in humans.
But, before I share what these are, I want to point out two limitations in research.
First, sample sizes and populations.
Research is all over the place on not only the style of IF used in the study design protocol, but also the body structure of participants used to collect the data as well as the sample sizes of the populations.
Meaning, can we really say “intermittent fasting leads to body fat losses” for all if the study design used only 6 subjects who struggle with obesity versus subjects who were overweight or of normal weight.
No, we cannot.
Second, longitudinal data in humans.
Basically, long-term, repeatable studies that have shown the same results time and time again in humans. Also, what about maintenance? So and so did IF and lost weight, great! Were they able to maintain that weight loss? If so, for how long?
Unfortunately, most of the longer-term data is still available only for animal studies. I highly encourage you to read this great piece on the importance of further research, as well as not discounting the important health effects IF can offer as well chat about below.
To be completely honest, it would take me far to long to comb through all the research out there to bring you every single study on the matter. I’ve relied on the relevant and recent literature reviews (aka a synopsis of the current studies) to outline the benefits of IF for you.
Now, research does support intermittent fasting in humans (and both genders) for:
- Weight loss
- Body fat loss
- Lowering inflammation
- Improving cardiac health (Fasting may lower total cholesterol, triglycerides, LDL, and blood pressure.)
- Autophagy (This is a cellular process that removes wastes (or broken proteins, etc.) from cells that may cause dysfunction over time. Often noted as preventative benefits for cancer and Alzheimer’s disease.)
You’ll note I didn’t mention the role IF has been touted for in regards to improving insulin resistance or longevity as the research available in both male and female humans is sparse (or non-existent).
Is intermittent fasting for athletes?
Let me set the record straight here: Fasting is not recommended for athletes.
Why? Because athletes need fuel to help repair their muscles to be able to adequately nourish and replenish their body’s glycogen stores to continue to perform at peak levels.
Now, I’m not talking about fitness enthusiasts here who do a 60 minute class 4 or 5 times during the week (you may be able to modify a time-restricted fast to meet your goals.) I’m talking extreme endurance athletes who are constantly tearing muscles during strenuous workouts.
Most studies have actually shown that athletes do not benefit from fasting, which is pretty natural considering what a tremendous role proper nutrition plays in performance.
One of the studies even showed participants who fasted had impaired speed and power during sprint intervals even while controlling for variables such as nutrition, sleep and training loads in comparison to athletes who didn’t fast.
Now, most research on performance and fasting has been conducted using Muslim athletes who took part in Ramadan, a month long religious fast from dawn to dusk. Please note that I’m not instructing any religion here to not follow their customs and rituals, but rather explaining that athletes weren’t chosen and placed on a fast just because, it was due to an already intended and planned fast.
My concern as a healthcare provider is that athletes who take part in sports that are highly dependent upon weight (think weight lighting, dance, wrestling, gymnastics, etc.) will see the media hype surrounding fasting for body fat lost and get mixed messages.
Bottom line: there is no benefit to athletic performance for engaging in any form of fasting other than one’s NATURAL circadian rhythm fast (aka, just not eating while sleeping!)
Who should (or shouldn’t) try fasting?
Fasting may benefit adults who are looking to prevent chronic disease and have excess body weight and fat to lose.
There is no specific person that fasting is intended for, but there are MANY specific populations who SHOULD NOT fast.
These include (but are not limited to):
Pregnant, Breastfeeding Mothers
Diabetics (without the guidance of an RDN)
Individuals with an Eating Disorder (or past history who are not recovered)
Individuals with Body Dysmorphic Disorder
Can I eat or drink anything on a fast?
In a traditional fast no food is to be consumed, but many online programs say low-to-no calorie foods may be consumed on a fast.
In my humble opinion, if you’re fasting then your metabolism should be given the time to rest, so I would recommend abstaining from all foods (yes celery too) during the actual fasting hours if you are following either the time-restricted fast or periodic fast.
If you are on the alternate day fast (aka that 5:2 Method) than on the 2 days you have severe caloric deficit, you can eat the no-to-low calorie foods.
As far as beverages are concerned, many sites do say you can consume water, black coffee and tea during a fast. Some websites even say you can drink calorie-free beverages during a fast.
I do not recommend diet sodas or other diet drinks for they often contain artificial sweeteners (or even natural sweeteners) that can affect your gut and the way you metabolize foods.
My recommendation is to just stick with the water and infuse it with some fresh fruit or vegetables if you need a little variety. Some sources will say drinking anything but plain water will stimulate your metabolism, increasing your hunger.
I have yet to have a client actually report that drinking cucumber water makes them hungry. So, use your best judgement on this one!
What is the best time (and foods) to break a fast?
The best time is going to be very individualized as you may have guessed!
For instance, if you are an early riser and workout first thing in the morning, you’re going to want to break that fast within 30 minutes after your workout so you give your body the fuel it needs to repair muscles (more on workout recovery here).
On the other hand, if you are more of a night owl, you may prefer to wait until 10am (or whatever hour your stomach tells you it’s time to put something in it).
Bottom line: there is no “best time” to break a fast. It will be different for everyone, but what is most important is that you listen to your individual body’s needs and when it is telling you it needs fuel.
You don’t want to be “that hangry person” on a fast!
As far as the best foods to break the fast, I always recommend my back to basics formula: protein + fat + complex carbohydrate.
This could be an Avocado Smashed Bagel Toast with an egg on top.
Another option is a Greek Yogurt Parfait with Nuts and Fruit.
Or, how about a simple Protein Box.
Bottom line: there are a variety of healthy, nutrient rich foods to break a fast with! Just make sure to include variety in your diet and your body will thank you!
What is the best fast (or diet) to follow?
The one that works for you and makes you happy. Yes, happiness is a HUGE factor in making your healthstyle stick long term, so let’s get that quick fix mentality out of our brain.
Nutrition is so individualized and there is not a blanket answer here that will work for everyone.
What I recommend is working with a registered dietitian nutritionist to find out the eating pattern that works best for you to achieve your health goals. There’s a reason we spent 6 years in school understanding metabolism and how it works for each individual.
If you’re ready to make the first step towards creating a healthy lifestyle for the long haul, I’m here to help. Have questions on anything mentioned above? Shoot them over to me here, or connect with me on Instagram, Twitter, or Facebook.
Bottom line: fasting is not for everyone, but can be considered as an effective method of losing weight and body fat while improving cardiac health if done in a healthy, balanced way.