As a Diet Coach, Contest Prep Coach, Nutrition Program Coordinator at Life Time and Strength Coach, I have  A LOT of exposure to so many different people from professional athletes to the aspiring to be fit. The questions I have often gotten the last couple years revolve around intermittent fasting…. What do you think about it? How do you do it? Is it right for me? When do I strength train and do cardio? Well, look no further, here are your answers.

What is Intermittent Fasting (IF)

Intermittent fasting (IF) is a voluntary withholding of food for a period of time with the intention of weight loss and/or other health benefits.

Intermittent fasting is a hormetic stressor meaning that a stressor (such as no food), in mild or specific doses can  trigger adaptive responses for the better (such as fat loss and an increase mitochondrial number and function) but too much can cause stress an inflammation.

Dosing of the stressor is very individual. What’s good for one person may not be good for another.

Benefits when done properly:

(All with the caveat of differences between specific populations- read on)

• Rest and digest

• Clearing of cellular debris (aka: cellular autophagy)

• Increase mitochondrial function

• Inflammation reduction

• Reduce risk of cancer

• Manage body weight

• Increase in growth hormone (short term)

• Help gain or maintain lean mass

• Simple rules of when to eat and when not to

• Increase in mental clarity

• Regulate blood glucose levels

• Reduce the risk of coronary disease

Who should and should not intermittent fast. The Caveats.

First let’s cover who intermittent fasting is not good for or should do this under direct supervision of their doctor:

• Not good for pregnant women

• History of disordered eating

• Chronically stress females

• Females that don’t sleep well

• Anyone with thyroid issues

• Those new to diet and exercise- start with the basics of cleaning up diet and lifestyle first!!!
• Type 1 diabetics must be monitored carefully. Type 1 is when the pancreas does not make enough insulin to regulate blood sugar levels.
• Type 11 diabetics must also be monitored carefully. Type 11 is when the cells are insulin resistant and fasting may help greatly.

Notice most of the special populations listed above are female. Let’s dive in and see what the research says… what research there is anyway.

When it comes to research on intermittent fasting, there are limited studies done on women. And, many of the studies done I have found are utilizing a small sample size such as 9 men or 6 men and 7 women and of a short duration. But we can still extrapolate data from the conclusions.

Why is it important that research is done on both genders extensively? Because of our hormone differences. Our hormones are not only the sex hormones like testosterone and estrogen but many hormones like leptin, ghrelin, insulin, and peptide YY control our metabolism
(See more on metabolic hormones here: click). Along with hormone differences, the ultimate purpose of each gender must be considered.

The goal of any species is self-perpetuation. Your body doesn’t care if you want to look hot in a swim suit. It cares that you stay alive and reproduce.

If we consider only biological differences… NOT actual responsibilities Mothers and Fathers should have in a babies life, (don’t get your undies in a bunch now) the job of the male is done once the egg is fertilized. His body does not have to grow and sustain a new life for the duration of the pregnancy and breast feeding after.

This makes females far more sensitive to calorie deficits. Women’s super amazing giver-of-life bodies need the energy to fuel the preparation and act of the energy expensive duty of having children.

Now let’s take a look at some studies done on men and women.

The first study above done on rats shows that male rats stayed more even keel during various fasting periods while the females became more frantic and hyper alert. Most likely an adaptation to find food!

Another study showed that the male rats fertility increased while female fertility decreased. One theory male fertility increases is that they are compensating for females’ decreased fertility in an overall population during a time of famine. Also, if the female body is not getting enough energy to sustain another life, it won’t get pregnant in order to keep the female alive through the stressful starvation period.

As far as the rest of the studies, I won’t bore you by reiterating those here as you can see the lists above BUT as an over all summary, IF for the male population is pretty darn great but for females that are over weight or in a normal body fat range, it doesn’t seem like such a beneficial thing to do. Now if you are an obese female, this may work well for you. A female of 32% body fat or higher is considered obese according the the American Council of Exercises. Screw BMI- it doesn’t take into account all your amazing muscle mass from dead lifting 250 pounds. 😀

Now, in my experience, studies aside, I have had many female clients that are in the 20-31% range that do or have tried IF and it comes down to individuality. There are many ways to IF as we will discuss below and if any of the methods below make you feel great, and you are not trying to get pregnant or be a super athlete then perfect!! For the males I have worked with that have intermittent fasted, it has worked and made them feel great 99% or the time which does align with the studies.

But I want to discuss the what, when and the how of IF for general fitness and the athletic populations

Summary for who should and should not fast:

Great for men, not so great for females under 32% body fat (ish). Great for obese females and both genders undergoing chemotherapy. 

How to Intermittent Fast

First and foremost, before considering any special diet types, understand that solid healthy habits need to be in place.

• Make sure you have a solid and consistent exercise routine

• Consistently have the basics of whole food eating down!!! Check out this article: Reach Optimal Health in 5 Easy Steps.

• Manage excessive stress and poor sleep. These two factors are huge when it comes to health and fitness! Think high cortisol (stress hormone) and inflammation from the lack of recovery during a good long deep sleep.

AND…….

—Don’t expect to get shredded by restricting your eating window. —

You can binge eat all the calories you need for the day and more whether you spread the calories out through the day or eat them in a 4 hour time period! Still want to fast? Great! Let’s talk about how to ease into it and how to time it with workouts.

Intermittent fasting can be done many ways! There is no standard of time. 12, 16, 18 hour fast, alternate day fasting, IF during the weekdays and then not on the weekends and the list goes on.

Typically people will fast for a 12-16 hour window and eat with in the other 8-12 hours. Here is a great way to get started once healthy whole food habits are pinned down.

1. Start slow such as with a large window, say 8 AM to 8 PM and decrease this over time by 1 hour each week or each month. That is all up to you.
2. Know that its okay to be hungry! Be calm!
3. But, respect your body cues like mood and mental health, sleep quality, immunity, blood profile, and hormone health.
4. Pair IF with exercise, but don’t over do it
   1. Consider how much training you are doing and how intense the sessions are. For high volume training or intense exercise, it may be best to make sure your training sessions are during your eating window, especially for females.
   2. Have a solid rest and recovery strategy- get in sleep and leave in rest and active recovery days. Heart rate variability is also a great way to monitor stress and when to put in rest and recovery days.
5. Consider if intermittent fasting fits your lifestyle.
6. Consider other life stresses. For example, if you have a very stressful job, fasting may not be an added stressor you want to add. Again, listen to your body.
7. Consider fat adapting first with a ketogenic diet. It is easier to transition into intermittent fasting.

Types of Fasting

Again, there are many ways you can work a fast but here are some common methods:

Every other day fast- 36 hour fast/ 12 hour feed

20 hour fast/ 4 hour feed

16 hours fast/ 8 hour feed

Meal skipping where you randomly skip meals several times per week. This is supposed to simulate a more ancestral eating pattern.

Eat Stop Eat: 24 hour fast 1-2 times per week

Longer block fast such as 5+ days- make sure to get in enough electrolytes!! When insulin levels fall, the kidneys excrete excess water which could cause electrolyte loss (Ref 12). I had worked with a client who, 7 years prior be me having met her, had a grand mal seizure during a 7 day fast due to lack of electrolytes!

Even though I have mentioned fasting methods can be very individual, are you still asking if there is an ideal fasting time period.. why yes, yes there is but surprise, the study was done on young prime-of-their life men.

There is a study done called “Progressive alterations in lipid and glucose metabolism during short-term fasting in young adult men. (Ref 11)” that found the sweet spot for fasting to be 18-24 hours:

Training Fasted

If you are going to train fasted, you must consider your gender, are you lifting or doing cardio, how long are these sessions, what did you have the day before to eat.

If you are going to train fasted, you must consider your gender, are you lifting or doing cardio, how long are these sessions, what did you have the day before to eat.

You can gain muscle training fasted but you need to get protein in your system shortly after. You need to plan your eating window to start after your workout.

If your sessions are long- a good hour or more, you will find performance will decrease. You will find lifting session about the 20-30 minute range are more sustainable when fasted.

What ate the day before will also matter. If you have eaten plenty of calories the day before, you should be just fine lifting fasted, but if you are in a calories deficit, I suggest lifting during your eating window.

One thing is for sure…. drinking BCAA’s during those fasted lifting and cardio sessions!! BCAA’s are quickly digested, readily available within about 15 minutes in the blood stream and help to spare muscle.

And once again, listen to your body, if you feel like crap lifting fasted, don’t.

Female specific, highly consider lifting during your eating window. If you are utilizing a smaller eating window such as 4-6 hours, have about 30 grams of protein in the morning. This will help decease cortisol. Cortisol is a hormone that increases heart rate and blood pressure to get you out of bed and moving. Then is should naturally drop during those morning hours but if you are stressed or fasted, it can stay high. This not only causes inflammation but puts you in a catabolic state (think break down) where you are not only breaking down fat for energy but muscle as well.

Summary for training fasted:

Exercise just before the first meal of the day. 

Sip on BCAA's during your workout session. 

Females, train during your eating window, at least to start. 

The biggest meal of the day should be the one right after your workout session.

If you are still confused whether this is right for you male or female, obese or not, shoot me an email! Let’s chat. Contact me. Click here.

References:

Ref 1: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052416

Ref 2  https://www.physiology.org/doi/full/10.1152/ajpendo.00070.2006

Ref 3 https://www.ncbi.nlm.nih.gov/pubmed/15833943?dopt=Abstract

Ref 4  https://academic.oup.com/ajcn/article/81/1/69/4607679

Ref 5 https://academic.oup.com/ajcn/article/90/5/1138/4598070

Ref 6 https://www.ncbi.nlm.nih.gov/pubmed/28025637

Ref 7    https://www.ncbi.nlm.nih.gov/pubmed/29097329

Ref 8 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2815756/

Ref 9 https://www.ncbi.nlm.nih.gov/pubmed/20452283

Ref 10 https://www.ncbi.nlm.nih.gov/pubmed/23723099

Ref 11 : https://medium.com/the-mission/the-sweet-spot-for-intermittent-fasting-9aae12a2158c / https://www.ncbi.nlm.nih.gov/pubmed/8238506

Ref 12: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1795897/pdf/brmedj02254-0030.pdf

Make sure to check with your doctor before starting any new diet or fitness program!! This is not to be used as medical advise or to cure any conditions.