Steph’s Note: Today we are bringing back old pal Cory Jenks. You may remember him from his previous tl;dr posts on soft skills, adaptability, and Medicare Part D. He’s back, and he’s brought a friend! This time he’s taking off his soft skills and Medicare hats and putting on his clinical hat. But here’s a little about him just in case you’re new.

Cory Jenks is a practicing pharmacist, inhabiting the world of ambulatory care. However, ambulatory care is not his true specialty. Rather, crowd management, object work, and improvised rapping are more his speed. He’s been a practicing pharmacist since 2011, and he’s been a practicing improv comedian since 2013. Since that time, he has taught, coached, and performed improv for thousands of people. You can say hi to Cory on LinkedIn, Twitter @CoryJenksPharmD, and on Instagram @pharmacomedian. Also, be sure to check out his site.

Cory’s got a wingman, and it ain’t Maverick. It’s Brian Bisher, a fellow pharmacist and fitness enthusiast.

Brian Bisher is a practicing pharmacist in an acute care hospital. As much as he loves dosing that vancomycin in a complete, but practical manner, it’s not what he’s best at nor does it excite him as much as fasting, fitness, and the psychology behind habits. He’s been a pharmacist now for 10 years, and he’s been a certified health coach for 5 years. Since that time, he has taught and coached hundreds of people on practical, sustainable ways to improve their health and fitness. You can say hi to Brian on LinkedIn, Instagram and Facebook in his Fathers Made for More Community.

Take it away, Cory and Brian!

Quick, tell us what you think intermittent fasting is! Don’t be shy. Statistically, you, someone you love, or someone you care for has Googled it. Probably in late December or early January.

Google Trends: “Intermittent Fasting” Accessed 12/1/21

C’mon, you know your search history has something far more embarrassing than intermittent fasting.

Still a little shy despite those internet searches? Gone down a dubious rabbit hole? Have no fear, we are here to cut through the malarky, get to the evidence (or lack of evidence, cue dramatic music), and most importantly make sure you and your patients are keeping your fasting safe. Oh, and as a bonus, we’ll give you all the detes on how to incorporate your slick pharmacist skills with someone who is fasting intermittently.

A Brief History of Intermittent Fasting

If you think intermittent fasting is some new fad, you’d be sorely mistaken. No, us Millenials do not get credit for rebranding “skipping breakfast” to “intermittent fasting.” Fasting has been around for a long time.

We’re talking thousands of years long.

Now, of course there have been periods of “involuntary fasting” also known as “starvation” that humans have faced. It’s important to note starvation’s an involuntary abstention from eating. In contrast, we can define fasting as a voluntary abstention from eating for spiritual, health, or other reasons. There’s food available, but we choose not to eat it.

Which in Cory’s family is a scenario that has happened a total of never times.

Hippocrates would not have been a friend of Big Pharma, Big Food, or the cinematic classic Big Daddy. Word is he was just not that into Adam Sandler. (Image)

Fasting has actually been hip since the times of Hippocrates. Ancient Greek, Chinese, and Roman physicians were making fasting cool way before Jennifer Aniston. Some other examples of old school fasting traditions include Ramadan, Yom Kippur, and other cultures and traditions that choose not to eat when there’s food around.

If you consider the early 1900’s to be “modern times,” which for the purposes of this article we are since it’s technically the 20th century, then fasting did have some utilization in modern times. Way back when the current home of Cory’s beloved Chicago Cubs - and rival of Brian’s Cincinnati Reds - Wrigley Field opened in 1914, there were some initial studies showing fasting’s utility in treating type I and II diabetes. Of course, much like the juggernaut Cubs of the early 20th century, it wouldn’t be until the 21st century that fasting showed any signs of life again.

While not medical professionals, some of the smartest people in history had something to say about fasting, other than, “Ugh! I’m sooooo hangry.” Ben Franklin has been quoted as saying, “The best of all medicines is resting and fasting.” Mark Twain, when he wasn’t penning Huckleberry Finn, said, “A little starvation can really do more for the average sick man than can the best medicines and best doctors. I do not mean a restricted diet; I mean total abstention from food for one or two days.”

‘Merica! Thank you, Taco Bell, for this indulgence. (Image)

Ol’ Mark was not messing around. No food for one or two days?! It’s probably best he didn’t survive to learn about the entire concept of “4th Meal.” Speaking of no food for one or two days, how long do you think the longest recorded fast ever was? And as a follow up, how long do you think you could go without eating on purpose?

We’ll give you a second to think and take a snack break.

Ok, now that you’re all fueled up, the longest fast ever was by a Scottish man by the name Angus who went 382 days!! In fairness, he did feast on non caloric liquids, multivitamins, and various supplements.

What a glutton.

He started at 456 pounds and finished his fast at a svelte 196 pounds. He also managed this entire time to avoid any hypoglycemia. That’s impressive.

Now, to be clear, we’re not advocating for a year plus of fasting, but before we talk about time frames, let’s hip you to some of the physiology that makes fasting effective.

The Physiology of Fasting

If you grew up in the 90’s, then 1st off congratulations, we had the best childhood ever. Secondly, you were probably told of the importance of snacking regularly, eating multiple times a day, and never skipping a meal because this would “slow your metabolism.” Unlike the timeless lessons from Saved by the Bell, this advice has gone out of style, and we're here to show you why.

Before we even talk of the possible horror of skipping a major meal like breakfast, we want to show you that even cutting down the number of meals per day could help with weight loss and blood sugar control for those with diabetes. And if we had the money and time to conduct such a study, we would.

Fortunately, Jakubowicz et al did that study for us! And we’re pretty jakub’d up about the results! (Is this microphone on? Sorry, we missed your answer as our kids were rolling their eyes.)

This group performed a small study of 28 folks with diabetes. Each group got the same amount of food, calories, and macronutrients (we are not here to fight the macronutrient wars, we aren’t that brave), but one group ate their food over 3 meals while the other was over six. After 12 weeks, despite eating the same amount of food, the group that ate 3 meals lost around 10 pounds as well as 1.2% of HbA1c, had lower fasting and nocturnal blood sugar readings, and, maybe most shocking, showed a decrease in hunger and cravings.

How could this be? Did they just disobey the laws of thermodynamics? Maybe. But it probably had something more to do with hormones. And there are a lot of hormones we could talk about, but this is tl;dr. So we’re gonna keep it from getting too long and focus on one of the biggies:

Insulin.

As pharmacy professionals, we won’t insult your intelligence. We know you know about insulin in the traditional sense. It’s the magic key that unlocks the cells so glucose can get in and fuel the engine. (And if you need a refresher, check out these fine pharmacy blogs that keep you up to date on all things insulin.)

However, insulin plays another role you are likely aware of if you’ve ever had a patient start it: it gets your body to gain weight. If you think about this process, it makes sense. When our bodies eat something, blood sugar normally rises. Insulin also rises to lower that blood sugar, but it also tells our bodies that, “Hey, food is around, we’re not sure when we’ll get food again, so let’s store it.” And, if you look at the sobering statistics of obesity, storing fat is something we do well.

Before the advent of abundant, cheap, and unhealthy food available 24/7, this storage of fat served us well. It served as a fuel source. However, now that our eating patterns have shifted to eating more frequently, insulin stays higher, and it’s harder to get at those fat stores since we are telling our bodies to store fat all the time.

Yzma and Kronk, pulling the metabolic switch lever. (Image)

In essence, our bodies have two fuel choices: glucose and fat. In our fed state, we use glucose as energy, and fat is stored as triglycerides. In a fasted state, glucose and insulin are lowered, and we access our fat stores for energy as the liver converts our fatty acids into ketones, which are burned for energy. It’s like flipping a “metabolic switch” from burning glucose to burning fat and ketones.

If that explanation has your head spinning, let’s take a time out to use an analogy. Since we are both the parents of toddlers, we are going to use trucks as a metaphor, because kids love trucks.

Think of an oil tanker driving down the road with a trailer full of gasoline to deliver to your favorite gas station (Cory’s is QT, it’s so nice!). The trailer of gas is like the fat stores in your body. Abundant. Right next to your engine. But can that truck use that gasoline? Nope, it’s a diesel engine, so it has to fill up at a gas station, EVEN THOUGH it’s towing around all of that energy.

The diesel engine in that truck is like your body running on sugar. When you are able to lower insulin, your body can access your fat stores. So to use our analogy, it’s like we convert that diesel engine to a gas engine and run a hose from that giant tank to the truck’s engine. For us humans, fasting and lowering insulin allows us to convert our body's engine from running on sugar to running on fat, of which we have a large supply. This means we don’t need to shovel glucose in our face so frequently.

I mean, look at all these benefits! (Image)

And if that explanation wasn’t enough because you aren’t a truck person, here’s a simple graphic to show it in picture form. (Also, if you are not a truck person, Joe Diffie’s estate would like to have a word with you.)

In short, when we don’t eat, aka when we fast, glucose is lowered, insulin is lowered, and our bodies turn from “sugar burners” to “fat burners.” Voila, by burning our body fat, we can lose weight, along with a number of other benefits, including improved glucose regulation and insulin sensitivity.

What - Exactly - Constitutes Intermittent Fasting?

If you bop around the internet, and I am guessing you do, you may come across a number of different definitions of “intermittent fasting.” I think my favorite is still “millennials rebranding skipping breakfast,” but that doesn’t sound sciency enough, and it gives us millennials a bad name. So, let’s get on the same page with some definitions of the different types of “intermittent fasting.”

First off is time-restricted feeding, which is really close to what intermittent fasting is considered. With time-restricted eating, you generally eat in an 8 hour window and fast the other 16. For Cory, this means breaking his fast around 10:30 AM, with his last food (often toddler stress-induced peanut butter to numb his feelings) coming around 6:30 PM.

There are variations of this “16:8” plan. For example, some eat in a 6 hour window, and if you rocked your SAT’s, you can probably guess it is called “18:6.” The fasting community is very creative.

You could push the eating window down to 4 hours. Some even do what is called “OMAD,” which you might think is how you feel after not eating for 24 hours, but in fact stands for “One Meal a Day.” With time-restricted eating, it really is a choose your own adventure where the world is your oyster…provided your oyster is consumed in your chosen eating window.

Next up is alternate day fasting. As its name implies, this involves a 24-hour fast every other day. To ease the challenge, this can be modified as a “partial fast” with a 500-600 calorie meal eaten on the fasting day.

A close cousin to alternate day fasting is a “5:2 fast.” In this approach, two days a week involve a 24 hour fast, and like the alternate day fasting, these can be a “partial fast” allowing for that small 500-600 calorie meal. And, if two fasting days a week is too much, like if you want to have an alternative (like having all forms of two, too, and to in the same sentence), rock the weekly one day fasting plan. One 24 hour fasting day per week. Easy peasy.

Finally, there is the confusing “fasting mimicking diet” which involves five days once a month of a low calorie, non fasting, ketogenic diet that allows small amounts of macronutrients. Our personal opinion is that if you or your patients want to fast, trying to follow a diet where you eat seems counterintuitive and too much work for our lazy brains. So we won’t go into too much detail. You also may see fasting “bars” sold. We get it, it’s hard to cash in on something that involves NOT eating or NOT consuming a medication, but that seems to be missing the point.

Oh, and one final note on types of fasting. The last type is considered “prolonged fasting,” which is longer than 42 hours. Here’s where you really step into the longevity benefits of fasting. This duration can typically be done safely up to 72-96 hours as long as there is a focus on salt and electrolyte replacement. It will be challenging, and anyone going into a longer fast should be prepared mentally and find a partner to fast with.

Luckily, it’s not something that’s recommended to do all the time, maybe a couple times a year if you are wanting to really reap the longevity benefits. Oh, and unless you are like the World Champion Angus and under close medical supervision, we wouldn’t advise anything longer like a week plus. It can lead to refeeding syndrome, and the juice just isn’t worth the squeeze.

We’ve talked about the types of fasting, or in pharmacist terms, the different “doses" that are used based on duration. Now, let’s talk about frequency. How often should someone be fasting?

I hope you are ready for the most unsatisfying of answers: it depends.

How Often Should a Person Fast?

While fasting can be an excellent (and did we mention affordable?) tool, Brian can say from personal experience, you can definitely have too much of a good thing. Fasting is a stress on the body. And while pharmacists think of stress as something that means going to your 3rd code of the night, walking into a pharmacy with no technician support, or trying to get all of your board certification credit done on time, stress isn’t always a bad thing.

In our bodies, stress can lead to something called hormesis, which in simple terms means exposing the body to the right zone of stress which triggers a response that actually makes our bodies stronger. For example, think of exercise. The right amount of squats will leave your backside toned and strong for swimsuit season thanks to the right amount of stress on those buns. But spend too much time in the squat rack and good luck getting yourself off the commode when nature calls.

The same can be said about fasting, and while developing the fasting “muscle” can be super convenient (and close to a superpower when stranded in an airport), it also can cause major issues with digestion and possibly muscle loss if not done strategically. So here are a couple of things to keep in mind for yourself and when talking to patients who are considering fasting:

Stay true to the word intermittent and do fasts intermittently (A personal note from Cory, who likes to say he does “intermittent intermittent fasting” as weekends are for breakfast with the kids while the weekdays are too busy to eat at work. Hurray?).
It’s important to ease your digestive system back into food with easily digestible nutrition. The longer the fast, the more important this is. Ironically, even though it’s a break from food, it still is a stress on your digestive tract, and it’s most susceptible to damage from inflammatory foods with the first food it sees again.
- Lean protein, sources of collagen, maybe some healthy fats are the best options for treating your gut right when getting back to eating.
- Also keep it small because gut motility is down, and the last thing you want is to bolus a bunch of food that just sits too long in the wrong spot, fueling the growth of bacteria where you don’t want it.
Fasting isn’t some “get out of eating healthy free card.” Overdoing it during meals can stall the goals of those who are fasting.

Oh, sorry, we just checked our LinkedIn profiles and remembered we are pharmacists and you are pharmacy professionals as well. Let’s talk about fasting and medications because I guess that’s what we’re experts on. That and the fact that eating a fasting bar while trying to fast is, well, not fasting.

Managing Medications During Intermittent Fasting

When a patient starts fasting, it’s important to identify the reasons why. We are both biased based on what we have observed in our own practices. Cory manages diabetes in Primary Care, and Brian sees the consequences of poorly controlled diabetes in the Emergency Department. Most of the medication adjustments are based around changes in blood sugar. But we’ll touch on a few other non diabetes medication considerations.

The first, and most important, thing to focus on with a patient who starts a fasting regimen is safety. Fasting can be a powerful tool, especially to improve blood sugar control. Like, really powerful. Like, stopping all 80 units of insulin in 2 weeks powerful. So while we are the medication experts, all patients, but especially those on certain diabetes medications, need to be approached in a team-based manner for optimal safety.

Before a patient fasts, we need to make sure they don’t have any contraindications, like pregnancy; either young or advanced age; older frail patients; history of immunodeficiency, eating disorders, or dementia; or history of TBI or post concussion syndrome.

For the patient who clears the contraindication bar and jumps into their own intermittent fasting or time-restricted eating plan and is on diabetes medication, consider their blood sugar control over the past 2-4 weeks, what type of therapy they are on (we’ll get to the nitty gritty in a moment), their preferred fasting duration, and the type of fast (no calories versus partial fast), and their diet on non fasting days (carb intake is crucial).

The high risk hypoglycemia medications include:

It may come as a shock to Cory, but there are medications that are for conditions other than diabetes. Some other medications to watch for in a fast include antihypertensives. Like the rapid improvement in blood sugar, big improvements in blood pressure can also occur. Counsel your patients to be on the lookout for dizziness and to be monitoring their blood pressure. If needed, cut back and stop.

In particular, be on the lookout for diuretics. The lowering of insulin can also reduce fluid retention. (Did you know insulin can cause fluid retention? Boom, another fact!).

Any other medications that are treating a weight-based/metabolic syndrome condition may need to be adjusted (hopefully down and off). Also, if all goes to plan and a patient loses weight, recalculate any weight-based drugs. When this happens, it’s the happiest recalculation you’ll ever have to do.

These aren’t the only “take with food” medications to consider. Let’s dust off the ol’ basics of pharmacy counseling hat and touch on a few other medications/classes that you will want to discuss with patients. (And here is a nice little summary if you want more info). These may need to be adjusted based on a patient’s fasting window:

Corticosteroids
- Did you know that oral ‘roids can increase stomach acid release? You probably did because you paid much closer attention in class. Good for you. But taking these with food can help to neutralize some of that acid and thus reduce possible gastric irritation. If your patient is taking them once a day and doing some sort of fasting, emphasize the importance of taking these with their meal(s).
NSAIDs
- Another counseling 101 point, these puppies are better taken with food. Depending on the duration of action, this could get a little tricky for someone who is trying to have a 16 hour or longer “no eating window” but is also in need of pain relief. Cory knows from experience, and typically chooses the pain of pain over the pain of breaking his fast early. Because he’s tough like that. But your patients need not be a hero if they truly need pain relief.
Certain Antibiotics
- Nitrofurantoin and cefpodoxime are better absorbed when taken with food. Amoxicillin/clavulanate and rifabutin are better tolerated when taken with food. In these cases, it would probably be better to have your patient’s infection appropriately treated than to squeeze out a few more hours of fasting.
Chloroquine
- This is another one that can be pretty irritating to the stomach. Sorry hardcore fasters, it is likely a better choice to take with food than to deal with the “GI Trifecta” of nausea, diarrhea, and stomach cramps.

Now for a quick disclaimer about approaching intermittent fasting as a pharmacist…

As you can see, it can be a little tricky when a patient wants to fast but is on a bevvy of medications. And I think this is a good time to emphasize the statement that the “patient wants to fast.” Because while it is probably clear the two of us are really into fasting, it is not something we are advertising a ton to our patients.

And by “not a ton,” it’s more like “not at all.”

However, when a patient mentions to Cory that they skip breakfast or have tried fasting before, he investigates if the patient wants to either continue or try a time-restricted eating pattern again. This is then followed by the checklist of everything in this article to make sure it is done in a safe, controlled manner.

Our recommendation for you is to take a similar approach. As we all know as pharmacists, patients can ask us some wild things, and they come to us with questions from The Internet (see Google Trends at the top of this article). The goal of this article is not for you to open a fasting clinic but to be prepared for when (not if) patients or providers have questions about fasting and their medications. Now you’ll get to do what awesome pharmacists do: provide evidence-based information to provide the most safe and effective treatments.

The tl;dr of Intermittent Fasting for Pharmacists

Wow, this was a lot. If you can believe it, there is even more we wanted to talk about, but the tl;dr team reminded us that if we don’t stay true to the “tl”, then you readers will “dr.” In the spirit of brevity, we are going to leave you with our “Fast 5.” No, not a Vin Deisel movie, but five takeaways you can use for yourself and your patients right now:

Fasting switches the body from burning glucose to burning fat, and it allows the body to use its stored fat for energy.
Fasting has vast positive physiological effects on the body, and benefits can include improvements in weight, blood sugar, blood pressure, dyslipidemia, neurodegenerative disorders, oncology, and beyond.
A common form of fasting is “time-restricted eating,” which involves eating in a 6-8 hour window, and even this should be practiced intermittently.
When fasting, the most important consideration for pharmacists is medication safety, especially diabetes medications or others with food-dependent pharmacokinetics.
Fasting is like a muscle, and it takes time and practice to improve. Staying hydrated, taking in electrolytes, staying busy, and strategically breaking your fast will help improve your chances of success.

Cory and Brian breaking their fast after marathon writing this post. (Image)

Thanks for taking this fasting journey with us, and sorry for making you think for even a moment there was another Fast and Furious movie in the works. Even though we are pharmacists, when patients choose to engage in aggressive lifestyle changes, we are the experts in helping them navigate their medications safely. Now go forth and be experts! As for us, we’re actually kind of hungry after all that writing.

The Pharmacist's Guide to Intermittent Fasting