Mac and Jinger look at the science behind intermittent fasting, uncovering what works and what doesn’t for endurance athletes.
Intermittent Fasting has become one of the most popular nutrition topics in endurance sports over the last few years. Our Sports Science team dives deep into the research to find out what works, what doesn’t, and what questions you should answer before determining whether to incorporate fasting into your training.
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Mac Cassin 0:00
Hello, and welcome back to another episode of The Knowledge Podcast brought to you by the Wahoo sports science team here in Boulder, Colorado. I'm MaC Cassin.
Jinger Gottschall 0:06
And I'm Dr. Ginger Gottschall. Today we are discussing a hot topic in the world of nutrition and weight management. This is specifically intermittent fasting. And I'm just going to lay it on the line right now, the term fasting with me, especially with respect to the folks that I coach and mentor in the fitness world. I don't love the term.
Mac Cassin 0:32
What's wrong with the term fasting?
Jinger Gottschall 0:36
It's because endurance athletes especially really require a specific regimen of food and water intake in order to be successful in performance. So I don't utilize this specific term when I'm training people is the bottom line. Gotcha. But I do want to be honest, that I do love myself a fasted run in the morning. So I wake up and within 30 minutes, I'm out the door. And when
Mac Cassin 1:05
she says she loves that she means six days a week for how many years now?
Jinger Gottschall 1:09
I'm maybe approaching the 19. Ish.
Mac Cassin 1:13
So yeah, so clearly, there's got to be some upsides to it. If you're doing some fasted workouts, I think this is a good point to differentiate, you know what we're talking about when it comes to fasting, like fasted workouts versus intermittent fasting?
Jinger Gottschall 1:28
Great point? Yes. Have you ever done any sort of fasted training,
Mac Cassin 1:34
I have, I was actually a relatively big proponent of it, as long as it's specifically low intensity, got it, never any high intensity wouldn't fast. There are a number of benefits there that we can get into later, but it's not for everyone. And there's definitely some caution that has to be taken if you're gonna attempt it. And so intermittent fasting has become pretty popular in the last, you know, a couple of years, from all the research that's been done on it, you know, you get significant weight loss. And the big draw to it is really just how kind of simple it is,
Jinger Gottschall 2:06
right? You're not counting calories or macronutrient ratios,
Mac Cassin 2:10
right, you're free to do certain times where you can eat and times where you can't. And generally, if you follow that most people will get into a rhythm of the actual ratio of macronutrients, all that stuff won't change from just the regular diet, it's just, yeah, you have chunks of time when you can't eat. And so as long as you can determine the date and the time of day, you can complete intermittent fasting,
Jinger Gottschall 2:32
that does sound super simple. Not only is it simple in terms of when you eat and when you don't, the actual protocols you can lay out very simply, but there is also typically in research, there are three different types of intermittent fasting that have been utilized in actual research methods. And the first one is simply just alternate day fasting, you are eating anywhere from zero to 500 calories on, let's say, the odd number of days, and the even number of days you can eat what is called ad-lib, anything you want, whenever you want. So hit up the buffet every other day, Absa fricking, literally, you are going to that brunch buffet, and just bringing it all in as much as you want. That's literally the rules. The second type is called the five intermittent fasting diet, where you will have two fasting days that are a little bit more, they're 500 to 1000 calories. That's for two days, and then for five days, you have no limit. So that's the five, two, or two, five.
Mac Cassin 3:36
And for that one, is it two days in a row and then five days in a row or yes,
Jinger Gottschall 3:39
okay, yes. So in a seven-day week, you have two in a row of fasted and five in a row of eating. And the last one is time-restricted. And this is when you're just eating in a prescribed window. In terms of research studies, the most commonly studied is a 16, eight, so you have 16 hours of fasting and an eight-hour period of eating. And we will go through some of these species with respect to endurance athletes in a bit. But we're gonna actually start with just going through some of the pros and cons with respect to weight and energy and cardiovascular variables. First,
Mac Cassin 4:18
some big takeaways from the existing studies are for body weight and intermittent fasting basically produce the same reduction in weight in individuals who are overweight or obese or have type one diabetes or type two diabetes, it produces the same reduction in body weight as traditional dieting. So is it a normal daily restricted-calorie diet, which, again, the advantage of intermittent fasting is it's easier because there aren't many rules to follow? You don't have to really restrict yourself and then the other side of there's body weight and then the other important part is body composition because you have lean body mass and fat mass and what they found is intermittent fasting doesn't help innovate. drawls with obesity to lose more fat mass or to retain more lean muscle compared to a traditional diet. visceral fat loss of fat around the belly is the same in intermittent fasting and traditional diets. So again, we're seeing a lot of it has the same results as traditional dieting.
Jinger Gottschall 5:15
All right. So basically, it seems like the calorie restriction is the same in both. And it doesn't really matter how you go about it either smaller calories every day of the week or alternating days of fasting calories. Okay? That kind of makes sense to me. And I feel good about that with respect to the math, you're eating the same amount. And that actually goes into studies that looked at just energy intake specifically, and it doesn't look like individuals were eating double the amount or more on those eating anything you want days. So, therefore, again, no significant difference between a traditional calorie restriction and intermittent fasting.
Mac Cassin 6:01
And does that apply for the three different types of intermittent fasting that you talked about the alternating day five to one, it does,
Jinger Gottschall 6:07
for all three of those that have been tested, the energy intake looks to be about the same. Regardless, with respect to diet quality, there doesn't seem to be any difference with respect to the macronutrient ratio, so carbohydrate, fat, and protein, no big differences with respect to beverage consumption, and that's they've let study more actually Mac in the adult beverage consumption. So we're talking about alcohol use here. No significant differences in sugar or saturated fat, monounsaturated or polyunsaturated cholesterol, sodium, or fiber, which is actually all good news. Again, it seems to be safe with respect to the quality of food. But one thing that hasn't been looked at is those micronutrient intakes, specifically, something like vitamin D, or vitamin B 12. That's very important for things like the neuro system, your eyes, and muscle development. So those important micronutrients we don't know enough about yet to compare the two diets.
Mac Cassin 7:08
So another area of just general health, blood pressure is something that is often looked at when you're looking at different diets in research. And so far, with intermittent fasting, it's pretty variable, what the impact has, in general, it seems that it would only help lower blood pressure and people with hypertension or borderline hypertension. And it's only at the really the start of the protocol, it's not a continued drop over time, it's really the first couple of weeks is when a change that change in blood pressure will occur, and then it
Jinger Gottschall 7:37
levels out. So it's an acute change. And actually, a lot of these studies were only six weeks, so we don't know the long-term benefits of blood pressure. And then
Mac Cassin 7:45
regarding blood, you got your plasma lipids, so essentially fat in your blood system. And again, a direct comparison shows between intermittent fasting and traditional diets show a similar decrease in LDL cholesterol and triglycerides. But there was also a reduction in HDL with intermittent fasting and HDL is the good cholesterol. All
Jinger Gottschall 8:06
right, so that seems to be not so good. So
Mac Cassin 8:09
that's a check in the first negative check. But well, I guess the micronutrients we don't know enough yet. But yeah,
Jinger Gottschall 8:15
so the High-Density Lipoprotein goes down, we want it to go up. So that's something to watch. And I would say that might have to do so HDL is very influenced by the intensity of exercise, as well as fruits and vegetables. So that might lead to, if you're fasting, you're not actually doing as intense of exercise, which you mentioned at the beginning, which makes sense. And perhaps, you're just not getting the same amount of fruits and vegetables, that could be another concern. If we continue on with nonexercise-specific studies, it looks like glucose regulation, there is no change in the fasting levels of glucose, depending upon what type of diet either intermittent fasting or traditional you're doing. And the specific variables of insulin resistance and insulin sensitivity are highly variable so we can't really draw any conclusions, unfortunately, about glucose regulation. In terms of other blood markers, we could look at inflammation and oxidative stress, and there doesn't look like there's any benefit on circulating inflammatory markers. But there actually is some data that shows there's a reduction in oxidative stress markers, and that could be just because you're getting less oxidative stress on those fasting days, which makes sense,
Mac Cassin 9:36
right? You're not really oxidizing as much stuff.
Jinger Gottschall 9:39
Exactly. So with all this said, Is there anyone that you wouldn't recommend, doing this intermittent fasting?
Mac Cassin 9:46
Yeah, generally, you know, children under 12. That's an woman who is pregnant or lactating individuals with a history of eating disorders, which can be very common in the endurance athlete community, so that can definitely be something to watch out for, and then older built over 70? And then if you are on a medication you need to take with food, it's probably not.
Jinger Gottschall 10:07
That's really something, though to consider for sure.
Mac Cassin 10:11
And it's generally not recommended for adolescents who are in who have normal body composition.
Jinger Gottschall 10:16
Now let's get into the topic that everybody's on the edge about, is this a protocol that we could actually recommend or promote for endurance athletes out there listening to even try? Right. And again, back to my first point with the athletes that I coach, because endurance athletes are training for a long period of time, we don't have any data on these long-term studies. And it requires a greater metabolic and nutritional demand to do these long hours that have at times higher frequency intensity, is this something that we would want to promote?
Mac Cassin 10:54
I'd have to say it depends.
Jinger Gottschall 10:56
It totally does.
Mac Cassin 10:58
You know, you need to look at it to some extent, what is your goal as an endurance athlete? Are you doing it for general health and well-being? Are you doing it to lose some weight? Are you doing it to compete at a high level? Because that really dictates if you're looking to just kind of improve your health, maybe lose a bit of weight? It's probably worth trying, if you haven't done it before, just to see if it works for you. If the simplicity of I can eat now, or I can't eat now, it's a yes or no question. Maybe that is the strategy that will work for you. And I think it's important, regardless of whatever dietary, whatever diet you undertake, there's always going to be proponents out there who've been doing it for years and worked really well for them. And they'll seem to the mountains about how great that specific protocol is. And it's important to remember that everyone's different. And just because it works really well for one person, doesn't mean it's going to work really well for you.
Jinger Gottschall 11:48
And that is the bottom line. I think if you hear anything during this particular podcast is just if you want to give it a try, do so perhaps get some guidance from a coach and or nutritionist before you go about these specifics. But understand to what type of training you're doing and how to match workouts with the fasted days. And also be really aware of hydration, especially in summer months and particular climates.
Mac Cassin 12:18
Yeah, especially if you're someone who's used to say having a mixed sports drink, when you're writing, if you cut that out, you might be drinking a bit less, which again, is not a good thing detriment, because you also get a lot of hydration out of the food you eat. So not eating any food, you can just the water that's associated with that you don't have that coming in. So that can be a knock-on effect there.
Jinger Gottschall 12:42
Right? Good. It's compounding for sure. If you speak with people who this works for a lot of them say, It's great because you're going to switch your metabolism from being glucose-dependent to more ketone bodies, and therefore be burning more fats that you can do a longer exercise session and have absolutely no problem. Sounds good. It might work. All of these studies to date really only been done on animals. So, therefore, we need more data on endurance athletes before we make any assumptions about that potential benefit.
Mac Cassin 13:19
Yeah, and one of the big caveats there to that switch is it is dependent on the intensity of exercise you are doing, it needs to be low enough intensity, that it is predominantly fat oxidation as a fuel source. So just because you're fasting doesn't mean you go out and ride hard for two hours, that that will make the shift it's going out and ride pretty easy for four hours.
Jinger Gottschall 13:44
Exactly. And in fact that two hours of high intensity may be very difficult to do in any capacity anyway.
Mac Cassin 13:51
Yeah, because we know that with high-intensity exercise, your body prefers to use glucose. And your body is more effective at producing watts with the oxygen you have using glucose as a fuel compared to fat.
Jinger Gottschall 14:04
So and we do know that from multiple research studies, yes, that feels pretty solid. There are additional risks with respect to endurance athletes taking on this intermittent fasting diet that include increased fatigue, altered sleep habits, and we go back to the beverage, nonadult form of water, and energy replacement drinks, which typically lead to hydration with this type of diet. So yeah, keep those things in mind and really monitor yourself with respect to your rate of perceived exertion and energy levels when you're going.
Mac Cassin 14:44
Yeah, another thing to point out here again, as we've outlined that there's really there's not a lot of evidence as to what that there's a benefit here for intermittent fasting regardless of the protocol you use. And there's no real difference between it and regular restricted caloric intake dieting. There's No. So again, it could be good for you if it's just a simpler way to go about it. I would also, in my opinion, think that the time-restricted, intermittent fasting would be the most appropriate for athletes as opposed to alternating days.
Jinger Gottschall 15:16
Absolutely. So you're talking about that 16 hours of fasting and eight hours of eating? And that's seven days a week. Yes, right. Agreed,
Mac Cassin 15:25
having a little something for the fire at all times is good. And it's, it's interesting, there's actually been a lot of studies done on that a similar time-restricted fasting with athletes who are Muslim and participate in Ramadan, which is you for that for their religion, they have the ninth month of their calendar is they don't eat when the sun's up, right, which is actually really fascinating because their calendar isn't lined up with the 12-month calendar. So the time of year actually changes. So if it's in the winter, and you're in a high altitude, it's, you know, maybe only eight hours of fasting, and if you're, if it's the summer at a high altitude, it can be up to like 19 hours of fasting. That's a fact I find interesting. But there has been a lot of research done there. And again, with the time-restricted fasting, a lot of those athletes have been able to maintain their performance overlap month. Now, they haven't explicitly improved performance, right, but they haven't lost performance or capacity.
Jinger Gottschall 16:24
Correct. And there are also studies on other different types of ancient as well as modern practices of fasting and Judaism and Christianity. So, therefore, we also encourage you to respect your beliefs and what comes with those specific religions and our practices and know that you can make it work. You're just making some adjustments with respect to possibly your exercise intensities at that time. Cool. Well, that was a fun little chat about something that is a hot topic that I know, see, come I see come across my newsfeed multiple times, even in a week. These days.
Mac Cassin 17:05
Yeah, so hopefully you have a bit more information now to go out and maybe try this for yourself or maybe just decide that it's definitely not for you and go to other greener pastures.
Jinger Gottschall 17:17
So that is it for another episode of the Wahoo Sports Science Podcast. And we hope that you'll be able to take some of these tips, some things that you learned, and maybe give it a try or recognize that it's not for you, but regardless, we hope that it helps you become a better endurance athlete. So thanks for listening