January 2, 2020

MAF Carbohydrate Intolerance Test (and explanation): Day 1

Like I mentioned in yesterday's post, I decided to try a drastic dietary test to see if certain foods are causing random symptoms I've developed in the last few years. I spent October, November, and December running at a MAF (maximum aerobic function) heart rate, a formula that was developed by Dr. Philip Maffetone as a program to build your aerobic system for endurance training.

There is a whole lot of science around it, and I've been reading his book "The Big Book of Endurance Training and Racing" (Amazon affiliate link). I was never interested in the nutrition aspect of the MAF method, because I've always held my belief that moderation and variety is the best way for me to eat.

Like everyone, I know that eating a healthier diet is going to be better than eating junk food; but I wasn't willing to give up junk food. I'm still not willing to give it up entirely! However, I am willing to be open-minded enough to see if cutting way back on it makes me feel better and gives me more endurance when running.

Getting back into running, as well as reading his book (which I only started because I had questions about the MAF training that I wanted to find answers for), made me think a bit about his two-week test for carbohydrate intolerance.

Now, as soon as I hear the word "carbs" as far as dieting goes, I immediately feel cynical. I think that giving up carbs just isn't sustainable (at least for me) and I don't think it's healthy to cut them out. I think it's best to have a variety of foods in moderation. This is why I never paid attention to his ideas on nutrition, because after hearing about "carbohydrate intolerance" I assumed it was like any other low-carb plan. Maybe it's great for some people, but definitely not something I was interested in.

When I read about the two-week test, however, and the reasons for doing it, I was much more open-minded. I can certainly try something for two weeks. And the reason for it is NOT for weight loss, but to test how well your body burns fats versus carbohydrates (I'll write more about this below) and to see what foods agree best with your body and give you the best results for health and training.

The two-week test is very strict about carbs; but after that, you gradually add them back in, taking note on how they make you feel. The other purpose is to make your body sensitive to carbs so that it learns to burn more fat for fuel (something that is important in endurance training--running, in my case).

I'll try not to get TOO detailed, but the gist is that endurance training uses the aerobic system, which prefers to burn fat for fuel because it lasts a long time (and our bodies, even very fit ones, have enough stored fat to get us through long endurance races). If our bodies burn primarily fat, rather than sugar/carbs, then we can endure a sport much longer. (There isn't nearly as much glycogen, or stored sugar, as there is fat.)

The carbohydrate intolerance test is a way of seeing just how much your body relies on sugar versus fat to get through any sort of exercise or daily living. If you don't really see results from the two-week test, then it's likely you're already burning primarily fat. But if you see a drastic change as your body uses the fat for fuel (because you're not supplying it with more sugar/carbs all day), then it's likely that your body is used to using sugar for fuel.

I have a strong feeing that I am part of the latter group because I eat a lot of carbs. So, my body is burning carbs all day long for fuel. To be a better runner, and be more fit, I want my body to be able to rely on burning fat so that I can run longer with more ease.

Hopefully that makes sense! If you don't want to read the whole book, I'd at least check out Dr. Maffetone's website, where you can read more about the gist of it. (I linked to a few helpful pages of his site at the bottom of this post)

An example that helped me understand it better is when you think of "the wall" in a marathon--when a lot of runners just sort of crash around miles 18-22. I assumed it was just a normal right of passage for any marathoner. But from what I read in the book, the reason is because they are used to burning mostly carbs for fuel (and using simple carbs like gels to keep replacing the carbs they are burning).

At some point (usually around miles 18-22), the sugar reserves (called glycogen, and stored in the muscles and liver) are just depleted. If the body isn't used to burning fat for fuel, then it can cause a big crash--the dreaded wall. If your body is used to burning fat for fuel, then you shouldn't hit the wall; you have plenty of stored fat to get you through a marathon.

So, for me, this two-week test will hopefully help me to see what happens when I don't fuel my body with carbs and force it to rely on fat.

And since I'm expecting that my body primarily runs on carbs, in order to build up my endurance (aerobic system) in the most efficient way, I need to teach my body to burn more fat for fuel. There are several ways to do this, and nutrition is the most important one. Like I said, I can start adding back carbs after the two-week test, but I have to add them one at a time (each day) and keep in tune with my body as to how it reacts. I don't want to cause an inflammation response or to stress my body (the stress causes all sorts of problems as well).

I had a major lightbulb moment when I read about this, especially regarding overtraining and how stressful it is on your body. Overtraining can be super easy to do--running easy runs too hard (higher than MAF heart rate) or doing too much speed work, or just not letting your body recover from workouts--can cause serious stress.

When I trained for my 10K, I trained super hard for six months, and I ran the best race time I've ever had. Training very hard definitely works... temporarily. After that 10K, though, it's like my body totally crashed. I was burnt out from training, I gained 30 or so pounds very quickly, I developed depression that lasted 10 months, I developed chronic pain out of nowhere, and I just did not feel good at all.

While I was certainly doing well with running my easy runs at an easy pace (I used a heart rate monitor and did my MAF heart rate), and keeping my speed work to 20% of training, I was fueling my body with primarily carbs. So, my body was able to get through my workouts with no problem--I had lots of glycogen at the ready. However, there is no way I could run a marathon or even half marathon like that, because I would run out of fuel and crash (despite being super fit).

I suspect that all the problems I had after my 10K were related to the stress that the training had on my body. If I had truly focused on building my endurance the correct way (including nutrition), then perhaps I wouldn't have felt so terrible afterward.

When I start to add back carbs after the two-week test, there is a particular way to do it, which Dr. Maffetone describes, so that I'll continue to teach my body to burn fat for fuel and to develop my aerobic system by way of the MAF method.

I've written about it several times, but the MAF (maximum aerobic function) method is a way of building your endurance. You run with a heart rate monitor, keeping your heart rate under your personal MAF rate (there is a survey you can take on the MAF website and app to tell you your rate, which depends on a number of factors).

The way it works is that you train without ever going over your MAF rate (at least for several months), which may mean that you have to go SUPER slow or even walk for a while. Over time, though, you'll be able to run faster at that same heart rate. So, as you continue to train, your heart rate is always going to stay at MAF--but you will develop your aerobic system to be so efficient that you can easily run at a faster pace and it won't feel any harder than the first (very slow) workout. (During a marathon, you run--if I remember correctly--15 bpm over MAF. So, it'll only feel slightly harder than an easy pace, but you should never hit the wall and you should run a good race.)

As far as how long it takes to get to that point, it depends on how good your endurance is now. If your heart rate gets high really quickly, then you've got a lot of work ahead. MOST people, from reading all the comments from people who have done it, start out much slower than they want. It's frustrating to run so much slower than you're used to (or what you think you can, or should, be running). It feels like you're not doing any good for your body to go so slow!

So anyways, that's the explanation of the two-week test for carbohydrate intolerance and the MAF training. Since my next race goal isn't until May of 2021 (which I wrote about in yesterday's post), I have a long time to work on this method and see if it actually works! And unlike times in the past, I have the patience to do what it takes--even if it means walking most of my "runs" as I build endurance.

Once a month, you take a MAF run test to see if there is any improvement. I did my first one yesterday. After filling out the surveys, I was given 133 bpm as my MAF heart rate (which is a full 13 bpm lower than what I've been doing or the last three months!). I've been running slowly at 146 bpm, so I knew that dropping it to 133 bpm was going to mean that I'd be adding in walking.

I really don't like that I have to take 10 bpm off of the 180 formula (180 minus your age) for the simple fact that I take daily medication (for bipolar). But that's what the guidelines say, so I'm am putting faith in it for now.

My MAF test was to be as follows: 12 minute warm-up, where you gradually bring your heart rate up to MAF (he really stresses how important the warm-up and cool down are... something I never used to do). Then run two miles in the MAF range (123-133 bpm for me). Then a 12-minute cool down.

Jerry is doing this with me, so the two of us went to the local high school track yesterday morning. I chose the track because Dr. Maffetone suggests picking a consistent route (flat) that you can use for each test. A track is perfect for that.

It was FREEZING outside, and I definitely underdressed. I also didn't realize it would be so windy! Since I was going to keep my heart rate under 133 bpm, I knew I wasn't going to get much warmer. But I toughed it out. Jerry's test was slightly different from mine (he had to run one mile at his rate--141 bpm), so we didn't run side-by-side; just on the same track.

I started with a slow walk, and gradually picked it up over the 12 minute warm-up. My plan was to jog as slowly as possible (in order to run longer before having to walk) and then as soon as my heart rate hit 133 bpm, walk slowly until it dropped to 128 bpm. Then jog again. Over and over for the two miles of the test. Then for the cool down, do less and less jogging to get my heart rate back down slowly.

I completed the test without problems. I just had NO idea how much walking I'd have to do or how slow my "run" was going to have to be for two miles. (The goal is for my two-mile time to be faster at the same heart rate in a month.)

Here is what it looked like:

Warm-up: 12:00 minutes, 19:14/mile average pace, HR 121 average bpm
Two mile time: 32:11 minutes
Two mile average pace: 16:05/mi
Two mile average HR: 130 bpm
Cool down: 12:00 minutes, 17:17/mile average pace, HR 124 average bpm

As you can see, all those little spikes are the run/walk/run/walk to keep from going over 133 bpm.

I actually wasn't upset by these results at all. In the past, I would have pouted about how slow I had to go, that I had to walk, and then I'd just quit--saying it's ridiculous. But right now, I have lots of patience, and I truly am curious how all of this will play out. Maybe the training will work, maybe it won't... but it'll be interesting to give it a try.

I was only able to "run" for about 20-30 seconds at a time before my heart rate would reach 133 bpm. Then I'd walk for about 20 seconds or so until my heart rate was lower then 128 bpm. Then I'd jog again. Ideally, I'd keep my heart rate at 133 (or just under) for the entire two miles, but when walking/running, it's nearly impossible to keep a steady heart rate.

Once I'm able to jog the entire two miles without going over 133 bpm, then I'll hopefully be able to keep it steady. I suppose I could walk very fast (with no jogging) to keep my heart rate steady, but I was so desperate to warm up and the jogging actually felt better on my feet than the walking.

I wore my Altras, and because I was going to be jogging so slowly, I thought it'd be the perfect time to work on landing on the middle/balls of my feet instead of my heels. I learned what this felt like when I ran barefoot in the grass at cross country practice. When you run barefoot, you'll notice it's nearly impossible to land on your heels!

Based on these MAF results, my goal for February 1st is to see a faster two-mile time than 32:11. I'm looking forward to trying it! For now, I will run every other day: 12 minute warm-up, 30 minutes at MAF (133 bpm), 12 minute cool down.

Now as far as the nutrition part of yesterday--it was Day 1 of the carbohydrate intolerance test (Jerry is doing this with me as well). I was VERY surprised that I wasn't hungry all day. Carbs are my favorite foods, and I was sure I was going to starve without them. But Dr. Maffetone says to eat a lot of the approved foods during the test, because if you try to cut calories, it will stress your body.

We woke up late yesterday morning, after having a late night on New Year's Eve. We are supposed to eat within one hour of waking, so I got to work prepping veggies for scrambled eggs. I sliced mushrooms and chopped onions and green peppers. Then I scrambled some eggs (three for each of us) with the veggies and added some feta cheese, and that was breakfast.

I wasn't at all hungry for lunch since we ate breakfast at 10:00. For dinner, I had taco meat that I'd prepped the day before (ground sirloin with homemade taco seasoning) with lettuce, tomato, cheese, avocado, and sour cream. It was super filling.

For a snack later, I had some pistachios (in the shell, so that it would take me longer to eat them--otherwise, I could eat them by the handful!).

Notes about how I felt yesterday:

- I felt semi-full after breakfast (not stuffed, but certainly satisfied). Having breakfast and then running shortly after didn't cause any stomach upset.

- I felt fine during the run (other than being freezing)

- About an hour later, I had a headache. And it lasted ALL. DAY. LONG. I woke up this morning and I still have a headache.

- At around 2:00 pm, I completely crashed in energy. My whole body felt so sluggish! We went to the Apple store at the mall to get Eli's phone looked at, and walking around the mall felt so difficult. I just wanted to sit.

- I was very surprised at how easy it felt to get through the day without caving in and eating some sort of sugar or carbs. I wasn't tempted by the cookies at the mall or when the kids had some Christmas cookies at home. I don't think this is due to the diet, however; I think it's more to do with my determination to finish out the two weeks. When I get determined, I feel like nothing is going to stop me.

- Even though my body felt very tired, I wasn't ready to go to sleep until nearly 1:00 AM. I played a game with the kids, wrote in my journal, watched a show with Jerry, and just didn't feel sleepy. My body was tired but my mind wasn't.

- I woke up at 6:00 this morning and my head was hurting so badly I didn't want to try to sleep anymore. So, I didn't get much sleep last night.

- I ate the same breakfast (at 6:30 AM today) as I did yesterday. It's now 2:30 PM, and I'm still not hungry. We are going to have an early dinner, though, because Eli has his first lesson with the baseball coach tonight. For dinner, I plan to make chicken with homemade marinara and mozzarella/parmesan cheese. And saute├ęd Brussels sprouts to go with it.

- So far, I'm surprised to say, I don't hate this! (I could never do it forever, but I think I can handle it for two weeks)

Hopefully my updates won't be so long from now on. I just wanted to explain the whole two-week carbohydrate intolerance test before getting into the explanation of my first day.

Some links to Dr. Maffetone's website that explain things better than I can:

Two-Week Test (Nutrition/Diet) Explanation (There are at least a trillion comments, which someone who works for Dr. Maffetone replies to--I spent a lot of time reading them, and they were super helpful!)
MAF Training Explanations (this is the most beneficial read)
Aerobic Training Guidelines
Quick Explanation of the MAF Method Overall


  1. This is super interesting! I can't wait to hear how the rest of your two weeks go. This all makes sense though the way you lay it out. Excited to hear about the rest of your findings!

    1. Thank you! I can't even tell you how hards it's been the last couple of days. UGH!

  2. The headaches is a really common symptom of going low-carb. You might try searching for "keto flu" a for advice and upping your intake of water, salt, and potassium.

    1. This is exactly what I was going to say. Great advice.

    2. Thank you! I read about that, and it sounds very similar to what's going on. I hope it ends soon! Ugh.

  3. I do a carb detox similar to this a couple of times a year. It honestly really does help reset my diet; I don't have any issue not eating junk food when I'm out of the habit and I eat way more veggies to fill up when I'm not eating carbs and that becomes habit, at least for awhile. It can really work for a short while, for some people.

    1. That's exactly what I would love to see happen! I want a "reset" after eating so junky for a year. I know I can't fix everything in two weeks, but I'm hoping that it'll help, at least, while I come up with a long term plan.

  4. Stumbled across your blog, so I'm new. But your symptoms sound like the keto flu. Make sure you get plenty of salt (recommended amounts go up to 1-2tsp per day) and consider adding 300mg or more of magnesium bisglycinate. When you go low carb like you have and cook your own meals you end up with significantly less salt in your diet. A low carb diet lacking electrolytes will cause the headaches, contribute to poor sleep, and, in extreme cases of endurance athletes, rhabdomyolysis.

    1. Thank you for the advice! I was expecting some sort of "withdrawal" but this has been SO hard on me. I have absolutely zero energy, and I feel like I can't take it anymore!


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