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The 'Peter Attia' Approach to Dieting for Endurance Athletes - Part I

This post is the first of a two-part blog post written for TrainingPeaks.

I’ll start by declaring my bias from the outset. I’m a fan of Dr. Peter Attia. So I was flattered when asked by TrainingPeaks to write this blog post, and even more honored when Peter granted permission for me to take on the task. However, please note that while Peter’s fine with me trying to tackle the topic, it does not imply his endorsement of the approaches in this article. Herein begins a two-part blog post to try to do the topic of low carbohydrate/high fat dieting justice.

I first stumbled across Dr. Attia’s work during my own experimentation with lowering carbohydrates in my diet and when trying to understand the positive effects I observed it having on my blood pressure, fat oxidation and endurance performance, moving from a younger to an older Masters athlete. Like Stephen Phinney, Jeff Volek, and Tim Noakes, Peter has pioneered in the area, and has an extensive website that details his work at Peter is a physician, a researcher, former ultra-endurance swimmer and cycling time trialist who continues to forge new ground in the areas of health and longevity.

He has a super interesting background. A fellow Canadian, Peter took a different road towards developing his knowledge of exercise science than many of us in the field typically do. Peter is a self-confessed near high school dropout who was about to dedicate his life to the sport of boxing when a high school teacher inspired him to pursue undergraduate degrees in mathematics and engineering. Topping his class, he moved to Stanford medicine to complete his M.D., before becoming a surgical resident at The Johns Hopkins Hospital. Over time though Peter grew frustrated with certain challenges within the medical system, and eventually changed course to begin working privately. He shares some of the experiences that shaped his views today in this very moving 2013 TED talk, which has now over 2.4 million views.

So let’s try to answer the question that was posed: What might the 'Peter Attia' approach to dieting be for endurance athletes? While in the past he may have recommended diets such as Paleo, LCHF or ketogenic, his most recent podcasts on the topic suggest that he’s going much deeper than most of us have thought to do. In one podcast, Peter says: “I’m not a fan of religion or politics, and the area of nutrition and diet tends to be a bit like that… I don’t care if you’re Paleo, Vegan, South Beach or Atkins. I’m just interested in the biochemistry of these molecules in humans. One thing I’ve learned along the way is that different people can tolerate these molecules in different fractions. So to give a blanket recommendation, unfortunately, isn’t going to work for 100% of the people out there.”

And therein lies the challenge of writing the Peter Attia approach to dieting for endurance athletes. Peter’s developed an appreciation that we humans are all incredibly unique in how we function. In turn, like all good coaches out there, he appears to take a highly individualized approach to diet and the behavior modifications he recommends. In fact, he is an investor in a business that practices this for individuals with Type II diabetes, called Virta Health. If you can imagine being a patient of Dr. Attia’s, I’m guessing that the first thing he would do is learn as much as he could about you. He’d also be a good listener, interested in your goals. Like he’s done with his approach to longevity, my guess is that he’d try to reverse-engineer the performance aim in question, and discern how diet impacts that performance.

So let’s try to do that here. First, we need to specify some type of performance to optimize. Since most TrainingPeaks enthusiasts are long distance triathletes and cyclists, let’s narrow our target to an endurance-specific event we’re preparing for with a typical finishing time of between 4 and 5 hours, such as a half-Ironman triathlon or a GranFondo cycling event.

If we reverse-engineer such an event from an energetic process, we know that to complete it in the fastest time possible, we require high levels of sustained muscular output (power), with high economy or efficiency of that movement (including aerodynamics) also being important. There are other factors, of course, but those would be your ‘big rocks’. To accomplish this task well, we need energy for that power, and that energy comes predominantly from the burning of fuels (macronutrients) we store from our diet.

So let’s review the typical fuel reserves of the macronutrients we have on board:

As many of us are aware, our carbohydrate stores in the form of muscle and liver glycogen are relatively small when compared to our fat and protein levels. We don’t want to delve into our protein stores, and nor can we very well, as those are doing important things for us in terms of our make-up and functional skeletal muscle, so we’ll leave protein out of the picture for the moment. For argument’s sake, remember that we’re really just relying on energy from two main macronutrients when it comes to prolonged endurance performance; carbohydrates and fat. While there’s always a combination of both fuels burned in our muscle cells, there is remarkable variability in how much of each burns from one person to the next, for a variety of reasons. For example, we can see these levels as low as less than 0.2 g/min in recreational runners, and more than 7-fold higher at 1.5 g/min in fat-adapted runners. Fortunately, this is where diet comes to the party to make a big impact.

Back to the performance problem. We have a 4-5 h endurance event that we want to complete as quickly as possible. We know that every liter of oxygen that we take in and process gives us 5 kcal of energy. Take our middle-of-the-pack athlete, either the triathlete or cyclist in the above example, and let’s assume that they have a functional threshold power (FTP; 1 h time trial score) of 250W (proxy of lactate turnpoint). From experience, this is going to put their aerobic threshold (lactate threshold) somewhere around 200W. This aerobic threshold tends to be the exercise intensity that we can sustain for the 4-5 h duration. We can go higher into our capacity, towards or even above our FTP, but if we do, we’re ‘burning matches’, as they say, as well as our finite glycogen reserves. Continuing to calculate, if we use Best Bike Splits, we can see that 200W puts our typical athlete right around 34 km/h, getting in at about a 2:35 min mark for a 90km bike before venturing out on the half marathon run, or completing a 150km Granfondo event in about 4.5 h. Again, remember that we have less than 2000 or so kcal of energy from muscle and liver glycogen on board before we need to rely on carbohydrate ingestion.

If we consider that our athlete can burn around 1000 kcal in an hour at their FTP, it doesn’t take too long to see that if our effort is predominantly carbohydrate driven, we’ll have about 2 hours before our brains are going to tell us to lower exercise intensity back toward the level of our fat oxidation rate. Yes, we can push carbohydrates into our system up to rates as high as 90 g/h (theoretically 360 kcal/h), but this strategy doesn’t work for everyone, and is associated with a high incidence of gastrointestinal complaints.

Now that example is simply if we were to approach the problem from a ‘carb is king’ perspective. If we delve deeper, we learn that fat oxidation rates are of prime importance when it comes to endurance performance. For example, we showed in a cross-sectional study that fat oxidation rates were nearly three-fold greater in elite versus recreationally-trained runners, and that fat oxidation rates explained the high-intensity exercise performance difference between groups, with carbohydrate burning rates being equal.

So for the performance in question, Peter would tell us that it’s going to be all about fat-burning ability. The more we can make that 1000 kcal/h be done with fat burning, the more we’ll have on board to use for longer and later. Basically, this means that we’re programming our bodies to burn CHO as a last resort. Being able to access both, as needed, has been labeled ‘metabolic flexibility’. If you want to dive deeper into the weeds here, be sure to check out Peter’s blogs on the topic. Keeping it relatively simple, there are generally two ways we can affect our fat oxidation. We can simply train more, or we can lower dietary carbohydrate consumption to a certain level (more on this later). Both methods lower insulin levels and cause your muscle to burn more fat relative to carbohydrate.

Here’s an example from Hall et al. (2015) comparing fat oxidation (indirect calorimetry) in 13 highly-trained cyclists and triathletes when they were fed (CON), when they were overnight fasted (FAST) and 2 h after they trained (EXER). Granted these are one-off short-term effects in the same individuals on standard western diets, and the fat oxidation rates are pretty low for well-trained athletes, but it gives you an idea of how both diet and exercise impact fat burning. This is generally what we see. I know of many young athletes who train on high carbohydrate diets and have high fat oxidation rates. This comes back to the individualization issue that Dr. Attia professes. Some of us are going to have high levels of inherent metabolic flexibility, or appropriate levels of fat and carbohydrate burning for the performance in question, while others have what Peter has called, ‘inexcusable metabolic failure’, where athletes may have blood glucose and insulin at levels that ultimately are trapping stored triglyceride in adipose cells. For the latter situation, a dietary intervention can be a game changer.

So who needs a dietary intervention? How do we determine whether to do something about our diet or lifestyle from a performance standpoint? There are no doubt a number of signs, but a few simple observations could include: 1) an inability to get through a 3h bike ride without fuelling or needing to ‘pop a gel’ or take in a sports drink, 2) if you can’t get through your day without snacking often, or 3) having a waist circumference where your look in lycra indicates things could be better. Dr. Phil Maffetone and I term this condition ‘overfat’.

If you have experienced any of these conditions, following some of Peter’s suggestions might be worth a try.

Whether it’s fat oxidation for performance we’re interested in, or health and longevity, Peter will tell you that the name of the game is glucose disposal. Can you maintain a small daily average level of glucose, a low daily variance (minimal fluctuation) of glucose and a low area under the curve of insulin? To measure this, he wears a continuous blood glucose meter (CGM). His general daily targets for average blood glucose range from 91 to 93 mg/dL (5.0-5.2 mmol/L), with a variance or standard deviation of <10 mg/dL (0.5 mmol/L). While it would be ideal to measure the insulin response continuously, that technology is not yet available, so using a CGM is currently the most useful tool, as it can be used as a proxy measure for insulin; the primary regulator of your fat oxidation. It’s also very useful for understanding the non-dietary factors that affect your blood glucose, such as stress and sleep. We’re not all going to be fortunate enough to use a CGM, so alternatively a morning-fasted measurement is a good secondary marker to take.

My colleague, Dr. Dan Plews, and I have followed Peter’s lead here and we too wear CGMs from time to time in order to monitor the impact of exercise training, diet and lifestyle factors on our glucose levels. Here are a few examples detailing how glucose fluctuates in our lives and some of the lessons we’ve learned along the way.

In the first example below, I wore the CGM during a 3.5 h ride in the hills, accumulating an average normalized power of 218 W with an average heart rate of 144 bpm. The low warning on my CGM (red line bottom, lowest it can be set to) is 3.3 mmol/L (58 mg/dL), and as you can see, the alarm was going off just about non-stop, but I was feeling absolutely fine – just a normal easy ride – steady. A couple points to note from this graph:

  1. the low glucose (and proxy insulin) means that I’m signaling to my muscles to improve their fat oxidation in the future when they adapt, and

  2. there is no need to maintain high blood glucose levels during exercise, as we’ve been told in the past. In my particular situation, ketones and fat oxidation are easily meeting the requirements of this workout. It should also be mentioned that the ride was fasted, without any fueling and only drinking plain water (boring I know)

I’ll go more into why this type of fasted workout is important for fat oxidation, as well as more examples of glucose fluctuation in part two of my series on the “Peter Attia” approach to nutrition and training.

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