Metabolic efficiency test results: I’m a butter-burner!

Definitely not my most flattering photo

In the lead-up to the The North Face 50 Mile Championships in December, I was looking for any “edge” that could help me race to my potential and to offset some of the advantages that a comparably talented runner had over me, like more ultra racing experience and a training cycle longer than 6 weeks. Hence why I extrapolated a goal time based on my training, why I examined pacing data from past TNF50 races, and why I gave serious consideration to my clothing, footwear, and equipment selections.

Naturally, I also sought to find the optimal race day nutrition plan. Conventional wisdom for endurance sports lasting 2+ hours advocates consuming 240 calories per hour, mostly or exclusively from carbohydrates. This equates to one gram per minute, with each gram containing 4 calories. I saw this figure again and again: Ultrarunning Magazine, Runners World, Outside Online, elite ultra runners, and legends of the sport like Marshall Ulrich and Scott Jurek.

Shortly after I’d placed an order of Clif Shot Bloks and Clif Shot Gels — carbohydrate bombs that I expected to need during long training runs at a rate of, that’s right, 240 calories per hour — I received an email from Melissa Lott, a Minnesota-based kinesiologist who took a Backpacking Fundamentals course with me last year and who read my TNF50 training plan in which I’d cited this conventional wisdom.

Missy’s contention was not with the 240 calories/hour recommendation, but rather with the high-carbohydrate low-fat (HCLF) diet that would mandate this level of caloric consumption to sustain my energy level throughout the race, i.e. to avoid “bonking” or “hitting the wall.” The next day I received from her, Metabolic Efficiency Training, by Bob Seebohar. For an in-depth explanation of metabolic efficiency, read this earlier post. Basically, Seebohar argues that endurance athletes can train their bodies to rely more on fat stores for energy (rather than carbohydrates) through deliberate diet and exercise, reducing the need to ingest food calories during training and races.

Seebohar is not the only person making this case. See Dr. Jeff Volek and Dr. Stephen Phinney, Dr. Tim Noakes, Dr. Philip Maffetone, and personal trainer Ben Greenfield. Several ultra runners adhere or have tried to adhere to their suggested high-fat, low-carb (HFLC) diet. See Timothy Olson, Matthew Laye, and — my favorite — Jonathan Savage.

Generally, I’m skeptical of diets, e.g. Paleo, vegan, low carb, gluten-free, etc. Many sound too good to be true; benefits are anecdotal, individual-dependent, and/or “proven” by biased researchers; and for every diet out there, there is another that advocates the exact opposite. Besides, I’ve never followed a diet and my results have been pretty good over the years.

But I was intrigued by Seebohar’s argument. His scientific explanation seemed rational, and he had extensive lab data to support it. But perhaps more convincing, my experience in training sessions was very consistent with his predicted outcome for fat-adapted athletes:

  • I found that I could sustain my energy level on just 100-150 calories per hour, or 40-60 percent of the recommended amount.
  • I was having no GI distress and I was carrying astonishingly few calories for 25-35 mile training runs. And,
  • I had become much leaner than when my diet had been more carb-heavy.

Conveniently, Seebohar is a sports dietitian for eNRG Performance in Denver. I soon scheduled a metabolic efficiency test with his colleague, Dina Griffin, to learn exactly the state of my fat adaptions.

Test Overview

A metabolic efficiency test requires two pieces of equipment: a treadmill (or bike trainer) and a metabolic cart. The cart measures the volume of oxygen that I inhale relative to the volume of carbon dioxide that I exhale. Because different amounts of oxygen are used in metabolizing fats and carbohydrates, the cart can determine my ratio of carb- to fat-burning.

Before the test I purchased a heart rate monitor for my Suunto Ambit 2 watch, which I’d been wanting to do anyway. It’s not necessary for the test but it’s very beneficial since heart rate is a more reliable measure of effort than pace, which is notably impacted by current fitness, cumulative fatigue, vertical gain and loss, altitude, and pack weight.

Before I stepped onto the treadmill, Dina and I first discussed what I hoped to learn. With that understanding, we devised a test that would generated the needed data. We ran two tests:

1. Hiking test. I kept a steady walking pace of 3.o MPH, and every 4 minutes we increased the incline by 5 percent. We started at a 0.0 percent incline and increased to 5.0, 10.0 and finally 15.0. The test was 16 minutes long. I was not wearing a backpack.

2. Running test. I started at a pace of 5.5 MPH (a 10:54 minutes/mile pace), and every 4 minutes my pace increased by 0.5 MPH, with the last interval at 9.5 MPH (a 6:19 minutes/mile pace). We kept the incline at 1.0 percent. The test was 36 minutes long.

To reset the measurements between tests, I recovered by walking at 3.5 MPH for 4 minutes at a 1.0 percent grade.

Before sharing the test results, there is some important context I wish to share:

  • The test was done in a fasting state. It started at 8 AM, and I had not ingested any calories since dinner the night before. Also, no morning coffee.
  • I was as fit as I’d been in years, after backpacking all summer and running intensely all fall.
  • Even before learning about “metabolic efficiency,” my diet and exercise was consistent with metabolically efficient athletes. Amanda and I generally avoid processed goods and refined grains; all summer I had been running in the morning (on an empty stomach) to avoid the heat; and for 75+ days last year I was out backpacking, an activity that is precisely in the fat-burning cardio zone.

Hiking Test Results

At a normal hiking speed and on common gradients, I overwhelmingly burn fat stores for energy. Even while keeping a 3 MPH pace on a 15.0 percent grade — equivalent to climbing just over 4,000 vertical feet in an hour — three-quarters of my caloric expenditure was from fat. At that effort, I could hike for almost 12 hours before depleting the 2,000 calories of glycogen (carbs) stored in my muscles and liver, at which point I would finally need to start ingesting carbs in order to avoid bonking.


My energy use from fat and carbohydrate at the various hiking paces and grades for each stage. At all stages, I was burning a higher proportion of fat than carbohydrate.

I don’t have a clear explanation for why the fat/carb differential continued to narrow after 16 minutes even though the last interval (3.5 MPH at 1% incline) was less taxing than the two before it, as evidenced by my heart rate and perceived effort rating. Perhaps it was an emotional response to the breathing tube, or perhaps my body had not properly warmed up yet.

Dina sent my test results in an 18-page PDF full of tables, charts, and graphs. I won’t share them all, but I thought this one was worth sharing too:

Total calories that I burn per hour at each stage of intensity and the total contribution from carbohydrate and fat calories.

Notice the dramatic increases in my caloric burn (“oxidation”) as the incline increases. At a 15 percent grade, I burn 3x as many calories versus level terrain, almost 2x as many calories versus a 5% grade, and 30% more calories versus a 10% grade. This explains why I notice an uptick in my appetite on days with above-average vertical gain and loss — I’m working much harder to carry myself and my backpack up those climbs.

Running Test Results

Finally at 6:44 minute/mile pace and at a heart rate of 158 bpm, my body reach its “crossover point” — it began relying more on carbohydrates than body fat for energy. At slower paces, it relied predominantly on fat.

My energy use from fat and carbohydrate at the various running paces for each stage. Also shown is my heart rate and pace at my Metabolic Efficiency Point (MEP).

My energy use from fat and carbohydrate at the various running paces for each stage. Also shown is my heart rate and pace at my Metabolic Efficiency Point (MEP).

For context, my average heart rate during TNF50 was 142 bpm. At that effort, two-thirds of my energy is from fat. This explains why I did not bonk despite only consuming 100-150 calories per hour during the race and avoiding food entirely for the first 90 minutes. According to the data, I could actually have run for over 6 hours before depleting my glycogen stores and needing additional carbohydrates from food. At 142 bpm, I burn 318 carbohydrate calories per hour.

To further improve my metabolic efficiency — essentially, to push the crossover point to the right, perhaps even off the chart — I can work on my diet and/or my training. The chart below shows my optimal training zones to become more fat-adapted. My normal training pace is a bit faster — I’m usually mid-140’s bpm and 7:00-7:30 min/mile pace.

The green shaded boxes indicate the zones where my body is burning the most fat (based on the deltas between calories, carbohydrate and fat calories oxidized at each intensity). Spending a portion of my training at these heart rates or paces will help me develop better metabolic efficiency.

The green shaded boxes indicate the zones where my body is burning the most fat (based on the deltas between calories, carbohydrate and fat calories oxidized at each intensity). Spending a portion of my training at these heart rates or paces will help me develop better metabolic efficiency.

Implications of test results on hiking and running

The test results give me a baseline, inform my training and diet decisions, and/or validate my anecdotal experiences and past decisions.

On future backpacking trips, I plan to start carrying less food weight overall by carrying more high-fat foods. Fat is 2.4x as calorically dense as carbohydrates (240 cal/oz versus 100 cal/oz) and a high-fat diet will weigh less than a high-carb diet with the same number of calories. Importantly, my body does not need many carbs to sustain my energy while hiking since it relies primarily on fat stores at normal hiking paces and gradients. A backpacker who is less fat-adapted may have less success with this approach. Also, there is a limit to high-fat: I draw the line when I feel like I’m eating couscous olive oil soup, and I never will snack on sticks of butter.

For ultra running, the test results simply give me confidence. Confidence that I can legitimately ingest fewer calories during training sessions and races than conventional wisdom suggests I need. This reduces my risk of GI distress, which can can cost many hours and places, and sometimes even a finishing buckle. It also allows me to carry less food weight on training sessions and/or self-supported races.

Posted in on January 30, 2015


  1. Doug Nelson on January 31, 2015 at 8:11 am

    It sounds like you’re genetically predisposed to burn fat. Which is one reason you’ve grown up to enjoy hiking and running. I doubt you trained your body to burn fat. I suspect it has no choice in the matter.

    • Andrew Skurka on January 31, 2015 at 8:34 am

      Perhaps, but there is evidence that that you can train your body through diet and exercise, too. Seebohar has a few case studies in his book that demonstrate some notable changes. He also says that it’s predominately a function of diet, not exercise. A few recent one-person experiments by ultra runners (my favorite is Jonathan Savage’s) give validity to this — by ingesting a wickedly high-fat diet, they went into full ketosis.

      I suspect metabolic efficiency is like endurance sports in general: you can train your body up to a point, but eventually the limits of your DNA kick in. One of my assistant guides who is also an elite triathlete (age group 50-54), Alan Dixon, has been on a low-carb diet (Paleo) for several years and includes ample low-intensity efforts in his training, yet his metabolic efficiency test still shows a scary sugar burner.

      In my case, I think all the backpacking must have something to do with it, on top of genetic predisposition. I’ve spent tens of thousands of hours hiking (at a heart rate that is square in the optimal fat-burning zones) and my caloric output often exceeds the calories that I’m willing to carry with me. This amounts to a lot of “base training” that does not go away if I put down a few beers and slices.

      • Shawn Bearden on February 2, 2015 at 2:07 pm

        Andrew, I think you are doing a nice job of presenting a forum for the discussion of these topics that are of interest today. These discussions are going on in many forums but you are able to bring it to a specialized community and it is nice to see. Pressing the envelope of thought is what helps us advance. It is sometimes frustrating to see so much leap and lack of rigor throughout the exercise physiology community but we do our best. Glad to see you are dialing in what makes you feel comfortable. I have a little bit of feedback.

        “I could hike for almost 12 hours before depleting the 2,000 calories of glycogen (carbs) stored in my muscles and liver, at which point I would finally need to start ingesting carbs in order to avoid bonking.” This is what one would predict for someone fit and good BMI. But do note that the research shows that starting to ingest carbs at this point would be too late – you’d still bonk. Studies by Ed Coyle and many others (maybe while you were still in diapers) indicate that you must start ingesting carbs earlier, appreciably before depletion, to avoid the bonk.

        “Spending a portion of my training at these heart rates or paces will help me develop better metabolic efficiency.”
        At present, there are no rigorous data to support this approach. I know that it is a very hot topic these days. It seems that topics resurrect every so often, perhaps with the next generation of scientists after the previous have moved on. Regardless, studies through the 1990s by Brooks, Coggan, and others repeatedly demonstrated that high intensity training is highly effective at raising the ‘cross-over point’. Those two had some very exciting debates at conferences (and in print) about relative vs absolute shifts but that point is more subtle than the topic here. I understand that there are some labs currently studying the concept of training at lower intensities to raise this parameter – they’ll likely find what was found many times before, that it is not as effective as high intensity training.

        Note that Seebohar is not an established research scientist and, in my view, falls prey to the same demons that plague so many writing such books/plans/programs. Of course, some research scientists do as well. Finding and sometimes skewing (whether intentional or subconscious) a modicum of results, while ignoring or dismissing relevant data, to present a theory as if secret fact. You’ve given a very nice list of some of the biggest offenders. It would be wonderful to see some of that effort and energy going into a rigorous testing of the hypotheses.

        “A few recent one-person experiments by ultra runners …. give validity to this” See how much even the scientific minded want to reach and stretch anecdotes toward science?

        As for your results, they are very standard and in line with a good athlete. I hope that doesn’t burst any bubbles. I would happily place money on the wager that your numbers while a runner in college (before your lower intensity hiking training years) were similar, if not better. At present, there is no solid evidence to support the suggestion that the diet and exercise regimen you’ve had for the past years has done anything to produce these numbers.

        Ketotic diets do, indeed, work to change substrate utilization when adhered to rigorously. They are even a clinical treatment in a severe form of childhood epilepsy – though note that these patients are all being studied at rest, not during intense prolonged exercise. This is an area for which I hope there will be rigorous research in the coming years. We don’t have any such published studies yet. Those who push this issue will use a lot of distracting language, cherry picked anecdotes, or attacking approaches; but an unbiased analysis doesn’t bare out sufficient supportive evidence to recommend it. Unfortunately, such studies are difficult to conduct properly – longitudinal studies, with large enough n, etc. – make these expensive and time-consuming projects. And, there just isn’t sufficient funding to give to such studies when stacked up against research proposals on disease and the like.

    • Kevin Strauss on February 1, 2015 at 4:05 pm

      A person can absolutely train their body to be a fat burning machine and it can be done in 3 months time. I understand why you might think someone is genetically predisposed to being a fat burner but I suspect that is simply because most Americans are sugar burners and exercise incorrectly to change this. As an endurance athlete, coach and expedition backpacker, I fully understand this concept and try hard to educate people whenever possible.

      In addition, most people who suffer from hypoglycemia can also be retrained properly, in 3 months, to reverse this condition, in most cases. Unfortunately, most doctors and dieticians do not understand this.

      End bonking forever by training correctly to achieve the kind of results Andrew enjoys.
      Cheers, Kevin

      • Doug Nelson on February 2, 2015 at 9:25 pm

        This is simple survivorship bias. Since we don’t hear from obese couch potatoes that at age 40 failed to retrain their metabolism, only from those who “succeeded”, a false causation is promoted. But guess which group is larger?

        Some checking of genetic privilege is in order.

  2. Jim Dean on January 31, 2015 at 9:20 am

    Andrew, Given the progressive convergence of the fat and carbohydrate metabolic curves in the cool-down after the walking test (albeit at a faster pace so not a perfect control), have you considered that these short-time interval tests might not accurately reflect changes in metabolism your body may undergo during your endurance events that occur over hours? Did the testing involve any prolonged data collection at a fixed workload (rate and incline) to test for this? As a MD/PhD biochemist and outdoor enthusiast, love your rational scientific approach to your outdoor endeavours!!

    • Andrew Skurka on January 31, 2015 at 9:53 am

      For practical reasons the test can only be so long. I suppose they could hook me up to the metabolic cart for 12 hours, but frankly I don’t know if I would have the tolerance for that: as it was, I had drool coming down my chin at the end of an hour, and I was bored. Nonetheless, I think I know how metabolic efficiency will play out over time:

      In longer efforts, I’ve noticed “pace drift” even at a constant heart rate. For example, at the 1-hour mark, I can run 7:30 min/mile pace at 140 bpm, but at the 5-hour mark I can only run 8:00 min/mile pace at 140 bpm. If I tried to maintain the 7:30 min/mile at the 5-hour mark, my heart rate would have to be higher, and I would therefore be oxidizing a higher ratio of carbs than at the 1-hour mark. The same thing will happen with hiking: even though I was burning 75% fat while hiking at 3 MPH at a 15 percent incline, I’m sure that as I fatigued I would have to work harder and harder to keep that pace at that incline, and would therefore start oxidizing a higher ratio of carbs. Alternatively, if I wanted to stay at the 75% fat level, I’d have to decrease my effort, either by slowing down or reducing the incline or both.

      • Jim Dean on February 2, 2015 at 8:08 am

        One thing to keep in mind is that the lipid-carb metabolism is only part of the picture. If the assumptions of this testing are correct, when maintaining a fixed workload, your lipid-carb metabolic mix should reach equilibrium and not change over some reasonable period of time. The other part of the picture for longer time stretches (maybe 1 hour, maybe 5 hours?), is that other metabolic byproducts will also start to build up, such as lactic acid from anaerobic metabolism. These could definitely reduce power output (pace) for a given metabolic expenditure (heart rate)- even without changes in the lipid-carb mix. Definitely very complicated!

  3. Kolby on February 1, 2015 at 1:08 pm

    Everyone should be skeptical of diet claims, nutritional “science” and lifestyle advocates like Paleo. Yet there’s a lot of compelling data about high fat / low carb from sources without a financial stake. For example, the results of this study by National Institutes of Health:

    It’s also worth checking out “Why We Get Fat” by Gary Taubes, if you haven’t already.

    A higher fat, lower carb backpacking diet is something I’m aiming to figure out in 2015. As you progress, please share updates about the kinds of food choices you’re making and the subsequent savings in pack weight.

    • Dave on February 1, 2015 at 4:10 pm

      The only ones that seem to be rock-solid is when it comes to competitive results, like sports nutrition.

      Otherwise, nutritional science seems to be plagued by ideology. Even government-sponsored studies are a bit iffy like the reason for the high-carb, low-protein, low-fat diet is largely because of the study in Karelia when Finnish government was trying to figure out why people were dying of heart-attacks at a young age. After that, almost every government in the world adopted that policy.

      Then Swedish government began rejecting those studies once they found out that high-carbohydrate is linked to obesity and started pushing for low-carb, high-fat about a year ago as a national health policy.

  4. Brian Robinson on February 1, 2015 at 8:58 pm

    Your higher than expected carb-burn rate during the cool-down phase may help explain why going out too fast in a long race is a particularly hard mistake to correct. It may be that once the carb-burning machinery starts up, it doesn’t shut down easily or quickly. Thus a too-quick start leads to a sub-optimal carb to fat burn quotient when pace is reduced to what would otherwise be a sustainable one.

    • Andrew Skurka on February 1, 2015 at 9:09 pm

      When we shut the test down after a 4-min interval at 6:19 pace, I cooled down at the original 10:54 min/mile pace. I think it took me two minutes or so to recover enough that I began burning more fat than carbs again. Dina thought that was a fast recovery (I assume based on what else she sees) but that is a dramatic slowdown, very extreme for a mid-race correction.

  5. Andrew W on February 3, 2015 at 4:32 am

    Thanks, Andrew, for publishing your results. I’ve been pursuing a fat-burning regime for about a year, with modest results–nothing spectacular. At hiking paces I’m fine fat burning, but it could be that my genetics are against me for endurance performance at anything like race pace for you guys. (I was a sprinter in university.)

    Where I’m more intrigued is fueling expeditions. The pasta and potatoes diets of the outdoor adventurers (yourself included) have clearly achieved some amazing feats, but I seriously wonder what could be done with a cleaner diet? It would be great to carry even less weight.

    Shawn makes good points about the hurdles to a true scientific understanding of metabolic issues that are inherently complex and difficult to isolate. But where there are no drugs or treatments to sell, it’s hard to finance expensive studies. I would like to see the whole fitness community crowdsource some serious, long-term studies on precisely this subject, as the stakes (heart disease, lifelong health) are so high. Maffetone and the paleo crowd (along with Taubes) make compelling arguments, much of it based on statistically significant samples, but there is a true need for studies that are much larger.

    Keep us informed about how it goes.

  6. Trace on February 5, 2015 at 3:09 pm

    Great discussion …. learning a lot but lots to learn! Andrew or anyone have any links to any charts or data that might show some general or more common fat vs carb oxidation rates that might apply to those that are in “good” shape but not at a world class / competitive level of fitness that Andrew is at? Have always focused on lots of carbs, but sounds like it is time to experiment with more high fat food when backpacking …

  7. Deb on February 24, 2015 at 8:22 pm

    Andrew, just curious if knowing that you are a ‘fat burner’ would change how you fuel during an ultra race? Would you consider consuming fats in addition to carbs? Or continue the lower-than-advised level of carb intake that you’ve already been doing?

    • Andrew Skurka on February 24, 2015 at 10:11 pm

      Definitely at least the latter, i.e. ingesting less than recommended because I simply don’t need the conventional 240 cal/oz.

      Some fat in my ultra diet, especially in a very long ultra, would be reasonable. I can burn it, and it’d probably be easier for my body to burn than fat stores. But maybe Dina can say more on this topic.

  8. Russell Johnson on February 25, 2015 at 5:31 pm

    “On future backpacking trips, I plan to start carrying less food weight overall by carrying more high-fat foods. ”

    I’m interested to see some new recipes that might come out of this plan. I switched to a predominately Paleo-ish diet a few years back. I’m not a zealot (life’s too short to not enjoy pizza or burgers upon occasion), nor do I proselytize. But it works for me; I can both quantify (inches off the waist, bloodwork improvements) and qualify (I feel better in many dimensions).

    Other than my inability to sleep well on the trail, my biggest problem with multi-day trips is that traditional carb-heavy backpacking food makes me feel like crap; I’ll spare you some of the details. I’ve looked at a few “Paleo backpacking options,” but they are either impractical from a transportation and storage perspective, or they are absurdly expensive.

    I know you didn’t write that you were planning on taking more Paleo meals backpacking, but higher-fat, lower-carbs trends in that direction.

  9. Dallan on March 11, 2015 at 8:33 am

    I have always struggled with nutrition when running ultramarathons. Currently I’m experimenting with less carb intake before a run and more protein intake. I have read that higher protein intake helps your body to burn fat as opposed to carbs. When this happens having an upset stomach is less likely to happen.

  10. Dave on June 1, 2015 at 11:39 pm

    Just stumbled across a website today which might interest you, Andrew.

    Much of the LCHF I have been following comes from Sweden or Norway. It’s not much practical use for me to search for the information in English due to the amount of pages dedicated to the Atkins Diet or the Paleo Diet. It becomes too overwhelming to sort through what is myth and what is scientifcally studied.

    Today, there was a discussion about how going too low carb or going carb-free can be detrimental to one’s performance in running due to depleted glycogen and other topics of interests.

    Anyway, I recalled athletic elites in Sweden perform on a moderate amount of carbohydrates around 100 g, but needed a source to cite it. Found out it was a person named Jonas Bergqvist. He pioneered the concept of “exercise-liberal LCHF” or “training-liberal LCHF”.

    Unfortunately, his books are not in English. Google Translate seems to be decent on the webpages though.

    • Dave on June 1, 2015 at 11:45 pm

      Forgot to add, “training-liberal LCHF” advocates athletes need a bit more carbohydrates than the mainstream of about 100 to 200 g, whereas someone on an LCHF who isn’t an athlete would get by fine with 50 to 100 g.

      Of course, Jonas operate under the assumption the ratio of protein/fat/carbohydrate will remain the same, so one naturally gains more calories from the increased amount of protein and fats just to keep everything proportional. I forgot what the ratio he recommends though.

      But going by this rule, even if loosely, probably would make your meals more palatable rather than pure olive oil cyclists are known to chug down.

  11. Tim on August 31, 2015 at 3:15 pm

    Special diets are needed if you have a problem with certain foodstuffs.

    I had no problems until a few years ago, when I got intestinal distress, which worsened until about 6 months ago. I wasn’t overconsuming food, never had a BMI over 25, and had all sorts of inflammation symptoms. I eventually had to give up wheat and gluten foods.

    I worked out that the gluten, having destroyed my microvilli, also meant that I had lost much of the Diamine Oxidase enzyme that clears histamine out of my system. This meant that most evenings I would get bad inflammation, almost no matter what I ate.

    I had gone to my doctor several times, but was prescribed creams and things for ecsema, but had no effect whatsoever. My doctor eventually said I might have Coeliac disease after I said I decided to give up wheat and dairy as I could feel my transverse and descending colon – yeh that bad. These symptoms are all now slowly subsiding.

    One thing I have found that with my compromised DAO levels, I have too be very careful which fats I eat, as fats high in Omega-6 oils e.g. nuts, chocolate, sunflower oil push my body into inflammation. It might be that combined with high basal histamine levels they act as promoters of inflammation as well. Also these tended to cause circulation problems for me.

    Unfortunately at the moment my histamine metabolism is severely compromised, and so I read it could take 2 to 5 years for my gut to heal.

    Needing a gluten-free diet means no beers, no bread, except special ones, no pastries, no battered foods, no cereals, the list goes on, you get the idea.

    Sulphites and other chemicals can inhibit the DAO as well, which when you have limited amounts is the last thing you want, so all foods are not good. I’ve even given up tea/coffee as caffeine really doesn’t help.

    Even too much carbohydrate (sugary stuff) causes inflammation, and dairy and other foods such as cheese with high histamine content also cause problems. At the worst time, my temperature control was so bad I almost over heated one night after eating some cheese, which gets into epileptic fits if you aren’t careful, but I had worked out that I had to exercise around 1am for an hour to control the histamine levels, i.e. get as much oxygen through my blood as possible.

    I can do a 10k run in 46 mins, I can do 40 miles in 2 hours 40 mins on a bike, and I am coming up to 50 years old. Perhaps it is with a dropping testosterone level, that my body isn’t repairing itself so efficiently now, hence the gluten intolerance, and the damage to my gut. The year after next I am aiming for 40 minutes for a 10k run, and 37 minutes the year after.

    If your metabolism isn’t compromised in anyway, then you might be alright with every type of food, but, just so that you are aware, there are some of us that have to look at our foods very carefully.

    Paleo/high fat/low fat/high/low carb, etc doesn’t matter at all if you have to deal with a specific metabolic issue.

    It might be that your metabolism is very robust, but over the long-term, high Omega-6 vs Omega-3 levels could lead to inflammation issues with joints etc, and possibly heart related issues or circulation problems, and only certain beans, fish, fresh green vegetables can keep the ratio on the good side.

    I would certainly wish you well in your next adventure, but the oldest man in America puts his own long life down to eating fish and vegetables.

  12. Tim on September 4, 2015 at 3:59 pm

    Your comment about the weight of foods, and not being willing to carry less calorie dense foods is interesting.

    I always carry about a litre of water, but it depends how often you need to replenish your water and what supplies are available.

    Some foods when cooked e.g. beans, about 55% of their weight is water, the same is true of lentils, and you get slow release protein and carbohydrate, without fat clogging arteries, causing diabetes, slowing diffusion across membranes, because not only does fat clog arteries, it literally coats the whole of the inside of arteries and veins, blocking capillaries, slowing oxygen diffusion/nutrient diffusion, unless you are drip feeding little by little.

    Carbohydrates cooled after cooking, e.g. rice, potatoes, even lentils and beans, can form more complex carbohydrate structures which are slower to digest, giving a longer slow release of nutrients.

    There are loads of issues concerning food, not just the carbohydrate/fat/protein content, but how it is prepared, thus changing the release/digestion rate, and the base foods that you are working from.

    With back-packing, as long as you have a good supply of water you can’t beat rice+lentils or rice+beans, or quinoa, chia and some other dried foods as a solid nutritional base. You can throw in a few nuts and other things that will also have their digestion slowed with the fibre present in beans/lentils.

    But with all this, if you don’t want to carry foods that need to be cooked, thus requiring a small camping cooking stove and a cooking can, you limit your options.

    These foods actually lend themselves well to being cooked for breakfast, and split in half or thirds, where cooking is only done at breakfast, or only in the evening, but cooking at breakfast does mean a shorter storage time if ambient temperatures are higher.

  13. Scott on October 19, 2015 at 7:20 pm

    Andrew, did you get a lactate test done as well? I’m looking to get either metabolic efficiency and/or a lactate test done and trying to figure out what makes the most sense. Thanks!

    • Andrew Skurka on October 19, 2015 at 9:30 pm

      I only got the ME test done.

  14. SteveL on December 16, 2015 at 11:30 am

    To make your into a fat burner look up the Maffetone web site and check out his two week carbohydrate test diet. It turned me from a carb burner to a fat burner and all my allergy symptoms disappeared from no longer having adrenal gland fatigue due to to many carbs.

  15. Timothy Naylor on May 8, 2016 at 7:51 pm

    Andrew, this is absolutely fascinating to me as I am currently in that 3 month period of conversion to a fat burner. I agree that I think you have arrived here because of lots of long slow cardio (slow being a relative term, but hiking at a high pace keeps you right in the fat burning zone) with minimal food, which is probably why when you present on food, you recommend 1.5lbs…you burn your fat stores very efficiently. My question is do you have any specific adjustments you have already tried to your backpacking food list. I have tried most of your recipes but I am wondering how to trade some carbs for fat. I am looking at several fat bomb options for my snack bags throughout the day, which have far more calories in less weight. I am also planning to add fat (coconut oil) to my dinners. Just wondering if you have any more Fat adaptive recipes to bestow upon us. Thanks for all the amazing information you have collected here.

    • Andrew Skurka on May 8, 2016 at 8:28 pm

      For dinners, add more oil and cheese (certain kinds are better than others) and decrease the amount of carbs. Personally, I like olive oil as a fat, as coconut oil is too, well, coconut-tasting.

      During the day, I simply try to stay away from high-carb items, e.g. Clif bars. But I don’t give it too much thought — while on a trip I mostly eat what I want to eat, and I don’t seem to ever bonk, and I always lose weight.

  16. Tanel on July 6, 2016 at 8:40 am

    I suggest you to read Christopher McDougall books “Born to Run” and “Natural born Heroes”. In these books are a lot about fat burning.

  17. scotty on April 25, 2017 at 11:15 pm

    Hey Andrew,

    A while back I downloaded your Food Guide. I’ve since been following a LCHF diet with similar results as you’ve noted. I’m curious if you had ideas of how to adapt some of your recipes. I’m also mostly veggie, but do eat fish, eggs and dairy. Its my goal to have a stash of meals ready to go to reduce my pre-trip anxiety. Any other resources anyone could suggest would be much appreciated.

    PS Refined coconut oil has a very neutral flavor and is very shelf stable at room temps.

    • Andrew Skurka on April 26, 2017 at 10:01 pm

      On a backpacking trip I tend not to worry about carbs, and I can’t say it has made a difference in how I feel or in my energy level.

      If you want to reduce the carbs in these meals, then simply adjust the ratios. More olive oil, less rice. More vegetables, less potatoes. Etc.

  18. Bryan Ausinheiler on June 19, 2018 at 12:34 pm

    Thanks for sharing your data! I would be curious to see how your fat intake tolerance varies according to the type of food. I can only add a max of 1/2c of olive oil to a meal before I run the risk of puking. Maybe its the tannins? But I can eat 1,500kcal of the following mix in one sitting without issue:

    Mix a 16oz jar of salted almond butter with a 16oz jar of filtered coconut oil and an 8oz jar of ghee. You get 8954kcal, at 221kcal/oz and $2.02/1,000kcal. All the ingredients are at trader joes. Its delicious, shelf stable and full of medium chain triglycerides.

    Give it a try and let me know what you think!

  19. Kevin aka “Lucky Strike” on January 22, 2019 at 9:24 pm

    I too have migrated towards more fats, especially those high in Omega 3 as they have less toxins. Have you tired Ghee vs butter? It has the MCT, Omega 3 benefits of butter without the casein and milk solids. Plus, it is shelf stable and ideal for longer resupplies.

    It took me quite a bit of trial and error to find out how many ounces of fats I can digest comfortably, and also the best foods to pair with fats. For me, that meant eating more fats from seeds (sunflower, pumpkin kernels, chia seeds and hemp hearts) and nuts (raw walnuts and cashews) with rolled oats or muesli with dried coconut, dates and dried berries (blueberry, strawberry, goji berry) in the mornings. If I pair my fats like this in the am, I’m able to consume about 3-4 ounces of pure fats which sustains the bulk of my daily calories. I also rarely eat first thing. I like to hydrate for two hour with various herbs, mushroom powders and electrolytes. I usually don’t eat until two hours into my hike.

    I transitioned my fat sources to ghee, MCT oil, avocado oil (fresh avocados near towns) and olive oil in the evenings and paired these fats with starches like rice ramen, potato flakes, dried beans and dried rice. I can comfortably eat 2 ounces of pure fats when paired with starches in my evening meal. These starchy carbs helped me fall asleep easier and the fats helped keep me warmer on colder nights.

    Overall my food carriy weight has decreased about 25-30% since carrying more fat based calories. I’ve also weaned off the freeze dried meals and now eat more fresh, enzymatic dense food on Trail. I loved my Trail food so much it is also what I eat off Trail most days.

  20. Alex Wright on October 23, 2021 at 9:20 am

    Regarding the graph with the green shaded boxes – were the total calories listed (633, 696, etc.) burned within the timeframe listed in the “time” row (22:00, 24:00, etc) or are they a calculation of calories per hour?

  21. Brock W on June 12, 2022 at 12:29 pm

    I got a VO2 test yesterday. Surprisingly not that expensive. I went to Dexafit in Tempe.
    Lots of interesting data. Puts my estimated fat/carb crossover at around 140 bpm. But I’m a few years older and far less trained than you, Andrew. So it’s to be expected.

    I have some room for improvement and this will help me dial in my exercise routine.

Leave a Comment