How to Train for a Marathon

Group of runners running on a street shown from the chest down wearing bright clothing and racing bibs.

As a former elite marathon competitor, I’m frequently asked how to train for a marathon in the healthiest way possible. Although I never intend to put my body through the rigors of marathon training again, I get the appeal. Running a marathon can be a huge bucket-list goal. Crossing the finish line is a major accomplishment. 

The time and physical demands of training also put tremendous stress on your body, not to mention your relationships and work/life balance. Endurance training simply isn’t conducive to optimal health and longevity.

That said, I promised myself that I wouldn’t try to dissuade people from running marathons or any long-distance races. I already do that plenty in other posts. So today’s post is geared toward the folks that simply are going to run a marathon—or half marathon or ultramarathon—regardless of what I say. The question at hand is:

How can I train for a marathon (or other endurance event) in the most Primal way possible, reaping the greatest benefit with the least amount of damage?

I wrote a whole book to answer that question. If you’re really serious about upholding the tenets of the Primal Blueprint while making necessary compromises to accommodate training, read Primal Endurance. Today’s post will touch on the big-picture issues and provide guidance on where to start. This isn’t about how to land on the podium (although truth be told, I could probably coach some of you to that goal). It’s about accomplishing something big, something special. It’s about training for a decent, respectable showing in a marathon. 

This post is about finishing the race without hurting yourself or burning out in the process. 

Priority #1: Become a Fat-burning Beast

To be an effective marathoner, you have to be an effective fat burnerAll of my advice around how to train, eat, sleep, and recover come back to the central goal of maximizing fat-adaptation. In other words, becoming as efficient as possible at burning fat for fuel at rest and while running. 

The stereotypical marathoner consumes massive amounts of carbs before, during, and after every run in an effort to stockpile as much energy (read: glucose and glycogen) as possible. But you don’t run a marathon on sugar. The beta-oxidation of fat, both dietary and stored body fat, provides much of the aerobic energy you will need to maintain a reasonable pace for 26.2 miles. I mean, 26.2 miles is a whole lot of miles. You aren’t sprinting that. When you’re driving somewhere that’s 26 miles away, you think, “That’s kinda close but kinda far.” Now picture that on foot. Yeah. Good luck doing that as a fully dependent sugar-burner. 

At that distance, fat’s the ticket. The more metabolically flexible you are—the better you are at deriving energy from fat, glucose, or ketones depending on the situation—the more successful you’ll be. With that in mind, besides training your body to remain upright and forward-moving for 26.2 miles, you’re also training your body to become more efficient with its energy. You’re actually reapportioning how your body uses various types of fuel at different activity levels. 

The Basics of Becoming a Fat-adapted Marathoner: Big Picture Stuff

Ultimately, training for a marathon comes down to three primary goals:

  1. Increase mitochondrial numbers and efficiency. Mitochondria are where fat, and some glucose, are converted into the ATP that cells use for energy. Improving the number and efficiency of your mitochondria will allow you to do more output (running) with less reliance on glucose and/or glycogen as a primary fuel.
  2. Increase the amount of fat you burn relative to carbs at any given work output. When marathoners “hit the wall,” it’s because they’ve severely depleted glycogen and are hypoglycemic. Muscle glycogen storage is very limited, so you want to dip into it as little as possible. The more fat you burn at any output (intensity) level, the slower your rate of glycogen depletion and the less you’ll need to fuel in real time with gels or other sugar bombs in an effort to forestall the bonk.
  3. Increase aerobic threshold. Without getting too technical here, aerobic threshold is the maximum level of output at which you’re still relying primarily on the aerobic, or oxidative, energy pathways. Fat burning is aerobic; it requires oxygen. Glycolysis (sugar burning) is anaerobic. Once you exceed the aerobic threshold, the cellular demand for glucose increases rapidly. Ideally, a prospective marathoner will train to increase their aerobic threshold so they can stay predominantly fat burning at higher intensities and speeds, and for longer.

Great, But How?

A lot of it comes down to the same stuff I believe everyone should be doing, marathon training or not: eat Primally, get enough sleep, manage stress, move a lot and mostly at a slow pace. Everyone who follows the tenets of the Primal Blueprint will upregulate their body’s ability to burn fat, free themselves from carb-dependency, and become metabolically flexible. 

But there are additional considerations and priorities when you commit to something as intensive as marathon training.

Keys to training for a marathon in the most Primal way possible

1. Make aerobic training the centerpiece of your training program

In short: slow down! The vast majority of your training, even during peak training phases, should be conducted below your aerobic threshold. The easiest way to determine your threshold is to use Phil Maffetone’s 180 minus age formula. It’s not perfect, but it’s good enough for the average athlete. Keep most of your runs easy enough that your heart rate doesn’t go over that number (140 beats per minute if you’re 40 years old, 130 beats per minute if you’re 50, etc.). 

Is it humbling to slow down enough to maintain that heart rate threshold? You bet. Will your running buddies give you a hard time about your slower pace? Probably. But if you’re diligent about it, you’ll rapidly train your body to run off fat. Soon, you’ll see your pace increase at that same low heart rate.

Strength training and high-intensity exercise also have a place in marathon training to promote overall fitness and build speed, but aerobic training should be your primary focus. 

2. Limit carb consumption

There isn’t one optimal eating pattern or macronutrient ratio that will work for all athletes. The overarching goal here is: eat only as many carbs as you need. 

You don’t have to go ultra-low-carb, although you certainly can. I’m all for endurance athletes incorporating periods of ketogenic eating, particularly during the off-season, to unlock a higher level of metabolic flexibility and supercharge fat burning. Keto is a top-notch strategy to achieve the three goals above, but it’s not required to become fat-adapted. Somewhere in the range of 75 to 150 grams or carbs per day—from Primal sources like sweet potatoes, in-season fruit, coconut products, nuts, and the like—is a good target for most people. During heavy training periods, you might bump it up a bit, but there’s no need to go much higher than that. 

It’s not that carbs are the enemy here, but excessive carb consumption prevents you from building that aerobic engine. By all means, use carbs strategically if you want. Fueling with carbs on race day—using a train low(carb), race high(carb) approach—means you’ll hit the starting line with a superpowered fat-burning engine to scaffold you throughout the race. On race day, any extra carbs you ingest act like rocket fuel. 

3. Prioritize recovery

I’ve coached a lot of athletes, and I can tell you that one of the biggest mistakes they make is failing to respect the need for recovery. Here’s a fun experiment: tell someone who’s facing down 26.2 miles to take days off from training or go for a walk instead of a run. Watch the anxiety break out. 

Rest and recovery practices like walking, gentle yoga, Pilates, stretching, and, yes, napping  are crucial to staying physically healthy and mentally balanced. They’re as much a part of training as the runs. I’m aware that most people training for a marathon are already struggling to squeeze in runs between work, family, and social obligations. But if you can’t find time to recover, that’s a red flag that marathon training doesn’t fit into your current lifestyle. 

4. Train intuitively

Primal Endurance contains a sample marathon training plan because I knew my readers would demand one, but I firmly believe that marathon training must be individualized and intuitive. These readily available one-size-fits-all training programs you find online are how most runners get themselves into trouble with injury and burnout. Daily training decisions should be based on how you’re feeling that day, respecting any fatigue, aches and pains, nagging injuries, mental load, and, importantly, motivation. 

That said, I know you still want me to provide you with some broad-stroke guidelines, so here goes nothing.

Marathon Training Plan

As with the 10 Primal Blueprint Laws, I’ll provide the framework, which I expect you to take and apply to your own life circumstances and goals. This is roughly how I’d structure a marathon training season. I strongly suggest that you pick up a copy of Primal Endurance to get the whole story on how and why.

Phase 1: Build your aerobic base

Spend at least 12 weeks during the off-season building your aerobic base. Run more days than not to get used to spending time on your feet unless you need the recovery. Occasionally swap a run for swimming, biking, hiking, or other easy activities for cross-training and interest. But do not—I repeat, do not—exceed a heart rate of 180 minus age during any of these activities. Invest in a heart rate monitor to keep you honest. 

Phase 2: Training for competition

Starting around 12 weeks before your race, you’ll start getting more structured with your training and introduce some higher-intensity efforts. 

A typical training week will include a mix of aerobic runs and intensity/interval sessions, with plenty of rest of course. My preferred method of adding intensity is to do brief speed intervals during a run where you pick up the pace and then return to your comfortable aerobic pace. Intensity sessions could also include tempo runs, fartleks, or even some sprints

Here’s the kicker: you’re only going to do three or four weeks of these higher-intensity blocks before you go back to aerobic-only running, as during the base building phase. The competition phase takes a periodized approach wherein you do several weeks of mixed training with more intensity, then several weeks where you back it off and focus on aerobic training, and repeat.  

This is when you’ll also test out your fueling strategies and figure out what to eat before and during your marathon. Do you feel and perform better when you supplement with carbs the night before or the morning of a long run? What about during the run? Do you want to start the race fasted or fed? These are all things to work out for yourself with trial and error and practice. 


Crush your goals!

Phase 3: Recovery

If you race continuously throughout the year, build in a mid-season break lasting six weeks or so where you significantly decrease your training load. Take two weeks off entirely, then ease back into aerobic training. 

If you’re a one-and-done marathoner, congratulations! You have time for hobbies again. 

Optional Phase 4: Periodized training

Leading up to additional races, repeat the cycles of three or four weeks of mixed-intensity training followed by an equal amount of time devoted to aerobic training only.

At the end of your season, take at least two weeks of total rest. Don’t run. Don’t think about running. Don’t sign up for another race. Sleep. Spend time with your family. Move your body in easy, gentle ways, but do not train. 

Well, that’s what I’ve got. Whew, I didn’t even mention the phrase “chronic cardio” once. I’m pretty proud of myself. 

Remember, this is just general advice for the wider public. If you were my client, I’d tailor the training to you, but you’re not. For what it’s worth, this is how I’d train myself were I crazy enough to get back into running marathons, because it’s effective, it’s low-cost, and it’s actually a fairly healthy way to go about training for one. 

Any runners out there? Any marathoners? How do you train? 

Thanks for reading.

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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