CrossFit Training: How to Lose Fat with Primal

Inline_CrossFit_and_Fat_LossNote: Many of you have written to me wondering about my newfound obsession with CrossFit. I’m responding to a steady stream of requests from CFers who want to do Primal but have been led to believe that the two are incompatible. Even if you have no interest in CrossFit, understand that much of the advice contained in this series also applies to people following a different training path.

As much as CrossFitters claim to concern themselves primarily with increasing physical performance and work capacity across broad modal domains, they also want to lose body fat. There’s nothing wrong or superficial about that, mind you. Excess body fat is unnecessary and, depending on the quantity and location, dangerous to your long-term health. It also impedes performance, acting as dead weight. We have every reason to want to lose body fat.

CrossFit is well-known for leaning people out. But there’s also a small but significant portion of people who struggle to lose body fat despite—or perhaps because of—hitting the box religiously and doing all the workouts. This post is for them.

What about Carb Intake? How Much and When?

Many people ask, “I’m CrossFitting. Should I go low-carb or high-carb to lose body fat?” My answer is “yes.”

You heard me right. You should do both. As I explained in a previous post, CrossFitters require carbs. How many depends on their level of fat adaptation, the intensity with which they train, the training volume they accrue, and other factors, but the fact remains that CF workouts are very glycogen-demanding. If you want to maintain and increase performance, you need to refuel that glycogen, and starchy carbohydrates are the best way to do it. Revisit the carb/CF post to get some ideas on good Primal sources of starch.

But it’s not just about recovery. Eating the carbs you earn can actually enhance fat loss. Here’s how:

If you engage in glycogen-depleting activity, your body will want to replenish the glycogen. You can do so by either eating the glucose directly or making it.

If you burn carbs and don’t replenish them, you’ll trigger a stress response to initiate gluconeogenesis (the creation of new glucose). This means cortisol goes up.

If cortisol goes up and stays up, you’ll lose lean mass (to provide amino acids to convert into glucose) and retain/gain body fat.

In most people, consistent low carb will help you lose weight, but the glucose demanded by CrossFit will trigger muscle loss and fat gain if the demand goes unmet.

But on rest days, where you’re not expending much glycogen, there’s no good reason to “carb up.” On the contrary, you want to keep insulin low to promote fat-burning. That means low-carb.

  • On training days, eat higher carb and lower fat with plenty of protein, with the bulk of the carbs taken in and around your training session.
  • On rest days, eat low-carb, higher-fat, and plenty of protein.

What about Calories? They Matter, Right?

Calories matter, sure.

Most people fail with carefully-curated calorie intakes. Counting calories seems to work a bit better if you’re training regularly, eating high quality, nutrient dense food that doesn’t interfere with satiation mechanisms, and eating plenty of protein. But even then, I’m skeptical. It’s just too much work for too little gain for most people, and there’s a good chance it fails. I find it far more effective to let your body control its own calorie intake.

That’s where the oscillation between high-carbs on training days and low-carbs on rest days shines:

Low carb rest days will almost certainly be reduced calorie thanks to well-established greater satiation on high-fat/low-carb diets. Training days become high calorie because you’re hungrier and you’re eating more carbs. This creates an organic fractal pattern of calorie intake, an oscillating schedule of deficit and excess, which allows both fat loss and performance gains. Studies show that intermittent calorie reduction in this manner is more effective for fat loss and lean mass retention than chronic calorie reduction.

Switch between low-carb on rest days and higher-carb on training days.  You’re naturally hungry after all that exercise, so you eat more on training days. You’re not as hungry eating fewer carbs and keeping intensity low, so you eat less on rest days. It just happens.

I anticipate some questions about what “higher carb” means in terms of grams. The answer is, it depends. It depends on your own genetic predisposition, how many days a week you’re at the gym, your gender (men tend to burn through glycogen faster then women) and your other mitigating lifestyle factors. With that qualifier in mind, my thought is pick a starting place that makes sense to you, say 150-200 grams on your training days, and see if your level of activity/glycogen depletion supports it. On rest days, if you stick to keeping your carbs to non-startchy veggies, then you are likely in good shape.

What about Nutrient Timing?

While I wouldn’t worry about nutrient timing to the point of inducing a panic attack if you get hungry at the wrong time, eating the bulk of your carbohydrates shortly after an intense training session offers several advantages:

Glycogen depletion is local. The muscles you use are the muscles that lose glycogen. Since CrossFit workouts tend to target the entire body, you’ll create a large glycogen debt that can be safely repaid.

You can take advantage of a process called non-insulin dependent glucose uptake. This allows your muscles to gobble up glycogen without needing insulin to do it. The more intense your training, the greater the effect.

Exercise increases insulin sensitivity, meaning you need less insulin to get the same effect (glycogen repletion). Your muscles are insulin-sensitive after a WOD, particularly the ones you used. Since insulin impedes fat burning, less insulin means fat burning goes up. Here are some other ways to increase insulin sensitivity, by the way.

These post-exercise enhancements to glycogen repletion last for about three hours on average, so you don’t have to rush.

You have even more time to eat protein and take advantage of enhanced muscle protein synthesis following a workout. Four hours after a heavy training session, muscle protein synthesis is elevated by 50%. At 24 hours post-workout, it’s up by 109%. At 36 hours is when it begins returning to baseline. For all intents and purposes, protein timing isn’t all that important. Just make sure you eat it.

Men and women may want to consider the following study done for the BBC last year, where Dr. Adam Collins placed men and women on different meal/workout timing protocols to see how they’d affect the fat-burning ability of both genders. For four weeks, participants took part in three weekly Zumba sessions (yeah, yeah, far from CrossFit) and either received a carb-rich drink pre- or post-workout. Women who ate carbs before training burned more fat, while men who ate before burned less. Men who went into the workout on an empty stomach and ate carbs after burned more body fat, while women who ate after burned less.

Though the short study didn’t note any differences in body weight or waist circumference, it presages a difference between how men and women respond to meal timing that could affect fat loss over the long haul. This jibes with my experience. I’ve always done well training on an empty stomach. Though I’m not exactly interested in losing body fat, I am interested in burning more fat—while the women I’ve worked with and consulted over the years function better when they eat prior to workouts. There are exceptions to everything, of course, but that’s the trend.

The Other Stuff

Primal truly shines in its dedication to all the “other stuff”—the lifestyle variables that play massive roles in our health, happiness, and fitness. Though fat loss depends mostly on diet, some of these other variables can impact fat loss.

Stress and Sleep

I include these as a pair because they form a vicious circle of metabolic derangement. Bad sleep can increase stress, which can affect your sleep. And on and on it goes.

We know from observational research that people who sleep the least and report feeling the most stress lose the least amount of weight.

Poor sleep makes junk food more enticing. It literally makes your hypothalamus respond more enthusiastically to the sight of the food you know you shouldn’t be eating. Some people are “stress eaters,” eating the sugariest, saltiest snack they can find to dampen the stress of everyday life. The thing about CrossFit is that you can probably “get away” with more junk and not gain much at all, but you’ll definitely lose fat more slowly.

A bad night’s sleep also impairs insulin sensitivity across multiple metabolic pathways, making you less tolerant of carbs and requiring more insulin to do the job.

Chronic stress is a notorious promoter of chronic cortisol, which can promote belly fat gain and make losing body fat extra difficult.

It’s absolutely imperative that any CrossFitter intersted in losing body fat optimize their sleep hygiene and get a handle on their stress levels. That could mean going to bed before 10 PM, wearing weird-looking orange goggles at night, or moving from the 5 AM class to the 6:30 AM class. It might mean finally trying meditation, doing regular float tanks, or spending more time in nature. I’ve written a ton on both sleep and stress, so check out the recommendations in those posts for more ideas.


Walking might feel like a waste of time. What’s the point of spending time doing something 95% of the planet can perform when you could be squatting, snatching, or doing box jumps?

Long, frequent walks in an energy-restricted state (as you should be on rest days) are one of the better tools for easy (but not quick) fat loss. At that level of intensity and volume, you’re running on pure body fat.

On rest days, don’t just binge Netflix shows. Get up and move around. Walk. Hike. You could even go for a long leisurely bike ride or do some really light rowing for long distances. The key is going at a pace you can maintain indefinitely.

That’s it for today. That’ll get you a big part of the way toward losing body fat. If anyone has any questions about the topic, go ahead and leave a comment.

Thanks for reading, everyone. Take care.

This article was co-written with Laura Rupsis, Level 1 CrossFit Certified, Primal Health Coach Certified, and owner of Absolution CrossFit in La Grange, IL.

TAGS:  body fat

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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36 thoughts on “CrossFit Training: How to Lose Fat with Primal”

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  1. I really think you should talk to some Eastern Europeans about this. You will find that many of them (the men in particular, especially the ones who were still required to join the Army back in the Communist days, so they’d be about 70 now)… are not what you’d call beefcake, but their physical strength will shock you like watching Superman. I’m really not exaggerating. I hired some of them when I was moving. Two of them were twice as strong as six college age men and women who were helping also. I base this on a particularly heavy piece of furniture that they lifted like it was made of balsa wood. Six of us had moved it about a foot.

    I would describe them both as “lanky” or “wiry.” We had a long talk about strength. I don’t think it’s fully true that muscle loss is always bad. Maybe the body can make smaller but stronger muscles and we just don’t know it scientifically yet. Take a look at gymnasts. You don’t find many bulky gymnasts, but their strength is amazing. Anyway they described having to work for days on end while eating diets that weren’t good at all. The meat they were given was often too rancid so they’d end up eating what they could find, often at risk of punishment for nothing more than wanting food.

    There is something to be said for demanding that your body make efficient muscles. But I am sure it wasn’t a pleasant process. They did it that way only because they had to. But I do wish we’d learn something from it instead of turn away from what they discovered.

    1. On a related, point, it would be good to get some discussion of which hereditary backgrounds tend to do better with lower vs higher carbs. I’m reminded of this because of Charles Poliquin’s mantra about “don’t eat a diet that’s wrong for your genetics” , and I remember one of his comments being that eastern europeans may not do well at very low carb intakes…

    2. Old man strength is a real thing. I saw an old man lift an engine block out of a car by himself. The thing must have weighed 300lbs and he was leaning over the hood.

      I think people that are incredibly strong for their size is about having a higher muscle activation. Say the average lifter can tap into 50% of their available strength an Olympic athlete or gymnast might be able to tap into 90%.

      I don’t know, would love to hear Mark do a write up.

    3. Hi, Meriel. Your observations of the eastern Europeans are very careful. I have similar experiences. I think there is an important factor – muscle explosive, which is the key to the performance of power. Thanks for the discussion, and I learned a lot from it.

  2. Though I am still refining my eating strategy the above information is accurate. On a day where my training consists of dead lifts and farmers carries coupled with some ring work my body will let me know that a greater portion of sweet potato and banana are required simply to replenish what I have exhausted. On days where I am biking or hitting the fitness stations at the state park I simply do not experience the intuitive desire for starchy carb sources.

    I have mentioned before that I chronically under eat starchy carbs on heavy training days. Through a bit of experimentation, education and simply listening to my body I have found that eating commensurate to my physical and mental output is critical. It is certainly a process and may require a foray out of our comfort zones but has the potential to pay huge dividends.

    Keep reading, keep training, keep adjusting your diet and keep moving forward.

  3. One of your best articles. I just like to add that hormonal balance (thyroid, sex hormones) are as important as adequate sleep and management of cortisol level. When out of sync, they hinder fat loss and encourage over eating. Except that over eating doesn’t necessarily mean reaching for junk food like you said. One can also overdose on whole nuts and nut butter..

  4. When it comes to crossfit, fat is baggage. It weighs you down, it holds you back. It’s purpose built for long term energy… for the harsh winters of our early ancestors… for times of famine. Been eating primal since my mid thirties. My profile pic defies my modesty, but a picture CAN speak a thousand words… Show them, don’t tell them (unless they ask of course?)… current age — plus 40. Definitively crossfitting my best years yet!

      1. You might be right… my comment was a bit egocentric. I generally strive to contribute something of value… my message fell short.

        That being said, I believe that it’s important for others to know that they can shape their lives to live their best years right now. I know this sounds cliche but Mark’s Friday Success Stories exemplify this. Regardless of age, you are the architect of your life… of your experience, and I for one am convinced that ancestral living is key to unlocking the strongest, healthiest and happiest version of ourselves.

        1. In a totally respectful way, I’d like to know what you think of the strength of strongmen who are not at all low body fat and their ethic says not to be because you lose strength. I think it’s sad we no longer see them much on TV because it was also an inspiration, even if it was exploitative of poor kids by offering prizes out of poverty. Watch someone tow a bus uphill and ask yourself… is it reasonable to whine about PE class? Obviously the human body can do much more than we think.

          1. I tend to agree with you… especially for Stongmen! My favorite Strongmen of all time though would have to be zero body fat Pudz and crazy Kaz!! Admittedly, I don’t know the new guys of the sport bc we haven’t had cable in years.

            If it’s strength you’re after, I’d say to stay in a bit a calorie surplus… let your body know that energy is plentiful and available so resources can be allocated to things like fertility, strength, performance and muscle building (aka hormones).

            If it’s crossfit you’re after, strength sits on an island all by itself… strength is fundamental and basic to life… nothing in nature survives without it. However, one must figure out how to become stronger, get good at olympic lifting, get good at gymnastics, get good at all skills, get good at capacity work and be great at being well-rounded… true strength comes from the mind.

            This is a personal journey that is very different for everyone… figuring out how to consistently become better is half the fun. Increased body fat can be valuable to those that are trying to increase strength in the off season but when it comes time for crossfit competition, you better be lean, well rounded and ready for battle.

  5. By the way, I so happened to watch some of Dr Eric Berg lectures on the causes of belly fat earlier today (YouTube)…. I highly recommend watching them, as they nicely illustrate what Mark wrote 🙂

  6. Excellent advice here whether you do Cross Fit or not. Totally agree that counting calories is way too much work, but keeping a more general food diary can be helpful with any type of health related goal. You don’t need to weigh or measure, just take note of when and what you are eating, what physical activity you have done, and how you feel. I find this really helpful if I ever feel like I am getting off track. Which thankfully happens less and less!

  7. Wow! This clears up several questions I have had for a long time about pre-/post-workout eating, nutrient intake post-workout, etc. I am not into CF (yet) but I am still loving these posts. Thanks Mark!

  8. I am experiencing the opposite, gaining weight while eating paleo and doing cf 4 – 5 times per week. In the days off from CF I am doing cardio, running. I also started doing IF to shorten the eating window and eat less calories. I am not a hard core cf arhlet, just your average 44 year old mom doing cf to stay fit and build a little bit of muscles. I work out at 6am in the morning and will not eat until 11am or so. I drink BCAA pre and post work out. What are your thoughts on that? Do I need to replenish by eating sooner? I feel fine but am I loosing muscle mass doing IF?

    1. Your regimen sounds pretty hard-core to me. Your body could be trying to store fat to protect itself from the exercise and eating extremes you’re inflicting on it, even while it’s consuming muscle mass for fuel. Pay attention to what it’s telling you! Try increasing healthy carbs and calories in general, and scale back the exercise routine. What you’re doing is obviously detrimental.

    2. The other possibility is that you are gaining muscle. I don’t know what you are eating, so hard to say whether you are undereating, which could lead to a stress response and storage of body fat.
      What is your opinion? Are you gaining muscle or fat?

    3. Assuming weight gain is not your goal (and even if, perhaps, it is), I agree with Shary. It sounds like a stress/recovery issue — that’s a lot of volume, probably, too much volume combined with IF. Why not add some carbs pre- and post-workout and see what happens?

    4. I agree with the rest. Sounds like a schedule that will lead to over training, which will slow fat loss and increase risk of injury. However, you could just be packing the muscle on. I surf every day and then do about one or two sessions of planking and one 15 minute HIIT session on my spinner bike – per week- just to keep the legs and core in shape. And surfing is pretty easy compared to CF. It’s mostly treading water, and moderate paddling punctuated by shorts burst of sprint paddling and riding the wave. Even then, when the waves are pumping you feel it catching up to you after 4 or five days of good surf. If it was pumping all the time, my biddies would probably just have to skip some days. So for you, with CF five days a week plus cardio on days off, it’s like having pumping surf constantly – and that can’t be sustained.

    5. Thanks peeps! I have gained muscle mass but I can’t seem to loose the muffin top that I have gained the past few years and my thighs have gotten bigger. Partly due to muscles, of course but my inner thighs did not use to be this size. By gaining muscle mass I mean arms, back shoulders, legs, but like I mentioned, the abfat has increased. I will try to play around with carbs, but like many people, I want fast results ?.

      1. Marie,I don’t have the answer but I’m in the same boat. I lost 13 pounds four years ago going primal (55 year old woman). I was exercising the standard 150 minutes a week. Last summer I increased my exercise (walking, cycling, gardening) to 5 to 6 hours a week – gained weight. Lost all but 2 in the winter when my exercise level went down. This summer back up to 5 to 6 hours a week and up 6 more pounds. While a couple of pounds night have been muscle, this is not. Could this kind of exercise really be stressing my body? I hate to give up the exercise since I have a desk job all week, but I don’t think I can gain 5 or 6 pounds every year either.

        Interesting note that women should eat carbs before a workout. I’m going to try the eating carbs before and low carbing it on rest days and see how it goes.

        1. That is the thing! Moving, aka, exercising makes me feel good! If I don’t exercise I don’t feel well, physically or mentally. Eating carbs before workout would be tough for me since I do all my workouts in the morning 5.30am or 6am. The body is a tricky thing.

  9. I think we often view recovery days as nothing more than “netflix and chill” days instead of still being physically active at a low capacity. I’m happy it was brought up.

  10. Brilliant article, Mark and Laura. However the Cx-fitters I knew were not interested in low carb in the least. Couldn’t even get them interested in a conversation about it.

  11. Mark probably addressed this in an earlier CF post (I know he has written quite a bit about this subject) but IF is another tool in the toolbox to aid in fat reduction, allowing you to consume more calories than a calorie restricted diet yet yield many of the same benefits. I eat two large meals, one at about noon and one at about 8 PM, both with lots of veggies, fish and/or fowl, bone broth, berries, nuts, some oils. At about 4 PM I eat a couple of pieces of dark chocolate and have a protein drink with greens and other stuff … works out pretty well for me.

  12. If it helps, I lost 35 pounds this past year and a half doing crossfit (heavily scaled) and eating primal about 80% of the time, and still included beer.

  13. Thanks for writing this series, Mark. I, for one, fell into the trap of under eating carbs while crossfitting ~4x per week and experienced some of the symptoms you described (poor sleep, poor recovery, elevated cortisol, fat gain, etc). I’m currently in the midst of a 2 month break from crossfit, but am now armed with a better eating plan when I return in the fall.

    1. I’m glad you’re enjoying the series, Scout. It came out of a lot of recent talks with CrossFitters – including those in our Primal Health Coach program.

  14. Really appreciate these recent CF posts – I often get questions about optimal eating when engaging in daily or near-daily CF.

    Sleep and stress have such an impact, and I’m so glad you brought those up here – many CF’ers in my local town choose to skip out on sleep to hit the 5:30am class…and are not losing the excess body fat they want to lose. Diet, sleep and stress are a big part of why.

    Personally, I’ve let go of CF over the past while, preferring a combination of walking, hiking, swimming and yoga. I also prefer to keep things really simple – following a high-fat, high-protein, low-carb, nutrient-dense eating plan WITHOUT counting numbers but WITH listening to my body.

    Love these thorough, useful posts!

  15. Best articles and i really love this to apply for my self. I am still new on this and i am thankful that this gives me more idea. Thumbs Up!

  16. Mark, this was a GREAT post. I’m wondering how or if this advice applies to those of us that are doing the Primal Blueprint’s regular type of strength + sprint training combo – i.e., a PEM 2x per week plus a sprint session 1x every 7-10 days, plus low-intensity activity every other day. Does the “highER carb / lowER fat” on PEM / Sprint days apply for those of us NOT engaged in HIIT? Guess I’m wondering if all training session days deserve this consideration, or if it’s just applicable for CF’ers and folks engaging in HIIT. Signed, Legitimately Scared of Carbs…

  17. Mark, We want a post about ‘old man’ strength and/or legendary Eastern European strength, or freaky gymnastics strength. It would inspire us to get strong in our older years like MichaelS in your forum. Thanks.

  18. I know this is kind of an old post but I was wondering about Marks thoughts on Chocolate Milk post workout. And by chocolate milk I mean real chocolate milk (snowville makes a version with lots of protein, real chocolate, and basic cane sugar). Most of the studies out there say chocolate milk holds up or outperforms all the other expensive stuff. Just wondering if anyone has any thoughts.

  19. Hi Mark, I realise that this is an old post but I was just researching my own fat loss journey and using Crossfit workouts and I’m slightly confused.

    In your book The Keto Reset Diet, you say that training while Keto is fine because your body will generate the glycogen it needs through gluconeogenesis, which is perfectly natural in fitting with this type of eating and training.

    However, in this (older) post, you say that gluconeogenesis increases the levels of Cortisol, which can lead to fat storage and a host of other damaging effects of the body.

    I have been training in Keto starting in February and have had some pretty good results, mostly in strength gain. I use a Crossfit workout regime. I am 39 and I have noticed that legs, arms and shoulders are looking good and tightening but the core has that puffy, traditional “man” shape of carrying most of the fat.

    I’m trying to gauge the effect of introducing carbs into my diet; if it’s necessary or not.

    Can you please clarify this?

    I really appreciate it and thanks again for all of your help over the years!
    Sean, London UK