Dear Mark: Growing Appetite, Boxing as Cardio, and Ammonia Sweat

BoxingFor today’s edition of Dear Mark, I’m covering three questions from readers. First, how does a Primal family handle the growing appetite of a growing prepubescent without resorting to cheap fillers? It may involve reassessing our definition of “filler,” for one. Second, does boxing – an intense, demanding sport by any measure – qualify as chronic cardio? It’s intense, to be sure, but what if you really, really enjoy and thrive doing it? And finally, should you worry if your sweat smells like ammonia? Some say it’s a sure sign of impending doom, others wave it off as totally benign. Find out what I think below.

Let’s go:

Dear Mark,

We have a growing 12 year old boy whose appetite has also been growing with him. His diet is 75% primal as he eats what we eat with a few exceptions (bun with burger, occasional pasta etc). We obviously want to stay away from the easy cheap fillers – white rice, potatoes, pasta so do you have any suggestions as to how we can feed his appetite without having him eat us out of Primal house and home? What foods/dishes would you recommend we incorporate into his diet that will satisfy his hunger while also continuing to live a healthy lifestyle?

Thank you,


Honestly, don’t underestimate the power of the filler. Growing kids sometimes just need sheer caloric density to maintain and support that growth. Yeah, micronutrients are extremely important, but you can’t satisfy all his caloric requirements with kale, chard, oysters, liver, and wild blueberries. Provide ample amounts of healthy fats, animal parts, and vegetables at every meal – which it sounds like you’re already doing – and round out the calories with some “filler” foods that contain starch to provide caloric bulk.

I can hear you balking. Adults for whom growth means bigger belts and added risk of chronic diseases? Filler foods should be limited, absolutely, in favor of the most nutrient-dense foods you can find. Kids are a different story. Growth is good, is physiological rather than pathological, and they need both. Some ideas:

White potatoes: Believe it or not, white potatoes are quite nutritious. And they make a good source of resistant starch when allowed to cool overnight in the fridge. They get a bad rap because of french fries fried in two day-old reheated oil, hash browns cooked in vegetable oil, potato chips, and other junk food. That’s how most people eat potatoes (and it’s why they’re the most widely consumed vegetable in the US).

Sweet potatoes: Primal darlings, the sweet potato family is both carb and nutrient-rich and perfect for a growing boy in need of energy. Check out an Asian grocer for the purple Okinawan sweet potatoes for a massive dose of anthocyanins (the purple pigments with antioxidant effects, also found in blueberries and other purple/blue foods).

White/wild rice: Yeah, rice. I said it. It’s easy to make, it’s relatively devoid of antinutrients, and it can be a great vehicle for nutritious ingredients. Best of all, rice absorbs anything you add to the cooking water. For example, instead of water, use homemade bone broth, a pat of grass-fed butter, and some sea salt to cook your rice.

Winter squash: Who doesn’t love a nice butternut squash? The downside to these is that quality really matters. With tubers, quality is fairly constant. It’s hard to find a really bad sweet potato, or a truly awful Russet. But a bad butternut squash is bad. It’s bland, watery, fibrous, and not even really worth eating. To avoid such tragedy, go for heavy squash, dense ones that just feel weighty in your hand. Hold two squash up of comparable size, one in each hand, and choose the heaviest.

Hope it helps!

Hi Mark,

Before embarking on my primal journey I was a keen boxer. Once I started to learn about the primal principles I gave up boxing in favour of weights and the occasional sprints, fearing that my boxing was too much like chronic cardio. Fast forward 3 years and a stall in my weight loss, I have recently taking up boxing again – and quickly remembered everything I loved about it – the sense of power, confidence, lightning quick reflexes and participating in a group. My weight is finally shifting again and after an intense boxing class I feel relaxed for days.

So I was wondering – is a 1 hour boxing class really like chronic cardio? Or is it more like ‘play’? I would love to continue to box guilt free.

Thanks so much


There was a huge physical component to my abandonment of endurance training – the arthritis, the tendinitis, the inhuman amounts of junk carbs it required me to eat and the subsequent metabolic fallout – but a big reason I stopped running marathons and triathlons was because I stopped loving and began hating it. Endurance grew into a chore that seeped into the rest of my life, intruding on my thoughts when I was trying to enjoy myself with my family and friends. You say boxing relaxes you for days after a session; all I could feel after a training session was the dread of having to do it all over again the next day. I couldn’t even read a book or enjoy a romantic dinner without worrying I was wasting my time, valuable time that I should be spending in preparation for some event off in the future. That psychological component in addition to the physical effects made it chronic cardio.

You should never feel guilty doing something you truly love, especially if the objective, empirical effects on your life are positive. You’re losing body fat – that’s an undeniably positive effect (as long as you’re not losing too much body fat). You’re more relaxed. You’re part of a community. When I read about the power and confidence and quick reflexes you feel when you box, it sounds like you’re hitting that “flow” state we’re all after where you merge with the activity itself and exist only in the moment. And maybe most importantly, you’re having fun.

Besides, the intensity of boxing isn’t like the intensity of training for high intensity endurance events. In one experiment, an hour of “boxing training” expended about as much energy as running 9 kilometers in 60 minutes (a bit slower than a 10 minute mile pace). That’s pretty easy and not too stressful just looking at total expenditure, but they don’t explain what the training consisted of. Was it lots of short bouts of sparring interspersed with short bouts of rest, as most sparring goes? That’s a far cry from ceaseless pounding of the pavement.

Definitely stick with it. Boxing can get incredibly intense, so depending on how you train, boxing may be able to replace or supplant the sprints. I would continue with weight training.

Just watch out for the head trauma.

Ammonia smelling sweat: Is it just normal (assuming your daily carb intake trails around 50g & approx. 1g of protein per kg body weight and a 40:60 protein to fat consumption ratio) or an alarm signal? Comments on forums (including yours) range from “Nah, take it easy, dude …” to “This is a serious warning signal and it should scare the sh*t out of you!”. Can you shed some light on this? Thank you!


Ammonia is a natural byproduct of protein metabolism. Whenever protein is metabolized for energy (rather than incorporated into muscle tissue), we produce ammonia. Normally, the liver converts it into urea, which is less toxic than ammonia and more easily excreted. But if urea is saturated or the liver is experiencing problems, ammonia can back up and require additional excretion avenues (like sweat).

Ammonia excretion in sweat during and following exercise is normal because our muscle protein is constantly being broken down. It’s also constantly being replenished, which is why lifting a barbell doesn’t result in a net loss of muscle, but rather a net gain over time. But the point is simple: exercise breaks down protein, and broken-down protein releases ammonia. And some of that ammonia shows up in our sweat. Cycling at just 40% of maximum heart rate – a relatively easy pace – produces ammonia-tinged sweat. It really doesn’t take much.

Low carb diets lead to increased ammonia production during exercise, and this is completely expected. Low-carbers often have reduced muscle glycogen, which leads to a greater reliance on protein during exercise. Not only are you creating ammonia via exercise-driven protein catabolism, you’re also creating it by converting protein into glucose via gluconeogenesis. All totally normal.

If this is worrying you, you can always eat a few more carbs on workout days. You can make sure those 50 grams of carbs you’re already eating come from starches and fruits, rather than green vegetables (which don’t really count toward your carb count). You can also get a liver function test to rule out hepatic insufficiency.

My bet? You’re turning to gluconeogenesis to fuel your intense training. You can get by and even thrive in endurance training on low-carb, provided you’re fat-adapted. But in the context of high intensity, glycogen-intensive training, your body’s going to get the glycogen however it can, either through gluconeogenesis from protein or by utilizing dietary glucose. You might as well just eat glucose, its direct precursor. It’s cheaper that way and minimizes the buildup of ammonia. Consider carb refeeds two or three times a week to saturate your glycogen stores; it doesn’t take much.

Another factor may be insufficient fat adaptation. I’ll be dealing with this very subject in my upcoming book, Primal Endurance, which is all about fueling and optimizing performance on a high-fat diet. The focus is endurance performance, but with a few tweaks you can get pretty close to optimal high-intensity, normally glycogen-dependent performance with full fat adaptation. Stay tuned for that one.

That it for today, everyone. Thanks for reading and keep the questions and comments coming! Be sure to chime in if you have any additional advice for today’s questioners.

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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28 thoughts on “Dear Mark: Growing Appetite, Boxing as Cardio, and Ammonia Sweat”

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  1. Kudos, Mark, for the carbs for kids info. It’s sad to think of all the strict Paleo parents who are starving their kids, despite their best intentions.

    1. Right on. It’s not just the low-carb people who do this, but also the vegan/vegetarian crowd. People fail to understand that the foods children require for optimal growth and health can differ from what their parents choose to eat. Thanks to Mark for pointing this out. I would try to limit the wheat products but let the boy have all the starchy vegetables and rice he wants.

      1. I second that. When I was in my teens and early twenties my caloric requirement were huge. You can’t feed that need following a diet that a middle aged adult, trying to stay lean, would find perfect for their needs. Just don’t eat junk. Pasta, rice and potatoes is not junk for a growing body.

        1. Umm, Clay, I wouldn’t include pasta in that trio. Pasta is usually made with refined wheat flour, water, and maybe a little bit of egg. Commercially made pasta in particular is, IMHO, the epitome of a “filler” food–fattening but mostly lacking in nutrition. It also tends to be somewhat addictive, like most wheat products. True, it can be made a bit healthier depending on what you sauce it with, but there are better options, even for growing kids.

        2. Pasta certainly isn`t the epitome of nutrient density, but the claim that “most wheat products” are “addictive” is not factually accurate; the “wheat exorphin theory” (as popularized by William Davis via “Wheat Belly”) has been thoroughly debunked.

  2. Very good topics that were discussed today. Especially interested in the “filler” foods for kids topic.

  3. What I tell all of my triathlete patients – The best exercise is the one you love to do. I would never dissuade someone from “chronic cardio” if it is what they love! If you’re passionate about the boxing, keep it up either way!

  4. Mark, when is the projected release of Primal Endurance? Eager to read it!

  5. Ah thanks for covering boxing as a work-out. I often do sort of tabata boxing workouts – short but intense. I’ve always felt like it’s probably pounding my joints a little even doing that, but as stated in the post, boxing confers a great deal of other lifestyle benefits that make it highly worthwhile. A great way to help vary your day to day exercise too.

  6. I consider my hikes and boxing sessions to be my “cardio”. I no longer do the traditional cardio…but I’ve still never been able to go completely primal without feeling like crap :/. As a result I still try to consume the “good” carbs at least one meal per day – I know enthusiasts will tell me I need to go to fat adaptation but I’ve never gotten over the 2 or 3 month hump when I’ve tried 🙁

    1. Interesting, it only took me a couple of weeks to be fat adapted but then again there’s nothing wrong with the good carbs you take and they only seem to problem with people who have metabolic issues.

  7. Mark, thanks for being so candid about how you felt psychologically with the endurance training, as well as the physical reasons that caused you to retire from the endurance sports.

    I must have spent the last few years (of my decade of LD triathalon) feeling that way but there’s such a drive in these communities to keep at it and it’s ‘not meant to be fun’ it can be very hard to walk away.

    1. That “it’s ‘not meant to be fun’” is the message you were receiving from your triathlon community makes me sad. Your choice of leisure activity should indeed be fun. When it feels like work, that’s when you know you are doing it wrong. There is nothing wrong with wanting to improve, and work hard because you like it, but triathletes often are Type A folk, and take it too far. Triathlon training and racing as an age grouper should be fun. Full stop. The training should be social, there should be brunch after, race day should feel exciting, and every finish should be celebrated regardless of time.

  8. I liked the part about the carb filler foods. Both my husband (who has a physically demanding job) and a very active 11 (and a half) year old boy get their carbs by both sweet potatoes, resistant rice and potato salads. And the occasional BAD food/drink that they consume w/o my blessing of course. 😛

  9. As with your advice to the boxer, I’m still an endurance trainer fanatic. Working on 3rd marathon now and while I can see a negative side from running as much as I do, I just LOVE it so much the benefits far outweigh the cons!

  10. Even though I’m not a kid anymore (29! haha), I find that during periods of time where I’m extremely active, my appetite can get ridiculous. I go for white potatoes and even some rice during these times just for the sheer caloric bulk.

    I also throw in lots of berries + coconut cream. The deliciousness factor makes them hard to beat, and I get a very easy-to-eat calorie smash. It’s delightful.

    Interesting about the ammonia too. I’ve never trained for long periods on low carb, so that’s not something I’ve experienced. Maybe I’ll try it out and see if it happens to me someday!

    Great post.

  11. Don’t forget bananas. If you’re lucky enough to live where you can get them at a reasonable price, if not cheaply, they’re an excellent (and delicious) non grain source of extra carbs.

    1. Try a green bannana in some kind of a smoothie. You get the same banana flavor without the high sugar content.

  12. I do Bikram yoga 3-4x/week. I reek of ammonia. I will have to pay better attention to what I’m eating on those days.

    1. As a Yoga teacher, there are a few things I feel people need to know before approaching Bikram Yoga as their preferred method of getting their Om on.

      First, traditional Yoga as practiced in India is done BEFORE the sun rises in the early morning in order to *avoid* overheating the body.

      Putting yourself in a room heated to 100+ degrees triggers an adrenaline response… and we know how Mark feels about corticosteroids.

      Second, your body’s temperature (barring fever) is pretty stable at 98.6F across the board. While there may be deviations by a tenth of a degree for people, typically, your body likes to stay at that temp.

      When you raise the degree of the room and participate in an exercise that naturally builds heat inside the body by its very nature, you are heating your internal organs in a very unhealthy manner.

      Your heart, your brain, your reproductive organs, and your adrenaline glands like the body at 98.6F. Sustained periods (say, 90 minutes) in high-temp environments will lead to thyroid issues, adrenaline exhaustion, and reproductive issues.

      I worked in an Ayurvedic & Yoga center for a while, and most of the people who came in complaining of being exhausted all the time, being unable to lose weight, insomnia, headaches, moodiness, etc. all seemed to have one thing in common… Bikram Yoga.

      Bikram seems to be a Yoga fad that does not lend itself to health or wellness. If you’re looking for the challenge with ALL of the benefits, consider a Vinyasa class… sometimes, they will warm the rooms to ~80F. It’s still warm, and you and your mat will BOTH be soaked, but you avoid all the potential long-term health problems caused by participating in Oven Yoga.

      Namaste! <3

  13. Looking forward to the new book. Sometime my long tennis singles matches seem like an endurance event – especially in the heat of South Carolina! I usually eat an avocado with lots of salt before the match, coconut water during, and a sweet potato soon after. I can still get pretty wiped out, so I am looking forward to the book and more hints.

  14. On teens and extra carbs,

    We use quinoa as a filter food for our growing tweeners. We cook up a big batch and store it in individual servings in the fridge. It takes on whatever flavors you add to it and it has more fiber and protein than most filler foods. It needs to be cooked in stock or it tastes like dirt. My 12-year-old son makes his own filler meals with leftovers and condiments and quinoa. His own creation is quinoa pizza. He puts the chilled serving of quinoa in a bowl, mixes in a few spoonfuls of bruschetta sauce, tops it with a slice of provolone cheese and pops it in the microwave for 2 minutes. The whole process takes less than five minutes. My daughter’s favorite is quinoa with chicken chunks flavored with pesto. I still can’t get them to eat Okinawan sweet potatoes, they call them Barney turds in reference to the life-size paleo-puppet of their childhood.

  15. i’m not a teenager, but i am a big eater. To help me not eat my wife and myself out house and home I do two things. First I eat eggs and bacon for breakfast every day. This curbs my appetite nicely till lunch. Second anytime I eat a filler food such as rice or steamed veggies, I add a more filling condiment to it like butter or coconut oil. This helps me eat less of the filler food but still feel full. 🙂

  16. I have to add something to the ammonia sweat topic:
    I had that too and found two reasons. First, the smell was stronger when I wore a certain kind of t-shirts and almost non-existent when I wore other shirts. Especially shirts I put on for exercising smelled pretty fast and harsh. A friend told me that it’s some kind of bacteria that leads to that smell and he gave me the advice to wash the smelly clothes in cold water right after wearing them, especially when they were sweaty. Then I would dry them and put them in the dirty laudry or even wear them again. That solved part of the problem.

    The other thing was caffeine. Whenever I drink coffee, black or even green tea I get a heavy ammonia smell under my arm pits. It’s especially strong with coffee and green tea. When I avoid these I have no smell at all.

    Hope that helps!

  17. I can relate to the joy felt by someone participating in a group activity while getting fit and training for some friendly competition. Long ago I aprticipated in a city soccer league. More recently, about 4 years ago, I was part of a dragon boating team and an outrigger canoe club here in AZ. It was a lot of fun, there were always a lot of people to chat with, and I definitely felt good in general (physically) at the time. I’ll have to see if I feel “relaxed for days” if I ever get back into them again. I think I was always too stressed about other life things to really be that relaxed! But I also wasn’t paleo at the time, so I wonder how different it might be now…

  18. Thanks for the post on carbs and kids. I think it can be hard sometimes as diet and health-conscientious adults not to project our own needs and issues with regard to food onto our kids. It helps to have some perspective! For instance my toddler eats what I consider to be a lot of fruit — now for me this would not work at all and not make me feel good, but he obviously needs the extra carb content and does fine on it. He also eats plenty of meat, veggies, eggs, good fats and a reasonable amount of nuts, so I don’t worry about it, although I have had moments of questioning his fruit intake. Lately we’ve been doing a lot more dairy and I am not sure it’s working but that is another story…Anyway, my point is, I appreciate this post and would love more geared toward kid issues.