Dear Mark: Does Physical Activity Affect Obesity Risk?

For today’s edition of Dear Mark, I’m answering one question from a reader. It concerns the effects of physical activity on obesity.

This is an evergreen topic, a constant in the queries I receive. Is exercise necessary for weight loss? Does physical activity improve body weight? Is exercise all about burning calories, or is there something else going on?

Let’s get to it:

Hey Mark,

I was listening to a recent episode of Joe Rogan where he was getting into it with his guest, a carnivore, about the role of exercise in weight loss. Joe thought it was important, his guest didn’t. I also just saw this paper, which seems to support the guest’s take?

Great question. I’ve addressed it before, and I’m sure I’ll address it again in the future.

Gary Taubes famously questioned the role of exercise in weight loss, citing studies in which not only did exercise not really help, but only prompted the exercisers to increase their calorie intake to match the extra expenditure.

Like Gary, I’m very skeptical of the top down approach, with you as the overlord orchestrating your calorie intake and expenditure, shaving off some here, adding some there, tossing in 1.5 extra minutes on the rower to counteract the Skittle you snuck—that’s tough, unrealistic, and ineffective for most people.

Maybe if you have a researcher providing all your meals and prescribing all your workouts.

Maybe if you have a trainer breathing down your neck and a personal chef weighing and measuring everything you eat.

Humans are the only organisms we know who possess the capacity for conscious, self-referential thought. It leads to great things, but it also means we can overthink things and trip over our own feet. Using exercise as a calorie incinerator is the perfect example.

The bottom up approach is far superior. That’s how all the other organisms out there maintain their body weight. You think starfish maintain their trim figures by crawling a few extra laps around the sea floor? Do sea otters count the oysters they eat? They just exist, move, eat, and it all works out.

But get that: They move. Sure, one of the most crucial pieces is that they eat a species-appropriate diet. Wild game, not fast food. Oysters, not Wonderbread. But they must procure their food by propelling their bodies through time and space. That cannot be ignored. Movement is necessary for true health, and that includes body weight and composition.

This doesn’t validate the calories in, calories out model. The beauty of physical activity lies in the second order effects. All the great stuff that happens after and in addition to expending calories…like:

The glycogen depletion—frees up room in the muscles for glucose disposal, makes our muscles more insulin sensitive, makes us more glucose tolerant, makes it easier to burn fat and get into ketosis, reduces the conversion of carbs into fat.

The body composition changes—even if we don’t “lose weight,” we may very well lose body fat and gain lean mass (both bone and muscle). This won’t show on the bathroom scale, but it will show in the bathroom mirror.

The improved sleep—poor sleep is one of the best predictors of weight gain, obesity, and unhealthy body composition. A poor night’s sleep makes junk food more attractive and neurologically rewarding, worsens our metabolic response to carbs, and triggers muscle wasting.

The improved nutrient allocation—when we exercise, our body makes better use of the nutrients we consume. Protein contributes toward muscle protein synthesis. Carbs go into glycogen stores.

The improved blood glucose control—a major, yet unappreciated cause of binging and diet-induced weight gain is reactive hypoglycemia. That’s when a person eats something, their blood sugar spikes, and the insulin response is intense enough to lower blood sugar even lower that it was before the meal. Their mood worsens, they start feeling dizzy and weak, and they need a snack right away just to maintain composure. That’s far less likely to happen if you’re exercising on a regular basis, as every form of exercise ever studied has been shown to improve glucose control.

The momentum effect—When you start training regularly, it feels good. You release endorphins, the brain’s own opioids. You see results and get reactions from others, which provide a steady stream of dopamine hits that perpetuate the initial behavior (exercise). The longer you train, the easier it’ll get to stick with it—and the harder it will be to sabotage your efforts with terrible food and sedentary choices.

Don’t believe the hype. Physical activity is a huge component of healthy weight loss. It builds muscle and makes you a better fat burner. It helps you make better food choices and gives you a place to store glucose in a healthy manner. We all need to be moving, so long as we’re physically capable.

I may write more on this in the future. I just wanted to get a quick message out to everyone, because it’s an important (and nuanced) one.

What do you think, folks? How has exercise helped your weight loss journey? How has it harmed it? Were certain types of physical activity more helpful than others?

Take care, everyone.


Mendelson M, Borowik A, Michallet AS, et al. Sleep quality, sleep duration and physical activity in obese adolescents: effects of exercise training. Pediatr Obes. 2016;11(1):26-32.

Buresh R. Exercise and glucose control. J Sports Med Phys Fitness. 2014;54(4):373-82.

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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24 thoughts on “Dear Mark: Does Physical Activity Affect Obesity Risk?”

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  1. I believe that what you do with your body is just as important as what you put into it… in maintaining a “healthy level of movement,” one develops a healthy approach to consumption, where instincts become far more identifiable and beneficial. The well-being that builds from balanced movement trumps the need for consumption based satisfaction, such as food, pain killers, alcohol, drugs etc.

    The story on movement is far bigger than the sum of its parts.

  2. Totally agree with this. So many benefits to movement, including better body composition, increased energy, and better sleep. Plus it just feels good to move. But I still see so many people using workouts to “earn” their food. And talking about how long it will take to burn something off.

  3. Weight loss is about 85% good sleep / stress reduction / diet and about 15% exercise. However overall good health requires lots of movement, so exercise is vital to quality of life.

    1. I think this is basically correct for most people in most situations, but a counter example does exist. In military boot camp or officer candidate school, they feed you three square meals of all the food you can eat, and it’s generally the same institutionalized cafeteria food you’d get in lots of other places, but it tends to eliminate obesity real quick.


  5. So basically, correct diet makes you lean. Correct exercise makes you healthy.

  6. I’d swear I saw an otter the other day wearing a FitBit and looking at it while deciding to eat two more oysters.

  7. Great post, and all too true, but it’s not quite what Joe’s argument with Mikhaila was about as I understood it. Joe wanted depressed people to just get off their ass and exercise. Mikhaila thinks it’s not so simple.

    1. For depressed people, it can seem to be a physical impossibility to get off your arse and exercise. Some days it’s az much as one can do to get out of bed, so basic grooming, dress and get to work. That’s on a good day.

      Stop doing es that show a beneficial effect of exercise show that it works on MILD to MODERATE depression. Extrapolating this to more severe depression is stupid and a form of wish-fulfillment for The Enforcer mentality.

      I’d like to see these studies broken out by whether the depression is situational or endogenous.

  8. Haha. 20 minutes later in that same podcast Joe says after he a sugary meal he has Zero Energy to work out. Talks about an insulin crash. I was thinking Joe just proved his guest, Michaela Peterson, right and neither of them realized. That’s how somebody with a terrible feels all the time.

  9. A great read, as always. I myself have had great success losing weight with diet alone. That said it’s a hell of a lot easier with exercise, for all the reasons above.

    I myself hate the gym atmosphere. I’m the type of person who needs a lot of alone time, so working out surrounded by others is hellish, as are organized sports. I prefer bodyweight exercises at home, walks in the park, or hikes in the mountains with the dog, chopping firewood is great! Anything outdoors.

    This year I’m just too busy with life for workouts. Luckily I’m a tradesman, so I spend my days walking, climbing ladders, hefting large bundles of copper wire or steel pipe over my shoulder (then walking with it, or lugging it up a ladder).

  10. I think you need both pieces for health – diet AND exercise. However, once you are carrying extra weight (extra fat), you need exercise to lower insulin resistance and regulate glycogen if you are ever to lose that fat. (And the fat will be trying to raise your appetite through endocrine production, because it wants to stay!) This is where I think the keto diet can be a life saver. It lowers appetite, and allows you to restore control. If you try to lose weight by dieting OR exercise alone, you will be fighting your own appetites.

  11. I lost around 50lbs going primal. The first 35 came off with virtually no exercise beyond nightly walks. In my own experience this article is on for so many reasons.

    Sleep is better (as long as I’m not hitting it harder than I can recover). Stress is lightened. While not specifically calories in/calories out, it’s much easy to say no to junk after busting my rear.

    Excercise and movement compliment virtually all healthy habits. I’ve found this to be even more beneficial since dropping weights/gym style and adopting more natural workouts and getting outside more, even if just to walk and jog. Also, especially as a guy, upticks in testosterone improve life in about every way.

  12. I definitely eat less on a more active day. That doesn’t mean a day with lots of workouts, just when I am busy moving around as part of having stuff to do. Even more so if I’m outside more during that day. I think it helps regulate my appetite, and of course, sleep.

  13. 4 years ago before going Primal, I hated the thought of exercise, I did try, as I was in a downward spiral regarding my health, I thought I HAD to exercise to lose the weight. After changing my diet first and understanding the biology (Thanks to the Primal Blueprint of course) and losing weight that way, I soon had the urge and the energy to exercise, and then it was up up and away from there.

  14. I really like this article. It taps in to both theories which in my (unprofessional) opinion, both work. I have been an athlete all my life. I have always been extremely active. I noticed a real change in my strength and my performance when I changed the way that I ate, and slept. When I began to eat MORE food, I gained weight. Not a big surprise. It wasn’t until I counteracted healthy eating with strict workouts that my body began to really change. Next, which gets talked about as well, is the importance of sleep. Sleep is the most important form of recover that there is. This is huge.

  15. It may not help me lose weight, but walking on a treadmill most mornings certainly improves my outlook on things, while helping me rehab from hip and knee surgery

  16. In my hierarchy of importance, exercise is #4. The list is: #1 Eating Right #2 Sleep #3 Stress Reduction #4Exercise. If exercising impacts me successfully achieving #s1-3 I don’t go to the gym and I don’t feel guilty either.

    I used to think that “eating decent” and “exercising hard” were 1A and 1B (the others were irrelevant) and that you could just do more cardio if you indulged. That was prime “calories in/calories out” conditioning.

    These days, I weigh less than I did for most of high school (10+ years ago). I focus more on trying to incorporate more physical movement into my daily routine, like longer dog walks or biking to work on nice days. Eating right is king though.I live by the phrase “you can’t out run a bad diet”. If you live a hectic life and all you can do is cook nutritious meals and get to bed on time: that will do.

  17. I have worked with people who are so restrictive in everything they do that they back themselves into a corner and can’t get out. They are self-punishing, overthinking, and become allergic to almost everything. This developed over time, or course, but despite their every effort to do everything “absolutely right,” they are attempting to exist in a very small prison cell.

    That is all a preamble to say that I believe, based on observation and personal experience, that how we treat ourselves overall, how forgiving and loving we are toward ourselves, is the real key. Measuring out our lives in distance and ingestion, input and output, cramps our very souls. If we ingest the most pristine, healthful bite of food without enjoyment of (and appreciation for) that experience, I don’t believe we actually absorb the nutrients from that bite of food.

  18. Anyone unconvinced about movement’s (movement, not “working out”) role in overall health should check out everything Katy Bowman at

  19. I think this line is backwards:
    “reduces the conversion of fat into carbs”
    Shouldn’t it be :
    “reduces the conversion of carbs into fats”

  20. The best perspective I’ve seen for exercise versus weight is to exercise for health, not weight loss. When you assume that your exercise is going to promote weight loss, it’s easy to get stuck on the numbers and feel like you’re failing if you don’t lose weight. But, when you focus on health instead, there are more improvements to watch out for.

  21. Another great article as always you have shared. It’s very true that the physical activity helps very much to maintain activeness of body and min. It also affects obesity risk. Physical activity is also necessary for true health that included a maintained body weight composition.