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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