In 2007, I trained for and ran my first marathon. I began the training at about 170 pounds, and months later, I remember getting on the scale the morning before traveling to NYC for the marathon, weighing 169 pounds, and thinking, “WTF?”

Over the ensuing ten years, I ran three more marathons and numerous half-marathons, competed in triathlons, and spent a summer averaging over 100 miles biking weekly, training for the Seattle to Portland ride that covered 204 miles in a single day. Despite all that exercise, I maintained the same weight over the decade. I bet you’ve had a similar experience—you start or increase an exercise regimen but don’t shed pounds.

My experience of exercising a ton and losing no weight highlights a surprising and often frustrating truth: while exercise is essential for overall health and fitness, it doesn’t necessarily lead to weight loss. This phenomenon, known as the “Exercise Paradox,” has been explored in various studies and offers fascinating insights into how our bodies work.

The Exercise Paradox Explained

The Exercise Paradox refers to the observation that increasing physical activity doesn’t result in a corresponding increase in calories burned or weight loss. You might think running more miles or spending extra hours at the gym naturally leads to shedding pounds, but the body doesn’t work that way.

One of the most compelling studies illustrating this paradox involved the Hadza tribe, a group of hunter-gatherers in Tanzania. Researchers found that despite being highly active—walking miles and miles daily in search of food—the Hadza burned about the same number of calories per day as the average sedentary adult in the U.S. This surprising result suggests that our bodies might adapt to increased activity by conserving energy in other areas, keeping total energy expenditure relatively constant.

And it’s not just humans — studies of other mammals reveal that physical activity doesn’t lead to greater calorie expenditure. Writing in Scientific American, the author of Hadza study said his team “found that captive primates living in labs and zoos expend the same number of calories each day as those in the wild, despite obvious differences in physical activity.” Plus, “In 2013 Australian researchers found similar energy expenditures in sheep and kangaroos kept penned or allowed to roam free. And in 2015 a Chinese team reported similar energy expenditures for giant pandas in zoos and in the wild.”

Why Does This Happen?

It makes sense if you think about this from an evolutionary perspective. Our bodies evolved to store fat as a reserve during lean times, not to be slim. In olden times, if we burned a lot of calories chasing down a gazelle during a hunt, our bodies compensated by reducing calorie burn in other areas of our lives so that we didn’t deplete our fat stores.

The reasons behind this phenomenon are still being studied, but there are several theories about why the body might conserve calories even when we exercise more:

Energy Compensation: One theory is that when we burn more calories through exercise, our bodies compensate by conserving energy elsewhere. This could happen in several ways:

• Reduced Non-Exercise Activity Thermogenesis (NEAT): NEAT refers to the calories we burn through everyday activities like walking, fidgeting, or even just maintaining posture. Increasing exercise levels might unconsciously reduce these activities, lowering overall calorie burn.
• Metabolic Adaptation: The body might become more efficient at certain tasks, requiring fewer calories to perform the same functions. For example, after months of endurance training, your body may become more efficient at running, burning fewer calories per mile than when you started.

Caloric Restriction Responses: Another possibility is that when we increase our energy expenditure through exercise, the body responds similarly to how it would during caloric restriction. It might lower the metabolic rate or reduce energy spent on non-essential functions, like immune responses or reproductive health, to conserve energy.

Hormonal Changes: Exercise can influence hormones like leptin and ghrelin, which regulate hunger and satiety. Increased activity might lead to increased appetite, causing you to eat more and offset the calories you burn through exercise.

Basically, Our Bodies are Unbelievably Complex. According to the blog Junkfood Science, “Balancing energy includes a lot more than just the calories we eat and the calories we burn according to those exercise charts. The energy parts of the equation include: calories consumed; calories converted to energy and used in involuntary movement; calories used for heat generation and in response to external environmental exposures and temperatures; calories used with inflammatory and infectious processes; calories used in growth, tissue restoration and numerous metabolic processes; calories used in voluntary movement; calories not absorbed in the digestive tract and matter expelled; calories stored as fat, and fat converted in the liver to glucose; and more. Add to that, to put it simply, each variable affects the others, varies with mass and age, involves complex hormonal and enzyme regulatory influences, and differs in efficiency.

Calories eaten and calories used in voluntary movement are only two small parts of energy balance and are meaningless by themselves, unless all of the other variables are controlled for, as our metabolism… which they can never be as they aren’t under our control.”

The Role of Lean Muscle Mass

Interestingly, one factor that consistently increases calorie expenditure is lean muscle mass. In the Hadza vs. the more sedentary Americans study, higher lean body mass was correlated with burning more calories.

This makes sense because muscle tissue burns more calories at rest than fat tissue. This means that weight training, which builds muscle, can effectively increase your resting metabolic rate. Unlike steady-state cardio, which may lead to minimal weight loss due to the body’s energy conservation mechanisms, building muscle can help you burn more calories even when you’re not exercising.

What This Means for Weight Loss

Given this paradox, it’s clear that while exercise is crucial for overall health—improving cardiovascular function, building strength, and reducing stress—it’s not a silver bullet for weight loss. Diet plays a much larger role in creating the caloric deficit necessary to lose weight.

This also explains why the adages “abs are made in the kitchen, not the gym” and “you can’t outrun a bad diet” hold true. Exercise should be part of a balanced approach to health, but if your goal is to lose fat, focusing on your diet is essential.

Conclusion

The Exercise Paradox teaches us an important lesson: our bodies are incredibly complex and efficient at maintaining balance. While this efficiency is beneficial for survival, it can be frustrating when trying to lose weight through exercise alone. The key takeaway is combining regular exercise with a mindful eating approach and incorporating strength training into your routine to build muscle and boost your resting metabolic rate.

So, while you should absolutely keep up with your exercise routines for the countless health benefits they provide, remember that the path to fat loss is largely determined by what you eat, not just how much you move.