Recreational exercise first became a widespread phenomenon in the United States in the 1970s. Jane Fonda’s workout videos were a cultural force in the 1980s, elliptical machines rose to prominence in the 1990s, and so on. Today, there are hundreds of different exercise regimens and routines. The fitness industry is always on to the next trend with higher-dollar classes and new equipment to buy. For all its challenges, the pandemic ushered in a more robust set of digital options or on-demand fitness resources, adding another dimension for exercisers to pursue their fitness goals.
Yet, despite the countless ways on offer to break a sweat, we have continued to see our collective weight increase, with obesity rates climbing relentlessly in each of the last 4+ decades. To be sure, this increase is multi-factorial. Even if we diligently set aside time for exercise, many of us find ourselves stuck spending the rest of the day sitting at a desk, sitting in our car to get to and from work, sitting at our kids’ soccer games and practices. You get the idea. Our 21st century lives are set up to do a lot of sitting. The food industry meanwhile has continued to innovate, pushing for more choice, more convenience, and (often) more indulgent high-calorie options at the grocery store, in restaurants, or with a few thumb taps on a delivery app.
Beyond our challenging food environments, one aspect of our modern world that perhaps hasn’t gotten as much attention as it deserves: exercise may not actually be all that helpful for burning calories and losing weight. Now, to be clear, even if this is the case, exercise is an incredible tool for optimizing many other aspects of our lives: a robust cardio workout might help us sleep more soundly and is great for our hearts and lungs, a challenging or soothing yoga class can serve as a stress reliever, going hiking with friends can strengthen social bonds, and lifting weights can help us deal with day-to-day challenges, like bringing in the groceries. But let’s spend a little more time on the idea that, while the list of benefits from exercise is quite long, weight loss likely isn’t at the top of that list.
This concept – that exercise may not be a prominent source of weight loss – has been around for a while, with some notoriety gained when evolutionary anthropologist Herman Pontzer published this paper in 2016 presenting evidence for the theory of constrained total energy expenditure and metabolic adaptation. What exactly does this mean?
Let’s start with a few basics. Through the foods we eat and the drinks we consume, we ingest energy to power our bodies in the form of calories. Our bodies use this caloric fuel to enable us to be active in many ways, powering our lives all the way down to cellular-level bodily functions that we don’t even have to think about. Our resting metabolic rate (RMR) is one term that describes the collective amount of energy (in calories) that our bodies spend fueling our brains, lungs, liver, kidneys, and more. If we spend our entire day in bed, it may not feel like we burn any calories, but in fact, the simple act of being alive causes us to burn a significant number of calories. Importantly, this number appears to vary substantially from person to person: height, weight, age, and muscle mass are key variables that drive RMR.
For most of us, resting metabolic rate accounts for the majority of the calories we burn in a day. We use up a modest number of calories digesting the food we eat; this calorie expenditure is called the thermic effect of food. Non-exercise activities also count for some calorie burn: items like walking or fidgeting are among the movements that aren’t formally considered exercise but do consume energy. And if we burn calories by walking, it only makes sense that we stand to burn a whole lot more with an intense boot camp class, or a tough bike ride. Why wouldn’t all those calories keep piling up in our burn column?
The theory of metabolic adaptation suggests that for every calorie we burn while we are exercising, our body’s basic everyday functions are forced to become more efficient: the exercise uses up some of the calories that our body would otherwise allot to our organs to execute their daily tasks. In so many aspects of our lives, efficiency is a good thing, but when it comes to weight loss, we lose weight when our bodies take in fewer calories than we burn throughout each day. We want our bodies to be less thrifty in how we use up calories, burning the maximum number of calories that we can each day!
Now, does this mean all calories burned with exercise are taken out of our body’s daily budget? Fortunately, no, it doesn’t. The data suggests that *some* of the calories we burn with exercise are taken out of the daily budget, but not all. And it takes time for our bodies to adjust to the quantity of calories we burn with exercise, so we may see more weight loss attributed to exercise at the start of a new routine, or when resuming exercise after a prolonged period of inactivity. Another dimension of this is that folks who are at the extreme end of the exercising spectrum – Olympians like Michael Phelps, ultramarathoners, bikers logging a couple hundred miles a week, or body builders in the gym several hours a day – may see slightly less adaptation than those of us exercising in a more normal, accessible amount, such as a few hours a week.
Another key consideration is that there may be some small ways to boost our metabolism. And no, we’re not taking about so-called “fat burners” or other similar supplements! Muscle mass was mentioned earlier as a key component of our resting metabolic rate. Muscle is metabolically active, and the more of it we have, it stands to reason, the more energy (calories) that muscle burns both at rest and as it powers our daily activities. Added muscle may well be a way to combat some of the energy expense challenges we encounter with metabolic adaptation.
This is why, at EverBetter Medicine, our exercise recommendations aren’t going to include pushing you to do an extreme amount of cardio, which sacrifices time for preparing healthy foods, or keeps you from getting enough sleep, or takes away time from other important stress relieving techniques or daily life tasks. Our recommendations will always include some form of strength training: lifting weights, swimming, yoga sculpt classes, Pilates, intensive ballroom dancing, or moving bales of hay on a farm. When we lose weight, our bodies will burn energy from wherever it can, including our muscle mass. If we’re not attuned to this, we may lose more muscle than we’d like. Most commonly, we aim to burn as much fat while preserving as much muscle as we possibly can. Some of us will be able to add muscle while we’re losing weight, which can create an even greater body composition change.
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For more research-based insights to drive your sustainable weight loss plan, book your initial weight management visit with Dr. Millard today!
