Brian Minor, MS, CSCS
Eat less than you expend. Fat loss really is that simple. However, adaptive mechanisms can make executing that objective an increasingly uphill battle the leaner we become. While body fat is a valuable reserve for energy during food scarcity, our bodies are fascinating in their abilities to deploy mechanisms to protect against starvation.
On the intake side of the equation, hormone fluctuations occur to increase hunger signaling. These mechanisms alone can lead to increased caloric consumption and become the bottle neck for many individual’s fat loss efforts. The magnitude of this impact is profound, as one study demonstrated that for every kilogram lost there is a regulatory drive to increase consumption by approximately 100 calories[i].
However, even in the face of dietary compliance, we can see robust reductions in the amount of energy we expend during prolonged fat loss efforts. While some of this is simply due to weighing less in general, there are adaptive components which also lead to a reduction in expenditure per unit of mass. How does this occur, and what can we do to combat it? First lets quickly go over the components of overall metabolism/total daily energy expenditure (TDEE).
- Resting Energy Expenditure (REE)
- These are our caloric needs at rest. Your heart beat, respiration, and organs all require calories to carry out their functions.
- Thermic Effect of Feeding (TEF)
- This is the energy required to digest and utilize the calories/energy we consume. This scales with intake, meaning the less calories you eat the less you will burn, and vice versa.
- Physical Activity
- Exercise- weight training, cardio, sports, etc.
- Non Exercise Activity (NEAT)- This is all the physical activity that occurs outside of dedicated exercise.
As a quick side note, I personally believe that much of the confusion on adaptive thermogenesis/metabolic adaptation is a result of operating under the different definitions. Many people hear the word “metabolism” and associate it solely with what is defined as resting energy expenditure (REE). This was how metabolism was first explained to me; as our body’s “internal furnace”. In that sense, it’s easy to overlook physical activity within the working definition. In reality, our overall expenditure is the totality of all the previously mentioned components. Not many people who complain about their slow metabolism realize they are largely complaining with their lacking desire to move.
That said, REE does see observed decreases with weight loss. While both weight loss and adaptive mechanisms play a role early on in fat loss efforts, further decreases appear to be primarily driven by weight loss alone[ii]. In other words, if we want to lose bodyfat, much of the reduction in REE is outside of our control.
When it comes to the thermic effect of feeding (TEF), outside of potentially further increasing your protein intake (it has a higher thermic effect than fat and carbs), there is not much you can do to increase your TEF in a deficit since its scaled with intake.
That leaves physical activity. Combating these decrements is where the chess match against our physiological and behavioral tendencies is won. Understanding what contributes to the reduction in activity expenditure is important, as it allows us to understand where to focus our efforts. The decrease in overall expenditure via physical activity is a result of both the actual weight loss itself, and adaptive component(s), which aimto further reduce our energy expenditure. The first part should make sense. The heavier we are, the harder our body must work to perform the same activity. When we lose weight, those demands (and the calories required to meet them) go down. Not much we can do about that. The adaptive component, however, appears to work in a couple different ways:
- We see a reduction in voluntary movement outside of exercise. Anyone who has ever gone through the deep stages of a contest prep have likely noticed a robust resistance to move. Getting through training alone often seems like a victory in itself.
- There can be an increase in work efficiency, meaning we burn less calories for the same amount of exercise/activity[iii]. Interestingly, resistance training has been shown to actually reduce work efficiency, which in turn, can offset this adaptive reduction to NEAT[iv].
Regardless of avenue, NEAT expenditure per unit of mass has been shown to decrease proportionally with fat loss[v]. In other words, the leaner you get, the less calories you are performing during daily activity for each lb/kg that you weigh. Assuming we are resistance training, then overcoming our body’s resistance to movement arguably becomes the most important objective to fend off adaptive thermogenesis.
What gets measured gets managed, but how can we ensure we are consistently expending what’s required to create/maintain a deficit? Unless we are going to live in room calorimeters, we must accept the fact we don’t have the same degree of control over the expenditure side of the equation. That alone begs the question: why do we see granular macronutrient recommendations being made on the intake side of the equation? Things like 67f/214c/183p. Knowing the variability on the other side, would it kill them to round? In many cases, I feel this level of precision often does more harm than good but that’s a different topic of discussion entirely. Regardless, it’s a bit naïve to think we have THAT much control on the bottom line.
Many athletes and coaches address the need for increased expenditure with assigned cardio sessions. There is absolutely nothing inherently wrong with this as it’s certainly a step in the direction of increased expenditure. That said, there is often a false sense of control here. As mentioned previously, we can see robust reductions in NEAT outside of training (and cardio). When energy is low, sometimes peeling yourself off your couch to go to train or go do the Stairmaster feels like a huge win. Maintaining sufficient levels of physical activity outside of those sessions is arguably just as (or more) important than performing the cardio sessions themselves.
So, it’s important to maintain sufficient expenditure outside of training and cardio, but what is the best method of managing this? Wearable activity monitors are marketed to play on our desire for caloric control. Many of these boast the ability to track how many calories you burn each day. Unfortunately, a recent meta-analysis demonstrated that there is a significant margin of error when estimating caloric expenditure when using activity monitors[vi]. They can, however, be extremely useful as a rough proxy for NEAT. By maintaining an assigned step threshold each day, we can effectively combat the reductions NEAT that may otherwise occur.
As some personal anecdote, I have gone through three contest preps in my time competing. The first prep was very HIIT intensive. Not only did I find my recovery from training seemed to suffer, I was a zombie outside of performing my training and intervals. My second prep saw the pendulum swing the other direction, with all cardio being low intensity in nature. I had caloric targets for each session, where I would rely on the algorithm of each machine to provide my expenditure. I remember having a favorite brand elliptical simply because I could “hit my target” sooner! And you better believe I didn’t stay on those machines for a “calorie” longer than I needed to be. In that second prep I ended up getting much leaner, and subsequently felt the amplified lethargy that’s a trademark of those deeper stages.
By the time my third prep rolled around in 2017, I had learned quite a bit more about NEAT and the impact that reductions can have in for halting fat loss. I decided to simply track my daily steps and see how far that alone would take me. I went on A LOT of walks and adventures with my family. Not only did those allow me to bring up expenditure, it was additional time spent with them that more traditional strategies wouldn’t easily provide. That’s important when you are dieting for 30+ weeks! As another “hack”, I never brought a water bottle to the gym. That forced me to rack up a surprising number of steps walking to the water fountain across the gym between sets. That said, some individuals may prefer to only track the steps outside of their training and formal cardio (if they have any). That makes more sense in some situations. Since walking isn’t the most time efficient means of expending calories, some moderate-higher intensity cardio may be required for time efficiency reasons. In those cases, tracking steps may not be the best way to capture that. While I still had my share of exhausting days with a lot of walking, it was much more tolerable (and effective) than simply performing formal assigned cardio. I got in my best condition to date, and it was easily the smoothest and dare I say, easiest prep to date. Sometimes it is about working smarter rather than harder.
When it comes to getting in shape,
be sure you give yourself more time than you think you need, adhere to your
diet, train and perform cardio intelligently, and manage your NEAT. Getting in
the best shape of your life really is that easy.
[i] Polidori et al., “How Strongly Does Appetite Counter Weight Loss?”
[ii] Rosenbaum and Leibel, “Models of Energy Homeostasis in Response to Maintenance of Reduced Body Weight.”
[iii] Rosenbaum et al., “Effects of Experimental Weight Perturbation on Skeletal Muscle Work Efficiency in Human Subjects.”
[iv] Rosenbaum et al., “Resistance Training Reduces Skeletal Muscle Work Efficiency in Weight-Reduced and Non–Weight-Reduced Subjects.”
[v] Rosenbaum and Leibel, “Models of Energy Homeostasis in Response to Maintenance of Reduced Body Weight.”
[vi] O’Driscoll et al., “How Well Do Activity Monitors Estimate Energy Expenditure?”