The Theory That Broke Fat Loss Science

Chapters:

00:00 Intro

00:37 The Constrained Energy Expenditure Model

01:27 A new scientific review

02:23 Degrees of Energy Compensation

03:44 A Walking Program Study

04:54 Constrained Energy Expenditure and Strenagth Training

05:26 Conclusion

Transcript:

It’s widely believed that a primary reason for the obesity pandemic is that we are less physically active. Our hunter-gatherer ancestors were certainly a lot more physically active than we are in Western societies. However, research has found that hunter gatherer societies like the Hadza do not actually have higher levels of total daily energy expenditure. Moreover, many studies have found that aerobic exercise programs result in disappointingly little fat loss compared to the energy expenditure during the program. So what’s going on here? These findings have led to what is now called the constrained energy expenditure model.

Scientists used to assume that higher levels of physical activity would linearly translate into higher levels of total daily energy expenditure. The more active you are, the more calories you burn. And to the extent that this creates a discrepancy between your energy intake and your energy expenditure, it should make it easier to lose fat. However, this does not seem to be the case. Research increasingly supports a constrained model of energy expenditure in which high levels of physical activity also cause a compensatory decrease in other levels of energy expenditure. Meaning that not all of the extra calories that you burn actually result in additional total daily energy expenditure.

You might expend 500 calories on a treadmill, but your total daily energy expenditure might only go up 300 calories because other energy expenditure, whether it’s from a metabolic rate or from other non-exercise activity thermogenesis, decreases. A new scientific review found that on average in 18 aerobic exercise programs energy expenditure was compensated for by 69%. That means that when you look at the treadmill and you burn 600 calories, your total daily energy expenditure actually goes up by less than 200 calories. In other words, less than a third of the calories burned during exercise actually resulted in increased total daily energy expenditure. The remaining calories that you burn during exercise in this case were not actually additive to your total daily energy expenditure. They were compensated for.

Other forms of physical activity and exercise resulted in lower levels of energy expenditure, including in this analysis basal metabolic rate. So technically, high levels of physical activity and step counts actually temporarily suppress your metabolism. It’s important to realize that the 69% is not a golden rule, although I think some people in the comments will have something to say about that. The exact degree of energy compensation depends on various factors. In particular, energy deficit seems to significantly increase the degree of energy compensation. So when you’re bulking, when you’re in energy surplus, the degree of energy compensation seems to be much less.

Lower levels of body fat also seem to increase the degree of compensation that takes place. These scientific findings align surprisingly well with the experience of many bodybuilders. Bodybuilding contest prep is a scenario in which energy compensation is theoretically predicted to be the most extreme. And indeed. Anecdotally we see that many bodybuilders have to add a surprisingly large amount of cardio to get further fat lost during their prep. I have received many questions from the coaches that I mentor about why the math doesn’t seem to add up. They do a predicted 500 calories of extra cardio per day with their clients, yet it’s barely resulting in additional fat loss.

I myself have a relatively adaptive metabolism, and I realized during my last prep that the decrease in energy intake was far more effective than an increase in physical activity level based on the additive model. So adding 100 extra calories of energy burn from cardio did not have the same effect as reducing my energy intake by 100 calories. By the way, if you’re into this type of evidence based fitness content you will love my online PT course. The link is in the description. Fortunately, in less extreme scenarios the degree of energy compensation is also less extreme.

In another study of a walking program of about 1500 calories of walking per week, the degree of energy compensation was 39%. Here too, most of the compensation occurred in resting energy expenditure, sleeping and basal metabolic rate were suppressed after the walking program. There was also an increase in walking economy, meaning that they burned fewer calories from walking after the program than they did before. This is normal, and it’s normally only a few percent. As you do any type of physical exercise your body gets better at it, it becomes more efficient, and it expends less energy for the same amount of work. Fortunately, you can compensate for this by doing higher levels of total work. As you get stronger and fitter you can do more work per session and therefore still increase your total daily energy expenditure even though your body is getting more efficient. But this requires progressive overload, which was not done in this study.

I would note that the last study had a serious limitation in that the degree of energy compensation was measured in any deviation from predicted energy balance. This basically meant that any energy deficit or surplus was attributed to energy compensation, which is probably not the case. Moreover, there was no control group.

Regardless, there are now well over a dozen studies finding compelling evidence of constraint energy expenditure in various settings. The good news is that strength training does not seem to suffer from constraint energy expenditure. Strength training is composed of very brief, but very high intensity bouts of energy expenditure. These result in adaptations that are necessary to adapt to the stress form exercise. It may be that this type of exercise is very difficult to adapt to for the body. In general, it seems to take some time before the constrained energy expenditure sets in. It’s not like when you just walk more for one day, and immediately your resting energy expenditure drops. The metabolic adaptations seem to occur mostly over the span of weeks.

Other than just being depressing, the knowledge that energy expenditure is constrained has useful practical applications that we can use to our advantage. First and foremost, lifting weights is underrated for fat loss. Lifting weights does not seem to suffer from constrained energy expenditure, which is a big advantage compared to aerobic exercise for increasing your step count. This probably explains in part why strength training interventions typically result in equal fat loss, or even better fat loss compared to aerobic exercise programs or cardio in most studies.

With resistance training, you can generally assume that the total energy expenditure from exercise linearly increases your total daily energy expenditure. Other forms of energy expenditure are constrained. This is especially true if you’re very lean, if you’re in an energy deficit for a long period of time, and if you already have a very high activity level.

While the exact degree of energy compensation seems to vary a lot per context and individual, a big take home message from this video is that your diet is a number one way to get leaner. “It’s very hard to outtrain a bad diet” “Abs are made in the kitchen”, as the cliché goes. Nevertheless, I would stress that there are many other reasons to exercise, and exercise does typically increase your energy expenditure. The degree of compensation is rarely 100%. In fact, in many studies, it is also far below the 69% found in the new analysis. Higher levels of physical activity, therefore generally do make it easier to lose fat. However, I would argue that you should optimize your training not for fat loss, but for health, performance, or muscle growth.

So let your diet take care of the fat loss, lift weights and don’t trust that the calories shown in your Fitbit or your treadmill actually result in a net increase in total daily energy expenditure of the same amount. If you like this type of evidence based content click here to check out my PT course, or here to continue watching some of my content.