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Exercise, Weight and Fat Loss: Part 2

On Tuesday in Exercise, Weight and Fat Loss: Part 1, I took a somewhat thorough look at some of the realities of exercise and weight/fat loss in terms of the direct impact on caloric expenditure.  And the fairly depressing conclusion is that moderate/realistic amounts of exercise (for the typical person) are unlikely to have enormous effects in terms of body weight/body fat per se, or in increasing the total amount of weight/fat loss when added to a diet.

Certainly larger amounts of exercise can approach significance (and as folks become fitter, they can burn more calories with activity) but the idea that a little bit of exercise is going to have a massive impact on anything is fairly misguided.  However, there are more ways that exercise might positively impact on weight/fat loss (especially when combined with changes in diet) and that’s what I want to look at today.   I’d mention that readers should check out PJ Striet’s comments in Exercise and Weight/Fat Loss: Part 1 for some other potential benefits of exercise outside of weight and fat loss per se.

Quality of Weight Lost

In Exercise and Weight/Fat Loss: Part 1 I sort of confusingly jumped back and forth between weight and fat loss (mainly using fat loss as a way of estimating how much exercise might actually impact on things); for the most part the big meta-analyses and a lot of studies have focused more on total weight lost in response to exercise with most of them finding, at best, a small impact.

However, anyone who hasn’t had their head under a rock for the past couple of decades, or who has read anything on this website, knows that there is more to the overall equation than just weight loss.  As I discuss in some detail in What Does Body Composition Mean? the body is made of a number of different components including muscle mass, organs, water, connective tissues, minerals, fat, etc.

Just looking at changes in body weight can be misleading; it’s more important to look at what’s happening to body composition; that is, under most circumstances, folks want to lose fat while minimizing or eliminating the loss of lean body mass (especially muscle mass).

Does exercise help with that? That is, does the addition of exercise to a diet change the proportion of what’s lost; that is does it change the quality of weight lost (ideally shifting the loss towards more fat and less muscle mass).  And when you look at the studies the answer is a big old it depends.  A lot of which has to do with the specifics of the diet (especially the amount of protein provided) and the type of exercise done.

For the most part, exercise is found to have a protein sparing effect of some sort; that is less muscle and more fat is lost in response to the same caloric deficit.  It’s not universal with not all studies finding an impact (depending on the, type, frequency, duration and intensity of activity) but certainly the trend is for that.

And here is a place where there does seem to be a difference in what type of activity being done with studies (and practical experience) finding that resistance training (especially coupled with adequate protein intake) being superior to aerobic activity (or a low protein intake) for limiting lean body mass loss and, thus increasing fat loss in response to a diet.  And while more mixed, there is some suggestion that this helps to limit the normal drop in metabolic rate that tends to occur with weight loss.

Put differently, as I phrased it in The Rapid Fat Loss Handbook, if there’s a single type of exercise to do while dieting, it’s proper resistance training.  Coupled with an adequate protein intake, that alone tends to limit (or eliminate) lean body mass losses such that the weight which is lost (in response to the caloric deficit) comes predominantly from fat mass.

So this is a place where even if exercise doesn’t increase the quantity of total weight loss per se (i.e. how much the scale actually changes), it can impact on the quality of weight lost; with proper exercise causing more fat and less muscle loss than would otherwise occur.  Here again, proper resistance exercise, especially coupled with adequate protein, seems to be superior to aerobic activity or diets with insufficient protein.  You can read more about proper resistance training in Weight Training for Fat Loss Part 1 and Weight Training for Fat Loss Part 2.



Perhaps one of the most potentially beneficial places that exercise can play a role during weight loss is with adherence.  I’ve mentioned this in articles before but, for many people, the simple fact of doing some sort of exercise on a given day makes it more likely for them to stick to their diet.  The underlying logic seems to be along the lines of “I worked out today, why would I blow my diet?”

In a lot of ways, this may actually be one of the single most important aspects of successful weight loss attempts, long-term adherence to the plan. I’ve ‘joked’ about this before, saying that the best diet is the one that you can stick to and there is much truth to this joke; at the end of the day after you work through all of the potential benefits of one diet versus another or what have you, the best one for a given individual is the one that they can stick to in the long-term.  If regular daily activity of some sort helps an individual adhere to their dietary plan, that benefit alone may be more important than any actual metabolic effects of the exercise bout itself.

Basically, for some people there seems to be a psychological coupling of exercise with good dietary habits on a day to day basis and clearly that can be of benefit.  Of course, there is a potential negative that needs to be considered: when/if people stop exercising often their dietary habits fall off just as quickly.

In fact, one odd study years ago looked at this issue comparing diet, exercise and diet+exercise for both short- and long-term results.  It found that the diet+exercise group ran into problems such that, when subjects stopped exercising, their diet habits fell apart too.

There is another potential place that this can backfire which I’m going to look at next.


Exercise and Hunger/Appetite

The impact of exercise on hunger and/or appetite is, to put it mildly, complicated.  This is because human hunger/appetite (I’m not going to bother making the distinction between the two here) is exceedingly complex being an interplay of biology, psychology and environment.  These are often separated out for convenience but they all interact.

Looking solely at biology, overall exercise seems to have a beneficial overall impact on acute hunger, showing a decrease at least in the short-term (other work has shown that the overall hunger/appetite regulation system works more effectively when regular activity is performed).

This seems to be related to increased levels of various gut hormones involved in signalling fullness, as well exercise can increase leptin transport into the brain (other studies suggest that long-term aerobic activity may improve leptin sensitivity which is good given that obesity is generally associated with leptin resistance in the brain).    There may still be as of yet undiscovered mechanisms for exercise to impact on hunger/appetite.

Other work suggests that even if exercise can increase hunger, any increase in food intake tends to be less than the energy burnt during the activity itself; that is exercise still has an overall benefit.   It’s worth mentioning that even here there tends to be a large degree of individuality, some people compensate for the energy expenditure of activity better than others and this may be part of what contributes to individual differences in results.

One thing I noticed years ago (and forgot to mention in the Training the Obese Beginner series) is that beginners often seem to get a slight increase in hunger following activity, at least in the first few weeks of training.  I suspect this is due to their general over-reliance on glucose for fuel (falling blood glucose being one of many stimuli for hunger).   At about the week 4 mark, as their bodies started to get the first adaptation to training and started to use more fat for fuel; this effect generally went away.

It’s worth noting that emerging research suggests that there may be gender differences in this effect (along with many others) with women, as usual, getting the short end of the stick when it comes to exercise and hunger regulation.  And this is consistent with earlier studies showing that, under uncontrolled eating conditions, women are less likely to lose weight in response to exercise than men.

Of course, the above tends to interact massively with the psychology of the individual and whether or not they are consciously controlling their food intake.  That second issue is a major confound in a lot of studies that people tend to forget about when they compared different studies.

However, this isn’t always the case and one trap that many exercisers often fall into is assuming that their exercise bout has burned far more calories than it has (you’ll hear folks figuring they must have burned at least 1000 calories in an hour of moderate activity when the reality is probably closer to 400-500) and figuring that they’ve ‘earned’ that big post-exercise junk-food meal.

As I mentioned in Exercise and Weight/Fat Loss: Part 1 it’s usually quite trivial to overcome all but the most massive exercise related energy expenditures.  You can put down 1000+ calories in a big post-workout meal with ease, more than compensating for the energy burn of the activity.

But as much as anything I feel that this comes down to an issue of misinformation and education; people need to be realistic about the number of calories they are burning during activity.  It’s simply almost never as high as they think and realizing this is a first step to avoiding habits that will tend to not only offset but actually reverse any beneficial impact of activity.


Weight Loss Maintenance

As a final topic, I want to look at an issue that is perhaps more important in the big scheme of things than actual weight loss per se.  The rather simple fact that needs to be recognized is that weight/fat loss per se isn’t really the hard part; people consistently do and can lose fat/weight all the time.

The issue is with keeping it off.  That is to say, although people successfully lose weight/fat all the time, they usually end up gaining it back. Frankly, I am of the opinion that strategies to lose fat/weight are no longer the important issue, rather research and practice needs to find out what makes people so poor at long-term adherence to dietary changes (or behavioral changes of all types) and find solutions to that.  Is it biological, psychological, is the distinction even meaningful?  And how do we fix it?

But beyond that issue, this is one place where exercise has routinely shown to have a benefit with regards to overall body weight/body fat reduction programs.  That is, while most studies have not found a massive impact of exercise on weight/fat loss per se, the impact on weight loss maintenance seems to be much much larger.

Both epidemiological and intervention studies have found that maintenance of regular activity following weight loss is associated with better long-term weight maintenance (I’d note that keeping protein intake high also has benefits) but with one major caveat: it takes quite a bit of activity (I’d note that this seems to assume that the diet is relatively uncontrolled after the active weight loss period).

Various lines of research suggest that a weekly exercise energy expenditure of 2500-2800 calories per week is required to maintain the lowered body weight.  If we assume an average of 5-10 cal/min for low to moderate intensity activity, this works out to between 280-500 minutes of exercise per week or somewhere between 40-70 minutes of activity (depending on intensity and frequency) per day.

Again, the above seems to assume that the diet is relatively more uncontrolled following the actual weight-loss intervention which isn’t automatically a good assumption.  But it does put into perspective what may be required in terms of daily activity to maintain weight loss.


Summing Up

So that’s a (for me anyhow) fairly brief look at the potential impact of exercise on weight/fat loss.  As I discussed in some detail in Exercise and Weight/Fat Loss: Part 1, the unfortunate reality is that all but the most extensive exercise programs are unlikely to have much of an overall impact on the absolute quantity of weight lost, especially in the absence of dietary changes.

The average beginner/overweight individual simply can’t burn enough calories in realistic amounts of exercise to have much of an impact.  Reducing caloric intake through various means (discussed in detail in other articles on the site) will almost always have a larger impact on overall energy balance.

However, that doesn’t make exercise useless and there are other ways that activity can positively (and negatively) impact on the overall goal of weight/fat loss.  The first of those is in shifting the quality of weight lost; even if exercise doesn’t affect the total magnitude of scale change, proper activity (with resistance training coupled with sufficient protein intake being superior to aerobic work/low protein) can decrease the loss of lean body mass and increase the total loss of fat.

There are also potential benefits to adherence/accountability with some people essentially coupling daily activity with adhering to their diet.  Anything that makes someone stick to their diet in the long-term can only be beneficial. As noted, this can sometimes backfire, where the person then loses all good dietary habits if their exercise program is interrupted for whatever reason.

In terms of hunger and appetite, exercise seems to have an overall beneficial impact but interactions with the individual psychology of the dieter can affect this greatly; some people will rationalize the consumption of food based on a misunderstanding of their actual calorie burn.  This can completely overcome any benefit of the exercise in terms of energy expenditure.

Finally, exercise appears to have the greatest potential benefit in terms of long-term weight loss maintenance; here studies have shown that regular exercise improves long-term weight loss maintenance.  However, it takes quite a bit with upwards of an hour or more of daily activity required to completely offset post-diet weight gains.

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