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Low Fat Loss Response After Medium-Term Supervised Exercise in Obese is Associated with Exercise-Induced Increase in Food Reward – Research Review

Finlayson G et. ao. Low fat loss response after medium-term supervised exercise in obese is associated with exercise-induced increase in food reward.  J Obes. (2011);2011. pii: 615624. Epub 2010 Sep 20.

Objective. To examine exercise-induced changes in the reward value of food during medium-term supervised exercise in obese individuals. Subjects/Methods. The study was a 12-week supervised exercise intervention prescribed to expend 500 kcal/day, 5 d/week. 34 sedentary obese males and females were identified as responders (R) or non-responders (NR) to the intervention according to changes in body composition relative to measured energy expended during exercise. Food reward (ratings of liking and wanting, and relative preference by forced choice pairs) for an array of food images was assessed before and after an acute exercise bout. Results. 20 responders and 14 non-responders were identified. R lost 5.2 kg ± 2.4 of total fat mass and NR lost 1.7 kg ± 1.4. After acute exercise, liking for all foods increased in NR compared to no change in R. Furthermore, NR showed an increase in wanting and relative preference for high-fat sweet foods. These differences were independent of 12-weeks regular exercise and weight loss. Conclusion. Individuals who showed an immediate post-exercise increase in liking and increased wanting and preference for high-fat sweet foods displayed a smaller reduction in fat mass with exercise. For some individuals, exercise increases the reward value of food and diminishes the impact of exercise on fat loss.


It seems like I haven’t done a research review in forever, probably because I haven’t done a research review in forever.  But since I’m holding off on my little surprise until next week, this seemed as good a time as any.  Today’s paper is also something that is rather important in the overall scheme for folks seeking weight/fat loss.

Now, in the Training the Obese Beginner series, one comment that I made was that most studies have not found a massive impact on exercise in terms of increasing weight or fat loss and I outlined some of the reasons that was the case (mostly focusing on the generally low calorie burn).

That, of course raises the question

But even there, there are often some confusing things that occur in studies of exercise and weight loss, situations where the deficit created by exercise and the measured weight/fat loss aren’t the same.  That is, even where the exercise should have generated X fat loss but doesn’t.  A long-standing question has been why this is the case and there are a number of reasons for it.

One of them, of course, has to do with adjustments to the out side of The Energy Balance Equation that can occur when you perturb things; sometimes people are less active during the day due to fatigue or what have you from exercise.  This works to offset the apparent deficit.

Of course, there are other potential reasons not the least of which is an increase in food intake that occurs with exercise.  That is, while exercise can impact on the energy out side of the equation, it can also potentially impact on the energy in (food) side of the equation; the problem is figuring out which way exercise is going to impact things.

What I didn’t really address in the Training the Obese Beginner series is that, for some people, adding exercise works stunningly to generate fat loss.  That is, while the average response is often poor, averages tend to mask individual responses.  Some people do great but others do not.  Raising the question of what the individual differences between folks are.  One of those is how exercise impacts on appetite and hunger.

Until I write another overwritten series on the topic, simply realize that there can be a hugely variable response in whether or not someone gets appetite suppression (through physiological or psychological means) from exercise or an actual increase in activity.  Clearly, in the case where calories are not being controlled, if exercise causes someone to increase their food intake (for either psychological or physiological reasons), the predicted weight/fat loss will not occur.

And that brings us to today’s paper.


The Paper

The paper wanted to address the question of why the obese don’t lose more weight in response to exercising by looking at how changes in the reward value of food changed with exercise; the basic assumption being that folks who showed a larger increase in the reward value of food would be more likely to overeat foods following exercise.

In looking at this, forty sedentary overweight and obese individuals (13 males, 27 females) with an average BMI of 31.03 and age of 39.3 years were recruited from a larger 12-week exercise study. The researchers examined the acute impact of exercise on the reward value of food before and following a 12-week supervised exercise program.

To assess food reward, the subjects were shown 20 pictures of foods varying in taste and macronutrient properties which were categorized according to sensory domain (sweet or non-sweet) and fat/carbohydrate content (high/low). Subjects rated the subjective reward value using a visual scale based on liking, wanting and preference.

I won’t detail this because it’s boring and uninteresting.  Results were tallied for each of the four food categories (high-fat/non-sweet, low-fat/non-sweet, high-fat/sweet, low-fat/sweet) to see if there were differences in changes in reward for different types of foods.  The foods were rated immediately before and after a single exercise bout (to see if exercise impacted on reward value) and both initially and 12-weeks later (to see if there were any long term changes).

Subjects were subjected to a 12 week exercise program where they burned 500 cal/session 5 days per week for a total of 30,000 calories over the total study length.  Weight loss was assessed and subjects were divided into responders based on their actual weight loss.

Only 34 of the original 40 subjects finished the study and of those there were 20 responders (6 of whom were males) and 14 non-responders (7 of whom were males) and the individual variability in net energy balance (based on measured weight loss) was massive (see graphic below).

Variability in Energy Balance
Variability in Energy Balance


Subjects below the zero line were those that lost the expected amount of fat or more (based on estimations of the energy values of body fat and muscle) and were termed responders; those who are above the zero line lost less weight/fat than predicted and were termed non-responders.  The average responder lost nearly 5kg (10+ lbs) over 12 weeks, the non-responders a mere 1 kg (2.2 lbs).

And, as expected, there was a clear correlation between the actual changes in fat mass and the changes in reward value of foods.  The non-responders fairly consistently demonstrated a different response in terms of reward value for foods following activity with the largest impact being seen for (drum roll please) high fat and sweet foods.  In contrast, the responders showed either no significant response or a slight decrease in the reward value of the different categories of foods.

I’d note that after 12 weeks, even in the non-responders there was a difference by week 12, while they still showed a greater response in terms of reward value following activity compared to the non-responders, the effect was blunted compared to at the beginning of the study.  Something had changed in the physiology of the non-responders; it wasn’t eliminated mind you but the effect was blunted.


My Comments

Clearly the results of this study (which I’d note fit into a previous data set showing that exercise tends to either have a neutral or increasing effect on food reward; it rarely has a negative effect) indicate one potential reason that exercise is either ineffective for weight/fat loss or, if not ineffective, shows such variable responses.

Clearly some people add activity to their regimen and lose fat/weight just as expected; others are frustrated.  And while there are other reasons that might cause this to occur, clearly an increase in food intake (and especially high-fat/sweet foods) would be a real problem.  Of course, this is only a real issue under conditions where calories/food intake isn’t being controlled.  Which is the condition that a lot of exercise studies are tested under.

Of some interest is that the impact of exercise on food reward is blunted after 12-weeks although it doesn’t appear to go away completely in the non-responders.  I actually mentioned in the Training the Obese Beginner series that I had often seen an increase in hunger in the first few weeks of exercise but that often switched itself as adaptations started to occur.  Clearly something may go on with long-term activity in terms of reprogramming some aspect of physiology.

If anything else, I think this study points out, yet again, that exercise is no magic pill for fat loss.  Clearly for some people, those who don’t find an increase in their hunger and liking for high-fat/sweet foods, exercise can work wonderfully even in the absence of explicit calorie control.  Since they don’t increase their food intake from high calorie/high-fat/sweet foods, they don’t get into trouble.   But for others, those who get an increase in the desire to eat such foods, there’s a problem.  Even if they don’t realize it, their increased desire for such foods will likely end up causing them to eat more after exercise sessions, eliminating the exercise induced deficit.  Results will be poor and they are likely to quit.

In that situation, either a diet that allows such foods in controlled amounts (e.g. a flexible dieting approach or something like Martin Berkhan’s Leangains) to be consumed or simply the realization that uncontrolled eating will cause problems has to happen.  Clearly left to their own devices, their bodies are causing problems.   They’ll have to find a workaround or count/control their food intake (at least until they stop getting such a pronounced effect).

And tune in next Tuesday for my surprise….

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