Another Reason to Go Predawn – Better Fat-Burning

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Photo creditRun by Flickr user Satish Krishnamurthy, used under a Creative Commons Attribution 2.0 license.  Image is included in the Predawn Runner / Running Manifesto Calendar and is also available as a Predawn Runner Mouse Pad.

A recent post in the Well Blog of the New York Times provides another reason to become a Predawn Runner (as if the 20+ reasons provided previously for running predawn weren’t enough).  It appears, based on a study out of Belgium, that exercising before breakfast provides greater health benefits than exercising at other times of day.  The benefits specifically focus around maintaining weight in the face of a deteriorating holiday diet – one can presumably extend this conclusion to cover losing weight or maintaining weight with a more reasonable diet as well.  This is great news for those of you already committed to exercising early – but note that there are certainly a lot of caveats regarding this study, as there typically are for any such “research” leading to such sweeping conclusions.

First, the benefits cited are really related to exercising in a fasted state, not specifically to running predawn. Obviously, for most of us, the only realistic time to exercise in a fasted state is before breakfast, so this is a minor caveat, but for precision sake it is best to make sure the cause-benefit relationship are more directly understood.

Second, the study focuses specifically on young men, and, as implied by the statement that the control group had to be convinced not to exercise, one can assume they were already in respectable condition with reasonable health habits.  This, again, may not be much of a caveat, but it would be fair to question if the same results would be achieved (at least as dramatically) with women, or with older men.  Perhaps metabolic patterns are different, and this may drive different results – though there is other evidence that exercising in a fasted state yields more fat-burning benefits, and the logic as to why this occurs is sound.

Third, the subjects seemed to participate in intense workouts for a 60-90 minute period.  Thus, it is unclear if performing a less strenuous workout or doing so over a shorter period (say, 30 minutes) would result in the same difference in fat-burning results. Thus, a three- to five-mile recovery run may be just as valuable at other times of the days (though you can refer to the other 20+ reasons as to why you may want to get it done early).

Finally, the benefits sought were strictly around weight loss or maintenance.  As the post notes, this doesn’t necessarily bring benefits to your performance during the workout or to your conditioning or preparations for a future goal (say, meeting a 3:00 marathon).  In fact, other studies have claimed that performance tends to be slightly better in the afternoon, for various (and perhaps not fully understood) reasons.  However, the same post points out studies that indicate the body adapts to the time of day you “normally” choose to exercise.  Of bigger concern is the fact that relying on fat to generate your energy is less-efficient than having carbohydrate stores to quickly draw from – this can be more limiting on a longer workout, for certain and may be reason to take in some calories in the morning before or during key long runs or even high-intensity workouts (admittedly, I rarely do this, and I can’t claim that performance has suffered because of it).

So, even if your intent is not strictly weight loss, it is likely that at least part of the benefit you seek from running is better overall health.  If you’re not already a predawn runner, maybe it’s time to consider making the jump and getting a quick start to meeting your New Year’s resolution to live a healthy lifestyle.

Hat tip to Nathan Adkins for sending this article along to me.

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  • jen small

    great info~and of course this could apply to any fun activity that gets your HR :)

  • Vera

    Interesting study – I went into PubMed and read the Abstract (of course there is a lot of methodology, etc that you can’t see without buying the article). There are a couple of red flags for me as a former exercise science researcher. Eating a diet that is 50% fat for 6 weeks and increasing caloric intake by 30% – assuming these young healthy males were not eating a high fat diet previously – could cause a whole slew of hormonal and regulatory physiological changes and increase total body fat oxidation on it’s own (especially if they were regular exercisers before the study began). Some exercise studies have shown that eating a high fat diet prior to exercise increases total fat oxidation, but does not improve performance. The GLUT4 levels are could easily be explained by diet alone also as this protein is involved in the transport of glucose into muscles and fat tissues and is regulated by the presence of insulin. GLUT4 was likely higher in the Fasted exercising group because their muscles were dying for carbs!!!! Consuming a high fat diet at the expense of carbohydrate ingestion could mean there is less glucose available to exercising muscles but we would need to see how many actual grams of Protein, Carbs and Fat subjects were consuming to draw any conclusions here (and know what the concentration of muscle glycogen was at the beginning of each exercise bout). Insulin responds primarily to carbohydrates so it is not surprising to me that the Fasted exercising group showed a higher sensitivity to insulin (insulin stimulates glucose uptake by muscle/fat tissue) and thus could explain the increased whole-body glucose tolerance. The question remains as to how active these college-aged boys were coming into the study, what type of exercise they did prior to and during the study and what their diets were prior to their participation.

    As regular exercisers (especially endurance athletes), we are better fat-burners in general because regular exercise increases the activity of enzymes (one big one in particular) involved in the fat-burning cycle, even when we’re sitting around watching TV (relative to non-exercisers and those who “overfeed” themselves). Exercising intensely for 60-90 minutes obviously increases your metabolism during exercise in order to keep up with energy demands (ATP production), but it will also keep your metabolic rate (and an important enzyme needed for fat oxidation) elevated for several hours after you stop. From what I’ve read (and believe :-) ), the benefits of exercising in the morning have to do with the increase in your metabolic rate early in the day with a lasting effect for the next several hours. There are a few studies that have shown exercising in a fasted state trains your body to utilize more fat for energy due to a decrease in glycogen availability (a result of fasting) which may be beneficial for say, marathoners whom in the final miles of race are approaching glycogen depletion. Training in this state may delay the point at which you would “hit the wall”.

    Anyway, that’s my 2 cents. I hope I didn’t bore the crap out of everyone. You know I love this science stuff! Thanks for sharing! :-)

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  • Anonymous

    Excellent cursory literature review. Another factor I wonder about that relates to what the subjects diets were prior to participation in the study, and the diet consumed as part of the study (50% fat and 30% calorie increase), is the fatty acid profile of the diet. Studies have shown that when rats are fed diets high in polyunsaturated fast, for example, over time these fats make up a greater proportion of fats associated with muscle and adipose tissues, and more fat is used in routine metabolism, and this is also correlated with great stamina during “burst” physical performances like treadmill running. If experimental diets were relatively high in saturated fats relative to others. Still, with appropriate experimental design, these sorts of things can be controlled for, and without the full text of the paper it is impossible to know whether the researchers addressed these issues, and what assumptions they were forced to make. That’s a pretty common problem with the way basic science trickles into practice. The descriptions of studies are usually overly simplified, leaving out many of the caveats addressed by the researchers in the original paper, and worst of all, the results are stated as rule rather than in the probabilistic terms they are reported in by researchers, and are overgeneralized with erroneous implications.

  • Greg Strosaker

    Great points Vera (and I wasn’t bored at all) – I didn’t go so far as to read the abstract but as all studies have limitations, I’m not surprised to read of your suggestion of further caveats to the conclusions. I had wondered about the potential benefits to marathoners in “avoiding the bonk” by running in a fasted state as well, thanks for raising the point.

  • Greg Strosaker

    It is clear that Predawn Runner draws a discriminating crowd, from your and Vera’s responses, Mark. Yes, press reports of scientific research always tells only part of the story, and the research summary itself often leaves out important considerations either out of laziness, a desire to keep it readable, or, sometimes a desire to reach a specific conclusion. Thank you for raising those points here and we are left to wonder how well controlled this actual experiment was (though that doesn’t dim my belief in the value of the predawn run!).

  • Jason Fitzgerald

    Really interesting. I’ve read before that exercising in a fasted state (in the morning or otherwise) can teach your body to a higher percentage of fat for energy as opposed to glucose. This is basically what this study is saying, but the practical application of this is that it can help marathon runners. By teaching your body to burn more fat instead of sugar, you’ll be less likely to hit the wall in your next marathon.

    There was an article awhile back (I forget where) that talked about using GU or other fuel during long runs. The main point was not to take in fuel during every long run because you’ll be teaching your body to rely more heavily on sugar.

    Same idea, different application. You can make a few simple changes to your training to enhance your body’s ability to burn fat instead of sugar, and therefore become a better marathoner.

  • Greg Strosaker

    Good comments Fitz, Pfitzinger (in Advanced Marathoning) discusses running in a glycogen-depleted state as a key competency for a marathoner to build for the same reason you mention above. I never take fuel with me on a run (not specifically to force the fat-burning – I’ve just never seemed to need it) and this is a good argument not to start doing so (fortunately, my stomach is tolerant of whatever gels race organizers have used in any marathons I’ve run so far, so I don’t feel the need to test things out).

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