DO THE MATH! If you have just begun to train for an upcoming fall endurance race or plan to start soon for a Thanksgiving weekend Turkey Trot those long steady walks or runs will likely get you on track to lose weight before the holidays, right? More calories burned in exercise can help create a calorie deficit, that will lead to lost body weight, right?
Maybe. A previous Summer Science Friday post revealed that those who ‘overcompensate’ for the energy that is expended during exercise tend to not lose as much weight as expected or may gain weight. Overcompensation occurs when, in response to exercise, food intake is increased and time spent at non-exercise physical activity decreases. In effect, we erase the benefit (in terms of calorie deficit) that was created by the exercise.
An article from the NYTimes.com WELL blog discusses another scientific study that revealed similar results with respect to food intake compensation. Researcher Dr. Kyle D. Flack and colleagues from the University of North Dakota and other institutions wanted to learn if exercise alone could lead to weight loss even if participants compensated for the extra activity by eating more.
Thirty-one sedentary, overweight women and men, aged 18-49 years old, were invited to join the project and 29 completed it. For 12 weeks, having been instructed not to alter their diets or lifestyles, about half of the group (14) aerobically exercised 5 days per week, such that they burned 300 calories per day (1500 calories total/week), about 30 minutes/session. The remaining 15 participants exercised twice as much, burning roughly 600 calories per day (3000 calories per week), about 60 minutes/session.
Each were prescribed a customized 5-day exercise plan, which included 2 lower intensity sessions and 3 interval sessions, that was based on an initial heart rate-zone training assessment session. When analyzed as a group there was no significant loss in fat mass or percent body fat in the 300cal/day exercisers; half of the individuals showed some decrease. Of the 600cal/day group, 80% lost fat mass, and significantly more than in those in the 300 cal/day exercisers, some greater than 10%. Curiously, both groups ‘compensated’ by taking in about the same number of additional dietary calories (943 and 1007 respectively) per week.
The GOOD NEWS message is that body re-composition in terms of fat mass loss is possible in persons who under- rather than over-compensate for the energy expended in exercise. However, it will likely require a higher level of weekly exercise-generated calorie burn to beat the usual dietary compensation that occurs. Roughly twice the level recommended by the CDC (it advises 150 minutes/week), at least 300 minutes, over 7 days.
The study authors admitted, as usual, the limitations of their work (too few subjects, too short a duration, no attempt to identify gender/racial/ethnic differences, not measuring or accounting for other factors, difficulty of tracking diet changes with recall, etc.), but the results it generated are encouraging.
Perhaps we cannot help bumping up calories taken in because of exercising, but this work suggests we might be able to overcome the response with a bit more effort working them OFF. Possibly there is a limit to how far our own bodies will go to sabotage fat loss attempts without our complete awareness. The participants did not report eating more in their food diaries, seemingly not recognizing they did so.
Other potentially GOOD NEWS might come from the exercise part of the fat loss equation; certain types of exercise may turn up the calorie burn after physical activity. Discussion of an EPOC, or Excess Post-Exercise Oxygen Consumption, research study informs us that resistance training and higher intensity intermittent aerobic training can provide a longer calorie after-burn when compared with steady state aerobic exercise performed at continuous, unvarying, moderate intensity, if the exercise duration and amount of energy expended is the same.
Post-exercise calorie burn, identified as a higher resting metabolic rate (RMR) in the study, continued at 12 and 21 hours after resistance or interval training had ceased, at the rate of about 12 calories/hour above that seen with steady state exercise (other studies indicate EPOC can continue up to 48 hours). Doing the math means that (21 x 12) 252 is possibly the number of additional calories can be burned almost one day after exercising.
Let’s switch back to the North Dakota study initially discussed in this post. It found that regardless of exercise duration (30-minute versus 60-minute sessions x 5 days/week), the amount of calculated weekly food intake compensation was roughly equal to 1000 calories for all participants.
Thus, if exercisers take advantage of EPOC, and perform 4 sessions of the tougher, higher calorie ’after-burn’ activity, like resistance and/or interval training, inadvertent extra food intake/increased appetite could nearly cancel out the benefits. Or, with training adaptation, exercise efficiency can attenuate EPOC effects.
It’s an exaggeration, but the point is that no matter how much we fine tune our exercise sessions in order to change body composition, such that fat mass is decreased (the reason to “lose weight” for many) we can override the burn with increased dietary intake or with reduced non-exercise activity..
The initial intent of this SCIENCE FRIDAY post was to cover the science of EPOC and discuss new research, in order to help myself and others plan fitness programs. It was a bigger subject than I realized. After getting deep into the details, it seemed to me that traditional advice might still be given but with a new perspective:
Research (above) suggests that exercise duration must be as long as an hour/day on 5 days/week over 12 weeks for it to be effective in assisting with body re-composition/fat loss efforts, such that an almost subconscious tendency to eat more after exercise can be overcome. [The subjects in the study did not report eating more, but their body composition data plus analyses indicated intake had increased].
If true, exercisers will need to persevere over a much longer time, especially to maintain body changes into the future. We will need to enjoy, even LOVE, this exercise in order to work at it for an hour on most days of the week.
As has been said many times, the best exercise for each of us is the form that we can stick with over the long haul. Activity we happily anticipate. It could be steady state running or elliptical work, HIIT speed walking, an aerobics jazzercise class, cycling studio session, lap swim, or strength training routine. A mix of many different activities is ideal, if we listen to the advice of trainers.
However, care must be taken to avoid unrecognized food over-compensation that might derail attempts to preserve lean muscle mass and shed fat mass though physical activity. The hopeful news to be taken from scientific work is that it may be POSSIBLE to exceed these compensatory responses by bumping up exercise duration!
The final word on the complex subject of using to exercise to assist with fat loss, often the origin of much discouragement when we gain weight after starting a tough training program, is mindfulness. Yes, it is an overused term lately. However, when it comes to physical activity, being mindful of the body’s likely response can be one defense against an unwanted outcome.
Do the math, or at least understand it; calories taken in shouldn’t exceed those burned in exercise if, over time, fat pounds are to successfully be subtracted rather than added.
RUN & MOVE HAPPY!
NOTE: An article by Amy Schlinger for Under Armor’s MyFitnessPal.com blog explains Excess Post-Exercise Oxygen Consumption, or EPOC nicely.
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Running, walking, and fitness activities enable us to experience our physical selves in a world mostly accessed through use of fingers on a mobile device.
EARNED RUNS is edited and authored by me, runner and founder. I began participating in road races before 5Ks were common. I've been a dietitian, practiced and taught clinical pathology, and been involved with research that utilized pathology. I am fascinated with understanding the origins of disease as well as health.
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