Health is what your body desires, and no matter what you do it seeks to repair and restore balance. Under eat and hunger will step in, over exercise and fatigue will kick in. We have the ultimate compensatory behaviours to attempt to maintain our existence no matter what we (or our Personal Drainers, Tracy Anderson, Boot Camp etc) throw at us.
Exercise brings with it a compensation factor, and after a hard trip to the gym, a class or a long run we typically become hungry and need to eat. Various arguments exist regarding whether the exercise always makes you hungry, or whether it is because you seek a reward for good behaviour (remember most of us are conditioned towards behaviours with so called positive reinforcement that is taught throughout our schooling/childhood).
I used to people watch between clients at the gym, mystified at the aerobics class members going for cake and coffee post class. Maybe its the reward factor, the social need, or the need to replace the energy they have just burned in "bums, tums and yogalates zumba class. So, in this respect the body compensates for the energy expenditure by inducing a behaviour that sees some degree of restoration of energy balance. An odd concept in a world built on burning calories...surely the net loss (if it were that simple) could be more easily achieved by avoiding the class altogether?
Since 2002 we have discussed the effects of dieting, or semi-starvation and the simple fact that we need energy to survive. The more we try and burn away energy stores the more the body will increase appetite to protect itself. Eric Ravussin, chair in diabetes and metabolism at Louisiana State University and a prominent exercise researcher agrees stating:
"In general, for weight loss, exercise is pretty useless" (1)
McClave and Snider (2) found that muscle uses 13 kcal/kg/day (22% of RMR) where as adipose tissue uses 4.5 kcal/kg/day (4% of RMR) So by converting (which is the mythical offer in most gyms), 10 kg of fat into muscle, you would in theory only get an extra 85 kcal allowance per day.
Despite spending our hard earned cash on personal trainers, fat or boot camps, aerobics, zumba, marathons, Tracy Anderson blah blah blah, we aren't any thinner (remember I tried all this **** in 1999-2001. After an hours class we crave sugary calories like nothing on earth. Some use willpower, and break down muscle tissue to help them cope, but for most a sports drink or a chocolate muffin replaces (and some) the energy burned in about 30 seconds. Now, I'm not saying that's a bad thing, remember the body is trying to stay healthy and you've just been personal drained so you need it.
Willpower can help a few people avoid the post exercise calorie craving, but our physiology isn't designed to do that. We are after all designed to replenish our energy reserves after a bout of activity/stress, so most people crumble and drop out of the perceived appropriate behaviour.
Steven Gortmaker, the head of Harvard's Prevention Research Center on Nutrition and Physical Activity, stated in the original Time article (1):
"The most powerful determinant of your dietary intake is your energy expenditure, If you're more physically active, you're going to get hungry and eat more."
And he suspiciously pointed a finger at McDonald's restaurants, asking
"Why would they build those?"
referring to the playgrounds they all seem to have nowadays. He points out that,
"I know it sounds kind of like conspiracy theory, but you have to think, if a kid plays five minutes and burns 50 calories, he might then go inside and consume 500 calories or even 1,000."
A paper published by Gortmaker and Sonneville (3) found that
"there is a widespread assumption that increasing activity will result in a net reduction in any energy gap"
Energy gap = the difference between the number of calories you use and the number you consume. Gortmaker and Sonneville found during 18-months observing 538 students they ended up eating an average of 100 calories more than they had just expended when they began exercising.
The other way our body can compensate for this outburst of activity is by making us less active post activity/exercise. As mentioned earlier, the body wants to stay in balance and preserve itself. We hear all the time that our leisure activity has decreased since the 1980's, how we are increasingly sedentary (ignoring the energy needs of an increasingly stimulated brain, in particular the visual cortex), yet exercise is now a commodity that we buy. Walking, getting out in nature taking a stress free stroll all sound great, but as a nation we seem obsessed with being abused by a personal trainer at the gym, and we seem to be paying for it more than we ever did.
Researchers from Peninsula Medical School studied 206 kids, ages 7 to 11, at three schools in and around Plymouth. (4) The first school was private academy where they got around 9.2 hours per week of rigorous physical education. Kids at the two other schools, one in a village and the other an urban school got just 2.4 hours and 1.7 hours of PE a week. The kids wore ActiGraphs which measure the amount of physical movement and the intensity. The kids at the private school had significantly more physical activity at school, but overall they didn't move more. Alissa Frémeaux from the study commented:
"Once they get home, if they are very active in school, they are probably staying still a bit more because they've already expended so much energy," and that "The others are more likely to grab a bike and run around after school."
What and how you eat is far more significant in weight loss than how hard you try punish your body. You may claim that you feel good after exercise, and I'll cover that in another post soon. Why not save your cash, avoid the beasting by your PT who makes your throw kettlebells around, skip the post exercise binge, avoid crashing on the sofa, and exchange it for, eating consistently, knowing your energy needs and going for a walk.
1. Time Magazine. Why Exercise Won't make You Thin. http://content.time.com/time/magazine/article/0,9171,1914974,00.html
2. McClave, S, A., & Snider, H, L. (2001). Dissecting the energy needs of the body. Curr Opin Clin Nutr Metab Care. 4(2): 143-7.
3. Sonneville, K, R., & Gortmaker, S, L. (2008). Total energy intake, adolescent discretionary behaviors and the energy gap. Int J Obes. 32(6): S19-27.
4. Fremeaux, A, E., Mallam, K, M., Metcalf, B, S., Hosking, J.,Voss, L, D., & Wilkin, T, J. (2011). The impact of school-time activity on total physical activity: the activitystat hypothesis. International Journal of Obesity. 35: 1277-1283.