Weight reduction: basic science fail

Recently, there's been a debate over at forskning.no regarding whether overweight is best dealt with by activity or diet, and which factor has the largest impact. This debate has also raged on in various fitness and nutrition magazines for as long as I have paid attention (and longer), and is important mostly because magazines can't sell ads if the rest of the magazine is empty. The differing points of view can be exemplified by the following feature articles - one from the diet-matters-most camp, respresented by Pål Tangen Jåbekk, and one from the activity rules camp, represented by Eivind Aadland. The former feature article by Jåbekk is perhaps the most entertaining. While the piece is quite rambling and incoherent (including the brilliant statement "Like the rest of the population, the "scientists" have also fallen into the trap" (of believing that there is a correlation between working out and losing weight)), the conclusions are very interesting:

"Vi har blitt lurt til å tro at vi kan redusere energiinntaket vårt uten at det påvirker energiforbruket, og tilsvarende at vi kan øke energiforbruket uten at energiinntaket også øker. Dette forutsetter som sagt at energiforbruk og energiinntak er det man kaller uavhengige faktorer. Det er de ikke. Basta.

Om du legger på deg eller ikke, blir ikke styrt av hvor mye du spiser, men hva du spiser. Om trening gjør oss tynnere, så er det ikke fordi vi forbrenner mer energi når vi trener.

Så til alle dere som står krokbøyd over stepmaskiner rundt i det ganske land og teller kalorier; dere har blitt lurt. Det har ingenting å si hvor mye du forbrenner. Det er ganske enkelt ikke sånn kroppen virker."

Loosely translated: "We have been duped into believing that we can reduce our energy intake without it affecting the energy expenditure, and correspondingly that we can increase the energy expenditure without a concomitant increase in energy intake. This presumes that energy intake and energy expenditure are independent factors, which they are not. Whether or not you gain weight is not controlled by how much you eat, but rather what you eat. If working out makes us thinner, it is not because we expend more energy when we work out."

I don't know about you all, but upon reading this, I got a flashback to one of my favorite Simpsons episodes, wherein Homer walks in on Lisa, points to her (functioning) perpetuum mobile and exclaims: "LISA!! In this house we obey the laws of THERMODYNAMICS!"

While I don't claim to have the be-all end-all answers to the question of whether dietary or activity-related factors are weighted higher (to the extent one can claim one ratio of variables to be true for the entire population or even for large population segments), what I DO know is that there are two extremely important aspects which are overlooked in this sample debate (although mostly by Jåbekk as exemplified by his conclusions above):

1: The human body obeys the Laws of Thermodynamics
There is a relationship between the energy input (i.e. caloric intake), the energy expenditure (i.e. calories consumed) and the variable body mass. If you keep the activity level constant and vary the caloric intake above or below the maintenance threshold (number of calories required to maintain your current body mass and composition under your present activity level), you increase or reduce your bodyweight, respectively. Unless you drastically change the nutritional composition of your diet simultaneously, that is. So making blanket statements about how it does not matter how much you eat but what betrays a fundamental lack of basic thermodynamics. And while there is no doubt that factors such as glycemic index and p/f/c ratios significantly affect the metabolic rates etc., you can't escape the basic truth that of you take in less energy than your maintenance threshold, you'll create a negative caloric balance, which over time leads to weight loss.

Beside the co-dependence of these variables pointed out by Jåbekk, there's this thing called free will. According to Jåbekk's conclusions, increasing your activity level leads to an increased caloric intake. What I suggest is the following experiment to test Jåbekk's hypothesis: Tomorrow, write down exactly what and how much you eat. The day after tomorrow, eat precisely the same amount of the same food at the same time, but increase your activity level - say by running up and down a flight of stairs instaed of just ascending or descending every time you have to traverse floors. If Jåbekk is correct, you'll wake up in the middle of the night with a mouthful of food exactly big enough to compensate for the extra activity, without knowing how you got there and with no chance of controlling your eating. In the likely event that you don't experience involuntary feeding following this experiment, the conclusion must be that Jåbekk is full of it.

Not only do Jåbekk's conclusions negate the possibility of free will, but it also makes it impossible for a person to be anorexic, for example. Wow - that was easy. I wonder if he does requests?

2: Body composition is more important than body mass
Why is it that the success of a diet and exercise plan is measured by the change in body mass? There are plenty of athletes who weigh approximately the same - or more - as Michael Moore at the same height, so why am I stuck with the sneaking suspicion that Moore is not as healthy as the body mass index would suggest? And what about the fact that muscle weighs more than fat, so if you start to exercise, you'll build more muscle mass, the added weight of which will offset the concomitant fat loss?

Gotta love soft sciences