Weighty Matters

America, they say, has an obesity crisis.  And god knows I’m doing my bit to contribute.

But diet and weight may be far more  complex than we like to think.  I recently heard a woman assert on the radio that we (as in, the nutritionists) know how to get people lose weight: Eat less, and exercise more.

Unspoken, of course, is the fact that only a vanishingly small fraction of Americans can lose weight and keep it off with this approach.  So we may know how people should theoretically lose weight, but we certainly don’t know how to make it work in practice.

So eat less and exercise more seems more akin to a slogan than a working solution in the real world.

Now, some simple math lets us see why this is so, and it may also offer some insights into energy and metabolism too.

Before we begin, I’d like to point something out that is infrequently commented upon.  While plenty of us are overweight or obese, a relatively few of us are actively gaining weight or losing weight on an ongoing basis.  It’s common, for example, for someone to be carrying an extra twenty pounds for ten years.  Far less common to see them gaining more and more weight year after year after year in an unstoppable march of weight gain.

Which means that people who are overweight but at a stable weight are not chronically overeating (since they would then chronically gain weight.)  Instead, they are eating enough to maintain their weight.  They are in energy balance.  And so gluttons they are not.

Energy Balance:

The classic view of diet and weight is that we consume energy (in units of Calories with a capital “C”) that we use to keep our metabolism running and to perform physical work.  We also expel some energy as waste products.  If we eat more Calories than we burn or excrete, then we are in Caloric excess, and those unneeded calories will get stored as fat.  If we don’t eat more than we need, the energy balance equation is simply:

Calories In = Metabolism + Work – Waste.

You balance that formula and you’re good to go.

Well, now we are in a position to explore why this is too simple to serve as a good basis for dietary control.  Let’s get to the numbers.

In very rough numbers, an adult human being needs to consume perhaps 2,400 Calories per day.

A pound of fat contains approximately 3,500 Calories of energy (stored as triglycerides)

Now, over a two year period, what must go wrong so that a person gains, say, five extra pounds?  Let’s see:

Required caloric input is 2,400 Calories x 365 days/year x 2 years = 1,752,000 Calories

Calories associated with five pounds is 3,500 Calories/Lb x 5 Lbs = 17,500 Calories

As a percentage of this person’s diet, they need to over eat eat by:

(17,500 C / 1,752,000 C) * 100 = 1%

That’s right.  If our caloric input is off by 1%, we will gain (or lose) five pounds over two years.

Now here’s the question.  Who on god’s great earth can consciously regulate their caloric input with 1% accuracy?  Can you tell a 300 Calorie hamburger from a 303 Calorie hamburger?  How about a burger at 297 Calories?  I suspect not.

Indeed, if such a small caloric imbalance can lead to weight gain (or loss, I might add), we should actually be much more astounded that there are human beings in the world who can maintain a stable weight at all!

We should also wonder about traditional diets that call for steep reductions in caloric intake.  Many diets will call for someone to reduce their intake by 500 or more Calories per day.  But this is an asymmetric response to a condition that our formula tells us has come about by only the tiniest of caloric imbalances over time.  Something that extreme ( a 500 Calorie or 21% reduction in energy input) almost by definition cannot be maintained indefinitely.  So of course traditional diets fail.

The fact that most people maintain a more or less stable weight (whether slim or overweight) actually tells us something very interesting.  Since our daily caloric input varies from day to day and cannot be consciously controlled down to the level that the energy balance equation would dictate, it is clear that our bodies are able to accommodate fluctuating energy input to some extent without gaining or losing weight.  Perhaps (within reason) we metabolically slow down when food is scare, and we metabolically rev up when food is plentiful, allowing our weight to remain stable.  Perhaps.

Now, understanding that the energy balance approach is highly infeasible as a weight control tool does not mean that we have a good alternative at hand.  But it does suggest that looking around for an alternative to eat less and exercise more is probably an idea whose time has come.