Over the years, I've had some patients tell me they only need to smell food to gain weight. Of course, I didn't entirely believe them -- and I'm sure they never expected me to! But they did expect me to believe the point they were exaggerating: that they gain weight more readily than others, that they don't need to "overeat" per se to get fat, and that they may find weight loss next to impossible.
And all of that, I certainly do believe.
Body weight is about energy balance, and that, in turn, is about calories in versus calories out. I have asserted this many times before, and the fact that I do so again is not stubbornness on my part. It is simply that the fundamentals of physics and the laws of thermodynamics have not changed over the span of my literary career! And therefore, neither has my opinion on this topic.
Despite the claims of some that weight is all about one kind of macronutrient; or of others that calories don't count -- the simple reality is that the relationship between matter and energy is fixed well above their pay grades (and mine). I believe that only the truly foolhardy enter an argument about physics with Einstein and Newton.
When calories are excessive, people can gain weight eating all carbs or no carbs; high fat or low fat; high or low sugar, or protein, or sassafras. When calories are restricted, I've found people can lose weight -- and have done so -- eating no cheese or nothing but cheese; no cupcakes, or nothing but cupcakes. When calories in exceed calories out, weight goes up; when calories out exceed calories in, weight goes down. Short of any hair splitting that, in my opinion, isn't worth our time, that's it.
But ... what determines how many calories in are needed to meet demands? What determines, for any given individual, how many calories in are required before calories out are exceeded -- or vice versa? Ah, there's the rub!
We know the basics, of course. Calories in can be counted in food, using a device calling a calorimeter. Within a modest range of error, we can say with confidence what calories are coming in.
And we know where calories out go. They go to resting energy expenditure, they go to fuel physical activity, they go to generate heat and, in children, they support growth. That's pretty much it.
But how many calories are required to support any given activity? How many calories are wasted in heat generation? How many are used at rest to support basal metabolism?
Where calories in match calories out is highly variable, and not a matter of choice. Any two people, doing the same physical activity, will burn different numbers of calories due to a complex interplay of genes, body composition and physiology. Any two people, eating the same foods in the same quantities, may experience entirely different effects on weight -- one gaining, one losing -- dependent again on genes, resting energy expenditure, body composition, body mass and a long list of factors we are just beginning to appreciate.
Among those factors, one getting particular attention these days is the bacterial population of our GI tracts. The so called "microbiota" exert a profound and diverse influence on our health, including but by no means limited to our digestion. This is not surprising when one considers that bacteria in the human body outnumber cells of the human body by at least 20 to 1. With variation in GI flora, there is variation in how many calories are extracted from food, and in whether fiber is the non-caloric roughage we have long contended, or a source of additional calories.
Variation in gut flora can be a factor in weight loss resistance -- the inability to lose weight under conditions of physical exertion and calorie restriction that would do the trick for most people. Other factors might account for this as well, including some viral exposures; various hormonal imbalances involving insulin, leptin, thyroid hormone and cortisol to name a few; insomnia; and genetic polymorphisms (different versions of a given gene) that in some cases render entire ethnic groups, such as the Pima Indians, extremely vulnerable to weight gain and extremely resistant to weight loss.
If you happen to find yourself at the extreme end of the weight loss resistance bell curve, you live daily with the injury of gaining weight you don't want, and the seeming impossibility of losing it. You also likely live with the daily addition of insult to injury, because people look at you and assume you aren't really trying.
Unfortunately, we don't yet know how to identify and fix all the factors contributing to weight loss resistance. But we can identify, and fix, the stigma of illegitimacy that further burdens those who live with it -- we can at least admit it's real. We can acknowledge legitimacy, and cultivate solidarity.
And, ideally, we can do better than that. Two heads are better than one, and the hive mind more powerful still. Perhaps by sharing both frustrations and insights, a community wrestling with this can find solutions that have eluded individuals.
Let's try. In support of these very goals- understanding, and overcoming -- I have launched the National Exchange for Weight Loss Resistance. If you are affected, please join us. Weight loss resistance will be a tough nut to crack, but in unity, we may muster the strength.
Follow David Katz, M.D. on Twitter: www.twitter.com/DrDavidKatz