Those Thanksgiving Calories: Of Hollow Leg, and Hypothalamus

Posted: 11/19/2012 3:57 pm Dr. David Katz

Among my family's Thanksgiving traditions, one reigns supreme: We must eat until we can eat no more. And then, eat some more just the same!

There is something of a mystery in this, and that will be the very point we address here -- but there is, admittedly, no great hardship in it. Thanksgiving has long been my mother's signature holiday, and she lavishes love and culinary talent on it accordingly -- with lesser culinary contributions from others, such as my wife.

We have, as I trust you may have, a truly magnificent feast every year. And as we indulge in it, we are indeed thankful for the bounty -- of food, and more importantly, the company around the table with whom we share it. I can forget on any given day how fortunate I truly am, and embrace the annual reality check.

But we will leave that sentimentality for the holiday itself, and focus for now just on the food, and in particular, the ridiculous quantities of it we manage to put away.

If you are at all like me, there is a particular "Thanksgiving moment" that occurs as the meal is winding down. I have by this time soldiered through a ton of turkey, a plethora of potatoes, and a copious congregation of cranberries. To say nothing of having stuffed myself with stuffing. I set down my fork -- groan -- and say something like: "My goodness, I couldn't eat another bite..." This, of course, is promptly followed by: "What's for dessert?"

Is it just me? I don't think so.

Conventional wisdom has an explanation for the mystery of this reserve capacity. We are told, inevitably by some particularly sagacious and avuncular relative, that we have a hollow leg and/or extra stomach, on standby for just such occasions as this. It's the hollow leg that makes room for dessert when we thought we were out of room entirely.

The only problem with this bit of folklore is that it is, of course, utter nonsense. During my anatomy course all those years ago in medical school, I went looking for that hollow leg or extra stomach, and couldn't find either of them. I have conferred with colleagues -- they haven't found them, either.

But anatomy does, in fact, hold an answer to this mystery -- just not in mythical organs. The answer resides well above stomach or leg, in a part of the brain called the hypothalamus. The appetite center lives there.

There is a large body of scientific research indicating that our appetite center responds in a taste-specific and, to some extent, texture-specific manner. What this means, in essence, is that we want or crave salty and savory food up to a point -- but then the "appetite meter" for that particular category registers full. But not so the "sweet" meter, which may be registering empty. So offer your taste buds dessert, and a whole new source of appetite turns on -- and doesn't turn off until that meter is also filled.

This has been part of our common experience for far longer than it has been science. We have long said that "variety is the spice of life." That may pertain to things other than food, but it certainly pertains to food along with the rest.

We all know as well what happens at an "all-you-can-eat-buffet" -- namely, we eat all we can, and more than we should. The variety at such buffets is a virtual guarantee that we will wind up overeating.

This, then, accounts for the Thanksgiving mystery of where we put all that food. We put it in our hypothalamus.

The tendency to fill up in a flavor-specific manner has a name; it's called "sensory-specific satiety." I think it's very important. I have addressed it in several of my books, and devoted one entirely to the topic.

Sensory-specific satiety is important not because it accounts for why we overeat on Thanksgiving. It's important because it may account for why we tend to overeat -- and reap the consequences -- year round.

That nutrition experts at all the big food companies know about sensory-specific satiety is established fact. That they use it in product development to maximize the number of calories it takes for us to feel full is informed speculation on my part -- but I'm quite convinced. I'm convinced that when they told us "betcha' can't eat just one!" they had done their homework, using functional MRI scans to see what made the hypothalamus light up like a Christmas tree. I'm convinced they knew it was a very safe bet, indeed.

We of course live in a "bigger is better" culture, in particular when it comes to food. And we are, indeed, surrounded by the enticements of all-we-can-eat buffets.

But even more pervasive, and far more insidious, is the goad of variety engineered into individual foods. In virtually every supermarket in the country, you will find salad dressings and pasta sauces with a higher concentration of added sugar than is found in many desserts. This seems pretty odd, since most of us would not be inclined to pour packets of sugar over lettuce or pasta. But the method in this apparent madness is sensory-specific satiety; by hiding "sweet" in foods that are salty and savory, more appetite is turned on -- and we eat more. I suspect someone laughs about this on their way to the bank.

Similarly, walk the cereal aisle of any grocery store, and you will see a whole array of popular breakfast items more concentrated in added salt than many, even most, of the items in the salty snack aisle. Few of us would think to sprinkle salt over our breakfast cereal, but the food industry has done it for us -- and for evidently good reason.

This may all sound a bit ominous, but there is a bright side to this dark tale. The process can be reverse engineered. Since variety can stimulate an excess of appetite, simply controlling variety can reduce the number of calories it takes to feel full. There are pasta sauces and salad dressings without added sugar; they taste fine, and are far less likely to put our hypothalamus into overdrive. There are breakfast cereals with less added salt.

I have long seen the benefits among my patients of trading up to "better" choices within any given food category, choices that don't have stealth additions of sugar, salt, or artificial flavor enhancers. There are benefits to health in general, but salient among them is this: When food is simpler and closer to nature, it fills us up on fewer calories. The beauty in this formula is that it allows for improving health and weight without being hungry all the time.

With NuVal now reaching some 30 million shoppers around the country, I have also heard many tales about people losing weight without hunger by trading up their groceries. Some report losing over 100 lbsthis way; at least one person has told me about losing over 200! Sensory-specific satiety isn't the only explanation for this effect, but it's an important component.

On Thanksgiving, I recommend indulging ourselves as the holiday warrants. We can be thankful that where feast meets hypothalamus, there's a bit of extra room for the delicious fare the fortunate among us will enjoy.

By renouncing the myth of the hollow leg, and knowing something about your hypothalamus, you have new means to control your intake of calories without going hungry. Ideally, that will give you something new to be thankful for all year round. I genuinely believe we can love food -- both the quality and quantity -- that loves us back.

For now, I wish you -- and your hypothalamus -- a wonderful holiday!