I’m thrilled to see the hypothalamus back in the
news. I've been intrigued for years with
this pea-sized area deep in the brain that plays such an important role in our
relationship to food. Indeed, the title
of a New York Times article that appeared on Sunday (April 28, 2013), “The
Brain: Our Food Traffic Controller,”
echoed a title from the same paper I quoted in the late 1960s: “Obesity is Traced to Signal Failure”
(January 23, 1968). Back then, long
before the days of imaging, it was found that the hypothalamus provided
“internal eating cues” to tell us when to eat and when to stop. The mechanism might get out of whack and “set
so high that normal amounts of food no longer satisfy.” The old source proposed a complimentary
theory that, without appropriate signals from within, people might become
overly dependent on “external eating cues” instead. To me, that meant diets, paying too much
attention to other people’s idea of what we ought to eat. And, I’m still convinced the stubborn,
long-term and constantly escalating problem of overeating owes a great deal to
this.
An approachable synonym for the hypothalamus was coined
in those days: “appestat.” I pictured a switch on the wall to regulate
heat in the winter and thought the workings of the human brain had to be more
elegant than that. The term is defined
now as: “the neural center in the brain
that regulates appetite and is thought to be in the hypothalamus.” My italics
emphasize the difficulty in pinning down exactly what goes on in there when we
eat. And that’s what Kathleen A. Page
and Robert S. Sherwin, authors of this Sunday’s piece, are working on.
Page and Sherwin call the hypothalamus a “primitive brain
region” that evolved to support survival in a time when food was scarce and
obtaining it was a lot more labor-intensive than a trip to either McDonald’s or
Whole Foods. As scientists and
endocrinologists, they have been focusing on observable responses in the human
brain to glucose and to fructose. For
example, they find that glucose – an energy source vital to brain activity –
while calorically equal to fructose (no commercial pun intended), does not
taste as sweet as its relative, and yet is associated with greater feelings of
fullness and satisfaction. Fructose, on
the other hand, gets screened out somehow by the liver; not much of it reaches
the brain, so the “appetite and reward areas remain active.” Thus, the notion that sugar is sugar may be
nutritionally accurate, but neurologically, it may be worth another look.
I find this stuff fascinating. New technology allows even the layperson an
appreciation of the elegance and complexity we all know is there. According to Page and Sherwin, the hypothalamus
constantly monitors blood glucose, hormones, and various contributors to
metabolism that are intricately involved in energy maintenance, appetite and
satisfaction. The “integrated circuit”
they outline includes “brain areas that control taste, reward, memory, emotion
and higher-level decision making.” They question how this wealth of new
information can be used to help combat the epidemic of obesity, but seem in no
rush to judgment. The work is just
starting.
Dr. Norman Jolliffe at Columbia University’s School of
Public Health wrote a piece available on the web entitled “How to Reset Your
‘Appestat’ and Reduce Hunger.” I cheer the following quote from his first
paragraph: “Infants do not have the natural ability to overeat. Overeating is a
learned behavior that needs to be unlearned to reduce hunger.” Wow! I couldn't have said it better, and I’m so glad he did.
Then, he loses me – fast.
“Eat less food more often to reduce hunger;” “Choose lean proteins and healthy fats to
keep your appetite at bay;” “Skip simple carbohydrates that cause sharp drops
in blood glucose and cravings for more;” “Exercise often, but not for weight
loss;” and “Skip the scale.” There is
not a single suggestion here without merit – even though 7 meals a day
absolutely does not work for me, and I personally find the Atkins diet
onerous. What I do object to – have
always objected to – is the list of guidelines that are nothing but “external
cues” as far as I can see. Jolliffe
makes an exquisite case for each item on his programme. Clearly, it works for him. But, how can one re-activate one’s own
primal, evolutionarily-tested internal cues while following someone
else’s? Sorry to criticize, but I think
that’s the wrong way to go.
It’s not going to be so quick and easy to glean solutions
to overeating from what we have begun to learn about the brain, I think Page
and Sherwin would agree. One statement in particular suggests to me an area in
which more study would be useful. They
write: “When food is restricted, the
hypothalamus sends signals that increase your desire to ingest high calorie
foods.” Wow! I knew that.
My body knows that. I couldn't have said it better, and I’m so glad they did.
So, how about doing a bunch of studies that follow brain
activity under dietary restriction? Does
restriction trigger deprivation signals all by itself, without regard to what
is forbidden? Let’s see what the brain does in the context of diet regimens of various
kinds. Let’s take a closer look at the
mechanisms of desire. In those gorgeous scanned images of indigo, gold and
magenta, could we observe the mechanism in the brain that makes going off a
diet a sure thing?
I want to know what happens in the hypothalamus when one
is made to feel chronically guilty or afraid about food choice. How do we store in our memory and constantly
reinforce the admonition that foods are fattening, unhealthful, or bad? For example, would the phrase “Sugar is
indeed toxic” trigger a stronger or weaker signal in my brain to eat more or
less of it? I only quote Mark Bittman
here because he’s one food writer whose opinions I truly value. Conversely, does a sense of
self-righteousness about healthful choices affect satisfaction levels in a
positive or perhaps in a negative way?
Do these effects last? How are
satisfaction levels affected by limited or unlimited choice? Could we study how hypothalamic activity is
conditioned, as well as the reversal of it?
Could we examine conflict of interest arising between “internal” and
“external” cues?
I don’t think we’ll ever free up the channels to our
“Food Traffic Controller” until we answer some questions like these. They may not be tops on the agenda for
endocrinologists, but they are certainly relevant to the issue of obesity, to
health and to pleasure in eating – which is of course the object of the
exercise.
