Last week we talked about food addiction and the compulsive eating behavior that makes many of us obese. Those are emotional, spiritual and psychological issues. Today we’ll have a look at some biological aspects of what makes us obese – our hunger, eating and satiety.
Before we start, let's play a classic kid’s quick quiz game.
Can you guess what this is?
Q: What’s black and white and re(a)d all over?
A: A newspaper.
Got the idea? OK, let’s try another one.
Can you guess who this is?
Q: She’s small and whiny, self-centered and never happy. She complains constantly, and nothing I do ever makes her happy for more than a few minutes. She’s been with me forever, goes with me everywhere and always speaks up at the worst possible moments. Who is she?
A: No, she’s not my spinster great-aunt Adeline. She’s my tummy.
With apologies to my long-departed Great Aunt Adeline, I have to say that I’ve never had a happy relationship with my tummy. She’s always been an interfering little piece of business, and trying to humor her has gotten me into trouble more times than I can count. Although she is small, fist-sized and shaped, she has a big mouth and a nasty temper. The little band of silicone at the top of her has done a wondrous job of keeping my tummy quiet, but every now and then she gets herself into a snit. Like today. As I write this, it’s 2:03 pm, 2 hours since my last meal (lunch), and my digestive diva is nagging me:
I said, I’M HUNGRY!
Isn’t anybody listening to me? Let me repeat: I’M HUNGRY! Feed me NOW!
It’s not just my stomach that’s talking about hunger. In researching the relationship between hunger and eating, I learned that the stomach tells only part of the hunger story. Wouldn’t you know, the rest of my body also has to have its say.
The purpose of the stomach is to store and process the food and liquid we ingest. It uses mechanical action (muscle contractions) and chemical action (enzymes, acids) to break food down into a form that can be handled by the small intestine, where nutrients pass through the intestinal wall and into the bloodstream for transportation to the rest of the body. When my stomach growls, it’s not necessarily communicating hunger. The growling sound is generated by peristalsis, the rhythmic muscle contractions that occur as my stomach and small intestine churn up liquid and solid food as well as air and gas, turning it into a sludge called chime and sending it on through my lower digestive tract.
About two hours after the stomach empties out, it begins to produce hormones that stimulate local nerves to send a message to the brain requesting more food, kind of like telephoning the China Supreme Restaurant to place an order for a Number 8 platter with a side of pork fried rice. The brain replies by telling the digestive muscles to restart the process of peristalsis, at which point the muscle contractions move out any remaining bits of food that were missed the first time around and also tell you, sometimes quite loudly, that you’re hungry again. The muscle contractions last 10 to 20 minutes and recur about every hour until you eat again.
But scientists know that the growling empty stomach isn’t the only reason you feel hungry because even people whose stomachs have been removed report feeling hungry. And bandsters with optimal restriction also report feeling no hunger even when both parts of their stomach (upper and lower pouches) are empty. So what else is going on in there?
Researchers have proposed a number of explanations for hunger. At its most basic level, the purpose of hunger is to motivate us to eat the food our body needs for survival. The body signals the need for fuel in several ways. We may feel hungry when our blood glucose level is low, but under normal conditions, blood glucose doesn’t change enough to account for extremes of hunger. I know this is true because I’m diabetic and spent several months last year dealing with frequent and extreme hunger no matter what I did and didn’t eat. I checked my blood sugar every time an “attack” hit me and not once did I get a reading that medically qualified as “low”.
We may also feel hungry when our insulin level increases suddenly, a theory that seems contradictory to me because the #1 way to increase insulin levels is to eat…in other words, our hunger is caused by eating. I don’t know about you, but most of the time, my eating causes satiety, not more hunger. And why then would Type 1 diabetics, whose bodies produce no insulin, ever feel hungry?
Another theory states that hunger is triggered by an increase in the body’s fatty acid level, while yet another theory states hunger is increased by a drop, and decreased by an rise, in body temperature, which might explain why we tend to eat more during the winter, but doesn’t account for hunger fluctuations in people who live in climates with unchanging temperatures.
Obviously, hunger cannot truly be explained only by biology. As human beings, we also experience learned and cognitive aspects of hunger. We use an external clock to dictate our daily routine: when to eat, when to sleep, when to rise, when to eat again. Before my band surgery, I felt hungry for lunch at noon every day even when I’d eaten a substantial snack at 11:00 a.m. That hunger was triggered by learned behavior: when I see the clock (which I learned to read), I want to eat lunch (a meal called lunch that happens only at midday is another learned behavior).
The smell, taste, or texture of food also triggers hunger. For example, the smell of fried food as I drove past McDonald’s once made me “hungry” for French fries (amazingly, that smell nauseates me now). This kind of hunger (triggered by taste, smell, or texture) is a culturally learned preference. In my travels overseas, I’ve been exposed to smells (such as the smell of rancid tofu) that turned my stomach but made my Taiwanese companion suddenly start a conversation about where to have lunch.
Colors also contribute to hunger. In experiments, a yellow banana made subjects want to eat it but a red banana did not. The colors of red, orange, yellow, green, and brown foods can trigger hunger while a blue food may suppress the appetite because so few natural foods are blue. Fresh white yogurt is appealing but aging yogurt covered with blue mold is not. Humans learn to avoid poisonous or tainted food based on color, smell and/or taste, and also avoid or favor foods based on their knowledge (whether or not it’s accurate) of what foods are good or bad for them. My father disliked bananas because when he was a child, his mother endorsed a trend at the time that said bananas are bad for you. My mother disliked chicken skin because her own mother repeated so often the lesson that fatty chicken skin is not just bad for you but that it tastes disgusting (which sure ain’t my own experience!). When traveling in Asia I used to get homesick for cheese, but a Chinese friend watching me eat a cheeseburger wrinkled her nose and said, “How can you eat cheese?” as if I were eating dirt (or rancid tofu).
Longing for a particular taste (sweet, sour, bitter, salty) is another learned behavior. If you say, "I’m hungry for something sweet" but eat a pickle instead of a strawberry, you’re probably going to go on eating until your craving for a sweet taste is satisfied. Unfortunately, many obese people seem to have a bottomless pit of a stomach (and brain) when it comes to satisfying a craving. Which brings us to what I consider (as a bandster) to be the crux of the matter: SATIETY.
The mechanism of hunger and satiety are not necessarily the same, and in obese people, hunger, eating and satiety often seem to have no relationship to each other at all. That’s what I mean by the bottomless pit. As a pre-op, I ate so much at each meal, I couldn’t possibly still be hungry, but I went on eating because I didn’t feel satiety. There was never enough food to satisfy me. As I wrote in Bandwagon, I suspect that my lack of satiety has a spiritual basis, but right now let’s stick to physiology.
Satiety – the sense of having eaten enough food – occurs in the brain (in the hypothalamus, which controls hunger and eating) and also in the gastrointestinal tract. Nuclei (clusters of nerve cells) in the hypothalamus send signals to tell you to stop or start eating, based on what your body’s estimated long-term fuel needs are. Since your body doesn’t know you’re going to compete in your first marathon in the next five minutes, it has no instant way to tell you to fuel up with the extra 2000 calories you’ll need to get through it; it can only use past experience to forecast your future caloric needs. If you’ve been training for the marathon for three months, there’s a good chance your body will forecast your calorie needs accurately, but if your previous exercise consisted of manipulating the television remote control, that marathon’s going to be a big surprise to your body in more ways than one.
On the other hand, signals from the gastrointestinal tract (including your stomach) control short-term eating. Enzymes and hormones secreted in the GI tract while you eat respond to your food intake by sending satiety signals to your brain and to the rest of your body (via the vagus nerves at the top of the stomach and via the bloodstream). Your body measures your satiety based on many internal conditions like how much body fat (stored energy) you have and on external conditions (like your habits, learned eating behaviors and preferences, the sight and smell of the food, the social setting of the meal, and stress).
All this may be far more than you ever wanted to know about hunger, eating, and satiety. If you think this is information overload, you should take a look at the scientific extracts I’ve been reading! If nothing else, my attempt at explaining all this shows you what a complex matter it is, and what a marvelously sophisticated machine the human body is (but not just a machine – don’t forget you have a soul, too). Our hunger and eating may also be affected by processes not even known to scientists yet.
Although all my research and thinking has helped me understand more about how my body works, but I still don’t understand why hunger, eating and satiety has made me, but not all my fellow humans, so fat. And I don’t think anyone fully understands how the adjustable gastric band helps me to function more like a “normal” human.
What Causes Obesity?This is a chicken and egg question. Which came first: the defective satiety detector, or the obesity that seems to have resulted from it? Why are some people are obese and others not obese? Is it because obese people have a different hunger and satiety mechanism from people who are not? Or is it because the obese peoples’ overeating overrode and eventually reprogrammed their inborn, “normal” satiety response?
We know that obesity can be caused biologically because so many studies show that twins who grew up apart still weigh about the same as each other, and because adopted children's weights are similar to their biological parents, not their adopted parents. But this does not explain all cases of obesity.
Set point theory, which states that we each have a predetermined weight, set by the hypothalamus, that our body attempts to maintain no matter what diet we follow. In fact, the more we try to reduce our calorie intake, the more our body wants to keep the weight that is set by the hypothalamus. According to this theory, our set point weight is too high due to damage to (or over-stimulation of) the Ventromedial Hypothalamus (the brain’s satiety center).
A study published in 1971 showed that obese people respond to external cues of hunger, such as time, more than non-obese people, who tend to respond more to internal cues of hunger. But why do they do that? A later study linked the external cue response to increased insulin levels. In one experiment, just the smell and sound of steak cooking increased the insulin levels of subjects who were “external cue responders”. But based on the decade I spent with my naturally slim ex-husband, who was tempted by the smell of grilling steak just as I was, I find it hard to believe that the external/internal cueing is a major factor in obesity. Since insulin’s purpose is to maximize the body’s use of glucose as fuel, it seems to me that the smell of steak would alert the brain and body of anyone, no matter what kind of eater they are, to get ready to process a meal by pumping out more insulin. And since my understanding of human physiology has holes in it the size of Rhode Island, I’m not going to propose an alternate theory…not right now, anyway.
Mind and Body
No matter what causes it, hunger is a very basic experience, one of the first that causes us distress when we are helpless infants. Hunger motivates our earliest communication: we cry for mother to feed us. As we grow older (both as individuals and as a species), we learn a variety of ways to prevent hunger – we hunt and gather food; we horde food; we grow, catch, or hunt food; we cook or otherwise prepare our food to make it palatable and safe to eat. It’s very natural for such a basic thing, something so central to our existence and our survival, should arouse a host of ideas, beliefs, and emotions as well as mold dozens of habits and behaviors. I don’t think it’s possible to separate mind and body when it comes to hunger and eating. They must be intricately entwined, and that’s one of the things that makes us human (that doesn’t make us superior to other animals, it just makes us human).
Try to imagine what it felt like for you as an infant, crying about your empty belly, to have your mother or another caretaker respond by feeding you, over and over again, until you acquired some very special feelings about her: trust, attachment, love. And imagine what it felt like to cry and cry and be ignored (because mother was absent, or trying to get you to function according to an imposed schedule): frustration, anger, despair. Is it any wonder that as obese adults we turn to food for comfort (rejoining us to safety of the mother we trusted) and to deal with our feelings of frustration, anger, and despair?
I ask you to be patient with yourself as you do the adult job of figuring out whether you need to feed your mind or feed your body. It ain’t easy, but it’s worth it!