Richard David Feinman

The reporter from Men’s Health asked me: “You finish dinner, even a satisfying low-carb dinner,” — he is a low-carb person himself — “you are sure you ate enough but you are still hungry. What do you do?”  I gave him good advice. “Think of a perfectly broiled steak or steamed lobster with butter, some high protein, relatively high fat meal that you usually like.  If that doesn’t sound good, you are not hungry.  You may want to keep eating. You may want something sweet.  You may want to feel something rolling around in your mouth, but you are not hungry.  Find something else to do — push-ups are good.  If the steak does sound good, you may want to eat. Practically speaking, it’s a good idea to keep hard-boiled eggs, cans of tuna fish around (and, of course, not keep cookies in the house).” I think this is good practical advice. It comes from the satiating effects of protein food sources, or perhaps the non-satiating, or reinforcing effect of carbohydrate. But the more general question is: What is hunger?

We grow up thinking that hunger is somehow our body’s way of telling us that we need food but, for most of us that is not usually the case.  Few of us are so fit, or have so little body fat, or are so active that our bodies start calling for energy if we miss lunch.  Conversely, those of us who really like food generally hold to the philosophy that “any fool can eat when they’re hungry;” passing up a really good chocolate mousse just because you are not hungry is like … well, I don’t know what it’s like.  Of course, if you are on a low-carb diet, you may pass it up for other reasons, or at least not want to eat too much.

Getting to the point here, if I presented you with a multiple choice question that asked what hunger is, the answer would be “all of the above.” We feel hunger when we haven’t eaten for a while. We may feel hunger if the food looks good or if we are in a social situation in which eating is going on, the congressional prayer breakfast, or looking at the petits fours that the caterer put in the lobby at an obesity seminar.

The coffee break at Jeffrey Friedman’s seminar on obesity at Downstate Medical Center. No kidding.

 Or we may eat because we think it is time to eat. This point was made by the Restoration poet and rake, John Wilmot, Earl of Rochester.  Rochester is famous for his bawdy poetry which is raunchy even by today’s standards (must be over eighteen to follow this link) but his Satyr against Reason and Mankind makes fun of dumb rules and phony reason:

My reason is my friend, yours is a cheat;
Hunger calls out, my reason bids me eat;
Perversely, yours your appetite does mock:
This asks for food, that answers, “What’s o’clock?”
This plain distinction, sir, your doubt secures:
‘Tis not true reason I despise, but yours.’’

For dumb advice, you can’t beat diabetes educators.  The letter to the online forum asked “My morning oatmeal spikes my blood glucose. How much carbohydrate should I have.” A diabetes expert from the site had a whole page of answers, vague recommendations with disclaimers but never saying: “don’t have any more oatmeal than that which doesn’t spike your blood glucose.”

Johnny Depp as the Earl of Rochester in The Libertine (2004).

Different people have different responses to external cues. In experiments in which subjects have a discussion with the researcher but incidentally have snacks available, thin people, not surprisingly, regulate intake by the clock on the wall, — “it’s almost lunch time” — whereas overweight people are less sensitive to this input.

The psychologist B. F. Skinner described the problem in a typically dense way.

“I am hungry” may be equivalent to “I have hunger pangs,” and if the verbal community had some means of observing the contractions of the stomach associated with pangs, it could pin the response to these stimuli alone. It may also be equivalent to “I am eating actively.” A person who observes that he is eating voraciously may say, “I really am hungry,” or, in retrospect, “I was hungrier than I thought,” dismissing other evidence as unreliable.

  “I am hungry” may also be equivalent to “It has been a long time since I have had anything to eat,” although the expression is most likely to be used in describing future behavior: “If I miss my dinner, I shall be hungry.”

 What he is getting at here is that whatever the actual causes of eating behavior, the behavior itself may precede the “motivation to eat.”  In other words, we may feel like eating or feel real hunger pangs but we tend to identify those feelings that come along with eating behavior as the cause of the behavior.

“I am hungry” may also be equivalent to “I feel like eating” in the sense of “I have felt this way before when I have started to eat.” It may be equivalent to… “I am thinking of things I like to eat”…. To say, “I am hungry,” may be to report several or all of these conditions. . . .”

The point is that “hungry” only means you are in a situation in which you are used to eating.  It doesn’t mean that feeling hungry will make you eat, or, more important, that you have to eat.

Lessons from Vagotomy.

The vagus nerve contains many nerve fibers that provide communication between the brain and other parts of the body (a nerve is a collection of nerve cells or neurons whose long extensions or axons are referred to as fibers).  Cells that send signals from the brain to distant organs are called efferent. Efferent fibers in the vagus nerve regulate the digestive tract — enlargement of the stomach, secretions from the pancreas  accommodate a larger volume of food (known to doctors as accommodation). However, most of the fibers in the vagus nerve are sensory afferents (afferents carry information from the body to the brain) providing sensations of satiety and hunger as well as feeling of discomfort.

Vagotomy, cutting the vagus nerve, was practiced as a means of controlling ulcers and is still a target, at least experimentally, for treating obesity. Dr. John Kral, Professor of Surgery at Downstate Medical Center, who has performed such operations, described to me how patients were upset and complained that they had lost their appetite. He had to explain that you do not have to eat all the time, that nothing will happen if you miss a few meals.

Hunger is a sign that you are used to eating in a particular time or situation. You are not required to answer the signal.

“You eat too much because you are fat.”

There is currently strong tendency to think of hunger in terms of hormones, emphasizing regulation by the hypothalamus analogous to temperature regulation.  The hormones are referred to as orexigenic, increasing appetite (from the Greek; the Greek equivalent of bon appetit is kali orexi), or anorexigenic, depressing appetite. While this is part of the picture, in the analysis of eating, it leads to some confusion because, in the end, for animals and humans, outside of a laboratory setup, behavior trumps hormones. The analogy is also not great in that animals (and humans) regulate their temperature hormonally only to a small extent.  The major control of temperature is behavioral: we put on clothes and we hide in caves.

An important aspect of this problem is the attempt to understand the error in “a calorie is a calorie.”  One critique of the energy balance model runs something like this: dietary carbohydrate ➛ insulin ➛ ( other hormones ➛) increased appetite ➛ greater consumption. In the extreme case, some explanations might boil down to “you don’t get fat because you eat; you eat because you got fat.” On the face of it, this is nonsensical (which is why I am not attributing it to anybody in particular) but presumably it means that the hormonal secretion from adipose tissue encourages eating.  The limitation of such an explanation is that it mixes up metabolism with behavior and implicitly accepts the idea that calories are what count, that is, the effect of macronutrients  affects how much you eat (total energy) rather than regulating the efficiency with which it is turned to fat.  Macronutrients clearly differ in their effect on satiety and hormones may affect your appetite.   However, regardless of what your hormonal state, if there is no food, you will not increase consumption but metabolism will keep running.  Also, the effects of insulin are not so clear cut. Whereas metabolically, insulin is anabolic, at the level of behavior it is probably anorexigenic in most cases.

The so-called metabolic advantage, less weight gain per calorie, where it exists, is a metabolic effect. The most likely mechanism is that, because of the effect of insulin on rates of reaction, anabolic steps may increase fat accumulation before competing feedback can catch up.  We explained this in the context of what is referred to as non-equilibrium thermodynamics, which recognizes the importance of rates as well as energy. The first 3 pages and Figure 1 in our paper explains the idea. (The rest of the paper would be considered technical, theoretical, tedious, or pretentious, depending on your taste).

What Can you do about it?

The suggestion at the beginning of this post is to make sure you know what kind of hunger you are talking about.  In this, behavioral psychology stresses the difference between “tastes good” and the technical term, reinforcing which only means that the food increases the probability that you will keep eating.  Anecdotally, we all have the experience of somebody (else?) saying “I don’t know why I ate that. It wasn’t very good.”

However little you have to eat, it is certainly bad advice to eat if you are not hungry. Professional nutritionists, even those on the Atkins website, are always telling you to have a good breakfast. Why you would specifically want to have a good anything if you are trying to lose weight is not easy to answer.  They say, of course, that you will eat too much at the next meal as if, in the morning, you can make the rational decision to eat breakfast in the face of not wanting to eat but, at noon, you are suddenly under the inexorable influence of urges beyond your control. It might be reasonable to say “if you find that you eat too much at lunch when you don’t eat breakfast…,” Many people have the opposite reaction — sometimes food is more reinforcing than satiating — and reasonableness is not the usual style of traditional nutritional advice anyway.

Portion Control.

 Yon Cassius has a lean and hungry look,

He thinks too much; such men are dangerous.

— William Shakespeare, Julius Caesar

In a previous post,  I described how nutritionists recommend “portion control” as if it were some great new scientific principle. What it actually means is “self-control” the usual moralistic approach to dieting. I suggested that it is this nagging that leads to the sense of deprivation that all higher (and maybe lower) animals feel if they are told that something is verboten.  Getting away from this attitude is probably the main psychological benefit of low-carbohydrate diets.  I recommended taking advantage of the lack of proscription on quantity in low-carb diets to actually eat less, namely, to have small portions (of low-carb food) and then, if you still want more, to have more. Following the points above, however, feeling hungry because you want to have a lean and hungry feel if not look, is different from feeling hungry because you are compelled to stick to somebody’s diet.

Exercise.

The only thing that people in nutrition agree on is the value of exercise.  While it is not as important as diet for weight loss, it does interact with diet and has obvious benefit.  One question is when to have meals in relation to exercise.  Although the details are outside my area of expertise, and it is likely that it is an individual thing — there is some good guide in the following old joke.

 The couple come to the doctor and don’t want to have any more children but they don’t want any artificial methods of birth control.  The doctor recommends exercise.

Husband: Before or after?

Doctor: Instead of.