The Hungry Brain: Outsmarting the Instincts That Make Us Overeat

by Dr Stephan Guyenet

Sclafani’s study was published in 1976, and to this day, the cafeteria diet remains the most effective way to get a normal rat or mouse to overeat—far more effective than diets that are simply high in fat and/or sugar.31

These findings are particularly remarkable because it’s normally quite difficult to get people to overeat substantially for more than a few days (imagine yourself eating twice as much food at each meal!). In other settings, researchers coax their volunteers to overeat using enticements such as money, and even then, volunteers have to force down the extra food against a growing sense of queasiness and impending stomach rupture. Yet in Ravussin’s study, his volunteers overate cheerfully without even being asked to,

Many behaviors we view as trivial, such as pumping gasoline or washing the dishes, are actually tremendously complex. Artificial intelligence researchers are keenly aware of the difficulties of reproducing even elementary goal-directed behaviors, which explains why today’s computers are good at computing but not so good at making complex decisions without human guidance. This is a testament to how much of the functioning of our own brains we take for granted.

is this true ?? how is pattern recognition and classification different from

The most extreme example of this is the dopamine-deficient mice created by Richard Palmiter, a neuroscience researcher at the University of Washington. These animals sit in their cages nearly motionless all day due to a complete absence of dopamine. “If you set a dopamine-deficient mouse on a table,” explains Palmiter, “it will just sit there and look at you. It’s totally apathetic.” When Palmiter’s team chemically replaces the mice’s dopamine, they eat, drink, and run around like mad until the dopamine is gone.

dopamine deficient mice

Analogous to what happens in the dorsal striatum, elevating dopamine in the ventral striatum makes it more sensitive to incoming bids, increasing the likelihood that it will activate motivational and emotional states. In fact, common side effects of L-dopa treatment include heightened emotional states, hypersexuality, and compulsive and addictive behaviors, such as gambling, shopping, drug abuse, and binge eating.30 These are called impulse control disorders because people lose the ability to keep their basic impulses in check.

impulse control disorders due to too much dopamine

Sweetness indicates ripe fruit, and glutamate indicates protein-rich food like meatfn8—both of which are important sources of calories and other nutrients in the wild.

did not know this about glutamate. this is why we have a weakness for sugary stuff and Chinese food.

If you’re starting to feel like you have a lot in common with rats, you’re right. Humans share most of our innate food preferences with rats, which makes sense if you think about it: We’re both omnivores that have been eating human food for many generations. Humans and rats are born liking sweet and disliking bitter flavors, suggesting that these are deeply wired adaptations that may have evolved prior to the divergence of our species seventy-five million years ago.22 In addition, people of all cultures enjoy the meaty flavor of glutamate, dislike odors of decay, and are repulsed by foods that have previously caused digestive distress.23 Humans also have a strong preference for salt (sodium chloride)—one inclination we don’t share with rats.fn10

difference between rats and humans in taste preference. rats don't care for salt eh ? how do they get their sodium then ?

When you examine this list, you’ll find it apparent that the human brain is extremely preoccupied with calories. Other than salt, every innate preference is a signal that indicates a concentrated calorie source. This is presumably because calorie shortage was a key threat to our ancestors’ reproductive success, so we’ve been wired by evolution to value high-calorie foods above all others.

our brain is optimized for seeking out high-calorie foods

that every known addictive drug either increases dopamine levels in the ventral striatum or stimulates the same signaling pathway in a different manner. Even relatively benign habit-forming drugs, such as caffeine, seem to act on the same pathway.27

huh...caffeine has a dopaminergic effect, eh

So is it possible to become addicted to food? Food triggers dopamine release in the ventral striatum, just like drugs of abuse, and we know food can be strongly reinforcing. Yet this idea remains extremely controversial among researchers. How is it possible to become addicted to a substance that’s essential to the body? Are we addicted to water and oxygen as well? Everything else that’s good in our lives, from sex to a new car to a job well done, also presumably provokes dopamine release in the ventral striatum. Are we addicted to everything? We aren’t, of course, addicted to everything. Most people have a constructive relationship with most of the good things in their lives—a relationship

a line of argument that i havent really seen before

The “system” in question was a machine that dispensed liquid food through a straw at the press of a button—7.4 milliliters per press, to be exact (see figure 15). Volunteers were given access to the machine and allowed to consume as much of the liquid diet as they wanted, but no other food. Since they were in a hospital setting, the researchers could be confident that the volunteers ate nothing else. The liquid food supplied adequate levels of all nutrients, yet it was bland, completely lacking in variety, and almost totally devoid of all normal food cues.

can soylent mimick this ?

Food variety has a powerful influence on our calorie intake, and the more variety we encounter at a meal, the more we eat.

Working hard for food makes a lot of sense when it’s the only way to survive. Throughout most of human history, and long before, our ancestors spent the bulk of their lives collecting, hunting, growing, and eating food—and it was often hard work. Without a powerful instinctive drive to obtain and eat food, we wouldn’t have survived at a time when securing food demanded so much effort. We still carry that instinct today, but in the modern world, where food is easy to get and highly rewarding, that powerful drive can often lead us to overeat. Yet, as with most traits, people differ widely in their level of food motivation.

the evolutionary basis of our strong desire to eat

In stark contrast to Western populations—which tend to be leanest in youth and grow wider with age—the !Kung San reached their maximum weight during peak reproductive years and declined thereafter.9

interesting contrast

A glass-blowingmachine patented in 1899 led to the mass production of bottles, reducing the cost of sweetened beverages.

aah....coca cola was around to exploit this. unexpected correlations.

These mice are unable to produce dopamine naturally, and as a consequence, they sit nearly motionless in their cages, unable to eat or drink until their dopamine is chemically replaced.38 I explained that this is because dopamine lowers the threshold for selecting behaviors, and without it, the threshold is so high that nothing gets selected. The research

is this why coffee makes me want to do things ??

If the brain was always rational in the way it computes value, few people would carry credit card debt, and no one would overeat. But we often make self-destructive choices, and this is particularly true when our decisions involve the future. As opposed to decisions that pit material objects against one another, like an apple versus an orange, we often make decisions that pit our present selves against our future selves. And the evidence shows that we often shortchange our future selves, with disastrous consequences.

dayumn.

One of the earliest and most influential studies was the Minnesota Starvation Experiment conducted by the prolific nutrition researcher Ancel Keys in the latter years of World War II.26 The goal was to understand the effects of starvation on the human body and mind. Over the course of six months of semistarvation, thirty-six young male conscientious objectors lost approximately one-quarter of their initial body weight. While this weight loss was no surprise, what happened after their food restriction was lifted is more interesting: Due primarily to a prodigious appetite, their body weights and adiposity rebounded rapidly. As they regained weight, their appetites normalized, and they eventually settled close to their original weights. It seemed as if a powerful internal control system was regulating their appetite and adiposity.

again...the body seems to be trying to get to a set-point of some sort

The striking similarity between leptin deficiency and starvation suggested that low leptin levels might be responsible for the human brain’s response to starvation, including the hunger, the obsession with food, the activation of brain reward regions, and, as we will soon see, the reduced metabolic rate. It seemed as if the absence of leptin in leptin-deficient children prevented their brains from “seeing” their fat, triggering a powerful starvation response despite the fact that they had extreme obesity.

hmmm

If you’ve never had the experience of fighting your own body’s starvation response, Jeff Friedman provides a helpful analogy:43 Those who doubt the power of basic drives, however, might note that although one can hold one’s breath, this conscious act is soon overcome by the compulsion to breathe. The feeling of hunger is intense and, if not as potent as the drive to breathe, is probably no less powerful than the drive to drink when one is thirsty. This is the feeling the obese must resist after they have lost a significant amount of weight. Friedman’s analogy is an important lesson for people who think weight loss is as easy as deciding to eat less and exercise more. The brain was forged in the flames of highly competitive natural selection, and it doesn’t take weight loss lightly. “[The starvation response] is there for preservation,” says Leibel. “Evolutionarily, it has played a very important role in our survival.”

the body does not take weight loss lightly...aah. if the brain's ancient parts think that it is being starved, it will show the modern parts who's really the boss.

High-reward foods tend to increase food intake and adiposity, while lower-reward foods tend to have the opposite effect. This suggests a weight management “secret” you’ll rarely find in a diet book: eat simple food. The reason you’ll rarely find it in a diet book is that, by definition, lower-reward food is not very motivating. It doesn’t get us excited about a diet, and it doesn’t make books fly off the shelves. We want to hear that we can lose weight while eating the most delicious food of our lives, and the weight-loss industry is happy to indulge us. The truth is that there are many ways to lose weight, but all else being equal, a diet that’s lower in reward value will control appetite and reduce adiposity more effectively than one that’s high in reward value. The trick, as with all diets, is sticking with it, because just as the set point can go down, it can go right back up if you return to your former eating habits. And that means designing an eating plan you can live with for the long haul. For most people, a “bland liquid diet” like those I described isn’t a viable long-term solution, but keeping added fats, sugars, salt, and calorie-dense highly rewarding foods to a modest level may be.

Although most of the direct evidence comes from rodent studies, a substantial amount of indirect evidence suggests that a high intake of protein may be able to lower the adiposity set point in humans too.

Eating a higher amount of protein helps keep you slim ?? Who would have thought ?!

Schwartz submitted his team’s findings to the journal Science—the highest-impact scientific journal in the world.

Nature is not the highest rated scientific journal ??

If there is such thing as a “hunger neuron” that drives pure, visceral hunger, the NPY neuron is it.fn4

The diagnosis was clear: My hungry brain wanted food. A lot. And it wouldn’t be satisfied by low-calorie foods, because the pattern of activation was almost nonexistent when I gazed at fruits and vegetables (see bottom two panels of figure 37). “When we’re hungry,” explains Schur, “our bodies don’t want healthy food.” Instead, powerful, instinctive brain regions draw us toward concentrated, quick, easy calories. “That’s what we’re all up against.”

our brains dont like vegetables

Finally, the protein content of a food was a major contributor to satiety. This is consistent with a large body of research showing that protein is more filling than carbohydrate or fat, per unit calorie.47 Both the lining of the small intestine and the pancreas have the ability to detect dietary protein, and they relay this signal to the NTS.48 For reasons that aren’t entirely clear, this protein signal seems to play a disproportionate role in satiety. Coupled with the effects of protein on the lipostat we discussed in the last chapter, this may explain why high-protein diets help people eat less and lose fat without feeling hungry.

eating protein helps you reach satiety faster.

If you want to be lean, the most effective strategy is to choose your parents wisely.

We know that when we sleep too little, do hard physical or mental work, or stay up longer than usual, we feel sleepy and we’re more likely to doze off. This suggests that some sort of sleep-inducing signal accumulates in the brain, and the longer we’re awake, the harder we work, the more it builds up. We now have strong evidence that a chemical called adenosine is that signal.6 Adenosine builds up in the brain while we’re awake, and it builds up even faster when we exert ourselves.7 As it accumulates, it begins to inhibit the arousal system and activate the VLPO. Eventually, when adenosine builds up sufficiently, it triggers the flip-flop switch, and we fall asleep.

Essentially, when you don’t sleep enough, your lipostat mistakenly thinks you need more energy, which activates your food reward system and causes you to eat more without intending to and often without even realizing it.13

the effect of sleep deprivation on hunger