x
While you eat, your GI tract and related organs (like the pancreas) tell many areas of the brain that food is coming in. Some of these signals travel up the vagus nerve, while others enter the brain by different routes. Some of the more important of these hormones are: Cholecystokinin (CCK): When we eat fat and protein, the gut releases CCK, telling your brain (through the vagus nerve) to stop eating. GLP-1 and amylin: Recent research indicates that GLP-1 may be the most unique, and important, satiation hormone. It seems to stimulate the production and release of insulin (a powerful satiation/satiety hormone itself) and slow down food moving from the stomach into the small intestine, among many other impressive mechanisms.
Similarly, amylin is one of the few satiation/satiety hormones shown to actually reduce food intake. Insulin: When we eat carbs and protein, we release insulin. This tells your brain that nutrients are coming in, and eventually tells it to stop eating. Many of these hormonal messages stick around. They can tell us to eat less at later meals, too. (This is why you should think about your food choices and eating habits in the long-term — over the course of a day, a few days, or even a week. For instance, a high-protein breakfast might prevent you from overeating at dinner.)
Together, these physiological responses (along with other hormones and signals) help you feel full and know when to stop eating. Yet these still aren’t the complete picture, either. Your brain also drives your food consumption over time. What really matters to your weight and overall health, of course, is what you do consistently — i.e. what and how much you typically eat, day after day. Your body has a system for managing your long-term energy and nutrient needs. It’s called the leptin feedback loop.
Leptin is a hormone that’s released by fat tissue. Leptin tells the brain how much energy we’ve just consumed and how much excess energy we have stored up (as fat). The more body fat we have, the more leptin in our blood. The brain makes decisions based on leptin levels about hunger, calorie intake, nutrient absorption, and energy use and storage. Then, it cycles back to regulate leptin production in a loop that can help keep our energy (and body weight) balanced over time.
If stored energy (fat) and leptin remain stable over time, we are more easily sated during and between meals. Smaller portions feel OK. And our metabolic rate stays high. If stored energy (fat) and leptin drop over time, it sends a message to the brain (mainly the hypothalamus, which links your nervous system with your endocrine system) that we need to start preventing starvation. The brain responds to lower leptin levels with several anti-starvation strategies:
We get hungry. Like real hungry. Like eat-your-own-arm hungry. We move around less. Our NEAT (non-exercise activity thermogenesis), or our daily movement like fidgeting, standing up, and anything other than purposeful exercise, goes down. The couch starts looking better and better. We burn fewer calories through movement as our skeletal muscles become more efficient. Our metabolic rate slows down significantly (as seen in the infamous ”Biggest Loser” study). It follows, then, that if stored energy (fat) and leptin go up over time, you’ll want to eat less… right? Unfortunately, you can’t always count on that response.
How much leptin will go up when you start eating more varies from person to person. And how your brain responds to increased leptin levels also varies from person to person. Clearly, people’s physiologies vary a lot. In some people, when leptin rises, their brain decreases their appetite and increases their NEAT output. In others, the response isn’t nearly so robust.
That being said, most of the time, for most people: The food you eat can change your brain.
Assuming we’re properly nourished, that well-balanced leptin loop will tell us when we’ve had enough. It helps us feel sated and allows us to eat reasonable portions, comfortably. But that nicely balanced loop can become disrupted — quickly — when we eat certain types of food.
“Junk foods” that are sweet, salty, creamy, and/or crunchy (maybe all at once), and full of chemical goodness that spins our pleasure dials… but contain relatively few actual nutrients. This type of diet prevents leptin from doing its job of regulating our energy balance. It can even make our brains inflamed and leptin resistant. We end up feeling less satisfied. We want to eat more. And our bodies even fight to hold on to the weight we gain.
Hyper-palatability. Palatability is more than just taste — it’s our whole experience of pleasure from food. That includes taste as well as aroma, mouthfeel, texture, and the whole experience of eating. Palatability strongly influences how much we eat at meals. That seems obvious: Of course we eat more of the foods we like. And of course, some foods are more pleasurable to eat than others.
They’re what you might call “too good”. Anything that you “just can’t stop eating” would fall into this category. Reward value. Along with palatability, some foods give us a “hit” or a reward from some type of physiological effect. We’ll go out of our way to get foods with a high reward value — in fact, we may learn to like them even if they don’t taste very good. For instance, few people like black coffee or beer the first time they try them. But coffee has caffeine and beer has alcohol. Our brains like caffeine and alcohol.
So we learn quickly that coffee and beer are good things, and we learn to like (or at least tolerate) their taste. Over time we discover we like — maybe even can’t live without — them. We’ll wade through a crowded bar to buy a drink, we’ll stand in an absurdly long line for our afternoon coffee fix, and we’ll pay exorbitant amounts of money for relatively simple products. We’ll also make room for high-reward foods even when we’re full. This is why at Thanksgiving, after moaning and groaning about how full you are, you miraculously make room for pie when it’s time for dessert.
Now, what happens when you put these two things — hyperpalatable (tasty) and high reward (fun) — together? A dangerous combination. We want these foods, we like these foods, and we’ll work hard to get them. When we do get them, we often don’t quit eating them. These types of foods have a winning combination for keeping us interested and eating:
This magical mix is rarely found in nature. It is, however, often found in highly processed foods like cakes, cookies, pastries, pies, pizza, ice cream, fried foods, and so forth.
.png)
