They are, however, a short-term solution. Many people report feeling hungry less than 20 minutes after drinking one of these shakes, and that’s largely because the stomach expansion signals are just one small part of the diet and appetite control. They’re the bottom rung of a long ladder that goes all the way up to the more complex elements of the brain. And the ladder occasionally zigzags or even goes through loops on the way up.6
It’s not just the stomach nerves that influences our appetite; there are also hormones that play a role. Leptin is a hormone, secreted by fat cells, that decreases appetite. Ghrelin is released by the stomach, and increases appetite. If you have more fat stores, you secrete more appetite-suppressing hormone; if your stomach is noticing a persistent emptiness, it secretes hormone to increase appetite. Simple, right? Unfortunately, no. People may have increased levels of these hormones depending on their food requirements, but the brain can quickly grow used to them and effectively ignores them if they persist too long. One of the brain’s more prominent skills is the ability to ignore anything that becomes too predictable, no matter how important it may be (this is why soldiers can still get some sleep in war zones).
Have you noticed how you always have “room for dessert”? You might have just eaten the best part of a cow, or enough cheesy pasta to sink a gondola, but you can manage that fudge brownie or triple-scoop ice-cream sundae. Why? How? If your stomach is full, how is eating more even physically possible? It’s largely because your brain makes an executive decision and decides that, no, you still have room. The sweetness of desserts is a palpable reward that the brain recognizes and wants (see Chapter 8) so it overrules the stomach, saying, “No room in here.” Unlike the situation with motion sickness, here the neocortex overrules the reptile brain.
Exactly why this is the case is uncertain. It may be that humans need quite a complex diet in order to remain in tip-top condition, so rather than just relying on our basic metabolic systems to eat whatever is available, the brain steps in and tries to regulate our diet better. And this would be fine if that was all the brain does. But it doesn’t. So it isn’t.
Learned associations are incredibly powerful when it comes to eating. You may be a big fan of something like, say, cake. You can be eating cake for years without any bother, then one day you eat some cake that makes you vomit. Could be some of the cream in it has gone sour; it might contain an ingredient you’re allergic to; or (and here’s the annoying one) it could be that something else entirely made you throw up shortly after eating cake. But, from then on, your brain has made the connection and considers cake out of bounds; if you even look at it again it can trigger the nausea response. The disgust association is a particularly powerful one, evolved to stop us eating poison or diseased things, and it can be a hard one to break. No matter that your body has consumed it dozens of times with no problem; the brain says, No! And there’s little you can do about it.
But it doesn’t have to be anything as extreme as throwing up. The brain interferes with almost every food-based decision. You may have heard that the first bite is with the eye? Much of our brain, as much as 65 percent of it, is associated with vision rather than taste.7 While the nature and function of the connections is staggeringly varied, it does reveal that vision is clearly the go-to sensory information for the human brain. By contrast, taste is almost embarrassingly feeble, as we shall see in Chapter 5. If blindfolded while wearing nose plugs, your typical person can often mistake potato for apple.8 Clearly, the eyes have a much greater influence over what we perceive than the tongue, so how food looks is going to influence strongly how we enjoy it, hence all the effort on presentation in the fancy eateries.
Routine can also drastically influence your eating habits. To demonstrate this, consider the phrase “lunchtime.” When is lunchtime? Most will say between 12 p.m. and 2 p.m. Why? If food is needed for energy, why would everyone in a population, from hard physical workers like laborers and lumberjacks to sedentary people like writers and programmers, eat lunch at the same time? It’s because we all agreed long ago that this was lunchtime and people rarely question it. Once you fall into this pattern, your brain quickly expects it to be maintained, and you’ll get hungry because it’s time to eat, rather than knowing it’s time to eat because you’re hungry. The brain apparently thinks logic is a precious resource to be used only sparingly.
Habits are a big part of our eating regime, and once our brain starts to expect things, our body quickly follows suit. It’s all very well saying to someone who’s overweight that they just need to be more disciplined and eat less, but it’s not that easy. How you ended up overeating in the first place can be due to many factors, such as comfort eating. If you’re sad or depressed, your brain is sending signals to the body that you’re tired and exhausted. And if you’re tired and exhausted, what do you need? Energy. And where do you get energy? Food! High-calorie food can also trigger the reward and pleasure circuits in our brains.9 This is also why you rarely ever hear of a “comfort salad.”
But once your brain and body adapt to a certain caloric intake, it can be very hard to reduce it. You’ve seen sprinters or marathon runners after a race, doubled up and gasping for breath? Do you ever consider them gluttons for oxygen? You never see anyone tell them they’re lacking in discipline and are just being lazy or greedy. It’s a similar effect (albeit a less healthy one) with eating, in that the body changes to expect the increased food intake, and as a result it becomes harder to stop. The exact reasons why someone ends up eating more than they need in the first place and becoming accustomed to it are impossible to determine as there are so many possibilities, but you could argue that it’s an inevitability when you make endless amounts of food available to a species that has evolved to take whatever food it can get whenever it can get it.
And if you need any further proof that the brain controls eating, consider the existence of eating disorders such as anorexia or bulimia. The brain manages to convince the body that body image is more important than food, so it doesn’t need food! This is akin to you convincing a car that it doesn’t need gasoline. It’s neither logical nor safe, and yet it happens worryingly regularly. Moving and eating, two basic requirements, are made needlessly complex due to our brains interfering with the process. However, eating is one of life’s great pleasures, and if we were to treat it as if we were just shoveling coal into a furnace, maybe our lives would be a lot duller. Maybe the brain knows what it’s doing after all.
To sleep, perchance to dream . . . or spasm, or suffocate, or sleepwalk
(The brain and the complicated properties of sleep)