Why Do We Eat So Much?

Dan DeFigioBehavior and Mindfulness, Nutrition Advice

Why do I overeat?

It’s no secret that humans are getting fatter all over the world. The average American eats over 400 more calories each day than the average American in the 1980s. Why do we eat so much? Sugar and processed foods are partly to blame, but there’s also the problem of people eating too much food overall.

Why Do We Eat So Much?

For decades, researchers, government agencies, and health spokespeople blamed this on a lack of willpower — people just need to “push away from the table”. Diet book authors, TV doctors, and other nutrition experts tell us we’re getting fat because of gluten, dietary fat, fructose, yeast, or whatever the devil-of-the-day day is.

But all this alarm never really explains why we are we eating so much food – and why it’s so hard to stop!

The answer lies in our brains.

You eat what your subconscious tells you to eat – Unless you do something different.

Ever open up a bag of pretzels planning to have a few bites, only to find yourself peering into an empty bag just a few moments later?

Your brain is to blame.

Your rational, conscious brain thinks it’s in charge. “I eat what I want, when I want it. And I stop when I want to”. But there’s a lot more involved than that. Behind your decision-making processes are powerful physiological forces you never thought of.

Deeper brain physiology — along with its co-pilots of hormones, fatty acids, proteins, glucose, and body fat – drives what, when, and how much we eat. Unless you train yourself otherwise, your conscious self just comes along for the ride.

In this article, I’ll explain:

  • how your brain wants to dictate your food choices,
  • how physiology leads to weight gain, and
  • what you can do to get control back.

Why do we eat?

Simply put, we eat for two reasons: energy and emotion.

Eating for energy:
We eat to get the energy our body needs, and to keep our biological system as-is (knows as “homeostasis”, or the “set point”).

Emotional eating:
We eat for pleasure (aka hedonism), or reactively (to attempt to manage our emotions).

Most meals are a mix of homeostatic and emotional eating. Your brain wants to eat enough calories to keep your body the way it is, and it wants to enjoy the process of doing that.

Your brain uses a host of different cues to decide it wants you to start eating:

  • Ghrelin, the “hunger hormone”
  • Social cues
  • Circadian rhythms
  • Stomach content
  • Blood sugar level
  • Other hormones
  • Visual cues (ever hear of the “see food” diet?)
  • Learned habits

You can retrain or control some of these eating cues – social cues, visual cues, blood sugar, and learned habits. The others, you cannot really control. So the “start eating” cue is complicated because there are lots of different signals. There isn’t one “secret”.

Why do we stop eating?

Once you start eating, there are two physiological factors that tell you when to stop: stomach stretch and hormonal satiation.

Stomach stretch

Your stomach is designed to stretch and expand (this is called “gastric distension”). When your stomach is empty it can only hold about two fluid ounces of space. When you eat, your stomach will expand to hold about a quart of food. In extreme situations, it can get as big as a gallon!

Your stomach is also designed to tell your brain how much stretching is happening. As your stomach expands to accommodate the incoming food, neurons in your stomach send this message to your brain.

Your brain gets trained to expect a certain amount of “stretching” every time you eat. One of the cues your body will give you is whether or not your stomach has reached the “correct” fullness or not.

You can lose weight by filling your stomach with more low-calorie and high-nutrient foods (like vegetables). Because these take up more stomach space, they can help you feel full, even though you’re eating fewer calories.

Unfortunately, gastric distension isn’t the only signal your brain wants.

Hormonal satiation

Your brain also receives many hormonal cues about when to stop eating. I won’t bore you with eye-crossing names like cholecystokinin, amylin, or glucacon-like peptide 1, but suffice to say that there are plenty of chemical signals that your brain receives when you eat.

Many of these hormonal messages stick around long after you’re done eating. They will affect later meals too. For instance, a high-protein breakfast can 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.

There’s one more big component to how much food your brain wants:

Your brain also wants you to stay “normal”

Your brain learns your consistent eating behavior —what and how much you typically eat, day after day. To your brain, that’s what “normal” is. It also includes how much body fat you have stored.

Your body has a system for managing your long-term energy and fat storage needs. It’s called the leptin feedback loop.

Leptin is a hormone that is 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 you have, the more leptin you have in your blood.

leptin feedback loop

The brain makes decisions based on leptin levels – decisions about hunger, calorie intake, nutrient absorption, and fat storage. It uses this “leptin loop” to keep your body weight balanced over time.

The reason that you always gain the weight back from a crash diet is that your brain will not accept rapid loss of body fat stores. When the leptin level drops too much, your brain kicks in several anti-starvation strategies:

  • You get hungry. Like, eat-everything-in-the-house hungry.
  • You move around less. Daily movement like fidgeting, standing up, and anything other than purposeful exercise, goes down. You feel sluggish, and the couch starts looking better and better.
  • You burn fewer calories through movement as our skeletal muscles become more efficient.
  • Your metabolism slows down significantly (as seen in the recent ”Biggest Loser” study).

You would think that once you gained a certain amount of body fat, your brain would chill out, right? Well, it does BUT: The problem is that several kinds of unhealthy eating will disrupt this leptin feedback loop.

The food you eat will change your brain.

Assuming we’re properly nourished, that well-balanced leptin loop will tell you when you’ve had enough. It helps you feel satisfied and allows you to eat reasonable portions.

But that nicely balanced loop will become disrupted when you eat certain types of food.

A diet filled with extra-sweet, hyper-rewarding, heavily processed foods can overthrow the brain’s “stop” signal.

Junk foods that are sweet, salty, and/or full of chemicals will punch your pleasure buttons, but contain relatively few actual nutrients. This type of diet prevents leptin from doing its job of regulating your energy balance. It can even make your brains inflamed and leptin resistant!

You end up feeling less satisfied. You want to eat more, even though you’ve eaten lots of calories. And your body fights to hold on to its body fat.

A food’s desirability is more than just taste — it’s our whole experience of pleasure from a food. That includes taste as well as aroma, mouth feel, 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.

The Food High

But along with palatability, some foods give us a “hit” or a reward in the pleasure center of the brain. Sugar produces a “dopamine high” just like some narcotics do. 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 alcohol the first time they try them. But they both make you feel good when you consume tham. Our brains like caffeine and alcohol.

So we learn quickly that coffee and beer are foods to be desired, 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 unnecessary products.

Tasty + fun = no shutoff switch

Now, what happens when you put these two things — hyper-palatability (tasty) and high reward (fun) — together?

A dangerous combination.

Our brain likes these foods, so when we get them, we often don’t want to quit eating them.

These types of foods have a winning combination for keeping our brains interested in eating:

  • energy density. i.e. a lot of calories
  • high fat content
  • high sugar content
  • saltiness
  • sweetness (often artificially flavored)
  • pleasing and specific texture, such as creamy or crunchy
  • drugs, such as caffeine or alcohol
  • other flavor enhancers or additives to improve ‘mouth feel’

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.

The more of those elements we have, the more addicted our brains get to them.

Make something salty, and sweet, and starchy, and fatty – then add in some extra flavors, scents, and appealing colors for good measure – and you have something that’s been scientifically engineered for us to over-eat.

We naturally love and seek out these things.

Evolution has equipped us for it.

If you love so-called “junk food”, and feel like you can’t stop eating it, you’re not alone, bad, or defective.

Your brain is doing its job. A hunter-gatherer wants to get as many high-calorie foods as possible. Find the fatty meat. Eat the sweet piece of fruit that has more calories than grass.

But our ancestors had to bust their butts with daily activity such as hunting, gathering, and digging, even for minor rewards like a meal of bugs and roots.

Today’s high-calorie foods aren’t nutrient-rich animal organs, or whale blubber that we had to hunt all day to get; they’re sugar-loaded Frappucinos and bacon-double-cheeseburgers that we bought while sitting in the car.

Evolution’s gifts now work against us.

Your brain on processed food.

Our brains may love processed foods, but our bodies sure don’t.

These addictive foods aren’t very nutritious. They have more calories than we need, and far fewer vitamins, minerals, phytonutrients, essential fatty acids, and fiber.

We don’t feel full or satisfied when we eat them.

On a diet like this, your brain ignores its natural “stop” signals in favor of getting more of those delicious food reward chemicals. Your pleasure system starts bullying your leptin energy-balancing system.

Over time, if you eat a lot of these foods consistently, you actually inflame the hypothalamus – the part of your brain that regulates your food intake and energy output. This makes your brain less sensitive to leptin, so your shutoff switch doesn’t work right.

Disrupting the leptin feedback loop

You may have heard of insulin resistance, the pre-diabetic condition where your cells stop “hearing” insulin signals, and slowly lose their ability to control blood sugar levels.

The same thing happens with leptin: Your brain will start to ignore or “tune out” the leptin, even if you’re eating enough and have plenty of stored body fat.

In insulin resistance, the pancreas can simply pump out more insulin to keep blood sugar under control (at least for a while). Since body fat is our main leptin factory, to make more leptin, we need more body fat.

You can see where this is going, right?

  1. When you’re leptin resistant, your brain thinks it doesn’t have enough leptin.
  2. The brain wants the leptin factory (i.e. body fat) to produce more leptin.
  3. Operation Get Fatter begins.

You feel hungry. Regular portion sizes are no longer satisfying; it’s harder to feel satiated, and you want to keep eating, and eat more often.

You gain fat. Mission accomplished, or so your brain thinks.

And to add insult to this injury, your brain will now want to defend the added body fat, because it considers it normal and necessary. Once you add body fat, your body will be very reluctant to give it up!

Change how you eat, change your brain.

You can’t control your unique genetic makeup, your past history of dieting, or your sensitivity to physiological responses. But you CAN control your behavior!

Here are three simple steps you can take to help your natural appetite regulation system get back on track:

Step 1:
Eat more whole, fresh, minimally processed foods.

  • Organic meats, poultry, fish, eggs, dairy, and/or plant sources for your lean protein.
  • A wide variety of vegetables and fruits, ideally colorful ones.
  • Slow-digesting, high-fiber starches: quinoa, brown rice, sweet potatoes, beans, etc.
  • Nuts, seeds, avocados, coconut, olive oil, and fatty fish for your essential fats.

Step 2:
Eat slowly.

No matter what you eat, slowing down will help your brain and GI tract coordinate their activities. It will help you feel more in control of choosing WHAT and HOW MUCH to eat.

Pay attention to chewing eat bite thoroughly (this will help your digestion too), and always wait 20 minutes before going for more food.

Step 3:
Eat fewer processed, hyper-palatable foods.

Step 1 will make Step 3 much easier. If you get more of the “good stuff”, there’s less room (and often, less desire) for the processed stuff.

Over time, if you do these 3 steps consistently:

  • You’ll notice that you crave highly processed foods less, and feel more in control of your food decisions overall.
  • You’ll feel fuller for longer as your leptin loop returns to normal.
  • You’ll start to lose body fat.

Enjoying a meal of whole foods, properly cooked and seasoned, with your family or friends is going to be much more satisfying than gobbling something in your car that you got at a drive-through window.

You don’t have to live in a world of bland and depressing “health food” just because you aren’t carpet-bombing your taste buds. Throw a little butter and salt on those veggies. Make them taste good — just not “too good”, too often.

Your brain will love you for it.


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