CHAPTER 4: HUNGER AND SATIETY

CHAPTER 4

Hunger and Satiety

Intermittent fasting gives you free reign to eat what and when you want as long as you’re within your eating window. Still, it’s worth embracing my number one rule for weight loss: if you’re not hungry, don’t eat. I don’t care if it’s dinner time. Your body doesn’t seem to need food, so why feed it? Consider yourself lucky for the extra hour, and go do something else! Take a walk, call a friend, clean your house, organize your vacation photos—use the time for something other than adhering to a made-up meal schedule.

This urge to eat on a socially acceptable schedule is something we really buy into as adults. Children have a much better understanding of their physical need for food, and if you watch them, you’ll notice they eat at irregular intervals, sometimes eating a lot, sometimes eating two bites or simply rejecting a meal outright (much to their parents’ concern). Yes, they’re growing, but that’s not the only reason they eat that way. They are also better at responding to what they need and don’t need when it comes to nourishment. Some very clever studies have shown that at the age of three, children are able to tell when they’re full and stop eating, whereas by age six, children start to become as confused as adults about when to stop eating. They respond more to whether there is food in front of them than to whether they’re hungry. They begin to eat more than they need, and they will probably do so for a lifetime.

But eating just because food is available or because it is a certain time of day is not the best strategy for weight loss. Feeling hungry sometimes is okay. No harm will come to you. But what makes us hungry anyway? Is there anything we can do to lessen sensations of hunger when we diet?

How Hunger Works

Many factors contribute to a feeling of hunger and the desire to eat or stop eating. Internally, hormones released in response to nutrients from a meal signal that the body has had enough nutrition, which prompts us to put down to the fork. A drop in nutrient availability (as happens when it’s been a while since a meal, or after intense exercise) will turn up the appetite, as will certain hormones released in response to circadian rhythm or nutrient balance. Externally, the smell of food or the sight of an appealing dish can make us start salivating, signaling the beginnings of digestion and the body’s anticipation of food to come. After you’ve eaten a lot, these same sights and smells might make you feel a little queasy, reminding you that fullness or satiety is just as real a sensation as hunger.

Ghrelin, the Hunger Hormone

One of the most powerful tools the body has to persuade you to eat is the hormone ghrelin. Ghrelin is often called the “hunger hormone” because it’s produced by an empty stomach to tell the brain to increase

appetite. It makes you eat more, and promotes fat storage. So you’re probably not a fan of ghrelin! But it makes sense that the body would have a mechanism to increase hunger when it senses that no food is coming in. The body is smart, and wants to prompt you to eat so it can store some food energy for future times of scarcity, when it’ll have to get by on your fat stores. Of course, that’s unlikely to happen in North America in the 21st century, but ghrelin doesn’t know that.

One of the reasons some people are reluctant to try fasting is that they think they will just get hungrier and hungrier until they finally give in and eat. There’s a misconception that ghrelin levels increase steadily the longer you go without food. But that’s not how ghrelin works. Think about a time when you were hungry but engrossed in a project at work and just didn’t have a chance to eat. Maybe the work distracted you from feeling hungry and you were surprised to notice a few hours later that your hunger was gone. That’s how ghrelin works—it comes in waves. The timing of ghrelin release is affected by your typical meal schedule, which is one reason why you’ll get hungry around the same time every day. It’s also why, if you start skipping a given meal consistently, you’re likely to be less hungry at that time of day. Hungry or not, it’s helpful to know that ghrelin will make your stomach grumble and make you feel hungry, and then after a while the feeling will pass and you won’t be hungry at all.

When you start fasting and you notice that sensation of hunger, you’ll have to decide if you want to wait out the ghrelin peak, stick with the fast, and keep burning fat, or eat and suppress the sensation (food rapidly drives down ghrelin levels). If you wait it out, your hunger will later decrease and you’ll be able to go a few more hours without eating or feeling hungry. That’s the great thing about ghrelin peaks and dips—if you get through the peak, the dip will work in your favor. What’s more, ghrelin has some positive effects in the body. It stimulates the release of growth hormone. Growth hormone, if you recall from Chapter 2, helps break down and get rid of body fat and build up muscle tissue. So if you can stick with your fast and ride one or two waves of a ghrelin peak, some very good things will happen!

If you choose to respond to ghrelin by eating, your fast will be broken, insulin levels will rise, and you won’t start burning body fat again until a few hours after your meal. The option to eat is always available to you, though you often won’t take it. Above all, be sure that you take good care of yourself and allow some flexibility in your fasting practice. Some days you’ll be more interested in going longer before eating—or more likely, you’ll just be busier and won’t really notice the hunger, which is why one of the tricks to fasting successfully is to keep busy. Other days, you’ll hear ghrelin shouting at you and you will choose to eat so that it quiets down. And that’s perfectly fine. Fasting should be challenging and push you to be more flexible with your eating habits. But it should not be so uncomfortable that you’re miserable. You’re trying to develop a new habit that you can stick with for a lifetime—and no one would keep up with something that makes them miserable!

Getting Acquainted with Ghrelin

The more you practice fasting, the less bothered you’ll be by ghrelin’s chirping at you to eat something. There are a couple of other practical things to know about ghrelin activity when you’re planning a fasting schedule.

1. Ghrelin levels tend to be lowest in the morning, around 8 to 9 a.m. So I’ll say it again for good measure: if you’re not hungry for breakfast, don’t eat it!

2. Ghrelin levels peak and dip a couple of times a day. The peaks will correspond to your typical mealtimes, and last about two hours. If you change your meal pattern, your hunger pattern is likely to change along with it.

3. For those who want to try fasts of more than a day, know that ghrelin levels are highest on day 2 of a fast and decrease steadily thereafter.

Leptin, a Satiety Hormone

The whole story of how the body receives hunger and satiety signals is complex, and better suited to an endocrinology textbook. So we’ll just get acquainted with one more celebrity hormone before we move on.

You may have heard of the hormone leptin, secreted by fat cells, which sends signals to the brain about the size of the body’s fat stores to help regulate appetite and energy expenditure. People with more fat have more leptin. If all is working as it should, an overweight person will secrete a lot of leptin, which will reduce their appetite and make their body use more energy, thereby reducing the size of their fat stores and restoring balance to the system. But things can go awry if a person has much too much fat and leptin. In that scenario, the brain becomes resistant to leptin’s signals and the person doesn’t get the message to eat less; as they continue to eat and store more fat, the fat cells produce more leptin, which just makes the whole problem worse. This is called leptin resistance, and it’s similar to the problem of insulin resistance we discussed in Chapter 2. People who are leptin resistant won’t get the benefit of a reduced appetite that leptin should provide, because the system is broken. Losing some body fat will reduce leptin levels and allow the brain to become re-sensitized to it.

Other Contributing Factors

Ghrelin isn’t the only thing that makes us hungry, and leptin isn’t the only thing that tells us to stop eating. There are many hormones that influence hunger and satiety, and other mechanisms in the body for regulating food intake. For instance, peptide YY is a hormone released from the small intestine in proportional response to food intake (more food, more peptide YY). It slows the movement of food through the digestive tract and binds to receptors in the brain that make you feel full. Like other hormones, it peaks and falls: levels are highest in the second hour after a meal and fall steadily thereafter.

In addition to hormones, there are other physiologic cues that adequate food has been eaten, or that more food is needed. For instance, certain sensors in the lining of the stomach stretch when food is eaten to signal the brain to decrease appetite. Foods and beverages that cause expansion of the stomach work through this mechanism to create satiety. This is one of the ways that fiber, which expands to absorb water in the digestive tract, helps to create a sense of fullness. Another trick sometimes used by people who fast is to drink lots of water to expand their belly if they want to prevent hunger. Deficiency or insufficiency of micronutrients can increase hunger and food intake. You can avoid this by eating a nutritious diet that provides adequate vitamins and minerals, or by taking a supplement to fill in any gaps if you feel your diet is falling short.

It’s interesting to realize that even though the body has such sophisticated mechanisms for controlling food intake to match its energy needs, hunger levels go way down after a couple of days of fasting, when we would imagine nutrients are sorely needed. Ghrelin levels peak on day 2 of a fast and steadily decline

thereafter, allowing hunger and the desire to eat to subside. Ketones, present in significantly higher amounts after two days of fasting, dampen the appetite as well. A conclusion can be drawn that a few days of fasting doesn’t rob the body of nourishment that it needs, and that short periods of fasting are not harmful. If the body was starving, it would use all the tools it has—notably, ghrelin and the sensation of hunger—to make you uncomfortable and persuade you to eat. But the opposite is true: most people feel very well after a couple of days of fasting and don’t really have a desire to eat.

It’s Good to Skip Meals!

I hope I have convinced you by now that it’s okay to skip meals. If you want to avoid gaining weight, it’s a good idea not to eat when you’re not hungry. If you’re overweight, skipping meals when you’re not hungry is a no-brainer. Skipping meals when you are hungry is a bit harder, but I imagine you’ve done much harder things in your life and I have no doubt you can do this too. If you can give yourself permission to set aside the hunger until it dissipates instead of reaching for a snack, and you can do that through breakfast and lunch twice a week, then you’ll be intermittent fasting for 48 hours each week! That’s 48 hours that you’ll give your body to burn through your fat stores, helping you lose the extra weight you’re carrying. That’s a really good thing!

If I haven’t convinced you by now that the body can thrive without three meals a day, I think I may know why. It’s breakfast, isn’t it? You have heard all your life that no matter what, you must not skip breakfast. Breakfast can be the last holdout. I hope you can believe me when I say that eating breakfast will not make you a healthier person. And moreover, eating before the hour of 9 a.m. does not magically make you lose weight. Eating breakfast is not the nutritional equivalent of doing three high-intensity interval workouts a week. It offers no special advantage to your metabolic health. It’s just a meal eaten in the morning—and one that most Americans can’t manage to consume without a day’s worth of sugar. If you are actually hungry when you wake up in the morning, then go ahead and eat breakfast. Choose something high quality that’s rich in protein and/or fat, with no sugar or flour. But if you are someone who does not get hungry in the morning, consider yourself lucky! You’ve been granted a free pass and can sidestep the nutritional landmine that is Breakfast in America. Please, for heaven’s sake, skip it. Skipping breakfast will not do you harm.

Don’t believe me? Then believe Mark Mattson. A 2016 article in The New York Times titled “Fasting Diets Are Gaining Acceptance” said this about Mark: “Mark Mattson, a neuroscientist at the National Institute on Aging in Maryland, has not had breakfast in 35 years. Most days he practices a form of fasting—skipping lunch, taking a midafternoon run, and then eating all of his daily calories (about 2,000) in a six-hour window starting in the afternoon.” Mark Mattson has devoted his entire professional life to the study of healthy aging at the biggest health research organization in the country. If he thinks skipping breakfast is such a good idea that he’s been doing it for 35 years, then maybe the rest of us should get on board.