The Science Behind Biological Food Noise: Ghrelin, Neuropeptide Y & Leptin- Intuitive Eating Dietitian Explains

If you’ve ever felt like you’re either starving or can’t stop thinking about food… you’re not broken.

Your appetite is regulated by a complex system in your body. It does not just come down to “discipline” for what guides your appetite and food choices.  🍽️

Let’s break down 3 key hormones that play a big role in your hunger, cravings, and fullness.

And before I continue I do want to highlight that I am talking about biological “food noise.” Other food noise comes from food rules, diet culture, and food fearmongers- I am not addressing this type of noise in this article, but rather why our thoughts get noisy from a biological standpoint. That “noise” is actually important communication for us to hone in on as it's our body trying to help us survive- Lets understand so we can feel more comfortable listening to it better!

Appetite Big Picture

Though not entirely understood, appetite is regulated by a complex cascade of over 25 hormones and neurotransmitters that send messages between the gut and brain by this nerve called the Vagus Nerve (1).

The 3 hormones were talking about today are are called ghrelin (think tummy grumbling) and neuropeptide Y (NPY for short), these are both hunger homrones, and the fullness hormone is called leptin.

Our appetite is synched up with our circadian rhythm ☀️🌙 and run by our metabolism, blood sugar levels, stored energy levels (glycogen and fat tissue), and stomach (1). And like a tide 🌊 appeite washes in and goes out- Hunger, fullness, neutral, hunger, fullness, neutral… About 3-5 hours is a totally normal appetite ebb and flow, especially when eating satiating meals and snacks throughout the day.

Remember, the sole job of your body is keeping you alive. And to do that, it needs food and water to stay alive and, therefore, help you feel safe- Safety then translates to feeling calm, cool, and collected around food.  😌

Ghrelin: The Hunger Signal

Ghrelin is your body’s way of saying 👋🏼 ‘Hey, we need energy.” It's produced in the stomach and increases when you haven’t eaten in a few hours, and especially if you’re undereating. It naturally rises before meals and in the morning and falls in response to eating meals, especially as leptin becomes on the rise (1, 2). Ignoring hunger makes ghrelin increase more (3). Chronic dieters are even shown to have higher levels of ghrelin even after eating (4, 5)- Makes sense, your body is even calling you out like 😤 “Hey, stop jipping me, I will still make you feel hungry until you finally eat enough.”

Stronger hunger isn’t lack of control. And your willpower stands no chance against your body’s biological drive to survive. Just remember when you’ve had that binge after a restrict cycle- Have self compassion as that’s just your body being on your team to try to protect you 💚. Instead of restricting again to compensate, just have your next regular meal or snack to get out of that cycle and move forward.    

Some of you may be like “but Caitlin, I don't even feel hunger like that.”

And yes, some of you probably don’t if undereating/dieting or going long hours without eating has been your norm.

You’re in what's called the zone of “biological indifference" (6, 7). In this zone, appetite sensations widen out so you can only feel extreme hunger or extreme satiety, but all the gentle signals that make up your trusty internal guide for eating throughout the day are buried and you become disconnected. This zone is why you have a difficult time identifying hunger (6, 7). Diet culture would give you pats on the back for suppressing your hunger so greatly- But if you’re reading this blog, chances are you’ve had a realization that not feeling your hunger isn’t a good thing… 😬 Read to the end where I give a tip on how to uncover your gentle appetite signals so you can reconnect!

Neuropeptide Y (NPY): The Carb Craver

Why might this hormone exist? To some, this hormone can feel like their archnemesis until you learn what this hormone's role is.

NPY is what ramps up your drive to eat with ghrelin, it's especially responsible for the desire for carbs 🍞. It’s produced in the hypothalamus of the brain and increases before a meal, when you’re undereating, and when your blood glucose is low (8, 9, 10).

Importantly, this hormone is needed to keep your brain functioning 🧠. You see, your brain relies on glucose for energy and has the highest demand for glucose compared to your other organs (11, 12). After a carbohydrate-containing meal, glucose is of plenty (carbs convert to glucose in the body ASAP upon entry), and some of the glucose gets tucked away into your liver for storage, becoming “glycogen.”

Overnight, however, your liver empties out its glycogen stores to release glucose back into the blood to keep your brain and other organs going. So by the morning, your body’s asking you to replenish your blood and liver stores with glucose, and so it increases NPY to encourage you to eat carbs to do just that (8,10). 

Regarding your brain, your body can make glucose from protein and fat sources to fuel it in roundabout ways, but it’s not the preferred or efficient option- Think surviving, not thriving when that’s the case.

To explain what’s so detrimental about using protein to fuel when you don't eat enough carbs: Your body still needs to make its own glucose, but fat alone won’t be enough to keep up. So your body pulls protein from your muscles 💪🏻 to make glucose instead ‼️. The more you exercise on top of this underfueling, the more muscle you lose because of the double burden demand effect- Your brain needs the glucose for fuel, but so do your muscles (13, 14, 15, 16, 17).

And no, eating more protein is not going to save your muscles when you're not eating enough, especially not eating enough carbs (18, 19). Yeah, so you’re definitely not thriving, I can tell you that… Fuel your brain, spare your muscles- Eat ya’ damn carbs! 🥨🍒

Leptin: The Fullness Signal

Leptin helps your body recognize 🙅🏻‍♀️ "Hey! We’ve had enough” as it monitors our long-term storage - aka fat cells. It’s also released by our fat cells and it supports other fullness hormones on a meal-by-meal basis. Those other fullness hormones let you feel those “I’m done” or “This is your last bite before you're about to feel absolutely stuffed” moments as we simultaneously feel the ballooning-stretch sensation from our nerves surrounding the stomach that also helps signal fullness. However, in the background, leptin travels to the brain and is what calms down ghrelin and NPY production (1, 20,  21). 

With that being said, it's very important that you understand this key concept: You can’t “trick” fullness with low-calorie or carbonated beverages to only feel full from the stomach ballooning effect 🎈. I know you’ve already learned that lesson the hard way, only getting overly hungry later on 👀.

True fullness = presence of nutrients in the GI tract + energy intake + stretch. And no- Your body does not mistake hunger for thirst… Eat when you’re hungry, drink when you're thirsty, and you can drink with your meals (22, 23).

Unsurprisingly, when you diet or lose weight, leptin decreases, which means you become less satiated after eating in general so you don’t feel full or get that “I’m done with eating” clear signal. This reduced satiety from suppressed leptin has been shown to last over a year after diet induced weight loss (24, 25, 26)! 

So if you don’t feel satisfied after eating, it might not be you- It might just be your body needing more food and more time to get its appetite hormones all situated. 💚💚 Have so much grace, patience, and self-compassion with yourself!! And do not blame yourself. Blame diet culture for this mess you may be in.

All in all, when you’re not eating enough, this is what your appetite hormones are doing:

Grelin goes up (more hunger)

NPY goes up (stronger cravings, especially for carbs)

Leptin goes down (you can’t feel like you hit the spot)

And doesn't it make total sense now? Your stomach signals hunger to keep you alive driving overall energy intake. Your brain drives you towards carbs in order to keep it running. And your fat cells tell you when your full as it monitors its energy storage. 

Of course there are two main other considerations for feeling satiated and staying full for hours inbtween meals when you ARE eating enough, which are plate composition and satisfaction factor, but that’s a whole other topic. 

This is why learning to listen to your body is so important so you can work with your body, instead of against it. Your hunger, cravings, and fullness aren't random, they’re information trying to communicate!

The goal won’t be to control these signals. It will be to understand them and then respond to them better.

Honoring your appetite cues (or bringing them back)

So now what? I've told you WHY "food noise" is loud from a bioloigcal standpoint, but what can you DO about it?

To start making more apparent your trusty internal guide for eating, start honoring hunger.

Many people want to start with respecting fullness, but it’s hard to respect fullness when you show up overly hungry, chaotic, and possibly with lowered baseline satiety (leptin). SO, we start with focusing on hunger. 

Below is the hunger scale adapted from the Intuitive Eating book.

Notice the 3 ranges of appetite: overly hungry, normal eating range, and overly full range.

Notice how even at a 2 in the overly hungry range, it's still not an unpleasant feeling of hunger. Llikewise for an 8 in the overly full range, notice how it's not an unpleasant feeling of fullness just yet.

It is not a rule that you “must eat within the normal range or you are a failure at eating.” No no. There is no failure, only learning opportunities and observations. 

For what to expect: Appetite can come in like a tide every 3-5 hours 🌊. When we account for the ~8 hours that we are asleep per day, that leaves 16 hours we’re awake for hunger to roll in. That then means we would need to eat for biological hunger ~3-5 times a day (ya’ here that, 3 meals a day minimum people 👀). The tide then rolls out once satiated from eating.

If you can’t feel hunger, eat at regular intervals every 3-4 hours. Eventually, your body gets used to being fed regularly and can sync up. For you guys especially, don’t go longer than 5 waking hours without food, and ask yourself each time you eat things like 💭 "What's it like to feel hunger?" "When is the last time I've ever felt hungry?" until the cues remerge. 

In general, I recommend eating something within an hour or so of waking up in order to let that first domino fall and set the tone and pattern for the day, and being consistent at that so your body catches on to the pattern. Your cues will then be way more obvious and even anticipated- 12 pm lunch break rolls around and, boom, hunger for lunch likely emerging right on schedule! 🤤

This is exactly what I teach and do is session with my clients. I also have them hugner food journal, which is great for slowing down to listen and understand your body’s communication! Just rate your hunger and fullness before and after meals for a while and see what you noticed about yourself!

As always, if you need help, you know where to find me - in sessions or on instagram!