Why We Eat: Hunger

I'm HungryIt sounds like the question of a 4-year-old making his first forays into understanding life, biology, and the nature of the universe: “Mom, why do we eat?” On some level, there’s an answer that’s both basic and true – the kind with which we’d respond to little Junior: “We eat because we’re hungry.” If it – and we – were only that simple…. Beyond the hormonal cues that tell us our bodies need feeding exists an intricate constellation of reasons. They stem from the gamut of higher order thinking, social reference and self-organization that characterize the human mind. And just when you thought the biological picture was at least an easy call, it’s important to note the environmental inputs that can skew our hormonal responses and convince us we need to raid the refrigerator at midnight. (Yes, analyzing human instinct can feel like nailing Jello to the wall.) So, what are the various reasons we eat? What influenced your food intake today? Truth be told, sometimes we’re not even conscious of our simplest motivations. I thought I’d take up the multifaceted question in a series of articles. We spend a lot of time talking about what we eat/should eat, and the why can lead us down some interesting roads in terms of both research and experience. But let’s start today with the fundamental biology behind our food intake.

However much we misuse or misapply the concept of “hunger” to justify eating what and when we want, genuine hunger itself is a basic physiological instinct and response to a host of physical cues in the body itself. If we ever allow ourselves to make it to the actual point of a truly empty stomach, we can feel when our stomach is empty with the characteristic gnawing. We may disturb those around us with the cavernous rumblings (and then make gestures assigning blame toward the person next to us). Hunger pangs feel like our stomach is doing somersaults or turning in on itself because it’s actually a contraction.

In truth, most of us could live several weeks (or even longer) without food, but our bodies have their own “idiot light” signals reminding us subtly or not so subtly that it’s time to refuel. Hormonally speaking, the body experiences a rise in ghrelin, the central hunger-stimulating hormone produced in the gastrointestinal tract that reaches the hypothalamus to spur the body’s hunger related mechanisms and messaging (i.e. Sparky should eat soon). Our sensory perceptiveness, for example, is kicked up, particularly our sense of smell because of how certain receptors activate the olfactory circuit. The result? Food seems more appealing.

Among the symptoms we most commonly associate with hunger is a drop in blood sugar in addition to the related energy slump and the physical (and emotional – a.k.a. “hangry”) agitation we can experience when we’re running on empty. Of course, this is where we begin to separate the sugar burners from the flexible fat burners. If you’re not fat-adapted and rely on glucose, you can feel the initial cues toward hunger (and that dragging sensation) within as little as 3-4 hours. Those who are fat-adapted (whose bodies can flex efficiently between glucose and fat for fuel) can generally go considerably longer without these cues.

Yet, hunger isn’t just hunger. The hormonal “hunger” cues can vary considerably in their timing and extent based on what kind of diet we eat as well as other physical inputs. The body, for one, senses the depletion of nutrients in the bloodstream, and this gauging of nutrient stores can influence hunger itself. It’s yet another reason people who eat a poor diet high in empty carbs and low in essential nutrients are prone to reaching for more. Research shows, for example, that a higher protein diet can increase the levels of a hunger-dampening hormone known as peptide YY. Likewise, the overall nutrient-density of our diets appears to impact our experience of hunger. Study subjects who switched to a more nutrient dense diet reported feeling hungry less often, experiencing fewer and milder hunger symptoms and even sensing hunger from different locations in their bodies.

Aside from diet influences, exposure to blue light at an evening meal time increased hunger (as well as insulin resistance). Likewise, even a single night of inadequate sleep has been shown to elevate ghrelin levels in healthy subjects. Not surprisingly, this translates to the next day’s choices in significant ways. Subjects who were sleep deprived chose bigger portions for meals and snacks.

All this begs the question: what is our relationship to hunger? Do we know what it even feels like? (Many people surprisingly don’t.) At what point or with what “symptoms” do we assume we’re hungry? How much consciousness do we bring to our physical sensations and cues? Have we given thought to how our food choices influence these sensations? These kinds of questions are why I’m such a fan of self-experimentation, not to mention fasting.

The Primal Blueprint isn’t a prescription but a guide that invites greater awareness around what does and doesn’t work for your health. It’s a challenge to let go of what we’re told we should eat or should want and instead consider the personal effects as well as relative costs and benefits of each choice. When we allow ourselves to fast, for example, we not only see what it can do for our mental alertness or weight loss but also how our body feels at different stages of temporary deprivation and how it responds to certain foods or the lack thereof. This sounds amazingly elementary, but it can be a revelation to some people that not every odd feeling in the stomach is a hunger pang. I’ve had any number of folks tell me after going Primal that the sensations they attributed to hunger were actually signs of food allergies or other digestive issues. Our culture pushes the concept of “more” so often that we forget how much we can learn from the context of less.

I’m not about deprivation for deprivation’s sake, but we do well to know what basic hunger is. This isn’t at all to minimize or romanticize the chronic, wasting hunger with which much of this world’s population lives. However, to be able to differentiate the extraneous messages and influences about our eating and health, it’s helpful to get in touch with our bodies’ basic cues. It isn’t something you can simply read about. Grok and his kin undoubtedly felt the range of their bodies’ functioning and learned about physical limits as a result. In a modern environment, we live with inputs grossly manipulative of our physiological instincts. Coming back to basic sensations – what it feels like to be genuinely hungry, what it feels like to lift to exhaustion, what it feels like to get in touch with circadian rhythm without artificial light sources – can be an illuminating first step in realigning our health with our bodies’ natural and evolutionarily set expectations.

Thanks for reading today, everyone. I’ll pick up the series again next week, but let me know your feedback on the biology behind why we eat.

TAGS:  hormones

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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43 thoughts on “Why We Eat: Hunger”

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  1. I have been trying to intermittent fast for the past few months and I feel like I can really tell when I am hungry vs when I am bored or thirsty. I have been listening to your podcasts all week and just downloaded the blueprint and 21 day transformation yesterday…I cannot wait to read both books and really fine tune the way I eat and exercise. Thanks for the post!

    1. Even though I had been primal for almost two years, this article (https://robbwolf.com/2013/08/14/kind-hungry-you/) by Rob Wolff changed my life.I did not have the epiphany I had when I started reading The Primal Blueprint, but it was certainly a big moment. This helped me realize that I experienced ALL those types of hunger, and by recognizing them, I was able to stop giving in to all but my true hunger.

      1. Great article. Reminds me of the Whole9 and Whole30 advice to only eat when you’re hungry enough to eat steamed fish and broccoli (no seasoning, no butter, and no, not salmon either).

        1. I have a similar “test” to work out whether I’m actually hungry or bored. Could I eat cabbage? I like cabbage but that sorts out the actual hunger from wanting a little something. Sorts out the need versus the want.

        2. I have started doing that to help me control my “I think I’m hungry” feelings. I will go so far as to walk in the kitchen, but if I am not hungry for just carrots or macadamia nuts, then I know it’s just a bored palate.

          I’m going to think about the steamed broccoli, too. That’s fantastic.

  2. Great post. Very interesting questions being raised here. I definitely think everyone should try IF. It has done wonders for me in learning to listen to my body and understand what real hunger cues feel like.

    I once fasted for 3 days. Once you get past the emotional and physical cues, you’re fine for a while. After a certain period of time however you get what can best be described as an “instinctual need” to eat. That feeling was much more powerful than the prior cues. At that point I decided to listen to my body and eat. 😛

    1. Heh. It’s funny how you know when to break the fast. For me, it was the point where I started daydraming about food like a 16 year-ol boy thinks about girls. Constantly.
      I already think about it a lot because I like to cook, but this was ridiculous.

      1. When I fast for a day or 3, I like to watch the Food Network. It’s a fun test to see how I cope. Usually it’s no problem.

  3. “’I’ve had any number of folks tell me after going Primal that the sensations they attributed to hunger were actually signs of food allergies or other digestive issues.” –This is exactly what I’m starting to realize. My other misunderstood “hunger” trigger is anxiety.

    1. Ditto – it’s a distraction I find from what’s worrying me.

      Also the disrupted sleep, this really is a big problem. As Mark says even one night makes a difference, and I have interrupted sleep for much of the time so feel I’m in a constant battle with myself on the drive to eat.

      IF really helps though.

    1. I doubt it, but it’s not a surprising unintended consequence. To quote a favorite movie:
      “Don’t think about elephants. Now, what are you thinking about?”

  4. I started IF two years ago and at age 55 my physical and cognitive abilities are better than I had 10 years ago. I have also adapted a Primal lifestyle this past year and feel great. Mark your site has given me a better quality of life and I have turned a few friends and family on to this lifestyle. Thanks Tom

  5. “…the overall nutrient-density of our diets appears to impact our experience of hunger.”

    It seems to me that the study (by Fuhrman et al.) cited in support of this idea actually demonstrates no such thing, seeing as the list of potential confounders not taken into account by the authors is practically endless; the myriad differences not related to “nutrient density” between the two compared “diet blueprints” alone make the authors` conclusion pure conjecture (not to mention that they collected their data via an anonymous survey, which is not that far removed from pulling said data out of their…*ahem* socks – nobody actually measured anything substantial regarding diet composition, hunger/satiety signaling, etc.).
    Amusingly, the ever so “nutrient -dense” diet that allegedly renders its adherents immune to hunger “is mostly unrefined, unprocessed plant food with minimal or no added salt, sugars, oils, and a minimal amount of animal products or no animal products” – because the latter appear to be “pro-inflammatory” “toxins,” and as such “a major contributor to compulsive eating and consequent obesity,” according to the authors of the study. Going by the “fat-burning beast paradigm,” shouldn`t those poor glucose-reliant study participants on their essentially vegan diet be ravenous instead of less hunger-prone?

    1. hi karl, when I clicked on the link and looked at that study I had similar reservations. The following raised a red flag for me:
      ” The survey questions referred to two types of diet: the participant’s previous usual diet and the high nutrient density diet. Based on our clinical experience, we assumed that participants’ previous usual diet received a majority of calories from processed, commercially prepared foods with added salt and sugars, oils, white flour as well as dairy and meats.”

      They are making alot of assumptions imho. Subscribers to that website most likely where already interested in nutrition, to assume they ate a SAD diet of ding dongs and cheetos without even finding out was pretty lame.

  6. It wasn’t until I adapted a primal lifestyle at age 52 that I discovered what being hungry and being full felt like. My previous hungry (hunger pangs, crankiness, shakiness) were sugar lows which could usually be sated with a small snack or meal, and my previous “full” was really bloating. I also needed to eat every 3-4 hours and always woke up ravenous. Left to my body’s natural cues, I’ve discovered that I eat everything I want within an 8 hour window and then don’t get hungry again for another 16 hours.

    1. +1

      It’s disconcerting to discover that you have misunderstood such a basic feeling, hardly seems possible. Having discovered that what I thought was hunger actually isn’t, I now wonder whether fear is really fear, or lust is really lust, and so on.

      I now find that hunger creeps up on me slowly, rather than staging an ambush.

      I also find that I only get really hungry *after* I’ve decided to eat. It’s as if my body is saying “incoming!’.

  7. The mention of inadequate sleep resulting in elevated ghrelin levels reminds me of something I accidentally discovered to be true for me. I unfortunately run on too little sleep far too often. Lack of sleep makes losing, or even maintaining, weight difficult. Quite by accident, I realized that if I add some more protein, to what I normally eating, I can still actually lose weight. It was quite a happy discovery for me. Now to work on getting enough sleep….

  8. I have noticed that a lot of “hunger” is a sign of being thirsty. I like to think I am pretty in tune with my body, but it still fools me with that signal. Sometimes I drink a pint of water and feel fine, other times I am even more ravenous.

    1. The sugar cravings completely go away for me if I make it a priority to drink enough water early in the day.

  9. When I wait long enough to eat I definitely know what hunger feels like! In the morning, and then again before lunch, I’m definitely hungry and there is no doubt. Later in the day, I think I still tend to eat more for emotional or habitual reasons than true ravenous hunger. But I’m eating good foods, I’m happy and feel great, and I’m okay eating out of habit sometimes. And that question does sound like something my 3 year old would ask, he is in that phase! “mommy why are we eating?” “because I said so” etc. yeah, not really the best answer 🙂

  10. Glad you mentioned blue light. It’s part of the reason people who look at their iPhones right before they go to sleep, they aren’t only shunting melatonin production (which fights cancers) but they are increasing hunger hormones, waking up in the middle of the night due to blood sugar crashes and creating a HUGE cyclical problem!

    Modern life can be friendly if we are conscious of our habits 🙂

    1. Yup. Blue-blocking goggles are great for this, btw – if you wear them, you can look at your iPhone all you want and it won’t affect melatonin levels. Yeah, you look like a dork, but isn’t health worth looking like a dork?

  11. I’m usually hungry every few hours or so. I used to joke that I have a tapeworm. I wish I wasn’t so hungry. I’d save a lot of money 🙂 lol

  12. even using the slightly measured phrase “we’re not even conscious” i reckon is far too hopeful given how our brains seem to work.

    Did you see the Horizon “out of control” if not you may like https://www.dailymotion.com/video/x112r6u_out-of-control_tech

    Seagulls wake me up.I live in a City and they abound and i adore them.
    It was frogs in Namibia (in a house made of old beer bottles by a dam) and occ lions roaring in Kenya and so now the wonderful fresh/salt water drinking gulls do similar in Wancouver.

    Jacques the Magnen if you’ve never read oodles about him please do
    Taubes featured him a little but his research is legion

  13. genius post. despite all the health, fitness, and diet advice out there, I don’t think I have ever seen this topic addressed.

  14. I have a different problem with hunger.

    I’ve been eating primally for ~ 2.5 years. I generally have two 24 hours fasts per week and on an average day I eat my first meal 5-6 hours after waking up (I eat maximum twice per day).

    This “schedule” makes me feel really comfortable, I love the feeling of being fasted and do all my workouts fasted. During the day I never feel hunger in-between meals and I’m full of energy.

    The problem is that I start to be really “hungry” after meals, especially after dinner. I usually have desert cravings so I eat a carrot or some raw cabbage. Sometimes it does the trick, but usually the craving continues and if I give in, I can literally keep eating until my stomach is physically full (which is a lot).

    This craving is usually for nuts, vegetables (not necessarily sweet) or fruit.

    Any advice on how to control it? Fighting it feels really uncomfortable and has a low success rate, giving in is just as bad as I end up being absolutely full to a point where it’s unpleasant afterwards.

    Thanks for any advice!

    1. I have exactly the same problem, only besides craving nuts, I also crave white chocolate. It gets much worse when for some reason I eat later dinner than usual. It’s like a normal dinner doesn’t allow my ‘hunger regulating system’ to catch up with the delay.
      I’m planning on fixing it with more chewing. Apparently the number of times your jaw chews, affects your feeling of being satiated. So I will make a point of sitting down to eat, eat small bites, chew them. And perhaps I will eat some cucumber slices whilst I’m cooking, to get a head start on the chewing. I still have to try this one out though.
      Something else that has proven to work for me, is to get out of the house (walk the dog). It feels that my body needs and uses that time realize that I have actually eaten enough and I start to feel satiated.

  15. Good article! I haven’t really thought about the cause of eating before. It just comes natural to me that when my stomach makes the sound, I take it as the last sign that I should stop and eat something. It can be in my mind, though. Of course, in comparison with other people who really suffer from hunger, I can’t even call myself being hungry. Thank you for your article!

  16. I live in Ethiopia, where real hunger is still very much a reality among some of the rural population – as in, not being to grow or afford enough food to feed a whole family with adequate nutritious food. This contrasts with life in the capital city, Addis Ababa, where middle class urbanites are starting to adopt Western eating habits like burgers and pasta and cheap potato chips fried in dodgy oils. It’s sad to see a society move from one extreme to another. On the other hand, I NEVER take food for granted anymore, never buy more than I plan to eat (and don’t cook by recipe, but by whatever ingredients are available that day in the markets and shops). Any leftovers from big restaurant meals are packaged up and given away to people living on the streets in front of my house. I may be too accustomed to plentiful food to really feel genuine hunger, but I certainly don’t snack mindless anymore – food here – even if you can afford it – takes on a whole new value.

    1. Interesting to me that there would be a cultural “leap” of eating habits happening in the 21st century. Just as many folks in the US are getting a real handle on what true nutrition is, other parts of the world are glomming onto the SAD diet, as if it’s part and parcel to better living. Thanks for the perspective!

  17. “Our culture pushes the concept of “more” so often that we forget how much we can learn from the context of less.”


  18. I’d really like to try fasting for over 24 hours, but my problem is that if I under eat I will wake in the night and I can’t go back to sleep until I eat something. This type of hunger doesn’t seem to fall into the categories described in the article.

    I think I’m pretty in tune with my body’s needs, I don’t eat out of boredom, habit.or for emotional reasons. I’ve been eating a nutrient dense, primal diet for over 4 years. I do have Hashimoto’s, I don’t know if that’s a factor.