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How to Activate Appetite-Suppressing Hormones

In the United States, we tend to get less than 20 grams of fiber a day, only about half the minimum recommended intake. Compare that with populations where many of our deadliest diseases were practically unknown, like rural China and rural Africa: They were eating huge amounts of whole plant foods and consuming up to a 100 grams or more of fiber a day, which is what we estimate our Paleolithic ancestors were getting, based on dietary analyses of modern day primitive hunter-gatherer tribes and by analyzing coprolites, or human fossilized feces. In other words, paleopoop.

“These most intimate of ancient human artifacts [were often] ignored or discarded during many previous [archaeological] excavations,” but careful study of materials painstakingly recovered from human paleofeces says a lot about what ancient human dietary practices were like, given their incredibly high content of fiber in undigested plant remains. It strongly suggests that for more than 99 percent of our existence as a distinct species, our gastrointestinal tract has been exposed to the selective pressures exerted by a fiber-filled diet of whole plant foods. So for millions of years before the first stone tools and evidence of butchering, our ancestors were eating plants. But what kind of plants?

One way you can tell if animals are natural folivores or frugivores is to map the area of absorptive mucosa in their gut versus their functional body size. Folivores are those meant to eat mostly foliage or leaves, while frugivores are better designed to eat fruit. (The faunivores, which is another name for carnivores, eat the fauna.)

If animals are charted this way, they fall along distinctive lines. So where do humans land? In my video Paleopoo: What Can We Learn from Fossilized Feces?, I show a fascinating chart that maps where humans fall on this spectrum. Based on our functional body size and absorptive area, while eating our greens is important, it appears the natural dietary status of the human species is primarily that of a fruit-eater.

Why does it matter how much fiber we used to eat? One theory for the rising levels of obesity in Western populations is that the body’s mechanisms for controlling appetite evolved to match how many plants we used to eat. Our ancestors ate so many plant foods we were getting about 100 grams of fiber a day. So for millions of years, food equaled fiber. No surprise then that one of the physiological mechanisms our body evolved to suppress our appetite involved this fiber.

Fiber is metabolized by our gut flora into short-chain fatty acids, which bind to and activate receptors on the surface of our cells that alter our metabolism. For example, activating receptors on fat cells increases the expression of the weight-reducing hormone leptin, and other hormones are affected as well. Until recently, food meant fiber and an increase in food intake meant an increase in fiber intake. This made our gut bacteria so happy they made lots of short-chain fatty acids, which activated the cell-surface receptors that released a bunch of hormones that made us lose our appetite and down-regulated hunger. So we ate less. But if we ate less, there was less fiber in our gut, which meant that less of those hormones were released, boosting our appetite and causing us to get hungry and want to eat. So fiber effectively regulates our appetite.

But what if all the sudden food doesn’t equal fiber, like on the standard American diet? Then we just keep getting these signals to eat, eat, and eat since there’s so little fiber. We’re always hungry. If we haven’t eaten our 100 grams of fiber for the day, our body may wonder if we’re starving.

Discovering this mechanism makes the food and pharmaceutical industries very excited. They figure they can now come up with new drugs in the fight against the current obesity onslaught.

Or we could just eat as nature intended.

Isn’t that a really fascinating mechanism? All along I was thinking of fiber more from just an energy density perspective (as in my video Eating More to Weigh Less), but the appetite-suppressing hormones are a whole new frontier. That underscores the urgency of the fact that 96 percent of Americans don’t even reach the recommended minimum intake of fiber, as I discuss in Do Vegetarians Get Enough Protein?.

Other paleo videos include:

For more on bowel function in the modern age, see:

My other videos on fiber include:

And to learn more about what your gut bacteria can do for you, check out my videos:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:


Michael Greger M.D., FACLM

Michael Greger, M.D. FACLM, is a physician, New York Times bestselling author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial.

38 responses to “How to Activate Appetite-Suppressing Hormones

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  1. One often-overlooked fact that points to humans evolving to eat lots of fruit, is our color vision. Predators don’t have color vision as it drastically reduces night vision.

    Looking at the spectrum of birds and animals, the fruit eaters have color vision – so they can tell ripe from unripe.

      1. Sv, You probably need more starch. Potatoes are the most satiating of foods. You may need bigger portions of things like beans, whole intact grains, potatoes, sweet potatoes, etc. These foods are also rich in fiber, especially beans.

        1. Yes, I agree. If you are overweight or hungry you are not eating enough starches. Potatoes, sweet potatoes, beans, rice, oats, corn, barley, wheat, rye. In unlimited amounts. Read “The Starch Solution” by Dr. John McDougall.

      2. Sv

        I would add the Calorie Density videos to the starches concept.

        They talk about things like that individuals tend to eat the same volume of food per day, even if their calories vary all over the place.

        They also add in the water content of food to this concept of fiber.

        They did experiments like having people eat lentil soup before dinner and they ate fewer calories (but kept the same volume of food).

        Dr. Greger has videos talking about stretch receptors and those are involved in the whole hunger phenomenon with this.

        It seems like you need to look at what you are eating and start asking questions.

        How much fiber are you eating?
        Are your foods Whole Food Plant-Based or some mixture?
        Are your foods starch-based or other-vegetable-based?
        Are you eating foods, which are drier or wetter?

        Also, are you missing any nutrition or are you dehydrated, because if you are, I have found that it will cause food cravings no matter how much food you eat.

        When I was eating a lot of junk food and fast food and drinking soda, I was hungry all the time, even though my calories were higher.

        1. After reading Panchito’s comments, I would ask if you have done calorie restriction recently?

          That tends to cause rebound hunger.

    1. The real question isn’t fiber, but fiber per calorie if weight loss is your goal. A cup of brown rice (cooked) has about 4 grams of fiber, but also about 220 calories. A cup of chopped celery (who eats chopped celery???) has only 2 grams of fiber but only 20 calories.

      In general, veggies are your go-to when you’re looking for fiber, though all whole plant foods have it.

      1. “A cup of chopped celery (who eats chopped celery???)”
        – – – – – – – –

        I’m not a fan of celery — raw, anyway. But as it supposedly has sodium, and I (feel I) need to get my sodium level within a decent range, I do chop up a stalk now and then. According to the Cleveland Clinic, celery does have salt/sodium, but not all that much; it has other good stuff, though:

        Paul, are you implying that you chow down on a whole stalk rather than chop it into bite-sized pieces first? If you eat it at all, that is? Some people smear peanut butter on the whole stalk — not a bad way to get it down, I ‘spect. The celery, I mean.

      2. Paul, great point about the fiber per calorie. This website has a list of 350 foods based on that metric (it’s a bit repetitive though, and same food has multiple entries)

        Of course mushrooms, greens, veggies, and legumes are all very high (8-18 grams per 100 calories). No grains are that high, but some seeds are. Grains tend to be in the range of 2-5 grams per 100 calories. Nuts a bit lower typically around 1-3.

        So even with some grains and nuts thrown in, on a true WFPB diet, it’s not hard to reach 100+ grams of fiber per day (eg assuming 2500 calories). And it’s a massive amount of food…

        1. Forgot to mention berries which are in the high range (9-12 grams per 100 calories), whereas other sweet fruits are a bit lower (eg apples and pears 3-5). Most of the fiber is in the skin so makes sense smaller fruits are higher given higher surface area to volume ratio.

    2. The most filling meals for me contain beans, some fat, loads of leafy greens (both cooked and in a mixed vegetable salad), and maybe a little grain or potato. Black Bean Enchiladas with guacamole and a side of cooked greens and mixed salad is a meal that leaves me and others I know stuffed.

    3. Hi!!
      All vegetables and fruits. Celery, apples, papaya, strawberries, berries, pineapple, melon, watermelon, brocoli, spinach and lettuce.
      Nuts and legumes contain fiber too but vegetables and fruits contain more.

      Yared, Health Support Volunteer

  2. Leptin resistance is a theory of obesity. There is also a design theory. It is that obesity is evolutionary success as evolution does not care about looks. When the body was being designed, food was scarce, and the body adopted the weight gain rule. If you compare populations with different diets/stress levels/activities, you also see body weight differences. So it is not a single theory but many.

    1. In the above design theory, people gained weight as preparation to an starvation period. But the starvation never manifested. And thus, they kept the weight.

      1. Panchito,

        When people are dieting, versus eating fiber and nutrition, that theory seems to be a good one for why people lose 10% of their body weight and then get so hungry that people gain that 10% back, plus some. 99% of the people who diet have that process.

        It doesn’t seem to be the experience once people are eating WFPB, whether because of fiber or nutrition or increased water or all of the above.

        Seems like the body doesn’t panic and set things into motion.

        That is my nonscientific thoughts about it.

        1. Actually, it is panic that drives people to overeat as panic prepares the body for the danger of famine. The panic continues through the later famine state, sure. But people should not be in panic if they are prepared to go through the famine phase. It would be like saying that the body does not know what it is doing. But the body and the mind are different.

    2. While some fat accumulation may lead to better famine survival, too much of it may impair performance and survival. So another theory is that diabetes and insulin resistance are a survival mechanism to prevent further fat accumulation.

  3. Re: frugivores, aka us, I’ve done all the searches I can think of and cannot find a detailed definition of frugivore. Specifically, does fruit refer to the botanical definition, the seed-bearing structure in flowering plants which includes a lot of what we refer to as vegetables, or to the colloquial definition – sweet, plus avocado and olives?
    Does anybody have an answer?

    1. Great question. Dr Gregers distinction between folivore and frugivore would seem to imply the botanical definition of fruit. Though I’m sure nutritionally everything sits on a spectrum, eg an unripe non-sweet fruit like a cucumber feels closer to a celery stalk than to a mango…

  4. Weight control is also helped by increasing muscle mass. Muscle uses 2&1/2 Times the calories of body fat. So converting your body fat to muscle raises metabolism and makes weight control much easier. In many people, high intensity exercise decreases appetite also. Just keeping on the move most of the day makes a difference. We are not designed to sit. Plus sitting gives you more time to eat, and some people eat out of boredom.

  5. Brilliant.
    More good news about fruit.
    Will Dr Greger start investigating fruit based diets?
    Will he become a raw food whole plant based eater?
    Love it!!!

  6. I have been wrestling with trying to get rid of my dog’s lung sounds for 11 weeks and every time I think they are gone, they come back.

    I ended up giving him garlic tonight and it has been such a peaceful night with him.

    If I could sleep, tonight would have been the easiest night to sleep.

  7. Did anyone do the Food Revolution Summit?

    Do they do something where they keep taking money?

    I have something on my CC from the end of July for $89 or something like that.

    I have been so focused on my dog for the past few months that I am trying to figure out when the Summit was. It seems like I did that, plus the Plant-Fit Summit, which ended near the beginning of July, and I never even finished it, so the end of July bill didn’t make sense, and I already deleted their emails, because I was trying to clean out my emails and I have way too many from signing up with them.

    Suddenly, I have no idea whether they have some small print that they keep charging you forever for something if you buy their package?

    So many places do that nowadays. I hate that.

    1. Yes, I got my CC and suddenly things are going to change.

      My vet bills are $600 per month and the supplements are in the hundreds and so is the organic food and dog food and pill pockets.

      I knew that I would hit the wall with property taxes and sick dog.

      Trying to live debt free. Some of the things like the bill from Food Revolution Summit hit me by surprise, but it is the dog process, which is too expensive.

      Time to try out the diet only version.

      I am going to be doing no oil vegan and I am getting rid of the supplements and the antibiotics.

      I knew that I would hit my limit on what I was willing to spend in this process and this bill was more than my monthly salary, so it is time to re-think things.

      I am going to see how diet stacks up.

  8. I am going to pause and thank you, with genuine gratitude for all of the information, which you have given to me in such an entertaining way.

    I didn’t finish watching the Plant Summit and I can use my dog as an excuse, but I don’t sleep at night and I have been here watching videos and have watched so many Dr. McDougall and Dr. Barnard and T. Colin Campbell and Mic the Vegan and Happy Healthy Vegan and Plant-Based London (who nicely replaced the Dr. Greger is wrong on the B-12, increasing my respect) I could keep going on my list and I am pondering why.

    I think it is because when I ordered Plant-Based Summit, at every level there was a sales spiel so you buy a package and they offer you another one and another one and I genuinely wish I had taken that money and given it to you. I did give you some, but they ended up with more and they were teaching recipes for things I won’t probably eat and were discussing pots and pans, but not in the same way you do with the whole visible study thing.

    I really enjoyed the Food Revolution Summit and I am grateful for that whole system, but I must be more interested in the science than the domestic part and I felt sold to and I appreciate that I don’t feel that here.

    Probably wouldn’t have ever said it if I hadn’t looked at the last day of July and wondered how that bill was possibly there.

    Anyway, this had nothing to do with them and I just appreciate that you genuinely have given me so much more understanding on so many subjects than I could have ever asked for.

    I had another person trying to get me to do The Plant Paradox and buy those supplements today and I had a man approach me at Starbucks and he said, “You give off the vibe of someone intelligent and empathic and compassionate.” and he was knowledgeable in the diet wars and was so into the supplements and suggested spirulina for my dog and I don’t take spirulina, because of some sort of risk of toxin exposure or something was all the not always intelligent version of me could say.

    There are so many mistakes I could make on this internet, but you have given me a safe place and I springboard off of this site all over the place, but I never get bored or feel manipulated or like I am sensing a sales job here.

    That is precious like gold to me.

    1. I should add that I am usually emotionally compassionate, but I just tell things straight out so I end up being insensitive and the man was a nice man and I couldn’t tell whether he was hitting on me, but he did know a whole lot of things, but not this site was obvious.

      Sorry that I talked about the other site. I know you all work together and it is insensitive to talk about them.

      The Food Summit Revolution was way up my alley. The other one, I lost interest, but also lost being bonded with them, because everything I bought, they did as if I bought the Ginzu knives and they were throwing in Sham wow and the Food Revolution Summit measured up to the hype, but the other one, I got the same extras agsin and at every level ten seconds after you pay another offer came up. That disconnecting emotionally from salesmen who go into sales mode versus human mode is a habit.

    2. Deb, I agree with you about how so many seem to be way too interested in getting us to buy that something extra. I am not familiar with the Plant-Based Summit. When I tried to look it up, there are actually a few legit looking programs that might be what you are referring to. That tells me that there’s probably a lot of plant-based proponent competition that’s after our money. I do know about and have participated in Food Revolution Summit and I can honestly say that I too have been put off by all the add-on enticements and cross-marketing pitches. I don’t recall being billed for anything I didn’t purchase, but I’m going to be on the lookout for that now that you have told us of your concerns.

      I’m sorry to hear that you may have gotten in over your head treating your dog’s cancer. Financial limits can be very upsetting for sure. I experience them all the time myself. My latest is trying to justify whether it is worth making yet more expensive repairs to my old car. I can’t really afford a new (used) car, so I guess I have little choice. Right now, I’m trying to bravely go find out what this latest bad noise is. A car isn’t a life, but where I live, it is a necessity of life. My current lifestyle isn’t sustainable for the long haul and I undoubtedly need some kind of reality check.

      I definitely agree that Dr. Greger is on a higher level of forthrightness.
      I know he wouldn’t want us donating to NutrtionFacts if we couldn’t afford it. My current very modest monthly donation isn’t exactly keeping Dr.
      Greger in business! I wish I had some answers for you, Deb. I sincerely hope you and your dog are sleeping peacefully right now…unless of course it’s time to get up already.

      Actually, I do have something that might be helpful. I’ve decided not to think of myself as a warrior in my efforts to ward off cancer. Instead, I have tried to create more of a mindset of being peace at with it. After all, at least in my case, it will never assuredly be said that the cancer was eradicated. Even if cancer ends up causing my death (and it might), it will not have won anything. That’s because I am not in a war against it. If this doesn’t resonate with you, just disregard it. It helps me a lot, but everyone is different.

  9. Hunger is an interesting thing I can’t seem to nail down and need some help understanding. For the last week I’ve been combining a 6 hour eating window with WFPB diet. Fresh/cooked veggies, lentils, some fruit and black rice. No processed foods. About 1100 calories per day. With all the fiber my stomach is flashing “full” in bright red letters yet I still feel hungry. It’s weird. It’s like my stretch receptors get the word, but my head tells me I need something more. It’s seems to be a fat craving. Peanut butter on a piece of 7 gram fiber toast seems to alleviate the hunger. Where is the disconnect? FYI, I am BMI 30 and need to lose 40-50 pounds to get into the normal range. How come my head overides my stomach and will it go away at some point?

  10. Patrick,

    I suspect that your blood sugars and signaling molecules ( are still playing games with your metabolism, based on the excess weight you describe.

    The good news is that it can change both with consistency of the PBWF diet and the concomitant weight loss. You might find that other nut butters, some avocado, hummus or other oily foods will buffer the cravings. Additionally you might also experiment with a shorter interval between meals, with a small snack.

    Dr. Alan Kadish moderator for Dr. Greger

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