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How to Boost the Fat Burning Hormone FIAF

Although recent increases in the availability of junk food and decreases “in institutionally driven physical activity” have created an obesity-permissive environment, several other factors may contribute. We know, for example, that the use of antibiotics is linked to obesity, so our gut flora may play a role. I discuss this in my video Is Obesity Infectious?.

Recently, specific bacterial species were identified. Eight species seemed protective against weight gain, and they are all producers of a short-chain fatty acid called butyrate.

Early on, we thought there might be some intestinal bacteria that were able to extract additional calories from what we eat, but the relationship between our gut flora and obesity has proven to be more complex, as you can see at 0:49 in my video. Our gut flora may affect how we metabolize fat, for example, such as through the hormone FIAF—fasting-induced adipose factor.

While we’re fasting, our body has to stop storing fat and instead start to burn it off. FIAF is one of the hormones that signals our body to do this, which could be useful for someone who is obese, and may be one way our gut flora manages our weight. Some bacteria repress this hormone, thereby increasing fat storage. In contrast, when we feed fiber to our fiber-eating bacteria, those that secrete short-chain fatty acids like butyrate are able to upregulate this hormone in all human cell lines so far tested.

“Currently, when an individual fails to lose weight…the only other option is surgery,” but “[a]s the mechanisms of the microbiota’s [gut flora’s] role in weight regulation are elucidated, one can envision transplanting intestinal contents from a thin individual into an obese individual.” Such so-called fecal transplants may suffer from “repulsive esthetics,” though. It turns out there may be easier ways to share.

We’ve known that people who live together share a greater similarity in gut bacteria than people living apart. This could be because co-habitants inadvertently swap bacteria back and forth, or possibly because they eat similar diets, living in the same house. We didn’t know…until now. Not only do co-habiting family members share bacteria with one another—they also share with their dogs, who are probably eating a different diet than they are. You may be interested in the charts at 2:22 in my video.

In fact, it’s been “suggest[ed] that homes harbor a distinct microbial fingerprint that can be predicted by their occupants.” Just by swabbing the doorknobs, you can tell which family lives in which house, as shown at 2:35 in my video. And, when a family moves into a new home, “the microbial community in the new house rapidly converged” or shifted toward that of the old house, “suggesting rapid colonization by the family’s microbiota.” Experimental evidence suggests that individuals raised in a household of lean people may be protected against obesity—no fecal transplant necessary. (Indeed, people may be sharing gut bacteria from kitchen stools instead.)

Moreover, as we know, people living together share more bacteria than those living apart, but when a dog is added to the mix, the people’s bacteria get even closer, as you can see at 3:11 in my video. Dogs can act like a bridge to pass bacteria back and forth between people. Curiously, owning cats doesn’t seem to have the same effect. Maybe cats don’t tend to drink out of the toilet bowl as much as dogs do?

Exposure to pet bacteria may actually be beneficial. It’s “intriguing to consider that who we cohabit with, including companion animals, may alter our physiological properties by influencing the consortia of microbial symbionts [or bacteria] that we harbor in and on our various body habitats.” This may be why “[r]ecent studies link early exposure to pets to decreased prevalence of allergies, respiratory conditions, and other immune disorders” as kids grow older. In my video Are Cats or Dogs More Protective for Children’s Health?, I talk about studies in which dog exposure early in life may decrease respiratory infections, especially ear infections. Children with dogs “were significantly healthier,” but we didn’t know why. Indeed, we didn’t know the mechanism until, perhaps, now—with the first study tying together the protection from respiratory disease through pet exposure to differences in gut bacteria. None of the studied infants in homes with pets suffered from wheezy bronchitis within the first two years of life, whereas 15 percent of the pet-deprived infants had. And, when comparing stool samples, this correlated with differences in gut bacteria depending on the presence of pets in the home.

There was a famous study of 12,000 people that found that a “person’s chances of becoming obese increased by 57%…if he or she had a friend who became obese,” suggesting social ties have a big effect. However, given the evidence implicating the role of gut bacteria in obesity, this “raises up the possibility that cravings and associated obesity might not just be socially contagious”—that is, because, for instance, you all go out together and eat the same fattening food—“but rather truly infectious, like a cold.”

Viruses may also play a role in obesity. How? See Infectobesity: Adenovirus 36 and Childhood Obesity. An Obesity-Causing Chicken Virus may help explain the link found between poultry consumption and weight gain, and you may also be interested in Chicken Big: Poultry and Obesity.

The important question: Can Morbid Obesity Be Reversed Through Diet? Find out in my video, and also check out Coconut Oil and Abdominal Fat.

For more on the amazing inner world in our guts, see:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live 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.

28 responses to “How to Boost the Fat Burning Hormone FIAF

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  1. I am confused. I understand people sharing the same eating habits having similar gut bacteria, but how else do we share bacteria? If people wash their hands after using the bathroom, how does your fecal bacteria end up on the doorknobs?

    How does a dog spread out gut bacteria to their owners, unless they drink the toilet water and then lick their owners or house objects and their owners touch them and then their mouths?

    BTW, I know several couples that one spouse is thin and the other not so. My parents, for instance.

    1. People with similar eating habits share similar gut bacteria because those bacteria share eating habits too. Families who consume lots of sugar and processed grain (same thing actually) will have sugar-loving bacteria in their intestines. And when they get hungry those bacteria release the hormone “ghrelin” which tells the brain to send down some more glucose. That is why processed carbs never “fill us up.”

      I am unaware of anyone being overweight who eats a Whole Food Vegan Diet. Fiber is not converted into fat very easily. And it is “calorie sparse.” But bacteria love the stuff. Yum Yum Yum. Half of the dry weight of stool is bacteria!

      Bacteria which feast on FIBER release the hormone “leptin,” which tells the brain we are satiated. That is why beans “stick to the ribs.”

    2. Carolina,

      The topic came up on the news yesterday that 100% of the touch screens at McDonald’s tested positive for fecal material.

      There were tests of toothbrushes where 60% of people’s toothbrushes tested positive for fecal material because people flush the toilet with the lids up.

      Here is a famous Dr. Oz episode where a woman finds out that her toothbrush and toothbrush cup are covered in fecal material.

      Bottled waters and touch screens and door handles are all covered in fecal material everywhere you go. Think of ATM’s and Credit card machines and if you share a keyboard with anyone.

      That is why steam cleaners, UV sanitizers and cloths like Silvertize are things I have invested in recently.

      We don’t really want to kill all of the good gut bacteria, but I really like the concept of not having fecal material on my toothbrush.

      I started putting mine in a cabinet and the FYI is brush your teeth BEFORE you flush the toilet the first time and put the toothbrush away because it takes 20 minutes for the air to clear.

      Forever solving the male/female lid up or down debate. CLOSED case.

  2. Our intestinal “flora garden” will flourish or vanish depending on what it fed. Regardless of how many times it is seeded with desirable bacteria, they will be of no benefit if they are fed processed food and sugar and animal cadaver.

    Those desirable bacteria do not have to be purchased; in nature’s wisdom they grow naturally on vegetable matter. Indeed plants and animals who eat them share much the same “suite” of digestive bacteria and fungi.

  3. This may be slightle off topic – nevertheless, here it is – I did post this elsewhere:

    “Hi Dr. Greger

    Thank you for all you, and your team, do to help us make “right”choices in order to stay as healthy and as vibrant as possible. However, one still can be lost when deciding what “right” lifestyle is. I, and I’m sure many other of you followers did too, came across conflicting information. Here is one I would love to see your comments on:

    “Being overweight is now believed to help protect patients with an increasingly long list of medical problems, including pneumonia, burns, stroke, cancer, hypertension, and heart disease…”
    Thank You So Very Much.

    1. About 650,000,000 internet results explain how it is that the Earth is flat. (and in only 0.59 seconds)

      If you are sincerely interested in health and nutrition (or geography and geology) you must read books, not internet citations. How Not To Die is a great place to start.

    2. Sceptic,
      There are lots of studies demonstrating associations between being overweight, at least excessively so, and in particular, visceral fat and chronic disease.

      Interestingly, a 2020 study determined that with respect to the association of excess visceral fat and cognitive dysfunction, the association is causal: excess belly fat causes inflammation in the brain.
      Visceral fat delivers signal to the brain that hurts cognition

    3. Sceptic

      This is probably a consequence of ‘reverse causation’.

      Many diseases cause weight loss or loss of appetite which in turn leads to weight loss. Common examples are HIV/AIDS, cancer and TB.but there are others eg see

      This weight loss can occur years before formal diagnosis is made.and therefore may be a preclinical indicator of disease as seen eg in Alzheimer’s

      It is therefore perhaps not surprising in a society where being overweight/obese is normal that simplistic observational studies find an association between lack or overweight and disease states and increased mortality risk. But suggesting that being overweight is ‘protective’ will grab a lot of media attention and make many people happy.

  4. Another common denominator not mentioned here is grain and dairy consumption. Dogs eat dog food loaded with grain and their owners eat the same thing. Most cats won’t touch grain given a choice.

    Dogs and do share gut microflora and fauna by virtue of the fact that dogs lick their asses as well as their coats. So dogs are coated in intestinal contents. When people fondle and pat them, they also pick up those same microbes. Later they pick their noses or their teeth and the microbes are self inoculated into new hosts. No doubt Dr. Greger knows this, but is too politically correct to say so.

    In that manner, an animal to human fecal transplant is accomplished. I’d say that is evidence of evolution since early man did not have dogs.

    1. A million bacteria can fit quite easily in the period at the end of this sentence. Far more live beneath each of our our fingernails. More still on our keyboard and mouse. A great proportion of them are E coli.

      The bacteria that my dogs bring in from the grass and brush we walk through on our hikes find their way in to all of those places too, as well as into my intestines. And of course they ride in on MY legs too.

      If I brought a cat with us, it too would contribute. But I don’t so it doesn’t. hahaha

      1. John Newell,

        Studies demonstrate that hospitals are quickly colonized by pathogenic microbes, which then quickly rise to very high concentrations, despite efforts to keep the environment very clean. But it would be much better if the windows could be opened.

        Florence Nightingale observed that soldiers in hospitals recovered more quickly from illnesses and wounds if the windows were opened. This is probably due to the dilution of the interior pathogenic bacteria by the huge microbial population outdoors, the vast majority of which are either neutral or actually beneficial (the concentration of pathogenic bacteria outside is very low).

        And dogs bring in LOTS of outdoor microbes, including lots of soil dwelling ones, which is where many antibiotics have been discovered.

        I love opening my windows whenever possible. Now I have one more reason to do so. We don’t have AC, so we open them in the summer during the cooler nights, and close them during the hotter days. In the spring and fall, we open them during the warmer days. I also love hanging my laundry to dry outside; I love the smell of sun-dried sheets and towels.

        Oh, and btw, I’ve owned both cats and dogs — and believe me, cats spend a LOT of time grooming, including their own little asses and other “private parts.” So, they are very similar to dogs in this regard.

        1. Dr. J.

          They were talking about the spread of disease in closed quarters because of the people quarantined on the cruise ship. (Dr. Greger, do you feel like you dodged a bullet that you got off the cruise ship just in time so you can continue your book tour?)

          They were saying what a bad idea that is keeping them there instead of quarantining them someplace else.

          As far as the hanging clothing out in the sunlight. Dr. Annies Experiments gave me an appreiciation for the disinfecting power of the sun. It disinfected clothing better than the washing machines did. Unless you use sanitize function and hot enough water.

          I think you do need to keep them out there for over 4 hours though, if there is something on your laundry.

    2. I’m surprised Dr. Greger puts a positive spin on dog ownership in this blog. The amount of meat consumption by humans and their dogs and cats is unequivocally bad for the earth as it supports the gargantuan cattle industry. Humans need to move away from the pet ownership paradigm and just enjoy animals in the wild.

  5. Off topic but here is a brand new Egg Study –

    Eggs will not increase your heart disease or stroke risk as previously feared, a thirty-year study has found. No association was found between egg intake and risk of Cardiovascular disease.

    Study author Dr Jean-Philippe Drouin-Chartier said: ‘The association between egg consumption and cardiovascular disease risk has been a topic of intense debate during the past decade.
    ‘Findings from previous studies on egg consumption and risk of cardiovascular disease have been inconclusive.
    ‘The results from our cohort study and updated meta analysis show that moderate egg consumption (up to one egg per day) is not associated with cardiovascular disease risk overall.
    ‘Results were similar for coronary heart disease and stroke.’

    Foods such as fish, poultry, legumes, cheese and nuts in place of eggs were not linked to CVD risk.

    Dr Carrie Ruxton commented on the findings, saying: ‘The debate about eggs and cholesterol has continued for years, despite public bodies in the UK and elsewhere saying time and again that eating eggs doesn’t present a risk to blood cholesterol levels or cardiovascular risk.’

    ‘This study is a helpful addition to our knowledge because it confirms that eating seven eggs a week is not linked to heart disease or stroke. It also backs up evidence from intervention trials which show no impact of egg consumption on blood cholesterol levels.

    ‘Given that eggs are rich in protein and nutrient-dense, providing one of the few dietary sources of vitamin D, it’s great that we can put people’s minds to rest’.

    Egg consumption was actually associated with a lower CVD risk in Asian populations.

    1. Greg,

      Thanks for sharing, as always.

      I do think that Dr. Greger might have talked about a factor during his stroke webinar called, over-adjusting, where they adjust so much for lifestyle and obesity and all sorts of other factors to the point where you can’t see the real benefit from healthier behaviors.

      I am trying to remember the examples he gave, but I don’t think I ever received my ability to watch that one over again. The webinars go pretty fast. The other webinars, I have links where I could watch them again. That one I never got the links.

      Well, there is a phenomenon called, over-adjusting, or something like that where if they were studying to see the benefit of a Whole Food Plant-Based diet, for instance, they have to cross off things like being normal weight, which might affect the results.

      I am not explaining it well. I can’t remember the exact examples.

    2. Where did this vague statement come from: “Eggs will not increase your heart disease or stroke risk as previously feared, a thirty-year study has found. No association was found between egg intake and risk of Cardiovascular disease.”?

      Makes it sound like you can eat several per day but in fact the conclusion states “moderate*** egg consumption (***up to one egg per day***) is not associated with cardiovascular disease risk overall, and is associated with potentially lower cardiovascular disease risk in Asian populations.”

      Also the claimed benefit in Asian populations is “potential”, i,e., not actually shown to be fact.

    3. Greg

      This is the usual misleading stuff we hear all the time.

      In wealthy, industrialised societies, what do people eat when they don’t eat eggs? Processed meats, red meat, refined carbohydrates and processed foods generally is the likely answer. Nobody should be surprised that eggs are no more unhealthy (or perhaps even less unhealthy) than those foods. We see exactly the same thing with saturated fat studies that similarly take no account of the replacement foods consumed eg

      We have also known for many decades that adding cholesterol (eg from eggs) to a ‘normal’ US diet that is already high in cholesterol and fat, makes no or very little difference to serum cholesterol levels. It does however make a very significant difference to the cholesterol lveles and hence CVD risk of people eating healthy low cholesterol diets

  6. Greg,

    I am not saying straight out that it is the case, but it happens often in studies where they are trying to get rid of all kinds of factors and some of those factors, maybe such as low blood pressure can be from the diet itself, so when you throw that out, you throw out the benefit of the diet and end up saying that there wasn’t any benefit at all.

  7. To the moderator, if I messed that up, could you fix it?

    I am hanging out on a different site learning science with science geeks right now. Yes, I found one and the Coronavirus helped me.

    I am starting to learn and I know that people don’t understand but up until a few weeks ago, it was still all words to me, but now cholesterol is something and the liver does something and fructose doesn’t go through glycolysis and I know what glycolysis is. I have been learning for a long time, but I just found a doctor who teaches science at a medical level, so I am finally moving from kids science to college and med school science and science geeks are commenting and I commented and got multiple comments back. They are passionate and so much farther ahead than I am and I think it will help. Plus, I can have two sites to interact on, so maybe I will be less annoying, but apparently not today.

  8. I am wondering if the elderly people in this audience have started isolating for a few weeks knowing that the coronavirus is on our shores and that the USA hasn’t been testing?

    I am going to take a few weeks off from social things.

    I know that elderly people will be the ones who die and I have too many elderly people who I love to not do my part.

    I feel like almost everybody around me is waiting to see what happens and they aren’t doing anything at all preventatively or proactively.

    I have stocked my pantry and will take a few weeks off from shopping and grocery shopping.

    I feel like I line up better with the world’s view on this situation than with America right now.

    All day long I have listened to announcers on the radio minimizing it because it isn’t killing as many people as the flu. For my part, I look at China trying heroically to reverse it and I watch Italy cancelling all of their sports – doing their share to contain it and we aren’t seeing it as that important and then we will panic after it comes or something equally as not helpful.

    Anyway, I am lending this particular conversation to the concept of telling your elderly loved ones that you love them.

    I had one of my young workers call in with flu symptoms today. Probably not the coronavirus, but he will not be coming in for a few weeks because he isn’t going to get tested at all either.

  9. This bog has a misleading heading. The heading is. How to Boost the Fat Burning Hormone FIAF.

    No real answer in the post unless one has a time machine to get raised in a lean household !
    Seriously this is a very confused ill expressed blog . Not usually the case -often helpful. Perhaps written in a hurry

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