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:

Is Triclosan Antibacterial Toothpaste Safe?

Why do dogs lick their wounds? They even lick our wounds. This leads to a question posed in the medical literature nearly a half century ago: Might there be some healing property of dog saliva? Well, it appears that there are a number of immune defense mechanisms in saliva, one of which involves nitric oxide. Licking of human skin results in production of nitric oxide from salivary nitrite, which kills skin pathogens and comes from the nitrates we eat in our diet.

How do we know we can get nitric oxide from licked human skin? Researchers had a bunch of volunteers lick their hands all over, front and back. Today, we have a better way to clean wounds: soap and water. (And we should never let our pets lick open wounds because cases of serious infections have been reported).

The reason I bring it up is that this transformation of nitrates from our diet into nitrites in our mouth has important implications for our health. Insufficient nitric oxide production is recognized as the earliest event in the onset and progression of a number of chronic diseases, including high blood pressure, peripheral artery disease, and a number of inflammatory conditions.

Nitrates come from vegetables in our diets, such as beets and green leafy vegetables. Good bacteria on our tongue convert nitrates into nitrites which can circulate throughout the body to create nitric oxide, and any nitrates our tongue bacteria missed the first time around get pumped by our body back into our saliva to give our tongue bacteria a second chance. One way we can become nitric-oxide-production-deficient is by not eating enough vegetables in the first place. So, eating vegetables should be the first step. But, if our tongue bacteria die off, the cycle is broken no matter how many vegetables we eat.

That’s why we should not use antiseptic mouthwash. Previously, I profiled an important study in my video Don’t Use Antiseptic Mouthwash. The most protective food for our heart may be green leafy vegetables because, like beets, they have lots of nitrates. So, if you drink some beet juice, you can get a remarkable drop in blood pressure within just hours, but only if you swallow.

The nitric oxide pathway can be interrupted if you use an antibacterial mouthwash or by spitting and not swallowing beet juice because of the critical action of our tongue bacteria on the nitrates in our saliva. So, we have to eat our vegetables and keep our tongue bacteria happy––so, no antibacterial mouthwash. But what about antibacterial toothpaste?

There’s a toothpaste on the market that contains an antibacterial chemical called triclosan. In my video Antibacterial Toothpaste: Harmful, Helpful, or Harmless?, I present a study was done that showed there was no difference in the levels of nitric oxide, nitrite, and nitrate after brushing with regular toothpaste and triclosan toothpaste. Our good tongue bacteria live in the cracks on the surface of our tongue, so if you just brush your teeth and not your tongue, the chemical doesn’t seem to get down there. Does that mean triclosan toothpaste is safe?

The use of triclosan toothpaste may not be associated with any increase in serious adverse cardiac events. And though studies on rats suggest the chemical can affect thyroid function, the use of triclosan toothpaste does not seem to affect human thyroid function. A study funded by Colgate concluded that triclosan was both safe and effective, producing “a significant reduction in gingivitis, plaque, and bleeding.” However, an independent review by the Cochrane Group suggested the reduction may be statistically significant but may not be beneficial enough to yield clinical significance.

Regarding safety, states are starting to ban the stuff because of data showing that despite the lack of efficacy, triclosan is so ubiquitous that most of the U.S. population is exposed to it. “Because the rapid rise in obesity in the U.S. parallels the introduction of triclosan, and because triclosan has two potential mechanisms by which it might alter human weight”—that is, by mucking with our gut flora or our hormones––researchers at Stanford decided to assess the association between triclosan levels flowing through people’s bodies and how heavy they are. And, indeed, they found an association between triclosan levels and increase in body mass index, and suggested further studies on how this chemical could be altering human growth and well-being.


If we shouldn’t use antiseptic mouthwash, What’s the Best Mouthwash? (Spoiler alert: It’s green tea!)

I’ve created an extensive video library on the benefits of nitrate-containing vegetables for both athletic performance and cardiovascular benefits. Here are some of the latest:

For more on nontoxic ways to maintain oral health, 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, year-in-review presentations: