By William B. Miller, Jr. M.D.
It’s holiday season and while we deck the halls and jingle the bells, we also indulge – while the average person consumes between 2,000 and 2,500 calories per day, one holiday meal can come in at over 3,000 calories. And while we’ve always been told that how much we eat is just a matter of will power, recent research indicates that there is another dynamic at work. How much we eat is actually deeply influenced by our invisible companion microbes. To a significant extent, we eat until our gut microbes say we’re full.
Tens of trillions of microbes live inside our gut and perform essential services for us. They serve crucial roles in mediating our immune systems, metabolism and central nervous system. They also assist in normal growth and development and protect us against unwanted pathogens. And they even affect our moods and mental states, with a direct link to depression and anxiety.
Important as well, our gut bacteria play a critical role in obesity. Two main types of bacterial strains are dominant in our gut microbiome. Obese and lean individuals differ significantly in the relative proportions of these two types. In experiments on mice, if those proportions are manipulated, mice can be reprogrammed from fat to lean.
Doctors have long assumed that our level of appetite or satiety was dependent upon circulating molecules and hormones given off by our own body cells that line our gut. As we eat and digest, those cells give off chemicals that are metabolic signals of fullness and satisfaction. These circulate from our gut tissues to specific centers in the brain. However, it is now understood that our gut microbes participate heavily in that circuit. As they take in nutrients from our food as we are eating, they give off circulating molecules that tell us if we are full. Surprisingly, this circuit is actually dependent on their assessment of their own needs. So our gut bacteria and our own cells are both directly participating in determining both hunger and satiety.
Research has found that the microbes in our stomach have a very large say on how large a meal we will eat. As we eat, our microbes are absorbing nutrients from our food. These extra nutrients trigger a phase of rapid reproduction that lasts for about 20 minutes. After that, they switch to a slower growth phase, and send signals to our brain that they are satisfied. It is currently estimated that it takes an increase of about one billion extra bacteria in the stomach and its close connections before their growth cycle switches and tells us that we’ve had enough to eat. So, although it may only take a small village to raise a child, it takes about 1 billion more bacteria to make you feel full.
We now know that it is not only the amount of food that counts. There is also a strong correlation between the level of fats in our diet and our brain circuits. When rats are placed on a high fat diet, their brain circuits are re-organized. Inflammatory signals go to the brain regions responsible for feeding behavior, alter those circuits, and encourage us to eat more. Not everyone is affected equally though. It’s just like changes in temperature when some people do fine but others get uncomfortable. The level of ingested fats in our diets changes everyone’s gut microbial populations, but some are affected more than others. For those who are sensitive, fats cause inflammatory changes that irritate nerve cells that carry signals from the gut to the brain. This can lead to gut-brain miscommunication and can lead to overeating and obesity.
So this holiday season, how do we best achieve that balance? How do we keep our essential microbes in harmony with our own cells before we dive into the gingerbread, sugarplums and eggnog? Here are five simple tips:
- Slow down when eating. Give your microbes a chance to increase in number while you eat. Remember that they’re at the table with you.
- When you have finished that main course of a big holiday meal, step away from the table before you decide to have dessert. Waiting twenty minutes to make a decision on dessert can mean a surprising difference on how likely you are to reach for the next piece of pie.
- As much as possible, try to lay off the fats.
- Experiment with incorporating prebiotic or probiotic foods into your diet before you start the holiday food festivities. Keep taking them on a regular basis in the New Year. These types of foods help to promote a healthy gut microbiome.
- Above all, be willing to actively experiment. Try to see what works for you. No two individuals are alike and a solution for one person may not be the same one that works for you.
Dr. Bill Miller had been a physician in academic and private practice for over thirty years. He is the author of The Microcosm Within: Evolution and Extinction in the Hologenome. Dr. Miller is an internationally recognized evolutionary biologist and an expert on the emerging science of the microbiome. He is the author/co-author of numerous academic papers on the microbiome and evolution, serves as guest editor of a major academic biology journal and is co-editor of a forthcoming textbook on developmental and evolutionary biology.