For only a few years, it has been clear that bacteria are completely dominant in a healthy human being: On top of our ten billion body cells, there are one hundred billion microbial cells that play a role in our metabolism. This enormously increases the options for our bodily processes: If we include the microbes’ genes, then we have over 100,000 genes at our disposal, as opposed to just over 20,000.

There’s little doubt that changing your diet changes the microbiome in your gut ... microbes in the gut are crucial for the brain and mental health ... Some strains of gut bacteria can secrete neurotransmitters such as acetylcholine, gamma-aminobutyric acid (GABA) and tryptophan. The enteric nervous system lining the digestive tract contains millions of neurons that can respond to these neurotransmitters and send signals up to the brain.

there is a link between a disruption in circadian rhythm and known metabolic risk factors for obesity, diabetes, and cardiovascular diseases ... This link arises because disruptions in circadian rhythm muck up our microbiome, bacteria in our gut that help us digest our food. Beyond diet, they may also be affected by our mealtimes. A disturbed host’s clock disrupts the microbes’ 24-hour rhythm—reflected in their composition and overall function

Looking back at carbohydrate consumption over the last century reveals some interesting trends. Americans ate about the same amount of total carbohydrates in 1997 as we did in 1909—just not the same kinds. Over this time period, the proportion of carbohydrates from whole grains dropped from more than half of what we consumed to about a third. What replaced whole grains was food products made from different kinds of refined grains.

In participants that took ciprofloxacin, microbial diversity was altered for up to 12 months. The antibiotic treatments also caused a spike in genes associated with antibiotic resistance ... clindamycin killed off microbes that produce butyrate, a short-chain fatty acid that inhibit inflammation, carcinogenesis, and oxidative stress in the gut.The oral microbiome saw some community shifts. But the communities surprisingly rebounded within a short time—in some cases a week.

It’s hard to say which microbes are helping or hurting our health because the science of the “built microbiome” is just beginning. But already, microbiologists know not all microbes are bad. For instance, dog owners’ homes contain dust with a high diversity of bacteria, and studies suggest that exposure to this dust may increase the proportion of bacteria like Lactobacillus johnsonii in dog owners’ guts and help protect them against allergies.

A given person, in 2006, eating the same amount of calories, taking in the same quantities of macronutrients like protein and fat, and exercising the same amount as a person of the same age did in 1988 would have a BMI that was about 2.3 points higher. In other words, people today are about 10 percent heavier than people were in the 1980s, even if they follow the exact same diet and exercise plans.

Typically, every person is home to about a hundred trillion microbial cells bearing five million different genes, totaling about 5 pounds of micro-organisms per person. Indeed, microbes in and on the body outnumber human cells about 10 to one...The body’s collection of microbes, called the microbiome, influences health in ways that researchers are only beginning to understand...Broadly speaking, city living leaves its mark on people. That includes the sorts of microbes that collect inside them.

It turns out that we are only 10 percent human: for every human cell that is intrinsic to our body, there are about 10 resident microbes — including commensals (generally harmless freeloaders) and mutualists (favor traders) and, in only a tiny number of cases, pathogens. To the extent that we are bearers of genetic information, more than 99 percent of it is microbial.

many different species were present in the Yanomami's microbiome. The tribe had about 50 percent more ecological diversity than the average American