68 MOTHER JONES |^ JULY / AUGUST 2019
MATT CHINWORTHFOOD FOR THOUGHTGUT
INSTINCTS
For decades, counting calories
was seen as the key to staying fit.
There are a few—actually a
trillion—little problems with that.
by tom philpottmore than 120 years ago, a scientist named Wilbur
Atwater launched what would become an endur-
ing dieting trend: He started meticulously counting
calories. In a series of experiments, Atwater set fire to
hundreds of foods and measured the released energy.
In another experiment, he and his team planted a
grad student in an airtight “room calorimeter” and
passed him portions of bread and beans and deter-
mined how much heat, carbon dioxide, and waste
he generated. To this day, when the food industry
lists calories on labels, as required by federal law, it
often relies on Atwater’s calculations.
Atwater’s work helped give rise to the nutri-
tional dogma that your body weight is governed by
whether you burn off all the calories you eat. Just ask
chips-and-soda giant PepsiCo. When “the amount
of calories you take in equals the amount of calories
you burn,” the company insists on its website, “you
maintain your body weight.” Excess calories will
stick around as “body fat and weight gain,” warns
the Department of Agriculture’s Weight Manage-
ment webpage. This is true whether they “come
from protein, fat, carbohydrate, or alcohol.”
But recent research challenges this belief. The
scientists during Atwater’s era saw the human di-
gestive system as a single engine producing a pre-
dictable quantity of energy from a given amount
of fuel. Yet the human gut contains a multitude
of engines, and they interact with each other in
ways science is just beginning to unravel. Over
the past 15 years, a fast-growing body of literature
suggests that the gut microbiome—the trillions of
microbes that live inside us—shapes the way we
metabolize food and may play an important role
in how we gain weight.
Our microbiome is sensitive to our diets—in-
cluding which medicines we take. Several recent
studies have shown that infants repeatedly treated
with antibiotics are at significantly higher risk of
being overweight in early childhood. Antibiotics, it
turns out, reconfigure your gut’s balance in favor of
microbes that help us store food as body fat. “We’refour generations or so into [the age of] antibiotics already,” says Martin
Blaser, a professor of medicine and microbiology at Rutgers and the
author of Missing Microbes: How the Overuse of Antibiotics Is Fueling
Our Modern Plagues. As a result, our microbiomes are better at helping
us store fat than those of our ancestors.
Antibiotics aren’t the only force shifting our internal ecology.
Modern diets are full of processed foods and low in fiber, the kind of
hard-to-break-down carbohydrates found especially in vegetables,
legumes, and whole grains that are crucial for a healthy microbiome.
The vast majority of our internal microbes live in the far reaches
of our digestive tract, the colon, explains Justin Sonnenburg, an
associate professor of microbiology and immunology at Stanford.
Because of their location, these microscopic critters “really only
get access to the dregs of what we eat”—the dietary fiber that ourorgans can’t digest. The microbes have evolved to process that fiber
by fermenting it with enzymes.
Researchers, including Sonnenburg, are still sorting out exactly
why, but feeding this fermentation process appears to be crucial for
averting weight gain and diseases like obesity and Type 2 diabetes. For
example, a 2017 study by Georgia State University professor Andrew
Gewirtz found that mice fed high-fat diets and no fermentable fiber
gained weight and added visceral fat—the kind that sits at the mid-
section and can trigger a range of metabolic problems. Adding inulin,
a fermentable fiber supplement, dramatically cut the effect.
However, Gewirtz adds, his team later found these fiber supple-
ments might also trigger liver cancer. “Right now, the only useful
advice I could give somebody would be to eat foods naturally rich in
fiber,” he says, like bran cereal and every kind of bean you can think
of. Other winners included pears, avocados, apples, seeds, and nuts.
Currently, we’re doing a pretty bad job of eating enough of those
foods. The Institute of Medicine recommends that women eat 25
grams and men 38 grams of fiber every day, but Americans only get
about 15 grams on average.
We’ve known for years that fiber makes us feel more full. Now
research ers think it’s doing double duty: By feeding our deep-seated
gut flora, it’s potentially staving off future pounds. The choice of
whether to lunch on a cup of black beans or five chicken nuggets—
which both contain about 220 calories—just got a whole lot easier. n