A Hidden Trigger of Obesity: Intestinal Bugs
If you're fighting the battle of the bulge, most of your attention — and
frustration — is probably aimed at your midsection. It makes sense, since
that's where the extra pounds tend to gravitate, especially with the creep of
middle age, piling on to form that dreaded spare tire.
The resent studies suggest that the tendency to eat more may not only be
driven by the fact that food is cheaper and more available, but by a change in
the bacteria in the intestines. People may be eating too much because their
appetite is stronger due to a low-grade inflammation they have, which could be
due to changes in their gut bacteria relative to what their grandparents or
someone else might have had 50 years ago."
Scientists led by Andrew Gewirtz at Emory University reveal that your
intestines harbor a universe of bacteria — the so-called gut micro biota — that
may play an important role in whether your body will store the food you eat as
extra pounds. The new studies suggest the relationship between gut bugs and weight.
New studies in mice showed a higher level of inflammation and what may account
for the extra weight. Inflammatory signaling can promote a condition called
metabolic syndrome, which causes weight gain, high blood pressure and high
cholesterol levels and a higher risk for developing diabetes and heart disease.
Gewirtz's study had been bred to lack a
protein known as toll-like receptor 5 (TLR5), which most intestinal cells
sprout on their surface.
TLR5 acts as a
traffic cop for controlling the mass of pathogens living in the intestine;
without it, the normally harmless gut bacteria tend to over flourish and expand
in number. When that happens, the study found, it triggers an inflammatory
state, as the body attempts to respond to the increasing population of bugs,
and at the same time makes cells less sensitive to insulin. In a way,
inflammatory factors and insulin compete for the attention of the same
intestinal cells; if the cells are busy responding to inflammatory factors,
then they are less likely to take up glucose and process it effectively. Such desensitization
to insulin and glucose then leads to the symptoms of metabolic syndrome, such
as weight gain, high cholesterol and triglyceride levels and elevated blood
pressure. "We don't think the bacteria are directly making you eat more,
but the bacteria are causing low-grade inflammation, which causes insulin resistance
and then makes you eat more," says Gewirtz.
Picture what the world eats
A more fundamental question, now, is what causes changes in gut micro biota?
Many things, says Gewirtz, including the use of antibiotics, cleaner water and
improved sanitation and hygiene in general, which influences the type and
amount of microbes that reside in the intestines. In the current study,
scientists found that in TLR5-deficient, the total percentage of 150 species of
bacteria in the gut was three to four times higher than in normal, while 125
other types of bacteria were less common. "Study says that they don't have
a sense of which is more important yet — that some of those species are
missing, or that some are in greater abundance. The net effect, however, is
that in the absence of TLR5, the community of microbes changes and, as Gewirtz
says, "when the intestinal bacteria is changed, the host response changes
with them, and that may predispose you to a variety of diseases of which
obesity and metabolic syndrome are perhaps the most mild."
An important part of the investigation involves having an accurate map of
the genetic makeup of those gut bugs.
The Science of Appetite
The Way We Eat
Nature prefers you fat, but you can take control. New
research could explain better approaches to dieting and how to curb your
Unrefined foods, especially those that are high in fiber, stimulate
appetite-suppressing hormones and make you feel full
Bad Diets Can Alter Stomach Bacteria for the
Bad diets can alter stomach
bacteria — leading to a big belly.
American scientists say they’re
finding reasons – beyond the obvious – that foods full of fat and sugar can
lead to a big belly.
There’s new research to suggest that a high-fat and high-sugar diet can go
beyond adding calories and can also alter the bacteria in the human stomach.
And this can lead to weight gain.
Bacteria currently being called “human gut flora” may prove to be an active
obesity trend. Scientists tested this idea on mice, inserting the human
bacteria into their intestines. When they fed the mice a high-fat and
high-sugar diet, they saw an immediate change in their internal structure. The
mice quickly showed an increase in body fat and the kinds of bacteria that are
linked to becoming obese.
What the Study Emphasized
According to the abstract of the study, "Diet and nutritional status
are among the most important modifiable determinants of human health. The
nutritional value of food is influenced in part by a person's gut microbial
community (microbiota) and its component genes (microbiome).
"Unraveling the interrelations among diet, the structure and operations
of the gut microbiota, and nutrient and energy harvest is confounded by
variations in human environmental exposures, microbial ecology, and genotype.
To help overcome these problems, we created a well-defined, representative
animal model of the human gut ecosystem by transplanting fresh or frozen adult
human fecal microbial communities into germ-free C57BL/6J mice.
"Culture-independent metagenomic analysis of the temporal, spatial, and
intergenerational patterns of bacterial colonization showed that these
humanized mice were stably and heritably colonized and reproduced much of the
bacterial diversity of the donor's microbiota.
"Switching from a low-fat, plant polysaccharide-rich diet to a
high-fat, high-sugar "Western" diet shifted the structure of the
microbiota within a single day, changed the representation of metabolic
pathways in the microbiome, and altered microbiome gene expression.
"Reciprocal transplants involving various combinations of donor and
recipient diets revealed that colonization history influences the initial
structure of the microbial community but that these effects can be rapidly
altered by diet.
"Humanized mice fed the Western diet have increased adiposity; this
trait is transmissible via microbiota transplantation. Humanized 'gnotobiotic'
mice will be useful for conducting proof-of-principle "clinical
trials" that test the effects of environmental and genetic factors on the
gut microbiota and host physiology."
The big picture in this study is that a poor
diet may alter intestinal bacteria to encourage weight gain, but also what kicks
in are genetics, environment, and physical activities. With a high fat and high
sugar diet, scientists know that sugar is fed to rats to raise their blood
pressure because salt affects the salt-sensitive rat, but sugar is an
all-around weight enhancer. The high fat diet works if your genetics is such
that your genes don't remove the fats. But which fats?
The moral of the story is if you eat a low
sugar diet, it helps. But if you have metabolic syndrome, maybe you need a
certain amount of specific types of fats. That's why talking with a health care
professional helps you to tailor your food to your body's requirements. Some
people need more of certain types of fats than others. And as for sugar, you'll
get enough in fresh fruits.
Gut Bacteria May Cause and Fight Disease,
Who lives here in the large intestine? What do they do? The bacteria in some
people's intestines are good at digesting Cheerios, whereas other peoples'
intestines don't process the cereal's calories.
These little guys, called Bacteroides thetaiotaomicron, are friendly
bacteria in your gut that help with digestion and health.
Quick question: Whose genes matter most
to you? Your mom's?
Or genes inside the trillions of bacteria
living in your intestine, your mouth, your nasal passages and a lot of
places we'd rather not mention?
The answer: Obviously, your parents'
genes matter, but it turns out we humans have two sets of genes in us: the
ones we inherited from our human ancestors and the ones that walk in
through our mouths starting when we're just hours old.
"We're all sterile until we're born," says Glenn Gibson, a
microbiologist at the
. "We haven't got
anything in us right up until the time we come into this big, bad, dirty
world." But as soon as we pass out of the birth canal, when we are fetched
by a doctor's hands, placed in a hospital crib, put on our mother's breast,
when we drag a thumb across a blanket and stick that thumb in our mouths, when
we swallow our first soft food, we are invaded by all sorts of bacteria. Once
inside, they multiply — until the bacteria inside us outnumber our human cells.
Bacteria Affect Your Weight
Because the bacteria are independent organisms, they have their own genes
and their own talents — and scientists are just now discovering what they can
matter. Apparently, they can digest food far more efficiently.
Gordon and a bunch of other scientists discovered that bacteria are not all
alike. There are as many of 500 different species in a normal human intestine
and maybe another 500 in our mouths. David Relman of
discovered that each tooth has its own bacterial community. Dr. Julia Segre at
the National Human Genome Research Institute found one set of bacteria on skin
at the bend of a human elbow and a completely different set higher up on the
Not surprisingly, a person who grows up in
and another who grows up in northern
tend to acquire different bacteria in their intestines and mouths — and,
stunningly, these differences seem to matter a lot when you move from culture
The Cheerios Experiment
Imagine a Cheerio sliding down the digestive tracts of an Inuit and an
Argentine. The Inuit's intestinal bacteria are great at digesting oats; the
Argentinian's bacteria don't much care for oats. What happens? The Inuit gains
weight. The Argentine makes more frequent visits to the restroom.
It is becoming increasingly clear that different bacteria provide people
with different advantages and disadvantages. All over the world, teams of
scientists are looking at how bacteria affect the folks they live in. Certain
bacteria have been linked to the incidence of stomach ulcers, but take away
those bacteria with antibiotics, and young people get more asthma, hay fever,
allergies and eczema.
So bacteria — or, rather, the genes that bacteria bring into our bodies —
can help us and hurt us.
Can I Change What I've Got Inside Me?
Naturally, that raises the question: Can I change what I've got? "The
obvious implication here," microbiologist Gibson says, "is that if
you find bacteria which are responsible for diseases — and you can include obesity
in this — you can then target them to reduce the risk of that disease."
immunologist Alexander Chervonsky, with collaborators from
recently reported that doses of the right stomach bacteria can stop the
development of type 1 diabetes in lab mice. "By changing who is living in
our guts, we can prevent type 1 diabetes," he told
The Wall Street
The bottom line: We now have two sets of genes to think about — the ones we
got from our parents and the ones of organisms living inside us. Our parents’
genes we can’t change, but the other set? Now that is one of the newest and
most exciting fields in cell biology.