Still, he’s optimistic the study will show some promising results and
that with proper screening, this could someday offer a safe,
less-invasive, less-expensive option than surgery for people with
obesity. Though, they’ll need to get over the ick-factor.
Obesity is an enormous health issue in the U.S. Since
two of every three Americans are overweight or obese, it’s no stretch to
say the problem has assumed epidemic proportions. There are many
explanations for our expanding waistlines, starting with insufficient
amounts of exercise and excessively large portions of inexpensive,
calorie-dense prepared and processed foods. But is it possible that
social interactions also play a role, and that the obesity epidemic is
in part a contagious disease? An important study suggests that answer
Researchers from Harvard and the University of California investigated
12,067 people who had been evaluated medically on multiple occasions
from 1971 to 2003 as part of the Framingham Heart Study. They found that
if one sibling became obese during the study, the chance that another
sibling would become obese increased by 40%. Genetics might account for
some of the parallel weight gain in siblings, but not for the fact that
if a spouse became obese, the likelihood that the other spouse would
follow suit jumped by 37%. Shared meals and other lifestyle habits might
explain that link, but the scientists also found that if a person had a
friend who became obese, his chance of growing obese rose by 57%.
The impact of networks depended more on social status than physical
proximity; obesity in a neighbor had much less influence than obesity in
a friend, regardless of how far away the friend lived. Friends of the
same sex were particularly influential; a man who had a male friend who
became obese experienced a 100% increase in his own chance of becoming
obese. And when two people regarded their friendship as mutual, obesity
in one member of the pair increased the other’s likelihood of becoming
obese by a staggering 171%.
Why does obesity spread in social networks? The effect extends far
beyond the impact of genetics and shared environmental influences. The
researchers did not specifically investigate diet and exercise patterns,
but they did find that changes in smoking did not account for the spread
of obesity in the Framingham network. Although scientists don’t fully
understand how obesity spreads, they suspect a major factor is that a
social network influences what its members perceive as normal and
acceptable. If a man sees his friends become obese over time, he may
accept weight gain as natural, even inevitable. Instead of exercising
more or eating less when his own weight begins to creep up, he may
simply go with the flow and join the crowd.
The notion that obesity is contagious may lend new weight to folks who
claim “you make me sick.” But the same researchers who revealed the
spread of obesity also tell us that networks can spread positive
emotions as well.
A new science
Epidemics have plagued humans throughout history. Before scientists
identified the microbes responsible for an epidemic as well as the way
the germs spread from person to person, people blamed things like human
misbehavior, divine intervention, and supernatural forces for epidemics
ranging from the Black Death of the Middle Ages to the Spanish Flu of
- But now that doctors understand the way infections spread through
communities, they can use tools such as immunization, hygiene, and the
isolation of sick individuals to control epidemics.
Social-network science is much newer than epidemiology, and its eventual
impact on medicine remains uncertain. The statistical methodology used
in the Framingham research on obesity and happiness has come under fire.
Still, the studies raise the intriguing possibility that noninfectious
phenomena can spread across communities through social networks, and
researchers have added alcohol consumption and depression to the list of
things that may be affected by social networks.
Natural social networks may already have a substantial impact on health,
and if doctors learn to harness them to spread healthful habits,
positive attitudes, and wise lifestyle choices through communities, they
may be able to improve public health. It might sound farfetched, but
support groups such as Alcoholics Anonymous and Weight Watchers already
function as small, artificial therapeutic networks.
More research is needed. Call it a network in progress.
With the help of a $1.5 million grant from the Canadian government,
Gaisano and his team are trying to see if swapping the bacteria from a
slim person’s gut into a person with obesity through a fecal transplant
will help that person lose weight. There’s already some evidence that
this may work. For one, studies on mice have shown that when germ-free
mice were fed the stool of obese mice, or even humans, those mice put on
weight. There’s also evidence that people with obesity who get bariatric
surgery not only lose weight from the physical changes, but also because
of changes to their gut bacteria.
Poet and pastor John Donne famously proclaimed “No man is an island.” It
was true in his day, and because society has become increasingly complex
and interdependent over the ensuing 400 years, it’s certainly true
today. Studies in the modern era show that people can be good medicine
and that individuals with strong social supports are healthier than
those who are lonely and isolated. Married men, for example, are
healthier than their single, divorced, or widowed peers.
“If you, who are skinny, and I, who is a little fatter, eat the same
amount of food, you’ll suck up less nutrients and I’ll suck up more,”
said Dr. Herbert Gaisano, a professor of medicine and physiology at the
University of Toronto. “Part of the reason is because my bacteria
metabolizes the food in a way that I’ll suck up more.”
Like the study of obesity, the Framingham Heart Study’s database was the
foundation of the happiness study. In this case, 4,739 people who were
tracked between 1983 and 2003 served as the primary study population.
Together, these subjects reported a total of 53,228 social ties to
family, friends, neighbors, and coworkers. Because scientists have kept
a close eye on the Framingham volunteers since 1971 — over three
generations — detailed medical and psychological information was
available for many of these people.
The researchers used the Center for Epidemiological Studies Depression
Scale to evaluate happiness at the start of the study and at subsequent
follow-up examinations. Just as the obesity study provided information
on how weight changed over time, the happiness study focused on changes
in mood over time.
The Framingham study confirmed earlier findings that the strongest
determinant of whether a person will be happy in the future is how happy
he has been in the past. And the study also confirmed that healthy
people tend to be happier than those who are ill; men tend to be a bit
happier than women; and more educated people tend to be slightly happier
than those with less schooling.
Previous research had validated the everyday observation that emotions
are contagious over a very brief time frame; if one person in a room
starts to laugh or cry, others often follow suit, but the effect wears
off in minutes. But the Framingham study added an unexpected finding:
happiness can also spread more diversely and broadly across
The scientists found that if one spouse became happy, the likelihood
that the other spouse would become happy increased by 8%. Siblings who
became happy increased the other sibling’s chance of becoming happy by
14%. But while the spread of obesity was not related to physical
closeness, the spread of happiness did depend on distance. Spouses and
friends only transmitted happiness to people living within a mile, and
although obesity did not spread between neighbors, happiness did. But
physical proximity on the job did not allow happiness to spread
Like obesity, happiness spread more readily between members of the same
sex than between people of the opposite sex. Like obesity, the spread of
happiness seemed to reach across at least three degrees of separation,
spreading, for example, from a friend to the friend of a friend and then
to the friend of that friend. But the impact diminishes with each degree
of separation, and even within first-degree contacts, it begins to wane
after six to 12 months.
Although the researchers did not discover exactly how happiness spreads
across social networks, they did speculate on the positive role that
spreading happiness may play. Humans are social beings, and the health
and well-being of one person influences others. Since happiness and
optimism are linked to better health and improved longevity, contagious
happiness might have a beneficial effect on the health of an entire
community. Interestingly, the Framingham study found that unhappiness
does not spread across social networks. If emotions were the flu, that
would mean that immunity could spread, but the virus itself could not —
it’s a fantasy for the flu season that’s just kicking off, but it’s a
real possibility for the way emotions spread.
Social isolation is a well-established heart attack risk factor, while strong interpersonal ties and community activities appear protective. Although studies show that marriage appears to improve the prognosis of prostate cancer, it’s not clear that social isolation is a cancer risk factor. A 2009 study from the University of Chicago suggests that isolation may have that effect — at least in female rats. As compared to animals who were allowed to live in groups of five, rats that were raised in isolation had a threefold increase in the risk of breast cancer, and their tumors were much more aggressive than the cancers that developed in the community dwellers. Changes in sex hormones did not appear to account for the difference, but excessive stress was a likely explanation.
Females are more gregarious than males, and men are not rats. Still, the animal experiment raises interesting questions for future human research.
It’s easy to understand how face-to-face interactions can be beneficial.
But research suggests that social interactions have a ripple effect that
extends far beyond household and family units. Some of these effects can
promote health; others are detrimental. But whether for good or ill,
these communitywide effects give networking a new meaning.
The team now plan to assess whether the same process occurs in people.
“We’re certainly not identical to mice in our physiology, but our taste
buds work pretty similarly, and the same factors related to inflammation
we think are responsible for taste loss are elevated when we become
obese,” said Dando.
Researchers found that within eight weeks of becoming obese, mice lost
25% of their taste buds. The findings suggest that weight gain not only
changes appetite but may also fundamentally alter the way taste is
They also plan on doing a very small trial of fecal transplants in
humans: taking the stool from healthy weight individuals and
transplanting it into the large intestine of people with morbid obesity.
They’ll compare this group with a control group to monitor the effects.
In the study, the mice were fed either a normal or a fatty diet. After
eight weeks, the mice on the high-fat diet weighed about one third more.
The scientists found they also had about 25% fewer taste buds than the
Over the last few years, we’ve learned that gut bacteria differs
dramatically between healthy-weight people and people with obesity. At
the same time, interest in fecal transplants as a treatment for
everything from superbugs to malnourishment has grown dramatically. As
these discoveries have unfolded, we’ve all been wondering the same
thing: can we just put the poop of skinny people into people with
obesity to help them lose weight? Now, a team of researchers in Canada
is trying to find out.
Dando said the findings could help devise new approaches to losing
weight, with a greater focus on the influence of taste perception on
what people eat.
Image: Kyle May/Flickr