1 A CALORIE is a calorie. Eat too many and spend too
few, and you will become obese and sickly. This is the
conventional wisdom. But increasingly, it looks too
simplistic. All calories do not seem to be created equal,
and the way the body processes the same calories may
vary dramatically from one person to the next.
2 This is the intriguing suggestion from the latest
research into metabolic syndrome, the nasty clique that
includes high blood pressure, high blood sugar,
unbalanced cholesterol and, of course, obesity. This
uniquely modern scourge has swept across America,
where obesity rates are notoriously high. But it is also
doing damage from Mexico to South Africa and India,
raising levels of disease and pushing up health costs.
3 Metabolic syndrome can still be blamed on eating too
much and exercising too little. But it is crucial to
understand why some foods are particularly harmful
and why some people gain more weight than others.
Thankfully, researchers are beginning to offer
explanations in a series of recent papers.
4 One debate concerns the villainy of glucose, which is
found in starches, and fructose, found in fruits, table
sugar and, not surprisingly, high-fructose corn syrup.
Diets with a high “glycaemic index”, raising glucose
levels in the blood, seem to promote metabolic
problems. David Ludwig of Boston Children's Hospital
has shown that those on a diet with a low glycaemic
index experience metabolic changes that help them
keep weight off compared with those fed a low-fat diet.
This challenges the notion that a calorie is a calorie.
Others, however, blame fructose, which seems to
promote obesity and insulin resistance. Now a study
published in Nature Communications by Richard
Johnson, of the University of Colorado, explains that
glucose may do its harm, in part, through its conversion
to fructose.
5 Dr Johnson and his colleagues administered a diet of
water and glucose to three types of mice. One group
acted as a control and two others lacked enzymes that
help the body process fructose. The normal mice
developed a fatty liver and became resistant to insulin.
The others were protected. The body's conversion of
glucose to fructose, therefore, seems to help spur
metabolic woes.
6 Jeffrey Gordon, of Washington University in St Louis,
says that many studies point to the importance of what
he calls “job vacancies” in the microbiota of the obese.
Fed the proper diet, a person with more vacancies may
see the jobs filled by helpful bacteria. In a paper,
recently published in Science, Dr Gordon explores this
in mice. To control for the effects of genetics, Dr Gordon
found four pairs of human twins, with one twin obese
and the other lean. He collected their stool, then
transferred the twins' bacteria to sets of mice. Fed an
identical diet, the mice with bacteria from an obese twin
became obese, whereas mice with bacteria from a thin
twin remained lean.
7 Dr Gordon then tested what would happen when mice
with different bacteria were housed together—mouse
droppings help to transfer bacteria. Bacteria from the
lean mice made their way to the mice with the obese
twin's bacteria, preventing those mice from gaining
weight and developing other metabolic abnormalities.
But the phenomenon did not work in reverse, probably
due to Dr Gordon's theory on the microbiota's job
vacancies. Interestingly, the invasion did not occur, and
obesity was not prevented, when the mice ate a diet
high in fat and low in fruits and vegetables. The transfer
of helpful bacteria therefore seems to depend on diet.
8 Dr Gordon hopes to be able to identify specific bacteria
that might, eventually, be isolated and used as a
treatment for obesity. For now, however, he and other
researchers are exposing a complex interplay of
factors.
9 One type of calorie may be metabolised differently than
another. But the effect of a particular diet depends on a
person's genes and bacteria. And that person's bacteria
are determined in part by his diet. Metabolic syndrome,
it seems, hinges on an intricate relationship between
food, bacteria and genetics. Understand it, and
researchers will illuminate one of modernity's most
common ailments.
De acordo com o texto, a obesidade é uma doença que é
