Of Obese Mice & Men

I came a very interesting and thought provoking article
the other day in a very prestigious scientific journal
(Vijay-Kumar et al, Science, 328: 228-231, 2010).

But first, a bit of background information:

It has been known for some time that the types of
bacteria found in the intestines of obese people are
different than those found in the intestines of lean
individuals.

But no one really knew the significance, if any, of
that observation.

The current study compared a strain of mice that are
genetically predisposed to obesity with wild type
(genetically lean) mice.

They first looked at the intestinal bacteria. It turned
out that the obese mice and lean mice had the same
differences in intestinal bacteria that humans have.

And just like obese humans the obese mice displayed
insulin resistance, and elevated levels of
triglycerides, cholesterol and blood sugar (They
were pre-diabetic).

Since the obese mice also ate more than the lean mice
many of the observed differences could have been due to
the excess calories and resulting weight gain.

To test that hypothesis, the scientists limited the
amount of food that the genetically obese mice (the
mice that were genetically predisposed to obesity) ate
so that it was identical to what the genetically lean
mice ate.

Even though the genetically obese mice were no longer
overweight they still displayed increased insulin
resistance compared to the genetically lean mice.

Based on this and other experiments the scientists
eventually concluded the it was the insulin resistance
that was causing the mice to overeat and, therefore,
become obese.

The scientists then decided to test the hypothesis that
the particular bacterial strains found in the
intestines of genetically obese mice might be causing
the insulin resistance.

In the first experiment they killed off the intestinal
bacteria in the genetically obese mice by putting high
dose antibiotics in their food.

Depleting the intestinal bacteria created some health
problems for the mice, but it completely prevented the
insulin resistance, overeating and obesity normally
observed with this strain of mice.

In the second experiment they sterilized the intestines
of the genetically lean mice and then colonized their
intestines with intestinal bacteria from the
genetically obese mice.

When they did this, the genetically lean mice developed
many of the characteristics of the genetically obese
mice including insulin resistance, overeating, obesity
and hyperglycemia.

In short, the genetically lean mice became overweight
and developed diabetes.

Based on these experiments and other studies the
scientists hypothesized that the wrong kinds of
intestinal bacteria can make a significant contribution
to insulin resistance, which in turn can lead to
overeating and obesity.

In short, they concluded that bad bugs may make you
fat.

Does this mean that you should rush out and buy some
probiotics (friendly bacteria) as part of your weight
loss strategy?

The simple answer is no. That would be premature. These
studies were performed in mice and genetics obviously
played a role in the results.

In short, we are a long way from knowing to what extent
intestinal bacteria might contribute to obesity in
humans.

However, there are many very good reasons to make sure
that you supply friendly bacteria to your intestinal
track on a regular basis.

For example, we know that bad bacteria in your
intestine can compromise your immune system, convert
foods that you eat to cancer causing chemicals, and
cause chronic inflammation - which contributes to a
number of major diseases.

We can't yet say whether good bugs will help keep you
slim, but we do know that they can help keep you
healthy.