Dose Of E.Coli In The Gut "Blocks Cravings For Sweet Food"

20 Apr 2016 --- A small dose of the bacteria E.coli into the gut could reverse cravings for sweet food, scientists have revealed.
The findings in mice have raised hopes of new therapies to tackle obesity in humans.

Fifteen hours after one small dose of E.coli, levels of leptin, the so-called 'hunger hormone’ rose, invoking a feeling of being hungry. Within seven days the taste for sweets and the number of sweet receptors on the tongue were reduced.

Researchers said the mice remained in good health and their taste for other foods, such as salty food remained intact.

Neuroscientist Dr Lynnette McCluskey from the Medical College of Georgia at Augusta University, said: “In our field, we are starting to think about how hormones and different factors affect the taste system, even at the level of the taste buds, and contribute to obesity.”

“Identifying the taste, whether it's sweet or not, is the first step in feeding.”

“We wanted to know if you change the environment in the gut, what happens to the taste system.”

She called the new finding “a bit serendipitous”, but added that it is a proof of principle that just a slight change to the gut's extensive bacterial environment can change the feedback to taste.

Dr McCluskey said the finding could one day help reduce the consumption of unhealthy, sweet foods and help tackle obesity: “We found that it was surprisingly selective and surprisingly effective,” she added.

Our sense of taste has evolved as a matter of efficiency, allowing us to make split-second decisions about whether what we put in our mouths gives us energy or kills us, Dr McCluskey explained.

She said while high-energy sweet foods were a means of ensuring survival in the past, in today's more sedentary world the opposite is true. Processed, calorie-laden treats instead spark spiraling weight gain and obesity.

Although E.coli is more often thought of as a bacteria that triggers painful bouts of food poisoning, there are only a few strains that can make a person ill. It is a normal constituent of the billions of bacteria in the gut's microbiota, that enable us to digest food.

However, this new study marks the first time E.coli's role in taste has been explored, the researchers note.

They found that a part of E.coli's bacterial wall, known as lipopolysaccharide, or LPS, when it is placed into the confines of the gut itself, has an effect on taste.

Dr McCluskey said it somehow triggers higher levels of the satiety hormone, leptin, which is known to reduce the taste for sweet foods.

It is a logical step that taste cells should talk to the gut. But, how the gut signals back is currently a hot, and sometimes controversial, scientific debate, that has researchers including Dr McCluskey focusing their attention on hormones.

Leptin, which has a normal home in the gut, is made by fat cells and is also found in the brain. Recent research has shown it makes its way into the blood to the taste buds, where it binds with receptors and dampens the typically positive response to sweets.

Dr McCluskey said while directly exposing taste buds on the tongue to lipopolysaccharide (LPS), they did not note an effect on taste, ingesting LPS did have an impact.

In the bacterial-laden gut, the researchers believe LPS activates a receptor that inhibits the proliferation of taste cells. This in turn, down regulates sweet taste receptor genes in the taste buds.

However, there remain a number of unanswered questions:
“There may be other gut hormones involved as well, but we know that leptin works,” she said: The finding could one day help reduce the consumption of unhealthy, sweet foods and help tackle obesity.

Her team now want to know more about why the effect on sweet taste takes seven days, and why the effect also seems to go away seven days later.

Dr McCluskey admitted that they expected any response to be immediate and longer acting.

Science continues to reveal how the balance is different in the billions of gut microbiota populating obese versus leaner individuals.

It's also shown that an individual's population changes over his/her lifespan, likely because of what his/her is exposed to in the environment and diet.

“They play a big role in obesity, inflammatory bowel disease and now people are even looking at how they affect the brain for psychiatric disorders like depression,” Dr McCluskey said.

The findings were presented at the Association for Chemoreception Sciences Annual Meeting in Florida, USA.