The Role of Intestinal Bacteria in Obesity

Eating a diet high in sugar makes it hard to lose weight. High glycemic carbohydrates stimulate the production of insulin. And when insulin levels are high, you can’t burn fat. That’s why some experts call it the “fat storage hormone.” 

But that’s not the only reason a high-sugar diet is associated with obesity. It can also alter the bacteria in your gut. This change makes it easier to gain weight and harder to lose it. And the effect can happen in just 24 hours.

Jeffrey Gordon, MD is one of the foremost experts on intestinal bacteria. He and his colleagues recently performed a study published in the journal Science Translational Medicine. It showed the clear connection between sugar consumption, intestinal bacteria and weight loss.

The Bacterial Connection to Obesity

Dr. Gordon had already established the connection between gut bacteria and obesity. His previous research showed that obese and lean people have different types of bacteria in their guts. The same is true in animals. Here’s what he found.

Ninety percent of the microbes in your gut fall into two major classes, or phyla:

  • Firmicutes – this strain of bacteria is dominant in those who are obese
  • Bacteroidetes – this strain of bacteria are dominant in those who are lean

Dr. Gordon and his team also discovered that when an obese person loses weight, their microflora revert back to those observed in a lean person. The researchers wanted to understand this connection better. So they designed a study using mice.

They began with a group of mice raised in a sterile environment. These mice had no intestinal bacteria. In half of the mice, he implanted bacteria dominated by firmicutes. These cultures came from obese mice. In the second group, he implanted bacteria dominated by bacteroidetes. These came from lean mice.

Both groups of mice ate the same diet. However, those with the “obese” bacteria soon became obese. Those with the “lean” bacteria stayed lean. They found the same results using human intestinal bacteria from lean and obese subjects.

So what is the connection between your gut bacteria and your weight?

Dr. Gordon and his team believe it has to do with digestion. To reach this conclusion, they analyzed the genomes of the two classes of bacteria. Their conclusion? Firmicutes are more efficient at digesting food that the body can’t. So if you have a higher population of these bacteria, more of the food you eat will be converted into digestible calories. This makes it easier to gain weight.

The Connection to Sugar

Dr. Gordon also showed what happened when the mice with “lean bacteria” were switched to a high-sugar diet. Within 24 hours, the “obese bacteria” asserted dominance. They began to out-compete and out-proliferate the friendly bacteria.

Bottom line: the bacteria in your gut play a big role in your ability to gain or lose weight. And a high-sugar diet helps the bacteria that promote obesity.

Now, Before You Grab that Container Of Yogurt…

There is something else that Dr. Jeffrey Gordon discovered that you should know. He found that commercial yogurts have very little effect on the composition of bacteria in the gut.

In this experiment, the team recruited seven pairs of identical twins. Each pair consumed a serving of a popular yogurt twice daily. The yogurt contained five different strains of bacteria. After several weeks, they analyzed stool samples from the volunteers. They found that the microbes from the yogurt did not change the make-up of the bacteria in the subject’s guts.1 They also found the same results in a study of mice.

Dr. Gordon was not surprised. “We were only giving several billion bacterial cells in total to the twins,” he said. Meanwhile, there are trillions of gut microbes in our intestines.

What’s more, most commercial yogurts are full of sugar. And they are also pasteurized.  This process kills many of the cultures these companies boast about in their marketing.

So, what can we learn from these studies?

First, if you want to lose weight (and maintain your health) it pays to avoid sugar, grains and high-carbohydrate foods. These foods stimulate the “fat-storage” hormone, insulin. And they also feed the “obese” bacteria in your gut.

The “lean” bacteria in your gut thrive on fiber. So, feed these healthy bugs lots of organic vegetables and colorful plant foods.

Also, yogurt is not the best source of probiotics. And always avoid sweetened yogurt. To get the digestive and weight loss benefits you seek, you should take a high quality probiotic supplement.

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Health Topic: Diet and Nutrition


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  3. Anonymous says:

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