Gut Flora Affects Fatness

Unbalanced gut flora results in the gut absorbing way more calories from the same amount of food as skinny people eat. When some overweight people complain "but I don't eat more than other people!" they are likely telling the truth. They might just be extracting more calories from the food:

In one study, Gordon and colleagues looked at what happened in mice with changes in bacteria level. When lean mice with no germs in their guts had larger ratios of Firmicutes transplanted, they got "twice as fat" and took in more calories from the same amount of food than mice with the more normal bacteria ratio, said Washington University microbiology instructor Ruth Ley, a study co-author.

It was as if one group got far more calories from the same bowl of Cheerios than the other, Gordon said.

In a study of dozen dieting people, the results also were dramatic.

Before dieting, about 3 percent of the gut bacteria in the obese participants was Bacteroidetes. But after dieting, the now normal-sized people had much higher levels of Bacteroidetes — close to 15 percent, Gordon said.

Balancing the gut flora is key. Things that put the gut out of balance:

• Viri
• Bacterial infections
• Antibiotics
• Stress (inhibits good bacteria)
• Food sensitivities

If an imbalance continues for a long time, nutritional absorption changes. And that, it seems, can make you fat.