The latest trick to fighting obesity isn’t a focus on eating less fat or sugar (although that would probably help): It’s eating more fiber. And not just any kind of fiber. It should be the fermentable type. Microbes in the gut chow down on this type of fiber. As they break it down, they release a chemical that moves to the brain. There it curbs appetite.
Researchers at Imperial College London, in England, say their study is the first to link eating fiber to the brain hormones that help you feel full. They published their findings April 29 in Nature Communications.
Scientists have known that obese people tend to eat foods low in dietary fiber. At some level, that made sense. Fermentable fiber — fiber that is broken down by gut microbes — makes people feel full after eating somewhat less. Such fiber is found in fruits, vegetables, oats and barley.
Hundreds of thousands of years ago, our paleolithic ancestors ate nearly 100 grams of fermentable fiber each day, says Gary Frost. He’s a dietician who led the new study. Today, people’s diets are very different. We eat only 10 to 20 grams of all types of fiber each day. Most comes from whole-grain wheat and bran. Those types do not break down in the gut, Frost notes. Modern diets also are full of convenience foods, such as snacks and frozen dinners. These tend to be high in fat and sugar. Add in our couch-potato lifestyle and it’s a recipe for obesity.
Eating more fermentable fiber reduces the risk of becoming overweight or obese. But until the new study, exactly how the fiber did that was unclear.
In the new study, researchers fed one group of mice a high-fat diet. It also was high in fermentable fiber. Another group received a high-fat diet with non-fermentable fiber. After eight weeks, the first group weighed less. Those mice also had eaten less food than the second group.
Next, the scientists looked at the effect of one particular chemical: acetate. Also known as acetic acid, it is a common by-product of the breakdown of sugars and starches by gut microbes.
To learn how the chemical affects weight, the scientists injected the mice with acetate. But first they labeled the acetate with carbon-11. This radioactive isotope of carbon has only five neutrons, rather than the usual six. The radiation it gave off allowed researchers to track its location. To do that, they put each mouse in a PET-scanner. This device creates a three-dimensional image showing the location of the radioactive “label” on each acetate molecule.
The acetate traveled through the blood and into the mice’s brains. There it collected in a region known as the hypothalamus, which controls appetite. By releasing hormones, that brain region can shut off hunger and promote satiety — a feeling of fullness. As a sign that’s indeed happened, mice injected with acetate ate less food than untreated mice.
Researchers then labeled fermentable fiber with carbon-13. This non-radioactive form of carbon contains an extra neutron. That bonus neutron causes the nucleus of this atom to spin. And that spin allowed investigators to track its movement through the body.
After feeding mice the labeled food, the researchers examined the rodents’ brains. Microbes in the gut had broken the fiber down into acetate. Again, the labeled acetate traveled to the hypothalamus. There it accumulated. This was clear evidence that chemicals released during fiber fermentation — or breakdown — act on the brain to control appetite, says Frost.
It’s a good study showing the benefits of fiber intake, says Satya Kalra. A neuroscientist at the University of Florida in Gainesville, he was not involved in the new study.
Should people start eating pure acetate to reduce food consumption? Absolutely not, says Frost. The best way to control weight is by eating food from natural sources. That means eating more foods with fermentable fiber. “The bugs in the gut will change the fiber into acetate in a way the body has always done,” he says.
So be sure to load up on those fruits and veggies.