The latest trick to fighting obesity isn't a focus on eating less fat or sugar： 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 （A） c called acetate（醋酸） that moves to the brain. There it curbs appetite.

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 （1） m - makes people feel full after eating somewhat less. Such fiber is found in （2）f ， vegetables， oats and barley.

Hundreds of thousands of years ago， our ancestors ate nearly 100 （B） g of fermentable fiber each day， says 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 （C） w 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 （3） l and it's a recipe for obesity.

Eating more fermentable fiber reduces the risk of becoming overweight or （4） o . 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 （D） e of 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. The acetate traveled through the blood and into the mice's brains. There it collected in a region known as the hypothalamus（下丘脑）， which controls （5） a . By releasing hormones， that brain region can shut off hunger and promote a feeling of fullness. As a sign that's indeed happened， mice injected with acetate ate less food than untreated mice.

Should people start eating pure acetate to reduce food consumption？ Absolutely not. The best way to control weight is by eating food from natural （E） s . It means eating more foods with fermentable fiber. The gut microbes will change the fiber into acetate in a way the body has always done. So be sure to load up on those fruits and veggies.

（A， B， C， D， E FOR CROSS， 1， 2， 3， 4， 5 FOR DOWN. The first letters of the absents were given）

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