爲什麼吃了燕麥片會覺得格外飽

Glance through a popular magazine’s listof healthy breakfast foods and you’ll likely find oatmeal in the group. Among other benefits, oatmeal is touted as having the ability to keep you full, effectively squelching the desire for that midmorning snack. In fact, a group of researchers recently found that a serving of instant oatmeal decreased the desire to eat more than the same amount of Honey Nut Cheerios, an oat-based cereal. I decided to talk with lead author Candida Rebello of the Pennington Biomedical Research Center to find out what makes oatmeal so special.

The story begins with dietary fiber, the part of plant foods that the body can’t digest, which has been shown to promote a feeling of fullness. Both the oats in oatmeal and ready-to-eat oat-based cereals contain β-glucan, a type of soluble fiber.

However, it’s not just the fiber content that matters, according to Rebello and her fellow researchers. Fullness and the desire to eat may also be influenced by a property of fluids called viscosity, which, in this case, is generated by oat β-glucan. Rebello described viscosity as the slimy feel of oatmeal that you can both see in the bowl and feel in your mouth. Scientists think viscosity affects appetite by influencing the way foods interact with the mouth, as well as the stomach and intestines. For example, increased viscosity in the intestinal tract can stimulate the release of appetite-regulating hormones. The oral and gastric effects work together, according to Rebello, meaning a food with both a high initial viscosity in the mouth and a high subsequent viscosity in the gastrointestinal tract will likely produce a greater feeling of fullness.

The study Rebello and colleagues recently authored looked at instant oatmeal, old-fashioned oatmeal and Honey Nut Cheerios and measured each food’s viscosity and effect on satiety. (I should note that though Rebello works for the Pennington Biomedical Research Center, the study was a collaborative effort with researchers from PepsiCo R&D Nutrition and was funded by PepsiCo R&D Nutrition’s Quaker Oats Center of Excellence.)

The researchers found that instant oatmeal improved several measures of satiety, or the feeling of fullness, over a four-hour period more than Honey Nut Cheerios did. Old-fashioned oatmeal improved one measure of satiety when compared to Honey Nut Cheerios. As might be expected, the study found that instant oatmeal had greater initial and subsequent viscosity compared to Honey Nut Cheerios. Old-fashioned oatmeal had greater subsequent viscosity but not higher initial viscosity, which could explain why it was less effective at promoting fullness.

Viscosity of oatmeal or cereal appears to be a key player in promoting fullness, so my next question was naturally about what determines differences in viscosity.

“Viscosity is generated by the particular fiber in oatmeal, which is called β-glucan,” said Rebello, who is a research dietitian. “The fiber is affected by the manner in which it is processed.”

Ready-to-eat oat-based cereals, instant oatmeal and old-fashioned oatmeal are processed differently, which can lead their β-glucan to have a different structure and result in a different viscosity.

So if you find yourself feeling satisfied until lunch after a bowl of instant oatmeal, now you’ll know why.據《科學美國人》（Scientific American）25日報道，隨便看看流行雜誌列出的健康早餐食物，你總會發現燕麥的身影。燕麥有很多益處，其中之一就是它能夠讓你有飽腹感，能有效地阻止你在早上10-11點吃零食的慾望。其實，一些研究人員最近發現比起同量的蜂蜜堅果麥片（含燕麥的穀物），一份速食燕麥更能降低人的食慾。我決定採訪一下潘寧頓生物研究中心的主任卡迪達·瑞伯樂（Candida Rebello），看看到底是什麼讓燕麥如此特別。

一切要從食物纖維說起。食物纖維是植物性食物不能被人體消化的那部分，正是這一部分提高了人的飽腹感。燕麥片中的燕麥和含燕麥的即食穀類食物都含有可溶纖維beta葡聚糖。

但是，瑞伯樂和其同事的研究發現，纖維不是讓人產生飽腹感的唯一原因。一種粘稠狀液體也可以影響飽腹感和食慾。這種粘液就是由beta葡聚糖產生的。瑞伯樂解釋道，這種粘液就像燕麥片的那種滑膩的感覺，不管是裝在碗裏還是吃進口裏你都能感到這種滑膩感。科學家們認爲粘液是通過影響食物與嘴和胃與腸接觸的方式來影響食慾的。比如，腸道內粘液增多會刺激調解食慾的荷爾蒙分泌。瑞伯樂說，口感和胃部感受共同作用使人產生了飽腹感。也就是說，能夠讓人首先在嘴裏感受到高粘稠度，其次再在腸胃中保持高粘稠度的食物很可能引起人的飽腹感。

瑞伯樂及其同事們最近聯名發表的一項研究觀察了速食燕麥，傳統燕麥和蜂蜜堅果燕麥飲品，測量了每一種食物的粘稠度和帶來的滿足感。（我要事先聲明：雖然瑞伯樂在潘寧頓生物研究中心工作，但是這份研究報告是他和百事公司營養研發部的研究人員一起撰寫而成，這項報告也是由百事公司營養研發部旗下的桂格優質燕麥中心出資贊助的。）

研究者發現，在四個小時內，速食燕麥能大大提高滿足感，也就是飽腹感，相比起來蜂蜜堅果燕麥飲品的效果比速食燕麥低很多。傳統燕麥比燕麥飲品效果好一些。跟預期一樣，研究發現速食燕麥比燕麥飲品的原始粘稠度和進入腸胃後的粘稠度都要高。傳統燕麥片原始粘稠度低，而進入腸胃後的粘稠度高。這就是它爲什麼在增加飽腹感的效果上要比速食燕麥稍遜一籌的原因。

燕麥片或者穀物的粘稠度似乎在促進飽腹感方面是至關重要的原因，所以我的下一個問題自然就是粘稠度的高低是由什麼決定的。

作爲一名做研究的飲食學家，瑞伯樂解釋說：“粘稠度是由燕麥片中一種叫做beta葡聚糖的特殊纖維產生的。這種纖維會受到處理方式的影響.

即食燕麥穀物類食品，即食燕麥和傳統燕麥的處理方法不同，那麼他們中所含的beta葡聚糖的結構也就不同，導致他們的粘稠度也不一樣。

所以如果你發現自己吃了一碗速食燕麥片後到午飯時間都還不餓，現在你應該知道其中的原因了吧。