为什么吃了燕麦片会觉得格外饱

　　　　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.

　　据《科学美国人》(Scientific American)25日报道，随便看看流行杂志列出的健康早餐食物，你总会发现燕麦的身影。燕麦有很多益处，其中之一就是它能够让你有饱腹感，能有效地阻止你在早上10-11点吃零食的欲望。其实，一些研究人员最近发现比起同量的蜂蜜坚果麦片(含燕麦的谷物)，一份速食燕麦更能降低人的食欲。我决定采访一下潘宁顿生物研究中心的主任卡迪达·瑞伯乐(Candida Rebello)，看看到底是什么让燕麦如此特别。

　　一切要从食物纤维说起。食物纤维是植物性食物不能被人体消化的那部分，正是这一部分提高了人的饱腹感。燕麦片中的燕麦和含燕麦的即食谷类食物都含有可溶纤维beta葡聚糖。

　　但是，瑞伯乐和其同事的研究发现，纤维不是让人产生饱腹感的唯一原因。一种粘稠状液体也可以影响饱腹感和食欲。这种粘液就是由beta葡聚糖产生的。瑞伯乐解释道，这种粘液就像燕麦片的那种滑腻的感觉，不管是装在碗里还是吃进口里你都能感到这种滑腻感。科学家们认为粘液是通过影响食物与嘴和胃与肠接触的方式来影响食欲的。比如，肠道内粘液增多会刺激调解食欲的荷尔蒙分泌。瑞伯乐说，口感和胃部感受共同作用使人产生了饱腹感。也就是说，能够让人首先在嘴里感受到高粘稠度，其次再在肠胃中保持高粘稠度的食物很可能引起人的饱腹感。

　　瑞伯乐及其同事们最近联名发表的一项研究观察了速食燕麦，传统燕麦和蜂蜜坚果燕麦饮品，测量了每一种食物的粘稠度和带来的满足感。(我要事先声明：虽然瑞伯乐在潘宁顿生物研究中心工作，但是这份研究报告是他和百事公司营养研发部的研究人员一起撰写而成，这项报告也是由百事公司营养研发部旗下的桂格优质燕麦中心出资赞助的。)

　　研究者发现，在四个小时内，速食燕麦能大大提高满足感，也就是饱腹感，相比起来蜂蜜坚果燕麦饮品的效果比速食燕麦低很多。传统燕麦比燕麦饮品效果好一些。跟预期一样，研究发现速食燕麦比燕麦饮品的原始粘稠度和进入肠胃后的粘稠度都要高。传统燕麦片原始粘稠度低，而进入肠胃后的粘稠度高。这就是它为什么在增加饱腹感的效果上要比速食燕麦稍逊一筹的原因。

　　燕麦片或者谷物的粘稠度似乎在促进饱腹感方面是至关重要的原因，所以我的下一个问题自然就是粘稠度的高低是由什么决定的。

　　作为一名做研究的饮食学家，瑞伯乐解释说：“粘稠度是由燕麦片中一种叫做beta葡聚糖的特殊纤维产生的。这种纤维会受到处理方式的影响.

　　即食燕麦谷物类食品，即食燕麦和传统燕麦的处理方法不同，那么他们中所含的beta葡聚糖的结构也就不同，导致他们的粘稠度也不一样。

　　所以如果你发现自己吃了一碗速食燕麦片后到午饭时间都还不饿，现在你应该知道其中的原因了吧。