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The "diet" in diet drinks may be a false promise for some soda lovers. True, they deliver the fizz and taste of a soda experience, without the calories. Yet, new research shows they also can leave people with increased food cravings.
A study published recently in JAMA Network Open adds to the evidence that drinks made with sucralose may stimulate the appetite, at least among some people, and the study gives some clues as to why.
"We found that females and people with obesity had greater brain reward activity" after consuming the artificial sweetener, says study author Katie Page, a physician specializing in obesity at the University of Southern California.
Both groups also had a reduction in the hormone that inhibits appetite, and they ate more food after they consumed drinks with sucralose, compared with after regular sugar-sweetened drinks. In contrast, the study found males and people of healthy weight did not have an increase in either brain reward activity or hunger response, suggesting they're not affected in the same way.
"I think what was most surprising was the impact of body weight and biological sex," Page says. "They were very important factors in the way that the brain responded to the artificial sweetener."
Page and her team measured the response to diet soda in three ways. They used functional MRI brain images of the 74 study participants to document the activation of parts of the brain linked to appetite and cravings. They used blood samples to measure blood sugar and metabolic hormones that can drive hunger. And they also tracked how much participants ate at a buffet table that was open at the end of each study session.
Determining whether diet soda helps or hinders dieters' efforts to lose weight has been tough. Some studies have shown benefits, but long-term research has found that diet soda consumption is linked to increased weight gain.
There's ongoing research into the complex ways that artificial sweeteners may influence metabolism and weight, says Susan Swithers, a behavioral scientist at Purdue University who was not involved in the new study but reviewed the findings.
One hypothesis is that it's not the artificial sweetener itself that has a direct effect on the body. The idea is that artificial sweeteners may confuse the body by tricking it into thinking sugar is coming.
"You are supposed to get sugar after something tastes sweet. Your body has been conditioned to that," explains Swithers. But diet soda may lead to a disconnect. The sugar never arrives, and this may blunt the body's anticipatory responses and throw off the ability to efficiently metabolize sugar that's consumed later.
This could mean that "when you get the sweet taste without the sugar, that changes how you respond to sugar the next time, because you don't know whether it's coming or not," Swithers says.
(From NPR News 2021/10/07)
Expression
document v. 用（文字、影片、照片等）记录
metabolic adj. 新陈代谢的
metabolism n. 新陈代谢
metabolize v. 使新陈代谢
blunt v. 使得迟钝
food craving 对食物的渴望
stimulate/inhibit appetite 刺激/抑制食欲
artificial sweetener 人工甜味剂
weight gain 体重增加
trick into 欺骗
throw off 使迷惑，使出错
Translation
无糖汽水可能引起对食物的渴望
对部分汽水爱好者而言，“无糖”饮料或许是一个虚假的承诺。诚然，这类饮料带来了气泡和口感，却不含热量。然而，最新研究显示，它们也可能增强人们对食物的渴望。
《美国医学会杂志·网络开放版》期刊近期发表的研究进一步证实，使用三氯蔗糖的饮料可能刺激食欲（至少在部分人群中如此），该研究还揭示了其中的原因。
研究作者、南加州大学肥胖症专科医师凯蒂·佩奇指出：“我们发现女性和肥胖人群摄入人工甜味剂后，大脑奖励区域活动更为活跃。”
与饮用常规含糖饮料后相比，这两类人群抑制食欲的激素水平有所下降，且在饮用含三氯蔗糖的饮料后进食量更大。相比之下，研究显示男性与健康体重人群既未出现大脑奖励活动增强，也未产生更强烈的饥饿反应，表明他们未受到同等影响。
佩奇坦言：“最令人惊讶的是体重和生理性别产生的影响。这两个因素对大脑响应人工甜味剂的方式至关重要。”
佩奇团队通过三种方式测量人们对无糖汽水的反应：首先利用74名研究参与者的功能性磁共振脑部图像，记录与食欲和渴望相关脑区的激活状态；其次通过血样分析血糖及可能引发饥饿的代谢激素水平；同时在每场实验结束后，追踪参与者在自助餐台上的进食量。
关于无糖汽水究竟有助于还是阻碍减肥，学界一直难有定论。既有研究显示其益处，但长期研究发现无糖汽水摄入与体重增加存在关联。
普渡大学行为科学家苏珊·斯威瑟斯（未参与本次研究但评审了结果）表示，人工甜味剂如何影响新陈代谢与体重的复杂机制仍是持续研究的课题。
她解释其中一种假说：并非人工甜味剂本身直接作用于人体，而是通过欺骗身体误以为糖分将至而产生影响。
“甜味本应伴随糖分摄入，人体已对此形成条件反射，”斯威瑟斯阐明。但无糖汽水可能导致这种联系中断。当预期中的糖分始终未至，可能会使身体的预期反应变得迟钝，进而干扰有效代谢后续摄入糖分的能力。
斯威瑟斯进一步指出：“这意味着当甜味与糖分剥离时，会改变人体下一次对糖分的反应模式——因为你无法预知糖分是否会如期而至。”
