最新研究称盐摄入量过少对健康有害 食品行业面临新难题

    盐绝对是大多数加工食品中不可或缺的一种原料。因此，食品行业因为一项最新研究结果而陷入混乱，也就不显得意外。该研究称，食物中含盐过少可能与含盐过多有同样的危害。

    但到目前为止，食品行业一直在小心翼翼地应对这项研究结论。原因有两个：首先，因为食品制造商尚不清楚该如何对待《新英格兰医学期刊》（New England Journal of Medicine）近期公布的这些新数据；其次，多年以来，食品行业已经形成了一个红火的“低钠”食品市场。任何与盐有关的概括陈述，都会对该行业的某个部分造成损坏。

    《新英格兰医学期刊》共发表了三项研究结果。其中两项研究的结论是，盐摄入量过低可能有害。第三项研究基本上符合此前的研究成果，这项研究发现每天钠摄入量超过两克，便会增加心血管疾病的风险。两克是世界卫生组织建议的最高摄入量（相当于5克盐，因为食盐中含40%的钠）。前两项研究因为使用的方法而遭到批评，但它们却引起了媒体的兴趣——这没有什么奇怪的，媒体就是喜欢这种违反直觉的科学故事。第三项研究则更为严谨，受到的批评要少得多。

    这三项研究当然都是合理正当的——都经过同行评议且在著名期刊上发表。至于研究人员所谓“过分低的”盐摄入量目标会影响人体健康，并没有具体的科学依据。前两项研究属于观察性研究，仅发现低钠摄入量与心血管疾病风险存在一种联系，但并非因果关系。需要进行更多研究才能确定两者之间的具体关系，但上周发表的三项研究均反对一项压倒性的科学共识（虽然并非普世共识）：一般而言，我们摄入过多盐会带来健康风险，尤其是高血压。

    研究发表以后，食品杂货制造商协会（Grocery Manufacturers Association）呼吁就该问题进行更多研究，这与《新英格兰医学期刊》本身的观点基本类似。食品杂货制造商协会非常谨慎，没有对新研究表示特别支持（或质疑），鉴于其所处的两难境地，这种态度在预料之中。从食品杂货制造商协会的声明中便能看出其面临的难题。这份声明更像是一段内部讨论：

    “数十年来，食品杂货制造商协会的成员一直在调整食品的成分，希望为消费者提供低钠选择，帮助消费者达到健康的钠摄入量水平。为了减少钠含量并满足消费者的口味偏好，我们的行业对数千种食品的成分进行了重新调整。此外，我们的行业还开发出各种减少钠含量、低钠或不添加钠的食品，以帮助消费者遵从医疗保健专业人员的建议。”

    Salt is an absolutely essential ingredient in most processed food. So it’s no surprise that the food industry is starting to make a little hay of new research concluding that too little salt in the diet might be as harmful as too much.

    But the industry so far is treading carefully. There are two reasons for that: first, because at this point it’s impossible for food producers to know what to do with this new data, all of it published recently by the New England Journal of Medicine; and second, because over the years, the food industry has created a whole thriving market for “low sodium” products. Any kind of sweeping statement on salt would hurt one part of the industry or another.

    Three studies were published. Two of them concluded that underconsumption of salt might be harmful. A third basically matched the findings of earlier research, showing that cardiovascular risk rises with increases in sodium consumption of over 2 grams per day — the maximum recommended by the World Health Organization (that’s the equivalent of 5 grams of salt, since salt is about 40% of salt). The first two have drawn criticism because of the methodology used, but those are the ones the media picked up on — which is not surprising given that the media love counterintuitive science stories. The third study was far more rigorous and far less assailable.

    All three studies are certainly legitimate — peer reviewed and published in a prestigious journal. And there’s not much science behind how what researchers called “aggressively low” salt targets might affect human health. But the first two were observational and found only an association between such low sodium intake and cardiovascular risk, not a cause-and-effect relationship. More study is surely needed, but none of the research published last week counters what is the overwhelming (though not universal) scientific consensus: that in general we eat too much salt and that it poses health risks, particularly hypertension.

    After the research was published, the Grocery Manufacturers Association called for more study of the question, basically echoing what the New England Journal of Medicine itself said. The GMA was careful not to specifically endorse (or dispute) the new research, which is not surprising given the quandary it presents. The problem can be seen within the GMA’s statement itself. It’s almost an internal dialogue:

    “GMA members have been reformulating products for decades to provide lower sodium options to help consumers achieve healthy sodium intake levels. Our industry has reformulated thousands of products to reduce sodium content and meet consumer taste preferences. The industry has also developed a wide variety of reduced, low or no-added sodium products to help consumers follow recommendations of their health care professionals.”