????鹽絕對是大多數加工食品中不可或缺的一種原料。因此，食品行業因為一項最新研究結果而陷入混亂，也就不顯得意外。該研究稱，食物中含鹽過少可能與含鹽過多有同樣的危害。

????但到目前為止，食品行業一直在小心翼翼地應對這項研究結論。原因有兩個：首先，因為食品制造商尚不清楚該如何對待《新英格蘭醫學期刊》（New England Journal of Medicine）近期公布的這些新數據；其次，多年以來，食品行業已經形成了一個紅火的“低鈉”食品市場。任何與鹽有關的概括陳述，都會對該行業的某個部分造成損壞。

????《新英格蘭醫學期刊》共發表了三項研究結果。其中兩項研究的結論是，鹽攝入量過低可能有害。第三項研究基本上符合此前的研究成果，這項研究發現每天鈉攝入量超過兩克，便會增加心血管疾病的風險。兩克是世界衛生組織建議的最高攝入量（相當于5克鹽，因為食鹽中含40%的鈉）。前兩項研究因為使用的方法而遭到批評，但它們卻引起了媒體的興趣——這沒有什么奇怪的，媒體就是喜歡這種違反直覺的科學故事。第三項研究則更為嚴謹，受到的批評要少得多。

????這三項研究當然都是合理正當的——都經過同行評議且在著名期刊上發表。至于研究人員所謂“過分低的”鹽攝入量目標會影響人體健康，并沒有具體的科學依據。前兩項研究屬于觀察性研究，僅發現低鈉攝入量與心血管疾病風險存在一種聯系，但并非因果關系。需要進行更多研究才能確定兩者之間的具體關系，但上周發表的三項研究均反對一項壓倒性的科學共識（雖然并非普世共識）：一般而言，我們攝入過多鹽會帶來健康風險，尤其是高血壓。

????研究發表以后，食品雜貨制造商協會（Grocery Manufacturers Association）呼吁就該問題進行更多研究，這與《新英格蘭醫學期刊》本身的觀點基本類似。食品雜貨制造商協會非常謹慎，沒有對新研究表示特別支持（或質疑），鑒于其所處的兩難境地，這種態度在預料之中。從食品雜貨制造商協會的聲明中便能看出其面臨的難題。這份聲明更像是一段內部討論：

????“數十年來，食品雜貨制造商協會的成員一直在調整食品的成分，希望為消費者提供低鈉選擇，幫助消費者達到健康的鈉攝入量水平。為了減少鈉含量并滿足消費者的口味偏好，我們的行業對數千種食品的成分進行了重新調整。此外，我們的行業還開發出各種減少鈉含量、低鈉或不添加鈉的食品，以幫助消費者遵從醫療保健專業人員的建議。”

????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.”