As a city boy, I have learnt to tread carefully through the organic farming debate, watching for what might stick to my boots. Big conventional food companies require scrutiny. But so do the champions of organic food.

When Stanford University researchers said this month that they had found no strong evidence that organic foods were more nutritious than conventional ones, I expected that organic advocates such as the Soil Association would immediately try to rubbish their conclusions, as they did when a 2009 UK study reached similar results.

The Soil Association, whose patron is Prince Charles, duly leapt in, declaring Stanford’s “American study” to be “of limited application in Europe”.

The problem with this riposte is that most of the studies the Stanford article examined were from Europe.

In their analysis, published in the Annals of Internal Medicine, the Stanford researchers looked at 17 studies of the effects of food on humans, of which 13 were from Europe, and at 223 studies of the nutritional qualities of food, of which 157 were from Europe.

When I asked the Soil Association for an explanation, it apologised and said “our choice of wording was unclear”. It said it was attempting to highlight that the Stanford project “excluded all papers not written in English, in a field of research where many published papers come from non-English scientists – in particular in Germany”.

All the papers are in English, but they come from a range of European countries, including Germany, Switzerland, the Netherlands, Denmark, Italy, Finland and Greece.

What did the Stanford study find? First, that with two exceptions, organic food was no more nutritious than conventional.

The two exceptions were milk – a few studies suggested that the organic variety might contain “significantly more” beneficial omega-3 fatty acids – and phosphorus, which was higher in organic than in conventional food. However, the latter didn’t matter much, since only “near-total starvation” was likely to produce human phosphorus deficiency.

The Stanford work did find two studies reporting “significantly lower urinary pesticide levels” in children on organic diets. However, there was little evidence that the higher level of pesticides in conventional food exceeded allowed limits. There was also a higher risk of finding bacteria resistant to antibiotics in conventional chicken and pork than in organic food.

So there is ammunition for both sides. But I was still interested in another research programme: a European Union-funded study effort, involving more than 30 institutions.

I first heard about this from Peter Melchett, the Soil Association’s policy director, when the 2009 study, commissioned by the UK Food Standards Agency, came out. He asked why they hadn’t waited a year or two for the EU study to be completed and I agreed with him.

So what did that project, called the QualityLowInputFood (QLIF) study conclude? According to its website, it found that organic food production resulted in higher levels of nutritionally desirable compounds and lower levels of undesirable ones. It also found that “health claims for organic foods are not yet substantiated”. These seemed to be contradictory outcomes, so I asked Carlo Leifert of Newcastle University, the original project leader, to explain. He said that, with one exception, the papers proving the nutritional benefits of organic food had not yet been published.

The QLIF website also said that “productivity remains a weakness of organic food chains”. What seemed like better energy efficiency and lower greenhouse gas emissions “partly melted away when calculated on a per ton basis”.

I reach three conclusions. First, although no one has been able to show organic food is more nutritious, I understand why people buy it, especially for their children. The authorities might regard pesticide levels in conventional food as safe but who knows the long-term effects?

Second, the way to marry the high farming productivity needed to feed a growing world population and lower pesticide use may be genetically modified food. We should press ahead with research on the health and environmental effects.

The Soil Association may object, but my third conclusion is that campaigners need to be asked the same hard questions as any business or government, particularly when they have trouble wording their press releases.

作为一个在城市中长大的人，我已学会在有关有机农业的辩论中谨言慎行，以免惹上什么麻烦。大型常规食品公司需要接受人们的监督。但有机食品的支持者们也需要被监督。

斯坦福大学(Stanford University)研究员最近表示，他们没有发现任何有力证据表明有机食品比常规食品营养成分更高。当时我猜测，英国土壤协会(Soil Association)等有机食品支持者会立即试图将这个结论斥为垃圾，就像2009年英国一项研究得出类似结果时他们所做的那样。

英国土壤协会的名誉主席是查尔斯王子(Prince Charles)，该协会果然及时加入辩论，声称斯坦福大学的“美国研究在欧洲适用性有限”。

这一回应的问题在于，斯坦福大学的文章所考察的多数研究都来自欧洲。

在这份公布在《内科医学年鉴》(Annals of Internal Medicine)的分析中，斯坦福大学研究员分析了17项有关食品对人类影响的研究（其中13项来自欧洲），以及223项有关食品营养质量的研究（其中157项来自欧洲）。

当我请求土壤协会做出解释时，该协会表示道歉，并表示“我们对措辞的选择不太明确”。该协会表示，该协会试图强调，斯坦福项目“排除了所有不用英文撰写的论文，而在该研究领域，很多已发表论文来自非英语科学家，特别是德国。”

所有的论文都用英文撰写，但来自很多欧洲国家，包括德国、瑞士、荷兰、丹麦、意大利、芬兰和希腊。

斯坦福大学的研究有何发现？首先，除了两个例外之外，有机食品并不比常规食品更有营养。

这两个例外是牛奶（少量研究发现，有机牛奶可能含有“显著更多”有益的欧米珈?3脂肪酸）和磷（有机食品中的磷含量要高于常规食品）。然而，后者关系不大，因为只有“接近完全饥饿”才可能会导致人体磷缺乏。

斯坦福的研究确实发现有两项研究表明，食用有机食品的儿童“尿液中的杀虫剂残留水平低得多”。然而，几乎没有证据证明，常规食品中较高的杀虫剂残留水平超出允许限度。研究还发现，相比有机食品，常规鸡肉和猪肉含有对抗生素具有抗药性的细菌的风险较高。

因此，双方都握有有利证据。但让我感兴趣的是另一项研究计划：一项由欧盟(EU)资助的研究计划，涉及30多家机构。

我是从土壤协会的政策总监皮特?梅尔切特(Peter Melchett)那里第一次听说这项计划的，当时由英国食品标准机构(UK Food Standards Agency)委托进行的2009年的调查刚刚公布。他问道，他们为何没有等上一两年等到这项欧盟调查完成，我同意他的观点。

那么这个被称为QualityLowInputFood (QLIF)的调查项目得出了何种结论？据该项目的网站称，调查发现，有机食品生产带来了较多的营养价值高的化合物，营养价值较低的化合物较少。调查还发现，“有机食品的健康主张尚未得到证实”。这些结果似乎互相矛盾，因此我请求项目最初负责人、纽卡斯特大学(Newcastle University)的卡罗?雷福特(Carlo Leifert)做出解释。他表示，除了一个例外之外，证明有机食品营养益处的论文尚未发表。

QLIF网站还表示，“生产率仍是有机食品链条上的一个弱项”。“如果以每吨计算，”貌似较高能效和较低温室气体排放的好处似乎在“一定程度上化为乌有”。

我得出3个结论。第一，尽管无人能够展示出有机食品营养更高，但我明白人们为何会购买有机食品，特别是给儿童购买。政府可能将常规食品中的杀虫剂残留水平视为安全，但谁知道长期影响会如何？

其次，把为养活不断增多的人口所需的更高的农业生产率与更低的杀虫剂使用量结合在一起的方法，可能是转基因食品。我们应推进其对健康和环境影响的研究。

英国土壤协会可能表示反对，但我的第三个结论是，活动人士必须被问到尖锐的问题，就像任何一家企业或政府一样，尤其是在他们的新闻稿措辞有问题的情况下。

译者/梁艳裳