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Snake oil tomatoes: As some much-hyped genetically modified tomatoes are launched in the USA, GM Freeze asks, why bother?

Posted 27th February 2024 in News

Genetically modified tomato seeds developed in Norwich, UK, went on sale in the USA this month, fifteen years after the project was first announced. Scientist Cathie Martin gushed about the “health-giving compounds and striking beauty of the fruit,” whilst news outlets including ITV News Anglia joined CNN and Forbes in covering the story – albeit at different times in the seeds’ long journey into the hands of apparently eager gardeners. But is the hype warranted, or as deceptive as cure-all snake oil? 

Unsubstantiated health claims

Back in 2008, the big news about the purple GM tomatoes in question was their cancer-fighting potential. Cancer Research UK immediately rejected the claims, which seem to have since been quietly ditched. Today the health claims relate to other benefits associated with increased levels of anthocyanins, which are antioxidants found in red and purple fruits. Their natural presence in tomatoes, however, is limited, so Martin’s team used genes from snapdragon plants in a process of genetic modification. The result: purple tomatoes, sold with added allusions to improved health. 

Snake oil tomatoes. Image credit:

The health benefits of anthocyanins have not been substantiated to a level acceptable to authorities. As of the last update of the UK nutrition and health claims register in 2022, all claims that involved naturally-occurring anthocyanins (for example, in pomegranate juice or blackcurrants) were not compliant with regulations because they were found to be unsubstantiated. To the best of our knowledge and research, there are similarly no health claims about anthocyanins authorised in the USA or Europe. 

In the UK, the Advertising Standards Authority is clear that claims must not imply that a balanced and varied diet cannot provide appropriate quantities of nutrients, and that “individuals must not be encouraged to swap a healthy diet for supplementation.” This throws up a number of questions, including that of dosage. 

As non-essential nutrients, there are no recommended daily intake levels for anthocyanins, nor are there recommendations on toxicity levels. One article about the new tomatoes states that by weight the levels of anthocyanins are comparable to the amount found in blueberries, but what dosage are we talking about exactly? We know that iron is needed by the body, but too much iron can kill you!

Even if anthocyanins are present in reasonable levels, and they are good for you, do they appear, in the purple tomato, in a form that the body can access? This is complex biology and there’s a lot we don’t know. Despite much research, many aspects of anthocyanin absorption and metabolism remain to be clarified. 

One thing we can perhaps be more certain of with anthocyanins is that they can prolong the shelf life of tomatoes, as found by scientists involved in the development of the purple variety. But is this, nutritionally, a good thing? We know for certain that tomatoes are an important source of vitamin C, that vitamin C degrades rapidly after harvest, and this degradation continues during storage. By prolonging shelf life, could purple GM tomatoes actually reduce the nutritional value of tomatoes? In terms of public health, surely this would be more of a curse than a blessing.

Public money, purple tomatoes and poverty

We already know what we need for balanced, nutritious diets, and nature is more than capable of providing these things for us. Malnutrition, and other food-associated problems we face as a society, are a result of lack of access, poverty, inadequate education, and inadequate regulation of unhealthy food. In the UK 1.2 million people live in ‘food deserts’, where fresh fruit and vegetables are simply not available. These are the things we need to address, and we need money and political will to do this.  

Yet Cathie Martin’s purple tomatoes were developed at the John Innes Centre, which states on its website that it receives more than half of its funding from UK government sources. Drilling down into its 2023 accounts, it states that 73% of its £58 million income came from the government-funded Biotechnology and Biological Sciences Research Council that year. How different could things be if this and other public money that is thrown at the biotech industry were used to address the root causes of poor diets and inadequate access to healthy food? 

Not so novel

Perhaps the strangest thing about this story is that purple tomatoes are not strange at all. Back in 2011 Jim Myers of Oregon State University released the first purple tomatoes containing anthocyanins, but these were developed using conventional breeding methods. Myers used genetic material from the University of California alongside wild stock collected by two breeders in the 1960s in Chile and the Galapagos Islands. 

An article on the OSU Newsroom describes the painstaking methods used by Myers and his students to cross – often by hand – plants that showed the potential to express the purple gene in their offspring. “Year after year, he and his team selected the best of the best grown in the field for observation and crossed those until he got a purple tomato good enough to release to breeders and home gardeners,” it explains. 

Myers told NPR that he began working on tomatoes around the same time as Cathie Martin, but today there are at least 50 progenies of his original Indigo Rose being grown by both small farms and big companies throughout the world. He highlighted the diversity that has come about through conventional breeding, whilst pointing out that “With the GMO tomato, it’s taken them all this time and more to get one variety out there.”

Non-GM purple tomatoes developed by researchers at Oregon State University (left, image credit OSU Newsroom, photograph by Tiffany Woods) and GM tomatoes by researchers at the John Innes Centre (right, image credit 

A danger to diversity?

The development of the conventionally-bred purple tomato was made possible as a result of diverse genetic material being available to the plant breeders. Our biggest concern at GM Freeze is that the genetic modification of organisms puts this diversity at risk. Far from being the answer to global food problems, GM could undermine our ability to breed and adapt to climate change in the future. 

A patent threat

At around the time of the GM tomato launch in February, a different variety of purple tomato seeds were withdrawn from catalogues across the USA in response to allegations of patent infringement by Martin’s company Norfolk Healthy Produce. As it withdrew the seeds, distributors Baker Creek said that testing “did not conclusively establish that the Purple Galaxy is truly free of any genetically-modified material.”

GM Watch have provided a detailed analysis of this case, pointing out that “either possibility – that the tomato was GMO or non-GMO – is extremely concerning”. Potential causes of concern include biosafety breaches, fraud, the threat of litigation quashing innovation, or the illegal patenting of naturally-occurring genes. “Plant breeders are becoming increasingly fearful of inadvertently infringing the patents of seed companies, in particular those of the large multinationals,” according to GM Watch.

You can catch GM Freeze’s Leonie Nimmo outlining the problems with GM food on ITV News Anglia’s piece on the purple GM tomatoes: