Often touted as a great source of iodine, feijoas in fact have… none?

Joseph Stalin was feeling poorly. At age 70, he was suffering from lapses of memory and attacks of nausea. While orange juice “made his tongue smart” and caviar “tasted like putty”, his doctors had told him to eat as much fruit as possible—and there was one fruit in particular that made him feel better. 

“Stalin…took a peeled feijoa from the little round table and bit into it. As he sucked it his nausea went away, leaving a pleasant taste in his mouth with a faint tang of iodine…You didn’t have to tell a Georgian to eat fruit! Half closing his eyes, he took another bite.” 

As New Zealand’s biggest feijoa nerd, I was enchanted and intrigued when I discovered this (fictional) scene in the 1968 novel The First Circle, by the famous Russian writer and Soviet dissident Aleksandr Solzhenitsyn. Presumably, Solzhenitsyn has the dictator eat a feijoa because Stalin was originally Georgian, and feijoas are almost as beloved in that Eastern European nation as they are here in New Zealand. 

But the other thing that captured my attention was that “tang of iodine”. Really? 

The unique flavour of feijoas has been compared—unconvincingly, I think—to that of pineapples, strawberries, guavas and bananas. But I’d never heard of anyone else likening it to iodine.

 I have, however, frequently read claims online that feijoas are a superlative source of this essential nutrient, as well as high in lots of other healthy-sounding things. They’re often labelled a “superfruit” and people I met in Colombia while researching my feijoa book even called it “the fruit of eternal youth”. 

Our bodies can’t make iodine, but it’s crucial for hormone production and normal brain development, especially in babies and young children. As a child, I craved feijoas – and today, my own children will eat bucketloads of these green, fragrant treasures. Was there something to this, I wondered? Do our bodies know something our minds aren’t consciously aware of? Are super feijoas helping us to meet this need? 

Unfortunately, when I asked botanist, plant-collector and University of Auckland professor of nutrition Richard Mithen to review the scientific literature on feijoas’ nutritional content for me, he had bad news. “There does not seem to be anything particularly remarkable about feijoa on the basis of the analyses of known nutrients and phytochemicals,” he wrote. And he added: “its iodine content is insignificant.” Weird. 

Mithen encouraged me to contact Carolyn Lister at Plant and Food Research, who manages the New Zealand Food Composition Database.  According to old New Zealand data, feijoas had just 0.13 micrograms of iodine per 100 grams. (There are one million micrograms in a gram.) For context, the recommended daily iodine intake for adults is 150 micrograms, she said. To get that from feijoas you’d have to eat around 1,200 decent-sized ones every day of your life – and look, I’m as obsessed with feijoas as they come and even for me that feels… unachievable. 

That was old data, though, and analytical methods have improved since then. Feijoa varieties have changed, too. As it happened, Mithen had just completed a fresh study of New Zealand feijoas’ nutritional content. In 2022, she and her team bought a couple of kilos from a few different supermarkets, scooped out the flesh, and subjected it to an array of different lab tests.

This time, the iodine content came back “below the level of detection” – basically zilch. Nada. No iodine to speak of in feijoas. (The best ways to get it are by eating seaweed, fish, shellfish – or simply to use iodised table salt.)

So where did this story come from? 

The claim that feijoas are high in iodine wasn’t just cited in “why feijoas are good for you” listicles, but also a few scientific papers. When I traced the references back, they led to one Italian study from 2001 and a Russian paper from 1934. 

With the Italian paper, only the abstract was available, so neither the scientists nor I could scrutinise the methods. The Italian researchers claimed they’d found 3mg of iodine per 100 grams of fruit – three milligrams, or 3000 micrograms – making eating just two medium-sized feijoa comparable to chowing down on an 80g serve of karengo seaweed, the heaviest-hitter iodine-wise on New Zealand’s food composition database.  Mithen suspected the researchers might have gotten the units wrong by several orders of magnitude. “We find that sometimes in the scientific literature…things get lost in translation.”

Neither could I access the 90-year-old Russian study, but a recent paper by another Russian scientist, Oksana Belous, suggests an answer to the mystery. Oksana set out to test the chemical composition of feijoas grown around the Black Sea coast of Russia, near Georgia. She said the amount of iodine was “small”, finding “0.34 mkg%” of iodine in her feijoas – a unit Mithen didn’t recognise, but Belous told me in an email meant micrograms per 100g or 100ml.  

In her own paper, Belous wrote that the author of the 1934 study, L.V. Sergeyev, found three milligrams of iodine in a decilitre, or 100 mls of feijoa – a similarly superlative proportion as in the Italian study. But Sergeyev also noted that the feijoas he studied back in 1934 grew near the sea, and that the soil around them was covered with seaweed, presumably as a fertiliser. “Probably these factors led to an increase in the content of iodine in fruits,” wrote Belous. 

Mithen thought that was possible, too. Imagine a ripe feijoa falling onto a carpet of iodine-rich, decomposing algae. It wouldn’t take much seaweed residue left on the skin to skew the results. Alternatively, it’s possible that the feijoa trees Sergeyev studied absorbed some iodine from the seaweed and soil and expressed it in their fruit, but new studies would be needed to prove it, Mithen said. 

“Different plants take up different minerals to different degrees, which is why some fruits and vegetables are better sources of certain nutrients than others. It’s not as simple as if the mineral’s here in the soil, it will be taken up.” 

Solzhenitsyn died in 2008, so we can only guess at his motives for including iodine-tasting feijoas in his political novel. My hunch is that he read that old Russian paper while researching a suitably “Georgian” fruit for Stalin to snack on. (Although, of course, feijoas originally hail from South America.) 

There are myriad reasons to enjoy feijoas – their delicious flavour, nostalgic fragrance, intense seasonality, and the way their ridiculous abundance encourages you to share them with neighbours, colleagues, and complete strangers (they’re not called New Zealand’s most socialist fruit for nothing!) They’re also a decent, if not spectacular, source of fibre, folate and Vitamin C, Mithen’s study found. 

Just don’t rely on them for your daily dose of iodine. 

 Kate Evans is a journalist and the author of a new book about feijoas, FEIJOA: A Story of Obsession and Belonging (Moa Press).