The study itself was based on an enormous sample size of 115,726 people aged between 40 and 69, drawing from a large-scale study called HEXA which collected lifestyle, diet and disease data from about 167,000 Koreans.
The study generated news stories across the world hailing the belly-busting power of kimchi.
Crunchy, funky, spicy … and backed by a government-funded cheer squad.Credit: Edwina Pickles
But the study was limited because people captured by HEXA self-reported their diets, which leaves the door open to inaccuracy (and perhaps a bit of wishful thinking).
Crucially, the study was observational, which means it could establish a general link between two things but not cause and effect.
Experimental studies, in which scientists actively make interventions in people’s diets and track the results, have not found a strong connection between fermented foods and weight loss, noted University of Adelaide dietitian Dr Evangeline Mantzioris in The Conversation.
The recent BMJ study was also bankrolled by the World Institute of Kimchi, an organisation linked to the Korean government with a mission to “scientifically demonstrate the excellence of kimchi”.
Make of that what you will.
The apple cider cure
The long-revered home tonic, apple cider vinegar, is back in the news after another BMJ study found overweight young people who sipped the elixir daily dropped a huge five to seven kilos, on average, over three months.
Some believe the vinegar blunts appetite, although the evidence on this is shaky (one study found it suppressed appetite only because guzzling vinegar made people feel sick).
Professor Helen Truby, an expert in nutrition at the University of Queensland, says there were several problems with the study despite its “remarkable” findings, including that a number of participants were already on a diet before the study commenced.
Apple cider vinegar is good for the gut. But can it kill the kilos?Credit: iStock
“Diet and activity were self-reported, so we cannot be sure that these large weight losses were not due to lifestyle changes, plus the use of weight-loss medications has not been reported,” Truby says.
“It would be wonderful if a teaspoon of apple cider vinegar caused substantial weight loss, but with the complexity of obesity and its management that we grapple with, if something seems too good to be true – it often is.”
The age range of the participants – 12 to 25 – is also a problem, says lecturer in nutrition and dietetics at Queensland University of Technology, Dr Fiona Willer.
“That’s like herding cats,” she says. “You’ve got people having their growth spurts everywhere in that cohort and our body shapes change from when we’re 12 years old to 24.
“They did do a nice randomised control trial there. But if it’s going to have actual applicable, interesting findings, adults would have been the population to test it on.
“There’s not a strong ethical argument for any adolescent losing the kind of weight that they’ve reported here.”
Resistant starch … delicious
Finally, a Chinese study found feeding overweight participants 40 grams of resistant starch (such as that found in legumes, chickpeas and lentils) a day led to three kilos of weight loss over eight weeks.
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The authors speculated that the effect was caused by the starch boosting a bacteria called Bifidobacterium adolescentis in the large intestine.
The species is associated with lower weight and smaller waist circumference because it helps block the absorption of fat in the gut. Mice with guts colonised by B. adolescentis were protected from diet-induced obesity too, the researchers wrote.
The placebo-controlled study was well-designed and published in Nature Metabolism. But size matters here. The experiment had a tiny sample size of 37 people. To garner true confidence that a finding such as this applies to people broadly, you’d need more like 1000 participants.
Holy grails, silver bullets and common sense
So the ability of these foodstuffs to melt away kilos remains unproven. But why do so many studies like these get published – and why are we always hankering for that weight loss silver bullet?
“There’s still this collective interest in body weight control because of all the social capital that comes with having a particular body at the moment,” Willer says. “We come to believe there’s got to be a ‘holy grail’ solution. It’s a needle in the haystack problem, but there’s no needle. It’s just a haystack.”
Eating resistant starch from chickpeas can block diet-induced obesity (if you’re a mouse).Credit: iStock
Willer says studies are often funded by organisations and groups that stand to benefit from associating a particular product with weight loss (looking at you, Big Kimchi). “Everyone wants to say that their ‘thing’ is a weight loss product because they know it will absolutely sell itself stupid.”
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Much of Willer’s work is based on redirecting society’s focus on dieting to actual good health.
“Because of the emphasis socially and, unfortunately, medically on weight, people think that [losing weight] is more important than ongoing, sustainable, nourishing dietary patterns. And that is a huge ethical travesty.
“People can be very well nourished and enjoy a good standard of health at a very broad range of body sizes.”
So eat the kimchi, chickpeas and apple cider vinegar. But do it because they’re delicious and terrifically healthy – not because you might lose weight.
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