The most eye-catching health claims for superfoods tend to be associated with particular groups of compounds: the glucosinolates in kale and broccoli, for instance, or the anthocyanins in blueberries.
Trouble is, although we can study how isolated compounds act on cells in a dish or in mice, it鈥檚 much trickier to get a grip on what foods containing these ingredients do inside the human body.
鈥淭he way we do experiments is almost like a drug trial, testing one nutrient against something that doesn鈥檛 contain that nutrient, says Duane Mellor, a nutrition scientist at the University of Canberra in Australia. 鈥淩andomised controlled trials are good for drugs, but we don鈥檛 eat foods in isolation.鈥�
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Nor do we have a great understanding of how the foods we eat are broken down into their molecular building blocks, how these interact with each other and what happens to them when, or if, they reach different tissues. There is also variation from person to person in the gut bacteria that influence all of these processes. And in some cases, cooking can reduce the levels of active ingredients before they pass your lips.
鈥淵ou put something in one end and it goes into this black box and we measure an effect,鈥� says Mellor. 鈥淚s that a true effect? Unless you do very, very meticulous studies to measure the peaks of all the compounds from every bodily fluid you can get, including stools, you鈥檙e not going to know what鈥檚 going on.鈥�
The upshot is that even when scientists do put superfoods to the test in human studies, it鈥檚 hard to figure out how they perform. Hence most claims you hear refer to cell or mouse studies, and should be taken with a hefty pinch of salt.
This article appeared in print under the headline 鈥淏reaking it down鈥�
