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reading matters 12: food mysteries

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New Scientist 3292 July 25 2020

Jacinta: So this cover story reminds me of something I read or heard a few years back  – that if you were to list the chemical ingredients of a hen’s egg, you’d never come to the end, or something like that. 

Canto: Well you’re on the right track, the cover story is titled ‘the dark matter in your diet’, but instead of a hen’s egg it starts with garlic. Both of these commonly consumed edibles, like just about everything else we eat, contain ‘nutritional dark matter’ that scientists have only recently started to focus on, surprisingly considering that we are, to a fair degree, what we eat. 

Jacinta: Yes, so we all know that food components or nutrients are usually divided into fats, carbohydrates and proteins, though these three can be subdivided to a near-infinite degree, but there are also vitamins, minerals and other biochemical elements in various quantities, and with variously vital effects. Currently the US Dept of Agriculture (USDA) has a database of 188 nutritional components of food, under which some info is provided on many thousands of chemical elements. 

Canto: So garlic, the USDA reckons, is found in 58,055 foodstuffs, including, uhh, garlic. Raw garlic itself is described as containing 67 nutrients, both macro and micro, some of which can only be found in very minute quantities. And yet many components, such as allin, which helps to give garlic its particular odour and flavour, aren’t listed on the database. 

Jacinta: Allin is converted into allicin, through the enzyme allinase, when you crush or chop garlic. That’s when that lovely/notorious stink hits you. 

Canto: Right, and this is apparently a major problem across the whole database. They added a few dozen flavonoids – plant compounds that can lower the prevalence of cardiovascular disease – in 2003, but recent researchers have been frustrated by the many gaps, and are building their own more comprehensive database, based on their own chemical analyses. It’s called FooDB, which now lists almost 400 times the number of nutritional compounds as the USDA database. 2306 for garlic, for example, compared to the USDA’s 67. But there’s a lot of work still to be done, even on garlic. Only a tiny fraction of those compounds have been quantified – we don’t know the exact concentrations. And this is a problem for the whole of FooDB, with about 85% of compounds unquantified.

Jacinta: Sounds like we need an equivalent of the old human genome project – but for every single edible product? Nice, a few hundred lifetimes’ work, if you can get the funding. 

Canto: Well, it suggests that we’ve massively overlooked the complexity of our food – and not only the foods themselves, but their interaction with the microbes and enzymes in our body. But here’s the thing – brace yourself – some nutritionists disagree!

Jacinta: OMG! Scientists are disagreeing?

Canto: The counter-argument is that ‘dark matter’ in nutritional terms is a beat-up. That, though much research is still needed in nutritional epidemiology, in relation to particular conditions and so forth, we know what the essential nutrients are, so the ‘dark matter’, which tends to exist in ultra-minute quantities, would make little difference. But the researcher who coined the term ‘nutritional dark matter’, Albert-Laszlo Barabasi, begs to differ – of course. He points out, for example, that vitamin E, or its absence, can have adverse effects at minuscule quantities, and it may be that all the flip-flopping advice we’re given about nutrition may have much to do with the gaps in our knowledge. Taking garlic again, it was found that of the 67 compounds listed for it on the USDA database, 37 had health effects one way or another, but of the 2306 on FooDB, some 574 had what they called ‘potential’ health effects. In any case, it seems to me that a more complete knowledge of what’s in our food can’t be a bad thing, and will very likely be of benefit in the long run. 

Jacinta: That makes sense, but isn’t everything even more complicated, when you think of how all these nutrients interact with our individual microbiota, and the enzymes that break down our food more or less efficiently, depending on how numerous and healthy they are, which no doubt varies between individuals? 

Canto: Yes, Barabasi and others working on all this ‘dark matter’ are well aware of these complex interactions, but they reckon that doesn’t detract from the need to know much more about this particular component of the food-nutrient-digestion-health cycle. And Barabasi does in fact compare the current state of knowledge with the days before the human genome project, when much DNA was considered ‘junk’. It’s just not a good idea to assume that such a large proportion of nutrients are barely worth knowing about. Let’s return to garlic again. It features quite a lot in the Mediterranean diet, which seems protective against cardiovascular disease. Steak, on the other hand, can be problematic. Our gut bacteria breaks down red meat, in the process producing a compound, trimethylamine, which our liver converts into trimethylamine-N-oxide (TMAO). High levels of TMAO in the bloodstream are linked to heart and vascular problems. But allicin, from garlic, which we’ve mentioned before, and which wasn’t on the USDA database, is known to inhibit the production of trimethylamine, so a diet containing red meat – not too much mind you – can be rendered a wee bit safer, and tastier, with a nice garlic dressing. 

Jacinta: And allicin appears to be an anti-carcinogen too. And luteolin, another component of garlic not on the standard database, is also reported to protect against cardiovascular disease. We love garlic! But what about processed foods. Surely there are all sorts of ways of processing, that’s to say transforming, foods and their component nutrients that won’t show up on the list of ingredients. And how do we know if those ingredient lists are accurate in the first place?

Canto: Well, baby steps I suppose. Cooking, of course, has vital transformative effects upon many foods. And I recall that when you whisk an egg it becomes ‘denatured’ – how transformative does that sound! The more you think about the interaction of foods, with all their barely recognised components, with transformative processes occurring both outside and within our bodies, the more it makes your head spin, and the more you realise that dietary science has a long long way to go. 

garlic cultivars from the Phillippines

Written by stewart henderson

September 30, 2020 at 7:33 pm