32 | New Scientist | 25 July 2020
(which, incidentally, the USDA says contains
11 compounds, while FooDB lists more than
4000). “We’ve severely underestimated
the complexity of food,” says Tim Spector
at King’s College London, author of the
forthcoming book Spoon-Fed: Why almost
everything we’ve been told about food is
wrong. “Food is incredibly complicated:
the chemicals are complicated; when it
enters our guts, it interacts with microbes
which make it into other chemicals, which
also have complicated effects on our body.
Because we’ve focused on macronutrients
and calories, the whole field has been
dumbed down.” Barabási’s research
is “opening people’s eyes” to the true
complexity of food, he says.
Why complicate things further? Because
dietary dark matter may be affecting our
health, both for good and ill. “Having more
detailed information of what compounds
are in food certainly would be helpful to
nutrition researchers,” says Larry Parnell
at the Jean Mayer USDA Human Nutrition
Research Center on Aging at Tufts University
in Massachusetts.Dark nutrients
Right now, it is hard to say exactly how
helpful, because so much remains
uncharacterised. “The health implications
are largely unknown,” says Barabási. But
there is good reason to believe that some of
the neglected compounds have meaningful
effects (see “Garlic crush”, page 34). “Certainly,
some of these dark nutrients are quite
important for human health,” says Wishart.
The idea hasn’t gone down well in some
established nutrition circles. There is an
urgent need to identify confounding factors
in nutritional epidemiology, says Mike Gilbey
at University College Dublin, Ireland, but
gaps in our knowledge of nutrients isn’t
one of them. “Nutrients are fully known,
and they alone account for almost all of the
impact that diet has on non-communicable
disease. There is no dark matter.”
Another obvious objection to the claim
that understanding the dark matter is
important for health is that most of the
compounds occur in tiny quantities. But,“ It would be
foolish to
dismiss 99.5 per
cent of what
we eat as
unimportant”
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IMAGESsays Barabási, that raises a misconception.
“The concentrations of mapped and
unmapped nutrients span about nine orders
of magnitude, yet concentration is not always
the factor: vitamin E comes at micrograms
per 100 gram intake of food, yet its absence
has adverse health effects. So it is not true
that low concentration chemicals do not
have an effect on health.”
To start to understand the scale of our
ignorance, Barabási and his colleagues
consulted another database – the
Comparative Toxicogenomics Database, an
inventory of how thousands of chemicals
interact with our bodies.
First, they looked at the 67 “official”
components of garlic, and found that 37
were already known to be linked to human
health and disease. Then they did the same
for the 2306 compounds in garlic listed in
FooDB, and discovered a further 574 with
potential health effects.
These vast tracts of uncharted complexity
could be the reason why nutrition science
so often produces inconsistent and
irreproducible results, says Barabási. This is
familiar to anyone who tries to keep up with
flip-flopping nutrition advice. One week red
wine is bad for you, the next week it isn’t.
Ditto red meat, eggs, saturated fat and many
more. Without a complete picture of the
nutritional composition of food, you can’t
be sure you are comparing the right things.
This is also true of individual
micronutrients. “Consider beta-carotene,”
says Barabási. “It tends to be positively
associated with heart disease, according to
epidemiological studies, but studies adding
beta-carotene to the diet do not show health
benefits. One potential reason is that
beta-carotene never comes alone in plants;
about 400 molecules are always present with
it. So epidemiology may be detecting the
health implications of some other molecule.”
Another probable cause is the effect
of the microbiome on dark nutrients,
says Wishart. “Most dark nutrients are
chemically transformed by your gut
bacteria. That’s probably why studies on
the benefits of different foods give relatively
ambiguous results. We don’t properly control
for the variation in gut microflora, or our