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have come to rely on are grains; these crops are exceptionally efficient
at transforming sunlight into macronutrients - carbs, fats and proteins.
These macronutrients in turn can be profitably transformed into animal
protein (by feeding them to animals) and processed foods of every
description. Also, the fact that grains are durable seeds that can be
stored for long periods means they can function as commodities as well
as food, making these plants particularly well suited to the needs of
industrial capitalism.

The needs of the human eater are another matter. An oversupply of
macronutrients, as we now have, itself represents a serious threat to
our health, as evidenced by soaring rates of obesity and diabetes. But
the undersupply of micronutrients may constitute a threat just as
serious. Put in the simplest terms, we're eating a lot more seeds and a
lot fewer leaves, a tectonic dietary shift the full implications of
which we are just beginning to glimpse. If I may borrow the
nutritionist's reductionist vocabulary for a moment, there are a host of
critical micronutrients that are harder to get from a diet of refined
seeds than from a diet of leaves. There are the antioxidants and all the
other newly discovered phytochemicals (remember that sprig of thyme?);
there is the fiber, and then there are the healthy omega-3 fats found in
leafy green plants, which may turn out to be most important benefit of all.

Most people associate omega-3 fatty acids with fish, but fish get them
from green plants (specifically algae), which is where they all
originate. Plant leaves produce these essential fatty acids ("essential"
because our bodies can't produce them on their own) as part of
photosynthesis. Seeds contain more of another essential fatty acid:
omega-6. Without delving too deeply into the biochemistry, the two fats
perform very different functions, in the plant as well as the plant
eater. Omega-3s appear to play an important role in neurological
development and processing, the permeability of cell walls, the
metabolism of glucose and the calming of inflammation. Omega-6s are
involved in fat storage (which is what they do for the plant), the
rigidity of cell walls, clotting and the inflammation response. (Think
of omega-3s as fleet and flexible, omega-6s as sturdy and slow.) Since
the two lipids compete with each other for the attention of important
enzymes, the ratio between omega-3s and omega-6s may matter more than
the absolute quantity of either fat. Thus too much omega-6 may be just
as much a problem as too little omega-3.

And that might well be a problem for people eating a Western diet. As
we've shifted from leaves to seeds, the ratio of omega-6s to omega-3s in
our bodies has shifted, too. At the same time, modern food-production
practices have further diminished the omega-3s in our diet. Omega-3s,
being less stable than omega-6s, spoil more readily, so we have selected
for plants that produce fewer of them; further, when we partly
hydrogenate oils to render them more stable, omega-3s are eliminated.
Industrial meat, raised on seeds rather than leaves, has fewer omega-3s
and more omega-6s than preindustrial meat used to have. And official
dietary advice since the 1970s has promoted the consumption of
polyunsaturated vegetable oils, most of which are high in omega-6s (corn
and soy, especially). Thus, without realizing what we were doing, we
significantly altered the ratio of these two essential fats in our diets
and bodies, with the result that the ratio of omega-6 to omega-3 in the
typical American today stands at more than 10 to 1; before the
widespread introduction of seed oils at the turn of the last century, it
was closer to 1 to 1.

The role of these lipids is not completely understood, but many
researchers say that these historically low levels of omega-3 (or,
conversely, high levels of omega-6) bear responsibility for many of the
chronic diseases associated with the Western diet, especially heart
disease and diabetes. (Some researchers implicate omega-3 deficiency in
rising rates of depression and learning disabilities as well.) To remedy
this deficiency, nutritionism classically argues for taking omega-3
supplements or fortifying food products, but because of the complex,
competitive relationship between omega-3 and omega-6, adding more
omega-3s to the diet may not do much good unless you also reduce your
intake of omega-6.