[email protected] (BroJack) wrote in
news:[email protected]:
> Pritikin convinced many of us as to the value of potatoes which he deemed a complex carbohydrate.
> I for one did exceedingly well on the Pritikin regimen. Now we learn of a glycemic index and the
> assertion that white potatoes are "simple" carbohydrates, much like white bread and even sucrose.
By the technical definition, starches are complex carbohydrates (note that potatoes are not
carbohydrates; they're food that *contains* a large amount of carbohydrates). However, many of them
[1] behave metabolically pretty much the way simple carbohydrates do. The moral of the story is that
the chemical distinction between "simple" and "complex" carbohydrates is too, well, simple to apply
to nutrition.
[1] Starches consist of long chains of monosaccharides (usually glucose). Some of the chains are
straight; others branch like trees. Starches that consist mostly of straight chains are called
amyloses; starches that consist mostly of branched chains are called amylopectins. Digestive
enzymes break down any starch (well, almost any starch; there are some "resistant starches")
into their constituent monosaccharides, which are then absorbed into the bloodstream. The
enzymes work by removing monosaccharide units from the ends of chains, and take a small but
finite amount of time to remove each monosaccharide.
That means that amylopectins are broken down much more quickly than amyloses, because their chains
have many ends and several enzyme molecules can be working on one starch molecule at the same time.
Amyloses break down more slowly because they have only a few ends (in the extreme, some amyloses
have only one chain, so only two monosaccharides can be removed simultaneously). And that means that
the more amylopectin-like a starch is, the faster the resulting influx of glucose into the
bloodstream from consuming it.
Note, though, that some foods (like whole grains) can contain amylopectins and still not produce a
fast glucose influx. The reason is that the starch is tied up in fiber and it takes some time for
the digestive process to extract it. Thus while the starch is converted quickly, only small amounts
of starch at a time are being converted.
