The Health Benefits of Fermented Milk

The bacteria in dairy products may do
more for us than just predigest lactose and
create flavor. Recent research findings lend
some support to the ancient and
widespread belief that yogurt and other
cultured milks can actively promote good
health. Early in the 20th century, the
Russian Nobelist Ilya Metchnikov (who
discovered that white blood cells fight
bacterial infection) gave a scientific
rationale to this belief, when he proposed
that the lactic acid bacteria in fermented
milks eliminate toxic microbes in our
digestive system that otherwise shorten our
lives. Hence Dr. James Empringham’s
charming title of 1926: Intestinal
Gardening for the Prolongation of Youth.
Metchnikov was prescient. Research
over the last couple of decades has
established that certain lactic acid bacteria,
the Bifidobacteria, are fostered by breast
milk, do colonize the infant intestine, and
help keep it healthy by acidifying it and by
producing various antibacterial substances.
Once we’re weaned onto a mixed diet, the
Bifidobacterial majority in the intestine
recedes in favor of a mixed population of
Streptococcus, Staphylococcus, E. coli, and
yeasts. The standard industrial yogurt and
buttermilk bacteria are specialized to grow
well in milk and can’t survive inside the
human body. But other bacteria found in
traditional, spontaneously fermented milks
— Lactobacillus fermentum, L. casei, and
L. brevis, for example — as well as L.
plantarum from pickled vegetables, and the
intestinal native L. acidophilus, do take up
residence in us. Particular strains of these
bacteria variously adhere to and shield the
intestinal wall, secrete antibacterial
compounds, boost the body’s immune
response to particular disease microbes,
dismantle cholesterol and cholesterolconsuming bile acids, and reduce the
production of potential carcinogens.
These activities may not amount to
prolonging our youth, but they’re certainly
desirable! Increasingly, manufacturers are
adding “probiotic” Lactobacilli and even
Bifidobacteria to their cultured milk
products, and note that fact on the label.
Such products, approximations of the
original fermented milks that contained an
even more diverse bacterial flora, allow us
to plant our inner gardens with the most
companionable microbes we’re currently
aware of.
Yogurt remained an exotic curiosity in
Europe until early in the 20th century, when
the Nobel Prize–winning immunologist Ilya
Metchnikov connected the longevity of
certain groups in Bulgaria, Russia, France,
and the United States with their consumption
of fermented milks, which he theorized would
acidify the digestive tract and prevent
pathogenic bacteria from growing (see box, p.
47). Factory-scale production and milder
yogurts flavored with fruit were developed in
the late 1920s, and broader popularity came in
the 1960s with Swiss improvements in the
inclusion of flavors and fruits and the French
development of a stable, creamy stirred

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