methionine & protein restriction

[thea]

From the best scientist in Oregon a e-mail:

Many fruits are good sources of protein and amino acid (typically, about 1% by weight). The amino acids tryptophan and methionine are needed during growth, but adults need only very small amounts of them, and in excess they suppress metabolism and accelerate aging.

Biochim Biophys Acta. 2006 May-Jun;1757(5-6):496-508. Epub 2006 Feb 24.
Mitochondrial oxidative stress, aging and caloric restriction: the protein and
methionine connection.
Pamplona R, Barja G.
Department of Basic Medical Sciences, University of Lleida, Lleida 25008, Spain.
Caloric restriction (CR) decreases aging rate and mitochondrial ROS (MitROS)
production and oxidative stress in rat postmitotic tissues. Low levels of these
parameters are also typical traits of long-lived mammals and birds. However, it
is not known what dietary components are responsible for these changes during
CR. It was recently observed that 40% protein restriction without strong CR also
decreases MitROS generation and oxidative stress. This is interesting because
protein restriction also increases maximum longevity (although to a lower extent
than CR) and is a much more practicable intervention for humans than CR.
Moreover, it was recently found that 80% methionine restriction substituting it
for l-glutamate in the diet also decreases MitROS generation in rat liver. Thus,
methionine restriction seems to be responsible for the decrease in ROS
production observed in caloric restriction. This is interesting because it is
known that exactly that procedure of methionine restriction also increases
maximum longevity. Moreover, recent data show that methionine levels in tissue
proteins negatively correlate with maximum longevity in mammals and birds. All
these suggest that lowering of methionine levels is involved in the control of
mitochondrial oxidative stress and vertebrate longevity by at least two
different mechanisms: decreasing the sensitivity of proteins to oxidative
damage, and lowering of the rate of ROS generation at mitochondria.

[johndela1]

how do you restrict it?

[Oscar]

I might be wrong, but after tryptophan, methionine is the lowest present anyway. Also, CR is correct, but not in extremis. Eat what you need. Most people eat too much.

[RRM]

The amino acids tryptophan and methionine are needed during growth, but adults need only very small amounts of them

True, and this is reflected in the 'given requirements'.
However, compared to those requirements, methionine on average is the most scarse amino acid in our foods.

in excess they suppress metabolism and accelerate aging.

Absolutely, and that is why their intake should be in perfect balance with the other amino acids and your protein requirements.

Methionine restriction by itself would not make any sense as it would make larger parts of your protein intake completely worthless, so that only protein restriction would make sense, as worthless protein still carries an ammonium load. And in the case of a protein restricted diet optimizing the amino acid balance would actually require a relative high presence of methionine (while the absolute level is low when compared to a high protein diet).