Benefits of 40% CR with 1% Restriction (????) Part 2. Some Implications

[Guest guest]

Hi folks:

There are many nutrients that are believed to be absolutely essential

in appropriate quantities but which are known to be dangerous in

excess. Vitamins A and D are well known for this. Many metals,

including calcium, zinc, selenium, iron and chromium fall in this

category. Met (methionine), also an essential nutrient, apparently

may similarly be harmful if too much is consumed. Possibly other

amino acids also.

In short, if PMID: 16770005 is confirmed by other investigators and

replicated eventually in higher animals and humans, then it may be

possible to obtain benefits similar to those of 40% CR, by

restricting just Met. This is truly a remarkable possibility because

for almost everyone Met intake accounts for less than 1% of total

calories. It stretches credulity that restricting by half the intake

of a single nutrient that accounts for less than 1% of calories might

have huge benefits for longevity.

For example, it is a little difficult to believe that the huge CVD

biomarker improvements seen in the WUSTL study, and the generally

poor lipids data of ad libbers, are purely a function of variations

in Met intake. Does this mean a person who restricted Met to the RDA

amount but consumed enough other calories to maintain a BMI of 30

would have CVD and diabetes risk biomarkers as good as those found in

the WUSTL study? Or cancer incidence rates as low as those of 40%

restricted mice? The logic of the previously posted papers

suggests " Yes " . But intuition suggests the opposite. If the

important details in PMID: 16770005 are confirmed then further

studies will have to be done to establish what the optimal caloric

intake is for someone restricted to an appropriate (perhaps the RDA)

Met intake.

It will be quite a number of years before it could be firmly

established by studies measuring actual lifespans, that Met

restriction is responsible for some, much, most, all or any of the

lifespan benefits of CR in rats and/or hamsters. It will be several

decades before that could be persuasively demonstrated in monkeys.

And it may never be conclusively demonstrated in humans because of

difficulty controlling the subjects' diets over long time periods.

Of course CR itself has not been proven in humans yet either. But

many of us here are doing CR. So how long will it take before we

have enough evidence to be persuaded to adopt a more strict control

of protein intake, and especially Met? As always, each of us will

have to make our own decisions about this, based on our own

interpretation of the evidence. The Met issue was very briefly

discussed here some time back. At that time I was not persuaded to

do anything about it. But now, having seen this further evidence I

have already removed most of the foods with the highest Met content

from the list of foods I buy. I have done this, even with the

substantial uncertainties at this very early stage of our

understanding of this issue, because it seems possible there could be

major benefits, and at the same time unlikely there could be material

risks associated with such a change. But if someone can see potential

risks, please speak up.

Here are a few numbers to put the issue into some kind of

perspective: The RDA for total protein is 0·8g per kg of body

weight. (The EAR - estimated average requirement - is 0·66g of

protein per kg body weight). The official requirement for

Met+cysteine combined is 25mg per gram of total protein, of which

about two-thirds is likely usually Met. So for someone weighing 70kg

the Met requirement is about 933mg. In round numbers about one

gram. Which is about four calories and, in an 1800 calorie diet, a

mere ~0·2% of total calories.

In contrast, the actual Met intake of north american males aged 51 to

70 years, is appreciably higher than the RDA. According to NHANES,

the mean is 2·01 grams, with the 90th percentile consuming 2·89g

daily. Many of the latter may quite likely be people on low fat

diets who are eating proportionally more protein. But another

smaller study found that the average intake, if you were to believe

what people say about how much and what they eat, is 48·2 mg/kg.day,

which translates into 3·4g per day for someone weighing 70kg., or

4·2g for someone weighing a more realistic 85kg.. And when in this

same study they measured how much these people were really eating

(using the doubly labelled water technique) they found they were more

likely consuming 61·5 mg/kg.day of Met, or 4·3g daily for someone of

70kg, and 5·2g for someone weighing 85kg! These numbers are many

multiples of times higher than the RDA for Met of about about one

gram! So dramatic percentage reductions would seem to be achievable

for most people without reducing intake below the RDA.

Taking me as an example, weighing ~67kg and with a Mifflin/St Jeor

caloric expenditure number of around 1800 calories daily, my RDA

amount of 895mg of Met amounts to almost exactly 0·2% of calories.

Today I consumed 1200 mg, which was 0·253% of the calories I actually

consumed. But on another day it was almost 0·8% of calories. My

average over four days was a little over 0·4% of calories - double

the RDA. This means that, if I can find foods that would enable me

to achieve it while at the same time satisfying all the other

nutritional requirements, reducing my Met intake to the RDA - a drop

of 3·6 calories - would result in ' 50% restriction ' (!)

In any event, there is no reason why each of us cannot make our own

decisions based on how seriously we view the available evidence.

Then, if we wish to, track our own Met intakes and, whatever we find

them to be, adjust them to whatever level we deem to be appropriate.

Also worth noting that calculating Met as a percentage of calories

may not be the only Met number of interest. Since we do need to eat

protein but, it seems, maybe not too much Met, we should also make a

point to consume protein sources where the Met contributes a smaller

than average proportion compared with the other, presumably

beneficial, amino acids. If we only ate the foods that contained the

smallest amount of Met, but which also had very small amounts of the

other amino acids also, we might find ourselves with deficiencies of

the other amino acids.

More to come ...................

Rodney.