Nutritional Needs in Cold and High-Altitude Environments Applications for Military Personnel in Field Operations (1996) / Chapter Skim
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Part III Discussion
Part III Discussion
Pages 271-292
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From page 271... ...
In many cases, an increase in catecholamine levels. With respect to the xanthines, there is possibly an effect on the inhibition of phosphodiesterase activity, possibly translocation of calcium, and possibly an antagonistic effect on adenosine receptors.
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From page 272... ...
We wanted to concentrate more on what would be the best means, either pharmacological and/or dietary, to enhance cold tolerance, and then possibly look at the mechanisms afterward. HARRIS LIEBERMAN: We have also given sympathomimetic drugs to animals and exposed them to cold stress.
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From page 273... ...
We have a large anecdotal body of information in which people argue that adolescent athletes are at especially high risk for being iron deficient. As an athlete becomes more advanced in terms of national caliber or ranking, the likelihood of iron deficiency goes down quite dramatically, because people are paying more and more attention to the balance between requirements and intake.
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From page 274... ...
So my comment was that there is a large group of people who exercise a significant amount and who may have a change in iron metabolism because of that exercise. In terms of the elite-caliber athletes, I think more recent data would argue quite the opposite, that one doesn't find iron deficiency anymore.
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From page 275... ...
So as somebody becomes iron deficient, you see more and more of these transferrin receptors floating around. IRA JACOBS: I know of one study where, in fact, cytochrome oxidase activity was measured in skeletal muscle of iron-deficient people.
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From page 276... ...
ORVILLE LEVANDER: Are you aware of the work that John Arthur did on the cold adaptation of rats on selenium-deficient diets and the fact that the iodinase is induced in the selenium-depleted but not in the selenium-deficient animals. JOHN BEARD: That is right.
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From page 277... ...
It is based, I guess, on one study, or perhaps two studies. We have also heard recommendations in some areas to decrease iron intakes on the basis of one study linking high iron intake to cardiovascular disease.
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From page 278... ...
The half-life of the protein is only 18 hours. If you have acute muscle trauma due to a forced march in which you have IL-2 being released as a normal response to that, and you have iron being sequestered; it is likely this deprivation of iron in the plasma pool leads to a decrease in deiodinase activity.
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From page 279... ...
ROBERT REYNOLDS: I really would have to spend more time thinking about what the different T Rations and the Rations, Cold Weather provide, how much is actually consumed, and the massive interaction of the B vitamins in controlling energy production. PETER JONES: The reason I am bringing it up is because an RDA, I think, is defined as the level of a specific nutrient consumed which, based on the best available information, meet the needs of the majority of individuals.
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From page 280... ...
We will likely have at some time in the near future a different requirement for public health officials to define anemia in a black population versus a white population. My main question is, do we know of similar sorts of differences for these biologic outcome variables related to temperature regulation?
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From page 281... ...
ANDREW YOUNG: It depends on the parameter. I think that body temperatures are probably tighter than that, but if we were to look at norepinephrine response to cold, we would see coefficients of variation greater than that.
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From page 282... ...
Polyunsaturated fats and fish oil have been shown by a number of groups, including our own recently in the Journal of Nutrition, to tend to up-regulate energy metabolism. JACQUES LeBLANC: I have a comment on the practical remark that was made this morning by COL Schumacher of the Marine Corps regarding meal frequency.
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From page 283... ...
Cold acclimatization or cold acclimation or cold habituation whatever process we are measuring—can be seen by physiologists, measured in the lab, and written about. But the reality is that in terms of gross temperature, gross defense of body heat stores and nutritional requirements, cold acclimation or acclimatization probably has no effect on the nutrient requirements, be they the macro energy requirement or the micro.
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From page 284... ...
We do not have any medical evidence or reports that the cold, per se, is causing health risks other than peripheral cold injury. JOHN BEARD: Do we have any information that ascorbate turnover or utilization has changed?
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From page 285... ...
As far as I'm aware, little data exist that bears directly on this issue. If others have additional data, please provide it, but I seem to recall there are only a few studies in the 1950s where they have tried protein supplements during the night.
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From page 286... ...
With respect to uncouplers of oxidative phosphorylation, I think that would be the next Nobel Prize. If one could localize uncouplers in a particular tissue, you could solve obesity problems and survival in the cold overnight with a hypermetabolic approach.
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From page 287... ...
PETER JONES: Studies that were conducted in noncold situations—actually, it was with the Irish hunger strikers some years ago showed that they did not actually start to show ill effects until they had nearly exhausted their fat reserves and reached a critical mass in terms of lean body fat-free mass. Once you reach the end of your fat reserves and begin to deplete your lean mass reserves, it is at that point that you become much more susceptible to disease.
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From page 288... ...
Were they at any greater risk of cold injury within that 8-wk scenario? ANDREW YOUNG: If you remember the slide that I showed that plotted the thermal conductance or the insulation as a function of subcutaneous fat thickness, I believe that about a 5-mm change in subcutaneous fat thickness would be a very physiologically significant reduction in insulation.
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From page 289... ...
We would like at some point to see some more definitive analysis done on the outliers with regard to body weight, because some of these people lost a large amount of body weight. It would be interesting to see what problems they experienced in terms of illness or injury, more than what was observed for the mean or the ones who maintained higher body weight.
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From page 290... ...
Someone who may have more of a prophylactic effect peripherally because of what might be called a good CIVD response is not necessarily someone who is going to be more resistant to decreases in body temperature in reaction to a given cold stress, everything else being equal. There does not seem to be any relationship at all.
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From page 291... ...
ROBERT REYNOLDS: High doses of niacin in the range of 1 g will create tremendous vasodilation, which is commonly used to bring cholesterol down. That is one nutritional example.
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