cron-web.org

[A1CR]

We all live in different climates, from tropical to near
polar. How might
this affect our outcome for CRON? It appears from the below
paper that CRON
when in cold temperature situations may affect many features
of metabolism
and body composition. A good introduction to the effects of
Antarctica
sojourns on thyroid hormones and energy requirements (and
mood) may be the
free-to-all-full-text http://tinyurl.com/j7qbu paper.

Case HS, Reed HL, Palinkas LA, Reedy KR, Van Do N, Finney
NS, Seip R.
Resting and exercise energy use in Antarctica: effect of 50%
restriction in
temperate climate energy requirements.
Clin Endocrinol (Oxf). 2006 Aug;65(2):257-64.

PMID: 16886970 http://tinyurl.com/gg65z

... energy restriction (ER) upon the previously
reported increased
resting and exercise-related oxygen utilization, reduced
body temperature,
increased serum TSH, and reduced serum free T3
concentrations found during
Antarctic residence (AR). Prospective, intervention with
both paired
controls and a similar reference control group (RG). Seven
subjects were
assessed before and after a 50% ER period of 60 h. This ER
was carried out
within 30 days of arriving in Antarctica in October (OCT)
and again after 10
months AR in August (AUG). During the periods of ER, mean
energy consumption
was 5662 +/- 1344 kJ/day in OCT and 5529 +/- 967 kJ/day in
AUG. Resting
metabolic rate (RMR), a calculated resting metabolic rate
(RMR(reg)) ...
tympanic http://tinyurl.com/m2o76 temperature (Tty) were
measured. These
values were compared with a similar RG of 12 subjects
reported previously
who were studied in California, USA before and then again
during AR. Weight
declined by 1.1 +/- 0.1 kg/day (OCT) and 0.92 +/- 0.2 kg/day
(AUG) with ER,
resulting in a reduction of body weight by 3.1 +/- 0.4% in
OCT (P = 0.0001)
and 2.5 +/- 0.4% in AUG (P = 0.0015) during AR. The RMR
before ER did not
change with AR and it was not significantly different from
the RG studied in
California. With ER the RMR tended to decline in both OCT
(132 +/- 5 to 122
+/- 4 mlO(2)/min/m(2)) and AUG (134 +/- 5 to 126 +/- 5
mlO(2)/min/m(2)), but
these were not significant. By contrast, RMR(reg) obtained
before ER was
increased with AR by 22.5 +/- 7.8% (P = 0.01) in OCT and by
28.1 +/- 7.0% (P
= 0.0008) in AUG over the RG values obtained in California.
RMR(reg) did not
decrease with ER in either OCT or AUG. The total energy
expenditure derived
from these measures of weight loss suggests that 24-h energy
requirements
are 74.4%[95% confidence interval (CI) 2.6-146.3; P < 0.05]
more than those
expected in temperate climates. Tty declined by 0.6 +/- 0.2
degrees C (P <
0.01) with AR compared with the RG measured in California,
but was not
affected by either period of ER. ER had no effect on FT3 but
tended to
decrease serum TSH in AUG (P = 0.06). Exercise-related
energy requirements
are increased with AR. Moderate ER may reduce resting but not
exercise-related energy expenditure and it is associated
with a weight loss
exceeding expectations for 50% restriction of temperate
climate energy
predictions.
... Antarctic residents can develop ... (1) cold
adaptation, (2)
increased 24-h energy requirements and (3) increased T3
production,
clearance and distribution volume.5 Surrogate markers of T3
kinetic
parameters that may be observed include small declines in
serum free T3 and
free T4, elevations in serum TSH and thyroglobulin2,5,6 and
TRH-stimulated
TSH.7 Manifestations of human cold adaptation observed in
this group can
include declines in core temperature and decreased response
to standard cold
air tests.1 Contributions to the increases in energy
expenditure may include
increased resting metabolic rate (RMR) and oxygen use during
submaximal
exercise as well as decreased muscle efficiency.4 Finally,
cognition
declines in this syndrome and that decline is reversed with T4
supplementation.4 ...
... Thirteen (10 male and three female) healthy
euthyroid subjects ...
subjects in the reference group (RG) were 12 (11 male and
one female)
healthy euthyroid individuals who were part of the annual
military group who
wintered over at McMurdo Sound and had been studied
previously.4 ... body
surface area (BSA), body mass index (BMI), RMR and maximal
oxygen
consumption (O2max) ...
... During the periods of ER, food intake was limited
to Carnation
Instant Breakfast® (Nestlé's Corporation, Glendale, CA, USA)
packets mixed
with reduced-fat milk (2% fat). Each packet when mixed with
the reduced-fat
milk provided 1047 kJ of energy per serving, and consisted
of 37 g of
carbohydrate, 12 g of protein and 6 g of fat. ... To the
best of our
knowledge, the subjects consumed all of the nutrient given
to them. ...
drink water ad libitum. ... not drink alcohol for 24 h
before or during the
ER periods. ...

Table 2. Metabolic and thyroid studies during energy
restriction and
Antarctic residence with comparisons to the reference group
=======================================================
Variable OCT-Pre OCT-Post AUG-Pre AUG-Post RG pre-
deployment RG Oct-Jan
AR (4 months)
=======================================================
Weight (kg)^* 86.9±9.1 84.2±9.0 91.1±11.3 88.8±11.0 84.8±5.0
79.3±2.5
RMR (mlO2/min/m2)^# 132±5 122±4 134±5 126±5 126±4 138±3
RMRreg (mlO2/min/m2)^#** 283±20 277±21 296±16 274±20
231±8 269±7
WRs (W)^#§ 14.3±1.6 13.5±1.7 11.0±1.0 14.6±1.6 18.2±0.9 14.1±0.6
FT4 (pmol/l) 14.0±0.56 13.6±0.62 13.8±0.39 13.8±0.69
13.4±0.3 13.3±0.3
FT3 (pmol/l) 3.94±0.31 3.84±0.28 3.71±0.30 3.81±0.18
3.90±0.11 3.84±0.09
TSH (mU/l) 1.80±0.25 1.88±0.34 2.95±0.34 2.28±0.38 2.06±0.28
2.0±0.23
Tty (°C)^#**£ 35.8±0.2 35.5±0.2 35.4±0.3 35.0±0.3 36.4±0.1
35.5±0.1
=======================================================
... standardized work rate (WRs). RMR and RMRreg are
normalized for body
surface area (BSA) and the reference group (RG) is listed in
the reference
indicated. The statistical differences are noted.
Comparing pre- with post-ER data in OCT and AUG [*(P <
0.002)].
Comparing RG predeployment with RG AR (4 months) [#(P <
0.05)].
Comparing pre-ER data in OCT and AUG with the RG
predeployment [**(P <
0.01)].
Comparing pre-ER data in OCT with the RG predeployment
[§(P = 0.03)].
Comparing pre-ER data in OCT and with post-ER data in
AUG [£(P < 0.01)].

... Weight decreased with each period of ER,
initially in OCT by
2.7±0.4 kg (-3.1±0.4% of body weight) (P = 0.0001), and
again by 2.3±0.5 kg
(-2.5±0.4% of body weight) in AUG (P = 0.0015). There were
no significant
differences between the time periods in either the amount of
weight lost or
in the percentage of weight lost. Although the subjects
tended to gain
weight during AR, body composition did not change over the
study, with
measures of percentage body fat of 18.6±3.4% and 18.2±3.3%
in OCT and AUG,
respectively, and lean body mass of 69.1±5.7 kg and 72.6±6.8
kg in OCT and
AUG, respectively. Plasma volume decreased by less than 1.3%
with ER (ns)
and blood volume decreased with ER by less than 73 ml (ns).
... The RMR before ER was not changed from that
measured in the RG in
California in either OCT or AUG. With ER, the RMR tended to
decline by
7.6±2.1% in OCT and by 6.0±1.9% in AUG compared with
measures taken just
before ER, but these were not significant using anova.
Additionally, RMR
reported in the RG after 4 months of AR (January) of 138±3
mlO2/min/m2 was
no different from the RMR measured in the current study with
AR in either
OCT or AUG. ... The RMRreg was increased over the RG
measured in California
by 22.5±7.8% in OCT and 28.1±7.0% in AUG (df, 2, 21; F =
6.60; P < 0.01).
With ER, the RMRreg did not change. The RMRreg measured in
the RG during AR
of 269±7 mlO2/min/m2 was not different from that of the
current report of
RMRreg measured before ER in either OCT or AUG (Table 2).
... The WRs measured in these subjects in OCT before
ER of 14.3±1.6 W
was decreased from the RG measured in California (18.2±0.9
W) by 21.4% (P =
0.03). The WRs did not change with ER (Table 2) or during
the course of the
study, with a mean value of 11.0±1.0 W preceding ER in AUG.
There were no
differences in the slope between the O2 (mlO2/min) and
workrate (W) when
comparing the RG in California (9.17±0.34 mlO2/min/m2/W) and
either the OCT
measure before ER (9.23±0.38 mlO2/min/m2/W) or the AUG
measure before ER
(10.14±0.34 mlO2/min/m2/W). Testing with anova showed no
effect of time or
treatment in Antarctica. Specifically, ER did not change the
slope when
measured after ER in OCT (9.33±0.25 mlO2/min/m2/W) or after
ER in AUG
(9.74±0.50 mlO2/min/m2/W). However, although not
significant, the slope
tended to increase during the time in Antarctica by 9.8%.
... There were no significant changes in serum FT3,
TT3 or FT4 during
AR or with ER. Serum TSH increased 63.9±21.6% between OCT
and AUG with AR (P
= 0.06) and in AUG it tended to decline with ER (P = 0.07).
... The Tty was
lower in OCT and AUG (0.6±0.2 °C, P < 0.01 and 1.0±0.2 °C, P
< 0.01,
respectively) before ER compared with the RG measured in
California. During
the 11-month period of AR, there was no change in Tty
pre-ER. Although anova
revealed no significant changes in Tty as a result of ER,
the post-ER Tty in
AUG (35.0±0.3 °C) was significantly lower (P < 0.01) than
the pre-ER Tty in
OCT (35.8±0.2 °C).
... we would predict that 0.35 kg/day (ca. 0.5%/day)
would be lost with
a 50% ER diet.3235 Even with total ER for 72 h or 96 h,
subjects similar to
our group are reported to lose 0.70 kg/day (0.9%/day);30
female subjects
lost 0.68 kg/day (1.1%/day).31 ... total energy deprivation
and over 100%
more weight reduction for similar energy C.32-35 ... they
consumed a mean of
5595±1155 kJ/day while losing 24% more weight than we would
have predicted
for a totally fasted person in a temperate climate.30 We can
then predict
their 24-h energy requirements in Antarctica as the total of
these two
values, or approximately 19 522±2875 kJ/day. This total
energy expenditure
is approximately 74.4% (95% CI 2.6-146.3; P < 0.05) more
than the 24-h
predictions in a temperate climate for similar gender and
age subjects.23
... There were no significant changes in FT3, TT3 or FT4
with ER in contrast
to previous studies on energy restriction.8,9,15-21 ... Some
have suggested
that the carbohydrate content of the diet may be an
important factor in
regulating serum T3,17,19,42,43
... In summary, a 60-h period of 50% energy
restriction induces a loss
in body weight that is far greater than that observed in
studies carried out
in temperate climates. Additionally, the energy restriction
does not reduce
resting or exercise-mediated metabolism. Taken together,
these findings
suggest that 24-h energy requirements are substantially
increased with AR by
approximately 74.4%.