March 6, 2005
Do You Burn More Calories in Hot or Cold Weather?
You burn fewer calories when you exercise in cold
weather than you do when it's hot. The hotter it is, the more extra
work your heart has to do to prevent you from overheating. More
than 70 percent of the energy produced by your muscles during
exercise is lost as heat. So the harder you exercise, the hotter
your muscles become. In hot weather, not only must your heart
pump extra blood to bring oxygen to your muscles, it must also
pump hot blood from your heated muscles to your skin where
heat can be dissipated.
On the other hand, in cold weather, your heart only has
to pump blood to your muscles and very little extra blood to your
skin to dissipate heat. Your muscles produce so much heat
during exercise that your body does not need to produce more
heat to keep you warm. So your heart works harder and you burn
more calories in hot weather. This information should not
discourage you from exercising when it’s cold, because staying
in shape is a year-round proposition. However, it may help to
explain why so many people find the pounds creeping on in the
wintertime, even when they stay active.
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Dear Dr. Mirkin: What causes dark facial hair on a woman?
Five to ten percent of North American women have
hirsutism, or excessive hair on their faces and bodies. Women
have the same number of hairs on their bodies and faces as men
do, but the male hormone, testosterone, makes hairs thicker,
darker and longer, so they are more noticeable. Some women
with heavy facial and body hair have normal amounts of
testosterone and inherit this tendency. Others have a medical
condition that causes their bodies to produce larger amounts of
testosterone.
Women with noticeable facial hair should get blood tests
for testosterone to measure male hormones made by the ovaries
and DHEAS to measure male hormones produced by the adrenal
glands. They should also get a sonogram of their ovaries to test
for polycystic ovary syndrome (PCOS) in which the ovaries do
not release eggs each month. Other PCOS symptoms include
storing fat primarily in the belly, irregular periods, acne, or
infertility. For more on diagnosis and treatment of PCOS see report #8124.
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Dear Dr. Mirkin: Can I exercise after donating blood?
A healthy person should be able to recover completely
from donating blood in eight weeks, but you may lose some of
your ability to train for a few days. Following a donation of one
pint, blood volume is reduced by around ten percent and returns
to normal in 48 hours. So, for two days after donating, you
should drink lots of fluids and probably exercise at a reduced
intensity or not at all. Donating blood markedly reduces
competitive performance for three to four weeks as it takes that
long for blood hemoglobin levels to return to normal.
You should not donate blood more often than every eight
weeks because it takes that long to replace lost nutrients. If you
donate blood frequently you need to make sure to replace the B
vitamins and iron that you lose with the blood. You can meet your
needs for iron by eating meat, fish or chicken or by taking iron
supplements; and you can meet your needs for the B vitamins
with whole grains and diary products. Donating blood at least
four times a year may help to prevent heart attacks by lowering
blood cholesterol levels significantly and reducing iron levels.
Iron in the bloodstream converts the bad LDL cholesterol to
oxidized LDL which can form plaques in arteries.
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SHARE YOUR FAVORITE HEALTHFUL RECIPE
One reader asked if we take "donated" recipes – the answer is
YES! If you have a recipe you’d like to share, please send it to
info@drmirkin.com
Diana’s guidelines for healthful recipes
This week, try
Mediterranean Seafood Stew
We’re cooking up a batch today. Leftovers freeze well.
List of Diana's Healthful Recipes
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