5 Surprising Holiday Health Myths

[Ivan Seeking]

Many supposed holiday hazards are as innocuous as a tepid mug of apple cider. A review article in the current issue of the British Medical Journal cites five fears that can officially be crossed off the holiday worry list...

http://www.livescience.com/health/081217-holiday-health-myths.html

 

[russ_watters]

Some of those appear to be either misleading or wrong. The one about losing heat through your head is the easiest and their explanation is clearly wrong:

Body heat leaves from any skin surface in proportion to the area exposed, said Vreeman.

This is true if all skin surfaces are both exposed and at the same temperature and have the same insulation (fat), but they aren't. Your body regulates temperature by adjusting the blood flow to the surface of your extremeties, but it can't do that with your head. And perhaps if you are naked, you lose nearly as much per surface area on your torso, but people don't go naked outside - they only go hatless.

 

[Ivan Seeking]

Most of those appear to be either misleading or wrong. The one about losing heat through your head is the easiest and their explanation is clearly wrong: This is true if all skin surfaces are both exposed and at the same temperature and have the same insulation (fat), but they aren't. Your body regulates temperature by adjusting the blood flow to the surface of your extremeties, but it can't do that with your head. And perhaps if you are naked, you lose nearly as much per surface area on your torso, but people don't go naked outside - they only go hatless.

They also provided the context that it makes no sense to wear a hat while wearing shorts.

Please provide as source regarding blood flow to the head. Sure, blood to the brain is probably constant, but what about cappilaries near the surface?

 

[Danger]

people don't go naked outside - they only go hatless.

When's the last time that you checked Astro's photos?

 

[Art]

Heat loss through the head at rest is 7%. This can increase to as high as 55% when exercising. However if exercise is continued then vasodialation takes place as part of the bodies temperature regulation mechanism accompanied by increased blood flow to the muscles demanding oxygen and so the head once again falls to only 7% of total heat loss.

If suffering from hypothermia a mixture of shivering and vasoconstriction (which reduces the blood supply to the skin) will also result in heat loss through one's head rising to 55% of total heat loss and so although the myth is not strictly correct there is more than a grain of truth to it.

 

[TheStatutoryApe]

So far as I can find myth number one is sort of true and sort of false...

Behavioral problems Numerous studies have confirmed that sugar does not cause hyperactivity. In fact, a few drops of sugar water (a half teaspoon in an ounce of water) can soothe a fussing baby. When sugar enters the bloodstream and reaches the brain, it temporarily increases calming neurochemicals, such as serotonin.

That's not to say you're just imagining those post-birthday-cake meltdowns. The problem is what happens when blood-sugar levels rise too high. The body responds by producing a large amount of insulin, a hormone that sweeps sugar out of the blood and into body cells. Blood-sugar levels may then drop so quickly, your child may feel shaky or sluggish. Not surprisingly, low blood-sugar levels can trigger a craving for more sweets, which creates a vicious cycle of sugar highs and lows.

http://www.parenting.com/article/Child/Recipes--Nutrition-For-Children/Sugar-Does-It-Make-Kids-Hyper/2

 

[russ_watters]

Please provide as source regarding blood flow to the head.

Here:

The cerebral blood flow is supplied via the carotid and vertebral arteries (4 in total) and is constant. The blood flow to the brain does not change as the demand for oxygen is constant.

http://wildernessmedicinenewsletter...4/heat-loss-through-the-head-and-hypothermia/

Sure, blood to the brain is probably constant, but what about cappilaries near the surface?

Compared to the amount of blood flowing to the brain, we may as well disregard them altogether. Consider them zero and it doesn't change the issue. More:

The cerebral blood flow does, however, vary based on cardiac output - the harder your heart beats, the greater the blood flow to the brain. And as you increase the blood flow to the brain, you also increase the percentage of heat loss. As it turns out, when you begin to exercise, there is increased cerebral blood flow. This increases the percentage of heat lost through the head to about 50% of total body heat loss. But as the person continues to exercise, the muscles demand more oxygen which increases blood flow. To ensure thermoregulation and maintain normal core temperature (exercises increases body heat), the skin vasodilates which increases blood flow to the skin to cool the blood. The net result is a decrease in the total blood flow to the brain and a decrease in percentage of total body heat lost through the head to about 10%. Once sweating begins, the percent lost through the scalp returns to 7%.

Now this still doesn't address the issue of insulation. If the fraction of heat loss is 7% when you are buck naked and at equilibrium in a 79F degree room, if you go outside when it is 29, and you're wearing ski clothes but no hat, it'll be 21% (low estimate that wrongly assumes a direct proportion, which is only true of conduction).

Now since people throw this myth around a lot, the fractions quoted can be huge, but even at 21%, that's a pretty substantial fraction and definitely worth wearing a hat.

Also, I'm pretty sure that number doesn't include your neck. Here's another link:

As far as I've been able to find (I feel your pain - it´s been pretty to hard to find!), about 30% of one's body heat can be lost through the head. About 13-16% of the body's blood volume is in the head at any given time, but it is a very exposed structure, allowing it to lose heat pretty quickly. Incidentally, the neck is also a place of easy heat loss, so keep that scarf on as well!

Here's an actual study (abstract) that says the heat loss from the head is linear with temperature difference (surprising), and that vasoconstriction plays almost no role (compared with your finger, where it decreases the heat loss by a factor of 6): http://jap.physiology.org/cgi/content/abstract/10/2/235

 

[russ_watters]

So far as I can find myth number one is sort of true and sort of false...

#5 is at least that way as well: The explanation says eating at night does make you fat, just not any more fat than eating at any other time. Duh.

 

[tmc]

#5 is at least that way as well: The explanation says eating at night does make you fat, just not any more fat than eating at any other time. Duh.

That's also incorrect. The time at which you ingest nutrients is extremely important as to what your body will do with them. Eat sugar after working out and it'll go to your muscles; eat sugar before bed and it'll go to fat (it's a gross oversimplification, but that's the idea). The amount of mass gained will be pretty much the same, but it might make the difference as to whether that mass is fat or muscle.

Course, most people being sedentary, it'll get turned to fat regardless of when you eat it, as there isn't much difference between sleeping and sitting in a cubicle. I think that was their point.

 

[grant9076]

That's also incorrect. The time at which you ingest nutrients is extremely important as to what your body will do with them. Eat sugar after working out and it'll go to your muscles; eat sugar before bed and it'll go to fat (it's a gross oversimplification, but that's the idea). The amount of mass gained will be pretty much the same, but it might make the difference as to whether that mass is fat or muscle.

Course, most people being sedentary, it'll get turned to fat regardless of when you eat it, as there isn't much difference between sleeping and sitting in a cubicle. I think that was their point.

Not exactly.

K. J. Acheson and colleagues conducted an experiment (which is documented in Vol 246 Issue 1 62-E70 of the American Journal of Physiology) where they fed 500 grams (2000 Calories) of maltodextrin (a high glycemic index carbohydrate) to several subjects and used the respiratory quotient (also known as the respiratory exchange ratio) to accurately measure the amount of net lipogenesis. The highest reported net lipogenesis was 9 grams (81 Calories) of fat produced for the group that was previously on a high carbohydrate diet (replenished glycogen stores) prior to consuming the 500 grams of carbohydrates. This is roughly 4% of the ingested Calories. Similar experiments have been conducted by Burszstein et al and had similar results. The findings were that the body switched over to primarily glycolysis in order to burn off the carbohydrates. In addition, diet induced thermogenesis accounted for a significant amount of lost calories after a high carbohydrate meal.

Note: Respiratory Quotient = Carbon dioxide expelled divided by oxygen absorbed. By balancing the chemical equation, the amount of lipolysis, glycolysis, or lipogenesis can be determined.

Although I have a hard copy in my library, the closest online source that I could find is this synopsis.
http://ajpendo.physiology.org/cgi/content/abstract/246/1/E62"

As you can probably guess, I am not a fan of Dr. Atkins.

 

[tmc]

That's all fine and all, but...what part of my post do you disagree with? It seems that your article agrees that if someone's glycogen stores are full, the carbs will be converted to fat more often than if glycogen stores are empty (which happens, for example, after working out). This was the essence of my post, and is kind of obvious really.

And while I also disagree with most Atkins people, ketogenic diets have shown themselves quite useful for healthy individuals and for short-term, small weigh loss (short-term is important here; Atkins as a lifestyle change is downright stupid).

 

[grant9076]

Perhaps I should have done a better job in explaining my disagreement.

eat sugar before bed and it'll go to fat (it's a gross oversimplification, but that's the idea)

Course, most people being sedentary, it'll get turned to fat regardless of when you eat it, as there isn't much difference between sleeping and sitting in a cubicle.

When you combine these 2 statements, they imply that eating carbohydrates before being sedentary results in most or all of the carbohydrates being turned into fat. If that was the case, then 2000 Calories of Carbohydrates should have produced over 200 grams of fat. Instead, it only produced 9 +/- 1 grams of fat (about 4% of ingested calories). This is a far cry from your claim. Keep in mind that the subjects had to sit around for several hours while some apparatus measured what was going into and coming out of their lungs.

Also, you did not account for the Basal Metabolic Rate (BMR), which accounts for calories burned when you are doing nothing. In addition, every credible person (Masters or Phd in Nutrition) that I have ever spoken to agrees that the brain uses well over 100 grams of carbohydrates per day (child or adult, sleeping or awake). These numbers also agree with those quoted by the http://books.nap.edu/openbook.php?record_id=10490&page=265". This is over 500 Calories per day and can be up to over 40% of the BMR of a small person. This explains why carbohydrate deprivation results in gluconeogenesis via the Glucose-Alanine Cycle (conveniently ignored by Atkins). It also explains why the head generates so much heat.

ketogenic diets have shown themselves quite useful for healthy individuals and for short-term, small weigh loss

Much of the weight loss on low carb diets is due to lost muscle and water. If there is any fat loss, it is because by cutting carbs, they have simply cut Calories.