I understand that a great deal of the body’s energy is used to generate body heat. I can’t find a cite right now, but I vaguely remember statements suggesting 60 or 70% of your energy usage per day goes to heat. These vague memories were backed up by statements in the thread linked above that in cold weather one burns a lot more energy and thus must eat much more.
So how come we don’t see people hawking miracle diets where you sit in a chilly bath to force the body to burn more energy and thus more food / fat? I assume it doesn’t in fact work, as I haven’t heard about it, but why doesn’t it?
A bonus question - a commonly stated fact is that some ridiculous proportion of body heat loss occurs through an uncovered head - figures range from 40 or 50% up. Is this true? How can this be?
Read my post in this thread. You will have to epend energy to stay warm in a bath but food energy is measured in kilocalories which makes it far less efficient than you would think.
Thanks, mate, but your post seems to be mostly about cold foods, rather than cold in general. I accept that a chilled Coca Cola give you just about as much energy as a room-temperature one, but I’m talking about a whole lot more cold (yeah, I know, less heat). Like in a winter, where you apparently must eat more to keep yourself warm.
How long do you think peiopel would be wiling to sit in a bathtub full of ice?
At best, only your skin would need to get reheated back to 98.7, or thereabouts. You aren’t going to get your core body temperature down this way, and as such, you’re not going to burn that many calories.
I’ve never seen ice baths endorsed as a calorie-burner, but I’ve seen ‘add ice to all your drinks, your body burns calories bringing the beverage to body temp’ in numerous diet tip lists.
To lose weight without effort? Till hell also freezes over.
But that’s not really my point. The ice bath was just an example, and I’m not actually suggesting such a “diet”. I’m more asking if my understanding of human metabolism (most energy spent on body heat) is roughly correct and, if so, somehow lowering body temperature could provide an appreciable increase in energy output.
I see where the OP is going with this.
Were not talking about a bathtub ful of ice here. But let’s say a guy doing laps in a heated pool for and hour versus a guy doing laps in some really cold lake for an hour?
Does the guy in the cold water burn more calories? How much more?
I have heard even more. There are too parts to this. One is that your brain has a whole lot of blood flowing through it, proportionally much more than other parts of your body. The brain uses a lot of energy. That makes your head like a little radiator.
The second reason is more mundane. The phrasing usually goes something like “On a cold day, 50% of your heat loss occurs through your head”. I have heard 90% as well. The reason is simply because your head or at least part of it is uncovered while the rest of your body is covered. You can’t just put on a hat and strip mostly naked and expect to keep warm.
Because they it doesn’t work, and weight loss is a medical claim. As soon as you make a medical claim about a process all sorts of regulatory bodies become interested in your evidence for those claims. Since nobody could demonstrate that sitting in a bath under any reasonable conditions will cause weight loss they can’t make any such claim.
Because it’s totally impractical. The first reaction of the human body to low temperatures is to ramp up the appetite, so chilling the body will actually cause a person to become more hungry and eat more. Without a calorie controlled diet in place at the same time the process will actually result in weight gain. There’s a good reason people put on weight over winter.
Then there is simply the amount of energy needed. If someone sits in a body of water much below 20oC they will start to suffer hypothermia within a few hours. Yet if the water temperature isn’t significantly lower than 20oC you will be chewing less energy then you would simply by walking around slowly. If someone won’t engage in light exercise for half an hour a day then why would they be prepared to lie in a freezing bath for 2 hours a day? The whole concept is impractical (and too silly even for Tony Robbins).
It depends entirely on what you mean.
If someone were wearing a well insulated suit that covered the entire body and left the head uncovered then of course most of the heat will be lost from the uncovered head. That’s simply because heat can’t be lost at all from the rest of the body. Imagine an extreme example of an astronaut on Mars in a near perfectly insulated suit. He obviously isn’t losing any significant heat from anywhere. He then takes his helmet off and freezes to death in minutes. Obviously all that heat was lost through the uncovered head, he can’t have lost it form anywhere else. But that’s just common sense.
Yes, swimming in extremely cold water will burn more energy.
How much more? Depends on how cold the lake is and how fast he is swimming.
The thing is that swimming by itself generates heat, quite a lot of heat. The body actually uses energy to get rid of that heat under normal circumstances . So a person swimming in a moderately cold lake may actually burn less energy than a person in a heated pool because no additional energy is needed to dissipate the heat.
As the temperature of the water falls the energy gain will dissapear, but their will still not be any net energy loss from the cold water because the body is still generating excess heat. At some point the temperature will become so low that the body can’t maintain sufficient heat even through vigourous exercise. But swimming is already using most of the skeletal muscles, so it’s doubtful if shivering will work to generate more heat. At taht point you body starts initiating all sorts of interesting repsonses to keep your freezing to death, including shunting blood out of the limbs. That makes the muscles much less efficient and will cause significantly more energy to be burned. Probably more importantly the body will need to try to raise that temperature agian when you get out.
It’s a farily complicated process with too many variables to be able to answer how much additional energy is used at various water temperatures.
Thanks to Hampshire, Shagnasty and Blake, that’s the kind of explanation I was looking for - not enough energy expended under any reasonably tolerable conditions, tendency to eat more.
To follow up on the head question, is it your position that the 50% (or whatever percentage) heat loss through the head statement is effectively meaningless, since it depends entirely on the situation?
But swimming isn’t “normal circumstances”. Water will disipate the heat from your body very effectively. I doubt that someone swimming in warm water would burn fewer calories than someone swimming in cold water.
And keep in mind that even a heated pool is only about 80 deg F, so that’s still retty cool compared to your body temp. 80 deg air might not cool you down much, but 80 deg water will.
That’s why I said exactly the opposite would occur: swimming in cold water may burn fewer calories than someone swimming in warm water.
Nonetheless body temperature still rises, and significantly, while swimming and blood still floods the surface capillaries. Without any doubt the body still devotes energy to cooling itself in 80oC water. Swimming simply generates too much heat to be eliminated under normal conditions. The only debate on this topic is whether a person swimming actually sweats to try to eliminate that excess, and the best evidence suggests that yes, they do. Not that sweating underwater achieves anything, but the point is that the body has to actively try to dipserse that heat via process that use energy.
Another point not brought up yet - your body reacts to its environment in gradual as well as immediate ways. THe initial reaction to a cold bath will be contraction of the capillaries in the dermis to retain heat and other immediate physiological reactions. However, if the ice bath were a regular occurence, the body would try to prevent heat loss by adding more insulation. It would pack on more subcutaneous fat to protect itself from the cold water (assuming you didn’t die of hypothermia first). So the ice bathing regimen would have the opposite effect over the medium to long term.
Does anyone kn ow if the converse is true? Instead of keeping it cold, try to force your body to believe it has too much insulation by always staying uncomfortably warm. This won’t by itself shed any weight, but it will it (for normal people without other conditions contrary to weight loss) cause your body to be less willing to add fat?
OK, I’m going to need to see some strong evidence to believe that for even one moment.
Low temperatures certainly stimulate appetite, which may lead to a weight gain, but that has nothing whatsoever to do with adding subcutaneous fat to protect the body. The fat itself is laid down in perfectly normal patterns AFAIK, not in any manner that would aid temperature regulation. All else aside human subcutaneous fat is almost as well supplied with blood vessels as the skin, and those vessels are harder to regulate. As a result human fat has almost no insulative properties.
It certainly has some benefits, but in practical terms they are minimal.
The biggest problem is that the body responds to cold temperatures even in short bursts. So you would need to ensure that you never got chilled even for a few minutes for it to work fully.
The second problem is that the body responds to changes in temperature, not to absolute temperature, hence people in the tropics experience the same increase in appetite in winter as people in Canada, even though a tropical winter is warmer than most Canadian summers. For your plan to work practically you would need to ensure that you started adding more clothing and keeping your car, house and workplace warmer as the year progressed.
Because of those practical problems most of the experiments done on this have come form animal studies because we can regulate temperature for animals far better. But there is some evidence from humans that avoiding cold temperatures helps suppress appetite.
Can you explain how this can possibly be true? If a person swimming in 20oC water exhibits all the signs of active heat dispersal, which a person in cold water obviously will not display, then how can that active dispersal be energy neutral?