One pound of bodyfat is equal to around 3,500 Calories of energy. This is a well-established fact. It will be important to remember this. So if you are on a diet where you reduce your food intake by ONE HUNDRED CALORIES, people seem to celebrate! But that represents only 1/35 of a pound of bodyfat, a really tiny amount. A primary reason why people lose interest in diets is that you must stay on that rigid food schedule for 35 straight days, to only see A SINGLE POUND of bodyfat having disappeared. The odds are that you did something opposite during those 35 days, where the benefits are wiped out. But even if not, it is hard for people to stay on a very rigid diet for 35 days only to see a single pound disappear, because they actually want to see 10 pounds or 20 pounds or 40 pounds disappear, and we are then talking about YEARS of staying on that super-rigid diet!
By the way, ANY diet or other weight loss system that claims to enable you to "lose many pounds in a week" can obviously not be true! Even if you ate NO food in a particular day, your body (an adult man, a woman a little less) only uses up around 2,200 Calories of your BMR (basal metabolism rate) plus a few hundred more Calories due to exercise and other physical activity. Therefore, even if you ate no food at all, you could only lose a little over half a pound of actual bodyfat per day! (Your weight can reduce more than that, but it is nearly entirely due to water content of your body, lost as sweat, urine, or moisture in the breath.) Anyone or any advertising that tells you otherwise is simply lying to you!
Your body constantly generates energy, which it needs to power all the systems of your body, heart, muscles, brain, nervous system, etc. After that energy is used to do the many processes, it ALL then gets later given off as heat, in several different ways. Some gets lost by your skin radiating and convecting heat away. More heat is carried away by your warm breath. Your perspiration evaporates from your skin, which gives off additional heat. These things ALWAYS happens!
On average, the total food energy content that you eat/drink is the same as the total energy that your body needs for all of its operations and it is also equal to the total energy that your body gives off after it is done using it. This is called that BMR Basal Metabolism Rate, and for adult men, it is around 2,200 Calories per day. For women a little less. For people of different body types, a little more or less.
During the daytime, you are more active, and so more processes occur inside you, so more energy needs to be processed and then discarded, and so your skin temperature is slightly higher than when sleeping. While you are sleeping, everything slows down BUT DOES NOT STOP!
Consider that this whole sequence can be affected by any of the three stages. (1) You could eat more or less food; (2) you could do a lot more work or exercise to get your body processes to convert more food/fat into energy; or (3) you might alter the ability of your body to dispose of the excess heat. Your body has the capability of adjusting its activity due to differences in any or all of these three areas. Specifically, in a really hot environment, your body can shut down many systems to reduce the energy that needs to be generated, down to a low of around 20 Calories per hour (research data from Frederick C. Hatfield, of ISSA), in order to try to avoid overheating.
We are going to consider the situation for the eight hours each night that we sleep. In a relatively cool room environment, your sleeping BMR (Basal Metabolism Rate) only drops a little from the daytime 100 Calories per hour, down to around 80 Calories per hour. Your body has many processes that it still needs to do, like digestion, operation of the heart, lungs and other organs, thinking as during dreams, etc, which is why the 80 Calories per hour is very common.
But a lot of people today use many blankets to sleep under, or they use an electric heating blanket, or they use an electrically heated water bed, or they keep the room extremely warm. Some of these actions can cause the body to HAVE to reduce all its activities down to near that 20 Calories per hour, just to keep from overheating.
See the point? Instead of your heavily blanketed or hot bedroom body burning up 20 * 8 or 160 Calories while you sleep, if you instead get rid of that heavy blanket and/or cool the room down somewhat (to 66F or 68F, for example), it could be in far more normal operation and burning up 80 * 8 or 640 Calories each night. That difference, of 480 Calories (640 - 160) that you COULD allow your body to NATURALLY burn up, if done over seven days (a week) is around 3500 Calories! (480 * 7) One extra pound of bodyfat will therefore burn itself up (each week) WHILE YOU SLEEP! Is THAT a great diet or WHAT?!
Say we are considering a relatively sedentary person, one with a desk job, for example. The ASHRAE Handbook charts indicate that such a person emits around 390 to 450 Btu/hr of heat. ASHRAE is interested in that subject because it related to how much air conditioning equipment would be needed for a sports dome where 30,000 people may be inside! 1 Calorie is equal to 3.968 Btu, so this body heat loss is around 100 Calories per hour of heat lost from the body. This lost heat is exactly the same as the amount of energy the body uses up in basal metabolism. This confirms that an adult person constantly uses up around 100 Calories per hour. One essential purpose of this is in maintaining the core body temperature, which is centrally important to good health.
During sleep, the skin temperature drops a little, and respiration slows somewhat so that heat lost in exhaled breath is reduced, but there is still at least 80 Calories per hour needed (used up) even with the cooler skin temperature. (Note that this is described for a situation somewhat similar to that while working, moderate clothing [and/or covering] in a relatively cool (say 65F to 68F, 18C to 20C) room). This is then a total of around 640 Calories used up while he sleeps. We can confirm these things by adding 16 hours at 100 Calories per hour and 8 hours at 80 Calories per hour for a total of around 2240 Calories, which is in decent agreement with the normal daily dietary intake for an adult man.
As long as he eats 2240 Calories of food and his body uses up 2240 Calories of energy, each day, his weight will stay fairly constant.
Now consider if he sleeps with an electric blanket or lots of heavy covers or in an especially warm bedroom. His body no longer has to generate so much heat to maintain core body temperature. In fact, the body alters blood circulation and changes other things that it can to keep from overheating. Essentially, the body is capable of self-regulating in this way to producing as low as around 20 Calories per hour during sleep. (If it cannot self-regulate low enough, the person starts to overheat, and eventually pushes off a cover!)
(There seems to be research data from Frederick C. Hatfield, of ISSA, that supports this figure of a sleeping minimum of 20 Calories per hour.)
Since his body is now generating 20 Calories per hour of heat, in the eight hours of sleep, he uses up 160 Calories (of energy obtained from existing bodyfat reserves) during the eight hours of the night. By being really cozy in bed, he has eliminated 480 Calories of energy that would otherwise have been used up and radiated away as heat! If we do our addition again, we now have him still eating 2240 Calories of food but now using up just 16 * 100 + 8 * 20 or 1760 Calories of energy. What happens to that 480 Calories that he did not use up? You know the answer! It turns into body fat reserves, because the body chooses to store that energy for some possible future emergency. Well, storing 480 Calories worth of fat every day really can add up! It seems likely that he would gain about one extra pound of weight EVERY WEEK! This seems like an EXTREMELY likely partial source for the overwhelming problem that exists regarding obesity in modern life. (Yes, food choices and quantities, gluttony, are important, too!) Just one year of this pattern could add 50 pounds to the bodyfat of that person! Not even necessarily related to what he eats or how much he eats or how much he exercises! Just the way he sleeps! Isn't that interesting?
The GOOD part is that it is very easily solved and even reversed! By simply throwing off that heavy cover or that electric blanket, or turning down the heating thermostat for that bedroom at night, you can MAKE your body use up those extra 480 Calories every night (as it originally expected to do)! Every week or so, you should now LOSE another pound of bodyfat! Interesting, huh? You don't have to buy anything, or pay anyone, or eat food you hate (although you can still do those things if you wish!)
Even massive workouts at a health club now become interesting to think about! The related web-page linked below (regarding overall thermal efficiency of a human) describes that our "useful work" over an eight hour work shift in a harsh factory environment, is at around a rate of 0.1 horsepower. A serious workout at a gym is generally in this same range, although certain extremely strenuous activities, if done for only an hour, can be somewhat higher. We are going to say 0.15 hp for a one-hour period of a workout. But we note that 0.15 horsepower-hour is around 96 Calories. The human body tends to have a maximum efficiency of around 20%. This suggests that our person is actually using up around 480 Calories in that hour of strenuous workout. (96 Calories of that results in actual "work" like in raising weights or moving water while swimming; and the other 384 Calories is needed by the body to maintain all the internal processes that maintain survival. This increased internal production of heat is necessarily dumped by the body as heat. Some is by radiation by skin that is warmer than the surrounding room. Some is by convective heat loss from the skin to the room air which is cooler. Some is by convective heat loss by exhaled breath that is warmer than the inhaled breath had been. Some is by latent heat loss in water vapor carried away in the breath. Some is by latent heat loss due to sweating.)
See the point? A strenuous hour workout at the gym might use up a total of 480 Calories. In comparison or in conjunction, you could use up just about as much energy (and therefore bodyfat) EVERY night while sleeping, just by throwing off the heavy covers!
(Have you ever wondered why you don't seem to lose significant weight due to working out every day? An hour of strenuous workout might use up 480 Calories, so around a week of those strenuous workouts would be required (7 * 480 or around 3,360 Calories) to use up one pound of bodyfat. You would only measure a difference of 1/7 pound in any one day, too small for standard scales to register. Worse, all that exercise tends to make you hungry, right? So you may actually eat more and gain weight. But at least you will tone your muscles!)
This discussion has not addressed "shivering". That would certainly use up a few more Calories, but we think they would be minimal, not worth the discomfort, and possibly even a health hazard! The idea here is "just a warm enough room or a light cover to avoid shivering". Commonly, people keep a bedroom at 68F or 65F at night (20C to 18C). The room should NOT be made cooler than that, unless you happen to LIKE it at 63F or 62F! So the person would not be particularly uncomfortable, unless that super-warm coziness is considered critically important! There does not appear to be any advantage of making the room any cooler than that anyway, as the body just shuts down blood circulation to the limbs to avoid excessive losses and to maintain core body temp.
There is an ISSA Basal Metabolic Rate (BMR) formula:
First, for Men: 1 x body weight (kg) x 24
For Women: 0.9 x body weight (kg) x 24
For a 170 pound man (77 kg), that's 1 * 77 * 24 = 1848.
Next, factor in your approximate body fat percentage. Multiply the result from above by the multiplier factor:
Men 10 to 14%, Women 14 to 18%: 1.0
Men 14 to 20%, Women 18 to 28%: .95
Men 20 to 28%, Women 28 to 38%: .90
Men over 28%, Women over 38%: .85
In the 20-28% group, we would have 1848 * .90 = 1663 Calories per day. This is your BMR. It's your BASE rate.
(Interestingly, this factor demonstrates that bodyfat has an effect of thermally insulating the inner workings of the body. People with more bodyfat need to generate less internal heat in order to maintain necessary body temperature. Skinnier people have to produce more energy to maintain that temperature!)
Finally, factor in your daily activity level. Multiply your BMR by the daily activity level multiplier factor: This essentially converts the BMR up to the ACTUAL metabolic activity of your life!
(These factors give energy consumption rates that are somewhat higher than the ASHRAE official figures regarding heat losses, but they do not affect the general concept of this presentation.)
If our example person was in the light activity category, the actual daily Calories = 1663 * 1.55 = 2578 Calories per day. So, using the ISSA system, our 170-pound man would use up around 2578 Calories every day, and he would need to eat food with that much energy content to maintain constant body weight.
No one can monitor every Calorie they consume each day, but efforts at aiming at a general average can help control body weight. This presentation is simply pointing out that a rather massive effect, about 480 Calories each day, is also probably available.
This web-page is based on the energy analysis of another web-page, Thermal Efficiency of a Human Being.
( http://mb-soft.com/public/index.html )
C Johnson, Physicist, Physics Degree from Univ of Chicago