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Thermal Dieting

In an ABC news story (, the concept of thermal dieting is discussed. Though it was probably hooked by a PR agent paid to help Tim Ferriss sell his book, it's an interesting proposal on a couple of levels. The physics of it make sense: If you expose your body to cold, it will burn more calories to stay warm. Ferriss points out that brown fat can burn calories to make heat. One problem is that adult humans have very little brown fat, though it's possible that routine exposure to cold could induce the brown fat cells to divide, thus making more brown fat. So the physics part of this make sense. Even drinking ice water will consume a few calories -- about 4 kcal (4 dietary Calories) per liter -- because when you urinate out the water, you lose the energy your body used to heat it from freezing to body temperature. It's not a good thing to do in mass quantities, though, because water intoxication is a serious problem.

Lets get back to the root cause of the problem for which this thermal-dieting alternative is presented as solution: Too much food. Are people so addicted to consuming food that it's worth sitting in a bathtub full of ice or forcing ourselves to walk in shorts and a t-shirt in freezing weather? I think going for a walk in the cold is an interesting exercise on several levels, and something that might be worth doing just to exercise mental fortitude, but doing it just to eat another bite or two doesn't make sense to me.

Isn't it a lot easier (and pleasant) to just not eat the calories in the first place? Finding a way to successfully and comfortably lower calorie intake means you exercise for the fun and health of it -- not to burn off calories. If you want a brisk walk, I'll walk with you for the fun of it, but not just so I can eat more. If I didn't know about Fast-5, I might consider an ice bath or a shivering walk. I might be that desperate, as I know many people are, but I'm glad there's the Fast-5 alternative.


This is yet another example of just how ridiculous the issue of weight loss has become in this country. Like all the other gimmicky approaches, this one is supported by "science" which is supposed to lend some credibility to it. I've done it all, tried it all, lost weight on them all. This method of intermittent fasting makes such good sense and feels so good to my body (much nicer to wait until 5pm to eat what I'd like than to sit in a tub of ice water with a book!) I hope I've found something I can do for the rest of my life and I think I have, only time will tell. I read Dr. Walford's information about caloric restriction years ago and even tried for a while to eat super low calorie but it was horrible both physically and mentally. For me, Fast-5 is easy, satisfying and so far effective. I've long been a believer that there are a lot of ways to do things right, so for me this may be right and for another ice baths, lol. Lucky me.

I agree, not eating the calories in the first place is always a good idea! But for those who are trying to drop weight in a healthy way- using the idea of ice packs in the places he mentioned as an adjunct - shouldn't be an issue. I've been doing it and it seems to work- plus I haven't found it uncomfortable , as compared to say an ice bath!

There's a piece of the puzzle that is missing here, which is that leptin and ghrelin, the hormones that control feelings of hunger and satiety, are affected by hot and cold. Your appetite diminishes on a very hot day, for example. So if you want to manipulate your environment to burn more calories, the effects might be counterintuitive. It might work better to turn up the heat and wear extra sweaters.

I enjoyed the challenge of driving in to the gym on winter mornings wearing just my workout clothes - t-shirt and shorts, sometimes just the sports bra on top. Even when the car and outside temp is 10 degrees, 20 minutes to get there is not a big deal and you appreciate the heat so much more once you step inside.

Just one little "hardship" that could help with health, or just help with life appreciation. :-)

I seriously doubt that drinking ice water, or for that matter sitting naked on a block of ice (how's that for a visual) can significantly increase your BMR.

The heat that warms the water comes from burning calories yes BUT, we generate heat when we metabolize food. In general we do not burn food to generate heat, the heat is a by-product of burning food for energy.

If we could burn food to generate heat on demand no one would ever freeze to death, they would starve first.
If we could burn food to generate heat the most effective weight loss method would be to turn your heat off in the winter and crank up the AC in the summer.
Every diet catalog would offer refrigerated chairs.
Fat Farms would lock people up in refrigerators instead of steam machines.
Keeping your windows open and going naked all winter would be socially acceptable.

Heat is a waste product of metabolism. In general your body has to get rid of excess heat and it has a variety of methods of doing this, perspiration, respiration, radiation, convection. When you drink something cold that just means that there is less heat that your body has to get rid of through these processes. When you fall below the equilibrium point and you continue to subject yourself to more cold your core temp starts to fall. If an effort to try to increase activity (and thereby metabolism) you start to shiver. So long as you keep shivering you will use a few more Kcals. I don't know how hard you need to shiver or for how long to burn up 1 Kcal. Anyone know of a study? My guess is that almost any form of exercise, even slow walking will use more Kcals than shivering. I know if I'm cold doing 10 pushups will warm me up, while sitting and shivering will not.
Continue to subject yourself to cold beyond your bodies ability to cope with it and your metabolic process will begin to slow down and shut down. Death follows in the extreme.

The whole, gradually increasing your level of brown fat, thereby increasing your BMR might have some merit, but lets see some data? Increasing your muscle mass is easily done, easily verified and does increase your BMR also.

Just the same, lets do some math. If you drank a liter of ice cold water your body will need the heat energy from
1000g * (98.6F-32F * 5/9 C/F) = 37,000 calories or 37 Calories (ie the units that food is measured with). Interesting, but I believe that the vast majority that energy will come from the heat that is produced by the 2000+ Calories that my body already burns each day. It just means that I'll perspire a bit less, or radiate, convect or exhale a bit less heat than I would without the ice water. Just think about breathing for a monent. Every few seconds you inhale 0.5 a liter of air at room temp and exhale 0.5 a liter of air at body temp. All day. There is thermal transport going on shedding excess heat.

Have you ever noticed that when you get cold your hands and feet get cold first. Your body is letting your extremities get colder than 98.6 while maintaining your core. Cold hands and feet will not of themselves burn more Calories. If you put on more clothing it reduces the level of heat radiating from your body and your feet and hands warm up again. Notice that your body did not seem to go into overdrive, producing more heat, so that your hands and feet could get back to normal temp without you doing something. To get warm you had to, turn up the thermostat, put on more clothing, or of free will increase your level of activity so that you generate more heat. It didn't magically happen all by itself.