The FastDay Forum

@BruceE the fallacy in your reasoning is that the body needs to burn an extra 200kcal worth of food to restore temperature. But don't forget your body throws away 2000kcal of heat every day, through processes like evaporation of sweat, dilation of blood vessels near the surface of the skin, etc.. So, to be efficient, your body doesn't need to burn 200kcal extra food, it just needs to reduce its heat loss by 200kcal worth. So sorry, no ice cream for you

[carorees]

Cold exposure stimulates brown adipose tissue (BAT). BAT generates heat to keep us warm by burning fat. So, yes, cold exposure can increase weightloss. Whether by enough to be useful, I don't know. Probably our desire for comfort food increases at the same time and negates the effect!

non-shivering thermoregulation. i love that term!

Ma3xiu1: Where does the 2000 KCal of waste heat come from? My BMR is only 1400KCal and that includes heat losses as well as breathing/pumping/thinking etc?

I can't go for this working at all. After all, fat is one thing our body uses to keep us warm. Just think of all those sea mammals - there is a reason why they are full of blubber - it's built in thermal insulation. I have a feeling that our bodies wouldn't want to let go of the fat if we lived in a cold environment, so there might well be some compensatory hormonal effect that then means you end up eating more. So unless you are very carefully counting the calories on every day and not just your fast days, you would end up making up for the minor extra loss on fast days by eating more on normal days.

Fat definitely keeps the body warm. I am far more likely to put on an extra layer this winter than I ever did before. My hubby has lost more than 3.5 stone on 5:2 this year. His casual wear has always been short sleeved T-shirts all year round. This autumn he has bought himself some jumpers and sweaters! I have never seen him in a jumper before!

@CreakyPete i just used 2000kcal as a typical average figure for the body's daily energy requirement when it is resting, but as you point out, the precise figure will vary from individual to individual. I would say of the energy spent on activities such as thinking and pumping blood around your body will end up as waste heat energy, although I suppose some may be converted to other forms of energy such as chemical energy and lost through the urine. Breathing in an interesting case, because the energy spent on that activity is doing work pushing on the surrounding atmosphere, but even that energy will end up beng converted to heat outside the body.

@carorees raises an interesting point about brown adipose tissue, so it seems the body may indeed burn some additional calories when subjected to cold. Whether this accounts for all of @BruceE's 200 kcal or only a part of it, I'm not sure, but my point was that you can't assume the body must necessarily burn an additional 200 kcal on top of its normal TDEE to compensate for that 3 degree temperature difference.

So @BruceE, maybe you can have half an icecream after all

I thought adults didn't have much brown fat? Babies are born with it,but only about 5% of body weight. I think the % in adults is less?

It's the white fat we want to get rid of anyway...

[carorees]

I thought adults didn't have much brown fat? Babies are born with it,but only about 5% of body weight. I think the % in adults is less?

It's the white fat we want to get rid of anyway...

See this thread: the-5-2-lab-f10/topic390.html
Some links to research on brown adipose tissue. Contrary to what was thought some years ago, it turns out that adults do have BAT and that lean adults have more than fat adults, so encouraging BAT is a good idea! Bring on the cold!

I understood from the OMG book that people who live in cold countries have more BAT. Too much of a whimp to find out.

Food for thought:

http://www.youtube.com/watch?v=UrQ_ldCwKUQ

This is kind of the opposite of this topic's focus; but it is where my mind went last night regarding temperature changes and weight loss. Does heat cause more weight loss than cold? I think it does at least temporarily...wrestlers and jockeys are known for sweating off weight quickly wearing plastic pants, sitting in saunas or sweat boxes. There are tons of products along those lines shorts, suits, waist trimming belts that you can wear to sweat off weight. I have always thought those things were mostly scams or gimmicks.

But, what about saunas and hot tubs? I take detox baths in the winter and I can tell a marked difference in my weight the morning after a long, hot epsom bath. It isn't just a lower weight but also a flatter belly the next day. Calories are a measurement of heat, right? I usually do detox baths only 2 or 3 times a week. I realize there are some issues with long exposure to heat for people with blood pressure, diabetes, etc. Also, some of the weight loss is obviuosly just water. But, I purposely drink tons of water before and after a detox bath because they really are dehydrating and if I don't get enough down; I get extreme dry mouth in the middle of the night.

Also, add into the mix that I have some issues with inflammation...so who knows whether the effect on me personally might be different than on others who don't have any medical issues.

Food for thought:

http://www.youtube.com/watch?v=UrQ_ldCwKUQ

I thought it was a bit of an odd topic for a TedMed talk and a bit biased towards thermal load, yet he only referred to the fact that he switched to a plant based diet too. I'm pretty sure that had quite alot to do with his weight loss!