There are a few questions somewhat related to this, but none dead on. Cold therapy has been shown to be helpful for fatloss. I am wondering if you guys think this is a paleo thing or a weird hack. When I think paleo I think African planes. How often did it get cold? Doesn't it stay pretty hot there? Is it cold at night? Are the rivers cold? What possible evolutionary reason could there be for this effect? I would think cold => need insulation => fat gain. But I guess not.
I'm pretty sure the reason for extra energy expenditure (leading to fat loss) in the presence of cold is that the body maintains its temperature by making its mitochondria "leaky" using the protein thermogenin in brown adipose tissue (BAT). Basically this decreases the efficiency of turning stored energy into energy that can be used by the body (ATP) - making more heat per calorie used. Babies are born with almost 25% BAT because there are a lot more factors that make them more susceptible to cold than adults. Most BAT in adults is located on the shoulders and the back of the neck, that's why cold showers that focus on those areas are most effective.
So in the short term, exposure to cold increases the body's mobilization of fat stores to create heat leading to weight loss. This is a very resilient strategy to immediate changes. This actually is more suggestive of a warm evolutionary milleiu as opposed to a creature like a whale or seal that has evolved to live in cold and has fat as insulation.
Sand/Desert has nothing to keep it warm at night.
When the sun goes down the temperature drops and drops fast. So while it may not get as cold as other places in the world. The temperature difference is by every definition extreme between day and night.
Although I can not really go into any more detail or specifics on your question.
UCP1 and UCP3 were present in paleolithic man's biochemistry therefore I see no reason why not to consider them part of the lifestyle. Now, do I think paleo man used the methods for your intended purposes? No I don't.
There is zero question that our biochemistry supports it.....and I think part of our current spontaneous evolution is how we think. How we think can effect our DNA and since we now know of distinct biochemical pathways to hack this system I see no reason for you not to pursue this.
Can't help but think cold showers would have a limited effect on overall fat loss if it only works on the brown fat in the chest and neck. Besides, I don't know about you, but after having an invigorating cold shower I feel a bit hungry!