These 2 papers should give you an idea of how our body's can burn more calories or not depending on the temperature and need to keep warm.
Does Brown Fat Protect Against Diseases of Aging?
Beige can be slimming
The is a paper I've linked to in another thread showing that EXERCISE (even though moderate during the day) was sufficient to enable an Australian sand rat (wild type not a lab rat acclimatised to living in a lab) to better maintain temperature when challenged with a drop in temperature. The rats that didn't get to run about on a wheel where less able to cope with a drop in temperature by getting brown fat to burn more calories.
It's possible that our lack of exercise (even lack of moderate exercise) may mean we don't respond to a drop in temperature at night. or possibly because some people have heating in their bedrooms and leave the central heating on at night there is no change in temperature so no need to raise thermogenesis?
I live in an old house with draghty windows (not double glazed) and a few weeks ago we had ice INSIDE the windows it was so cold. But no heating in bedroom, Just a duvet. But my brown fat must be OK because I'm as warm as toast even in those bitterly cold nights/days. I think that is where some of my excess calories are going.
You can improve mitochondrial function by exercise, intermittent fasting and a ketogenic diet. I use all three strategies though my exercise is basically going outside for an hour and pottering round the garden or a short walk. (It's not a calorie burning type workout. I couldn't manage that)
I think if you had a long time at a steady state temperature your body would adapt to that temperature. I think its the change in temperature that stimulates the need or for or initiates thermogenesis.
PS I'm also a user of MCT oil (MEDIUM Chain Triglyceride) I have both MCT oil and coconut oil daily. (coconut oil is a good source of MCT)
Effects of margarine containing medium-chain triacylglycerols on body fat reduction in humans. this shows how they work at improving calorie burning after meals. Don't go looking for MCT rich margarine. Skip the rapeseed oil and soybean oil margarine as they are not going to help you lose weight. But adding coconut oil and/or MCT may help stimulate thermogenisis.