I know that my weight loss stalled significantly and I went up a few pounds this winter, where I've stayed for a month or two. Ugh! Though I stayed gluten free and ate some chocolate and rice crackers (with dips) over the holidays, I think a huge part of it is not being able to do as much outside as I was last summer when I was dropping the weight.

Very much looking forward to warmer temps when I can get out more for casual low level activity.

Humans do not put on fat for the winter. Human fat is generally a poor insulator thanks to the way our bodies work, and our adaptation to winter climates is clothing and eating animals, not blubber layers and hibernation. The idea of some sort of programmed fat accumulation during the winter is a tempting speculation, but there is no physiological or evolutionary evidence to suggest that it is true in humans. Keep in mind that the majority of human evolution took place in Africa and "winter" there isn't the same as it is in the northern US.

There are a massive variety of reasons for why you might gain weight if you live in a cold climate, but I really doubt metabolic programming is one of them.

edit: lol, downvotes.

Since there's not enough room to address stuff in the comments:

@Eva: "Could be" is not "is". Science: propose hypothesis, test predictions, attempt to falsify. Hypothesis;Prediction: humans are seasonally fattening animals; we gain weight to prepare for winter. I don't gain weight in the winter - my weight is stable year round unless I consciously intervene. Uh oh. Either I'm not human or the hypothesis is wrong. (Note: I'm of Dutch and Irish descent, so I've got plenty of local winter evolution in my blood, and I live in NJ, having just received a foot plus of snow)

We clearly are not hibernators, and our evolutionary experience in cold climates took place in the context of clothing and fire. Seasonal fat gain in many animals could easily be an artifact of seasonal food availability rather than metabolic command, and such a thing could easily explain human fat gain in the winter; we have a string of food oriented holidays just when we stop doing anything physical.

Oh, and one more nail: if you're going to gain weight to prepare for the winter, you do it in the summer and early fall like every other animal. Not in November and December, well past the point of seasonal food abundance.

@fat insulation: Human fat is generally a poor insulator. This is a physiologically true statement. Your skin is full of blood vessels and your fat is not; toss a fat guy out in the arctic naked and he'll die slightly slower than a skinny guy and get frostbite at the same rate, whereas the seal watching in confusion will be perfectly fine. Our fat plays a role in regulating temperature but it is not its primary purpose, and it certainly doesn't have broad survival and evolutionary implications for a species that invented clothing and fire before moving into cold climates.

Random anecdotes about fat people and their clothing doesn't change the physiology of fat, and indeed easily suggest alternative explanations. When I weighed 160lbs, I was cold all the time. When I weighed 160lbs and started eating more food, I was warm all the time. Being fat is associated with eating more food; maybe fat people gaining weight are more dietary-thermogenic than skinny people losing weight. Just one possibility that isn't "fat people are better insulated".

Further edit: I should note that I do not mean to claim that fat has ZERO thermal effect; it clearly does and we clearly make use of it for that purpose. I dispute that this effect is particularly useful in adapting to a cold winter climate when compared to the effect of clothing and artificial heat, and I dispute that humans have some programmed desire to add fat to be warmer when it gets cold.

@inuit: A perfect test! If cold should cause humans to adapt by adding fat in the winter, we should definitely see this phenomenon in the Inuit, who suffer the worst winters out of any human population. Except there's no evidence this is true, and some evidence1 that it is false:

There is some increase of skinfold thickness in the winter months, but this is not associated with any marked weight gain or loss of muscle strength. Possibly, the hydration of subcutaneous tissue is increased by frequent exposure to intense cold.

If humans are a seasonally fattening species with metabolic urges to gain weight in the fall, how could it possibly be that the human population suffering the worst winters out of everyone has no fat gain adaptation?

Downvote away!

Could it be lack of sunlight, could it be a response to the shorter days?

Honestly, I have a hard time thinking we are not programmed to eat and retain more calories in the wintertime.

I live in a warm climate year-round, yet the lack of sunlight in the winter months leaves me groggy and hungry more often than when the days get longer and brighter. Maybe it's a response to lower vitamin D, maybe it's just a evolutionary trigger to store up for winter, or maybe (considering you were heavy at one time) eating is your method to cope with seasonal affective disorder and you are inadvertantly eating more than you normally would. I attribute a little "all of the above" to my own personal weight gain in the winter months. I've shot up 15lbs this winter and expect it to be gone by late February.

Either way, easy off, easy on. Don't sweat it too much. Once spring/summer is back, provided you've fixed your dietary indiscretions, 8-10lbs of weight will make it's way off your body.

I noticed that i put on a little bit of weight, in the winter, when i got more hairier. My winter 'coat' was lost during spring and summer along with a few kgs.

pfw, tell me if this changes your mind: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2917125/

The theory being that, through evolution, humans lost the ability to synthesize vitamin C as a way of enhancing the fat-storing properties of fructose. As winter nears, the fructose content of fruits increase and the vitamin C content decreases. If this theory is correct, it would suggest that people without the ability to synthesize vitamin C (and gain fat by eating fruit) were selected for because they were more likely to survive winters than those who could not synthesize vitamin C (and did not gain fat by eating fruit).

I have not ever seen my weight change due to the seasons. My weight changes based on what I'm eating and how I am moving my body. I can always correlate the gains and losses back to one of these two things.

Me: I've lost close on 100 lbs since 12/2008, about 45 lbs since going paleo in March 2010. I live in Minnesota, so if there is a place for functional body fat, this is it. I've continued to lose fat mass all winter and I'm contining to shoot for a few pounds more. Grok kills the mamoth, eats the meat, then wears the skin...he doesn't need fat mass to insulate his body.