Part of metabolism is simply to keep body temperature up. As it gets warmer, not as much energy is required to maintain body temp. Less output, less need for input. Oh my gosh! Did I just spout calories out = calories in? Oops!! (well, it is true but doesn't explain fatness - for that we have Taubes).

I think that on some level people have a subconscious knowledge of how much food they have access to. During the colder months, you would theoretically have less access to meat and certainly fruits and vegetables, so your body goes into a mode where it's "stocking up" on food.

I notice a similar effect when I'm low on money vs when I have a lot of money. The more money I have...the less hunger triggers I have.

I think it's a matter of your brain responding to scarcity and abundance differently.

That's my theory.

Hot weather stimulate NPY and increase appetite in most mammals to eat plentiful carbs in long light days.....it also stimulates reproduction. So I think you got it backwards. But it could also be that this is a symptom of a hormonal problem.

Wait, what? 75 degrees is hot weather? And it suppresses the appetite? Which would explain why the southern US has the highest rates of obesity? And why do people in the tropics have no problem eating? And how do we explain the phenomena of people eating delicious bbq in Texas in the middle of summer time?

Having lived in Texas for a decade, spent a fair bit of time in the Caribbean, and a good two plus decades in Southern California, I can say with some certainty that 75 degrees is not hot weather, and that it is has no effect on appetite for most people. Oh yeah, I lived in Minnesota too. 75 isn't even that warm for them in the summer time (but they start eating ice cream some where around 45 degrees).

I'm not saying you don't experience this phenomena on a real, physiological level, but it is probably some sort of gene x environment interaction specific to some genotypes. I mean we wouldn't have Thai cuisine if it weren't for someone getting a hankering to make delicious coconut curry when it is 98 degrees with 98% humidity. It is also worth noting that India is ridiculously hot and humid and, at least for those who can afford to eat, they have an obesity problem too.

Seriously though, there's few things better than Texas barbecue in the summer outside in the sweltering heat. With a cold beer. Yeah, that isn't paleo, but whatever.

It's all about the thermic effect of food. When I break fasts with feasts (think Churrasco and 2-3lbs of meat in one meal), I'll sweat even when it's cold out. It's because my body temperature is elevated due to the digestive process.

I eat less in the summer, maybe because deep down in my psyche, I don't want to be sweathoggin' at work.

I worked for two summers on the coast of NC as a sea kayaking guide. It gets over 100F there and we're paddling in hot sun all day. Two other guides (who happen to be male) that I work with have very little appetite out there. They typically only eat one meal per day, dinner, around 6 or 7pm. We paddle 15+ miles a day and then hike through deep sand across islands, and they seem to not get hungry. This amazes me, I eat 3 times a day plus snacks and drink about a gallon of water a day out there. I will say there are certain foods I definitely don't want to eat in the heat but I do get hungry. On a side note, I just came back from the middle east, so I went from 100degree weather to 60 degree weather in two days. For some reason (and it could very well be boredom) I find myself wanting to eat more often since I've been back and can't seem to satiate my cravings. I've been craving junk food much more since I've been back as well.

Doesn't happen to me, but happens to a lot of people. I definitely want COLD food and drinks when it's hot and I'm sweaty, but I still have a big appetite!