First, some soothing music...
I've been getting into arguments on the Internet again! People assume that I believe certain things and "put words in my mouth". As we all know, assume makes an ass out of u and me. I am therefore "laying my cards on the table", so that you have no excuse for being ignorant.
I believe that human beings are extremely complicated creatures both physiologically and psychologically. Our weights are influenced by a humongous number of factors, some of which I have listed below.
Calories count (but don't bother counting them)! If we eat more than we burn, we store the excess in fat mass, muscle glycogen & liver glycogen. If we eat less than we burn, we draw the deficit from fat mass & liver glycogen (and sometimes muscle mass). Insulin is involved in the storage of stuff, as is acylation stimulating protein (ASP).
Moving too little makes our skeletal muscle insulin resistant, as inactive muscles have virtually zero requirement for glucose and fatty acids, so they down-regulate the uptake of them. See also The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women.
Eating too much & moving too little has nothing to do with gluttony & sloth.
Our weights are regulated by our brains, which are influenced by a large number of hormones & chemicals, including insulin. There is no "set point" weight.
In the winter, when it's cold and dark, we eat more, sleep more and move less so we gain body fat. Subcutaneous fat acts as heat insulation, so having more of it in the winter makes sense.
Our weights can be affected by water balance, which is controlled by our kidneys.
How much of a particular food we eat is influenced by reward. Some foods are rather moreish, as we say in the UK, due to excessive reward. Deliciousness and moreishness are not the same thing. Reward theory and set-point theory are not the same thing.
Rapidly-falling blood glucose level in the normal range can stimulate appetite. I have had personal experience of this on three occasions where my blood glucose level was being monitored. As eating a load of high-glycaemic carbohydrates can result in rapidly-falling blood glucose later-on, this is a good reason to not overeat refined carbohydrates.
The exercise paradox. Exercise decreases appetite*. So, why do some people eat more when they exercise more? See Normal Weight Men and Women Overestimate Energy Expenditure – Research Review and Discrepancy between self-reported and actual caloric intake and exercise in obese subjects.
*If exercise increases your appetite, there may be a reason for this. See Move More: Solutions to problems.
The diet paradox. People think that eating a healthy food with an unhealthy food reduces the calories, discussed in detail in The Dieter’s Paradox – Research Review.
Manipulating the masses is easier than you think.
The Coolidge Effect applies to food as well as sex. Eating the same food at every meal gradually reduces reward to zero, no matter how moreish it may be, initially. This is how the Potato diet works.
I often leave concise comments on blogs. Just because I may not mention "X", "Y" or "Z" doesn't mean that I consider "X", "Y" or "Z" to be irrelevant. I may also go on a bit. I'm a nerd!
If I disagree with your point of view, I'll try to tease more information out of you (or I may tease you just for fun). The more I disagree with your point of view, the more I'll tease. If I utterly abhor something you stand for, I'll tease you mercilessly!