Originally Posted by !!Comatoa$ted
Could it not be a combination for some people? Sure calories in, calories out is fine way to look at it, but what affects the rates of people metabolism? Hormones for one thing, look at thyroid disorders, in some you can eat lots of food and never put on weight, in others metabolism is slowed considerably. Some people will naturally have a faster metabolism, and then others will alter it chemically to increase the amount of calories out. The good thing about biking is that you alter you metabolism for long periods of time, probably a lot more than any other sport.
Foods can also affect levels of hormones that circulate through the body, so IMO what you can eat can affect if you put on because your metabolism is being altered by the food you eat by affecting hormones. Circadian rhythms fluctuate throughout the day, and this is in part to hormones. Of course if one is like most of us here you will probably bike a lot and can burn off the extra that you eat that may not be that good for you.
In your examples, the hormones are changing the calorie out side of the equation. The equation still holds.
Thyroid hormones speed up cellular metabolism by stimulating the mitochondria ( I believe). The stimulated mitochondri speed up the oxidation of glucose and fatty acids and release additional energy as heat. A person experiencing hypothyroidism will have a lower body temperature than will a euthyroidic or hyperthyroidic individual. This extra heat from the stimulated mitochondria has to come from somewhere, and it comes from increased caloric intake if the person is to maintain their weight. On the flip side, the hypothyroidic individual will gain weigt with less food intake. Again, the equation still holds.