These are the things I can think of, are there any more?
Lipids, fatty acids, and fats are essential parts of cellular structure. One cannot build out of protein alone.
Sort of obvious, but…
stored in fat cells to ‘burn’ as energy later when needed?
Some types of fats (sterols) are precursors of hormones and bilirubin.
Maybe you were getting at this when you mentioned “conserv(ing) proteins”, but, and of course, fat is a great way to store calories. Likewise, depots of fat are a good way to release calories when they’re needed.
A lot of attention nowadays is being given to fat tissue as a secretor of hormones. Many of these have to do with apetite and energy homeostasis, but they also have other, unanticipated, effects. Here is an abstract of a recent review of the subject.
Men and women have different fat deposition patterns. At puberty, girls start putting adipose tissue on the thighs, hips, and breasts…and in a thin layer covering most of the body, which is one of the things that makes female skin softer.
Men, on the other hand, have a tendency to put fat on in the stomach and internally.
So, one of the roles of fat is to create sexual dimorphism…woo woo!
While it is true that different patterns of fat deposition contribute to both the male and female pheotype, it’s a bit misleading to omit the role of sex hormones in that regard. In fact, give a woman enough testosterone (or similar hormone) and she’ll soon have a pattern of fat distribution that is distinctly “male like”. Likewise, give a man enough estrogen and he’ll develop breasts, widened hips and thighs, etc. In other words, the hormones are the conductors and the fat tissue ‘merely’ second violin.
The effect of hormones on fat is not limited to estrogen and testosterone. Give a person enough cortisol (or similar) and fat deposits will start to expand in the upper back, above the clavicles, and in the abdomen. This is called Cushing’s Syndrome.
Speaking of fat tissue and hormones, I forgot to mention in my earlier post that fat tissue is able to convert androgens to estrogen. So, women with lots of fat have relatively lots of estrogen. This is why obese women are protected against osteoporosis. There are lots of downsides, though, including a tendency to develop cancers that are stimulated by estrogen (eg. uterus, breast).
Fat people are also more likely to develope Altzhiemer’s (sp?) in old age, and women are more likely to get it because they naturally have a higher body fat percentage.
