Quote
_Magus_
If you aren't positive, then don't say it's wrong. I am positive, however. Fat is a more complex source of energy, while muscle is readily available.

I knew my intuition wasn't wrong: [www.mhhe.com]

"...starvation takes about the same course and consists of three phases...In the second stage, which can last for several weeks, fats are the primary energy source...The third stage of starvation begins when the fat reserves are depleted and there is a switch to proteins as the major energy source. Muscles, the largest source of protein in the body, are rapidly depleted."

Also this: [www.library.csi.cuny.edu]

"Finally, the individual enters the prolonged starvation phase. Prolonged starvation is characterized by even less dependence upon gluconeogenesis, the energy needs of every tissue containing mitochondria being met to an even greater extent by either fatty acid or ketone body oxidation. As long as ketone body concentrations are high, proteolysis is restricted, and conservation of muscle proteins occurs. This continues until all the fat is gone, after which the body resorts solely to using muscle protein until death."

And this: [en.allexperts.com]

Guy asks "when people starve, at least initially, they loose MUSCLE, not fat." To which the expert responds: "The idea that people will lose lean muscle, initally, when on a 'starvation' diet cannot be considered accurate."

And finally: [strengthtraining.suite101.com]

"During cardiovascular exercise, the body will use glucose (carbohydrates) as the main energy source. The body will use fat as a secondary energy source. The body rarely, if ever, breaks down protein and uses it as an energy source.

The breaking down of body tissues is known as a catabolic process. For instance, if fat is to be used as an energy source, a fat cell is broken down into a fatty acid and glycerol. The glycerol can then be used for energy. Proteins, within the muscle, have to be broken down into peptide chains, then into amino acids and finally into glucose for energy."

That not only speaks against the idea that muscle is consumed before fat, it also describes the process by which each is consumed. Metabolizing protein sure sounds like a more involved process. We can also take a look at their chemical structures. I'm not a biochemist, but just looking at the pictures, the structure of a triglyceride looks a heck of a lot simpler than any of the protein models.

Fat: [en.wikipedia.org]
Proteins: [en.wikipedia.org]