What about sex?
More interesting is what sex and orgasms do for your emotional well-being which is dependant upon your brain chemistry, if the sex is a positive experience (e.g. not forced) there is release of endorphins which affects cortisol levels. Simplified I believe this is how all exercise reduce stress. Cortisol levels will fluctuate throughout the day but chronically high levels are common for individuals too stressed out, that would be a real "starvation mode". The ways in which cortisol affects metabolic, but not limited to, processes in our bodies are intricate and many, it is very important to understand cortisol in regards to weight loss, overall health and emotional well-being.