A process is discovered that lets human sexual fluids/breast milk serve as a cost effective energy source.
Men and women can 'volunteer' to be used as power sources for a day, or longer, where they are taken to a facility, strapped into a 'milking' machine, and then pumped full of drugs to promote the production of milk/semen and given a tube that feeds them a nutrient slurry that encourages production.
For a solid eight hours, or more, the person is basically sucked off/milked with some 'added stimulation' applied through an anal vibrator for men and women.
It's a highly addictive/pleasurable process and the nutrient slurry/drugs will promote testicle and penile growth in men and breast tissue growth and lactation in both.
The latter may be seen as a downside for some men along with the fact that the drugs also seem to feminize them a great deal, along with causing extensive weight gain from the slurry, along with heightened arousal.
Those who do it once every other week will hardly notice any physical changes other than small increases to their primary sexual organs but even visits once a week will result in weight gain, slight feminization, and more pronounced breasts, testes, and penises, along with an increased sex drive.
As can be imagined, those who regularly 'work' at such places on 9-5, mon-fri schedules inevitably end up as highly feminine, hugely overweight, barely mobile people with massive, milky chests and (for the men) hugely bloated testicles and dicks, that can barely be hidden by the long skirts they have to wear, which often do nothing thanks to the frequent erections they get.
As can be expected, the world gets a lot more sexual and filled with chubby, fat, or obese women/femmen that are almost always looking for release while enjoying cheaper electric/gas bills.
It's also possible for one to work there 24/7 but they quickly become immobile blobs of tits and balls that are too lust dazed to know what's going on