Advances in biotechnology and nanotechnology have allowed Transhumans to greatly decrease their resource consumption, and extend the amount of time they can survive without needing to consume normal foods. The Personal Power Plant (p. 153 Gatecrashing) utilizes exotic and rare isotopes combined with nanomachines to generate bodily energy for decades. The implant for Long Term Life Support (p. 189 Rimward) puts maker nanites directly in the body to recycle food and air, if the morph can stay supplied with chemical supplements and raw materials. Efficient Digestion (p. 197 Transhuman) optimizes the body to use less calories, at the expense of its natural aptitudes, while Digestive Symbiote (p. 198 Transhuman) nanobots allow the body to consume almost any organic material. Nano-ecologists have been able to produce their own tech which advances the Transhuman body's ability to survive on minimal supplies, though its environmental constraints limit its use.
Photosynthetic Skin: Developed by nano-ecologists, this nanoware implant places active nanite groupings in the skin of the morph, which absorb the energy used by sunlight, and use water and the body's natural waste CO2 to produce limited amounts of chemical energy. While it would be possible to use genehacking to simply build morphs with cells designed for photosynthesis, the implant is able to accomplish this with an efficiency without heavily altering existing structures, making it more cost-effective. This allows a morph with this implant to survive without eating up to a month using just sunlight and water, though as with the personal power plant, certain vitamins and other supplements may be needed for cell replenishment or to avoid unpleasant deficiencies with extended use. However, this comes at certain "cost", which is that in order to function, the morph must expose a majority of its bare skin to the sunlight for approx 8 hours a day, more or less depending on local light conditions - though certain artificial lights also meet this requirement. [Low]
Due to the sunlight and skin requirements, the Photosynthesis upgrade has very limited applications. As Mars gets more terraformed, it becomes possible for those in the Outback to utilize this to reduce food consumption, and certain Gatecrashers have been interested for use on exoplanets, as this can avoid problems with consuming "local" flora or fauna for extended periods. Where the implant is getting the most traction, however is with Reclaimers. Damage to the Earth's biosphere means natural food is fairly limited and will take much time to replenish, but with basic toxin filtration to remove worry about contaminants, there is still a great deal of water left on the planet which could allow a bimorph to survive extended periods on the surface. Supposedly, this application is "purely hypothetical" at this state.