Following this guide will result in Max metabolism between 200-500 raids. It will likely be the first skill that you max out.
As mentioned earlier, always consume Provisions in raid.
Constantly apply energy or hydration-draining painkillers throughout a raid, then consume provisions before extracting.
Ibuprofen painkillers and Golden Star balm are ideal for this because they have many uses. Additionally, if you have Medstation level 3 unlocked in the Hideout, you can craft these painkillers into Propital and sell the Propital on the Flea Market, effectively making this process free.
This has the added side effect of allowing you to run if something shoots out your legs, increasing your survivability.
When you cannot loot provisions due to lack of space, consume them for the skill points. Remember to consume the food first because most food drains hydration points.
Eat a hydration-draining food like Can of condensed milk, then drink a water bottle at the start of each raid.
This is only recommended for short raids. For longer raids, it is likely a waste of money if you employ the above methods.