To give more detail, both your stamina and health have now changed.
Max Stamina - This now equals your food. If you are full, you'll have more maximum stamina and if you are hungry you'll have less. Performing energy-intensive actions like fighting, building, and running/cycling will make you hungry and therefore reduce your maximum stamina. It can be regained, of course, by eating. Your max-max-stamina (i.e. the limit to which your maximum stamina can be increased by eating) is based on your Agility score.
Current Stamina - This goes down when you perform an energy-intensive activity such as fighting, building, or running/cycling, and goes up by itself over time, but never to more than your max stamina. The rate at which it goes down or up is based on your thirst. The more thirsty you are, the more quickly activity will drain it and the more slowly it will recover. Drinking will instantly recover some stamina, and will also improve the normal recovery rate by making you less thirsty. If you do a "power attack" by right-clicking with a weapon rather than left-clicking, not only will this decrease your stamina by more than a normal attack would, it will also prevent stamina recovery for a short duration.
Max Health - Max health goes down each time you take damage, by a percentage of the damage taken. It doesn't normally go up by itself, but it can be recovered by using bandages and first aid kits. If you have a high enough rank in the "Healing Factor" perk, it will recover slowly by itself. Your max-max-health (i.e. the limit to which your max health can be increased with bandages and first aid kits) is based on your Fortitude score.
Current Health - Current health goes down each time you take damage, and doesn't normally recover unless you've bought the "Healing Factor" perk. Eating food, taking painkillers, or using first aid bandages or first aid kits will increase your current health, but never to more than your max health.
I should also note that the above is true for Alpha 17.4, but will change slightly for Alpha 18. In A18, max-max-stamina and max-max-health will no longer be tied to your Agility and Fortitude scores, but instead they'll both by directly dependent on character level.