It takes a lot longer to die from starvation or exposure, or even dehydration, but it can still happen.
Starvation
Ignore this unless there is some situation where food is not available for a long, long time. These rules are not intended to force lunch breaks.
The starvation Grace Period is calculated as Dice+EN+WP. That is how long, in hours, the character can normally go without food without incurring a penalty. This is called the meal penalty, as an inside joke among the playtesters. This is a nuisance that can be hand-waved away unless a day or more has passed.
The real problem is that this penalty reduces the character's regular exhaustion Grace Period by an equal amount. So if a character has a normal Grace Period of 10, but has incurred a -3 meal penalty, their Grace Period is now 7. And that's a problem if you just stole food from the baker and have to flee from his giant, mutant dogs - or whatever.
If a character goes the starvation Grace Period in days without food, that character will suffer a dice of physical damage - even if he did nothing that would incur other exhaustion. This damage cannot be re-assigned to a Stat.
Dehydration
Dehydration works the same as starvation except that the character takes a penalty in minutes and damage in hours. Equally true: hand-wave this if they have access to water. You do not have to role-play hydration breaks.
Exposure
Ideal operating temperature for human beings is 70o F (Yes, we're Americans who use Fahrenheit, and use spell-check to spell it. Move past this.). This became room temperature for a reason. Humans are actually unimpaired for 20o either direction. Annoyed, maybe, but not impaired.
High temperatures for the most part affect Dehydration. For every 10o above 90oF subtract one from the Dehydration Grace Period.
For every 10o above 130oF characters take 1 dice/hour of physical damage from exposure. At around 170oF they are taking actual energy damage from burning.
For every 20o below 50oF, characters lose one point from their Starvation Grace Period, and take one dice/hour of physical damage from exposure. Note that for the starvation penalty to occur, they must be exposed throughout the entire Grace Period.
Exposure to cold can be mitigated by clothing, of course. You can assume each layer of clothing protects for 10o, unless there is reason to assume more.
All of the above assumes exposure to normal atmosphere. If the character is plunged into hot or cold liquid, hours become minutes in determining damage, and clothing is of little help unless specifically water-proof.