Eat at the wrong time and you could be out of the tournament.
Most athletes in other sports know exactly when they will be competing, but that's not true of tennis players, who often have to wait for other matches to finish before it is their turn to perform. So it's important to keep a close watch on the scores in the preceding matches to avoid having an enormous lunch just before they compete, which would bring on indigestion and discomfort.
"You don't want to have a big meal just before going on court," Madison Keys has said. "If you get the timing wrong, it's not going to be fun. I try to have a snack around half an hour before going on court."
Drinking water isn't the only way to prevent cramps.
Eating fruit and vegetables can help players avoid the agony of cramping. "Bananas and potatoes are high in the potassium you need to stop you from cramping," said trainer Gil Reyes.
Players won't wait until they are thirsty before reaching for their drinks bottle.
Many players will eat and drink during each and every changeover, taking little sips of their sports drink or water, and nibbling small amounts of a banana or taking on a tiny amount of an energy gel.
"Every time I sit down, I drink something with electrolytes in it, and I take a bite of something, whether that's a banana or an energy bar," Keys has said.
What you won't find players drinking at the changeovers is a fizzy beverage.
"Fizzy drinks aren't good as they can make you feel bloated," one player has noted.
Post-match recovery can still taste good.
Chocolate milk is favoured by some players after matches, with the protein in the drink helping to aid muscle recovery.
"You don't have to stick to traditional sports drinks - I also recommend chocolate milk," Jean-Pierre Bruyere, a fitness trainer who has worked with Victoria Azarenka, has said. "At one stage, Vika was drinking that and she loved it."
Time is of the essence after coming off court.
Players will be keeping an eye on the time after coming off court - they won't want to wait long before refuelling.
"It's very important to put some food in your body within an hour of coming off the court," Sloane Stephens has said.
It's OK to break the rules once in a while.
As long as they are disciplined most of the time, it's okay for players to occasionally indulge themselves. Venus Williams has described her diet as 'cheagan' - while she is vegan, she sometimes allows herself a 'cheat day'.