Elite athletes use the 4 p.m rule for better hydration and performance, says a top nutritionist

• Properly timed hydration can improve your physical and mental performance.
• A nutritionist for elite athletes explains how much water you need and when to drink it.
• Follow athletes' 4 p.m. rule by drinking most of your water early in the day for best results.

NBA champions don't have time for morning brain fog or an afternoon slump.

Their secret to staying sharp all day long: perfectly-timed water breaks, according to a top sports nutritionist.

Matt Jones, who worked with the Boston Celtics during their 2024 NBA Championship-winning season and advises the supplement brand Cadence, said the pros have mastered the art of optimal hydration.

"Fueling intentionally is probably one of the biggest things we can take from the world of professional sport," he told Business Insider. "Professional athletes are very good at repeating basic behaviors like hydrating, and it's those routines that allow them to perform to the best of their ability."

If you want to level up your hydration game, start paying attention to how much you drink and when, Jones recommends.

After years of experience coaching elite athletes and military professionals, he has five key tips for getting enough water and electrolytes for better performance throughout the day.

Use a three-part test for dehydration

Staying hydrated makes a big difference to your brain and body in the office or on the basketball court, Jones said.

"It can impact your mood, your decision-making; it can impact the way you just go about your normal life," he said.

Research suggests that mild or moderate dehydration can impair reaction time and memory. Physically, being dehydrated can reduce strength and endurance, and make it more difficult to recover after exercise.

Jones uses a gold-standard test to see if his athletes need to drink more water. It can tell you if you're dehydrated based on three symptoms:

• Waking up thirsty. You can lose fluids overnight, so morning thirst is a good sign to start drinking water.
• Daily weight changes. Slight changes in your daily weight are normal, but if it decreases by 1% or more overnight, you could be low on fluids.
• Dark urine. Normal urine is pale or transparent yellow, so a color closer to amber can indicate dehydration.

Work out how much water you should drink in a day

Everyone's water needs are different, based on how much energy you use.

Jones said the gold standard recommendation is 1 milliliter to 1.5 milliliters per calorie of energy expenditure (in normal conditions). Two liters — or that eight cups of water a day you've probably heard about — makes sense for someone who burns 2,000 calories a day, but you may need more or less depending on your body size and activity level.

Drink most of your water by 4 p.m.

Sleeping is a superpower for athletes, and a simple tip helps them stay well-hydrated without too many overnight bathroom trips.

Jones said the solution for his athletes, including the Celtics, is to drink 80% of their fluids for the day before 4 p.m. so that their bodies have time to process all that liquid before bedtime.

Hydrate with fruit, coffee, and tea

Plain water should be your first priority for hydration, but other drinks and even foods can count toward your daily total.

For instance, your morning brew can help keep you hydrated, since caffeinated drinks in moderation lead to a net gain in fluid. Just steer clear of artificially sweetened or sugary beverages, too much of which can cause health issues like chronic inflammation over time.

Hydrating foods such as fruits and veggies also provide electrolytes to regulate the fluids in your body.

Sodium, or salt, is a key electrolyte, but you probably get enough in your diet already. Instead, Jones said to focus on potassium to offset the side effects of too much sodium, such as high blood pressure.

Good sources of potassium include bananas, avocados, coconut water, pomegranate, and watermelon.

Start drinking before you're thirsty

Dehydration can sneak up on you before you realize it, especially if you're sweating a lot.

"During intense exercise, particularly in warm environments, thirst is not a good indicator of hydration status," Jones said. "People are often chasing their tails a little bit."

You can calculate your sweat rate to estimate just how much water you need to replace during exercise, like Jones does with the pros.

Prevent a dip in performance by drinking water at regular intervals.

"The first priority as soon as your big toe hits planet earth in the morning is to rehydrate," Jones said.