Whether you're trying a keto plan, a new plant-based routine, intermittent fasting, or the Whole30, experts agree: dieting is hard work.

Thomas Chi, a doctor at the University of California, San Francisco, urology department, said proper hydration tends to be one of the toughest things for his dieting patients to remember when they start a new weight-loss plan.

"People who are on extreme diets, they tend to have higher levels of salt and less hydration," Chi said.

Fortunately, your body is here to help. All you have to do is take a little time to listen to the brain's subtle cues: If you're feeling thirsty, drink some water.

This is especially important if you're eating more meats and high-salt foods, Chi said, because a combination of "tons and tons of meat" and not enough water could lead to kidney stones, especially if you have a family history of the issue.

"I'm not seeing this enormous uptick of patients with kidney stones because they're all doing a keto diet now," he said. But he still thinks it's a good idea to pay attention to when your body's asking for water.

No matter if you're on an extreme diet or no diet at all, that's generally good advice.

"A lot of times, people just seem to be a little dehydrated," the dietitian Jason Ewoldt from the Mayo Clinic previously told Business Insider.

But the popular notion that you must down eight full glasses of water a day is bogus. And nobody really needs any special sports drinks, even after a workout.

Just drink when you're thirsty because the body is designed to know precisely when you need more water.

There's actually a "thirst centre" in the brain that helps regulate thirst, and it's impressively tuned. Even though it takes tens of minutes for the body to hydrate once cool water touches your lips, drinking quenches thirst within seconds.

The brain's thirst cues can be relatively mild and easily mistaken for hunger pangs, or just ignored. Pretty soon, that can prompt dehydration and lead to overeating.

A 2016 study of more than 18,000 people in the US found that those who drank more water were consistently more satisfied and ate fewer calories on a daily basis. (Drinking with a meal both helps replenish saliva and aids digestion.) Steady water drinkers also consumed lower amounts of sugar, fat, salt, and cholesterol than dehydrated folks.

So if you're unsure if you're feeling peckish, try sipping on some water, waiting about 15 minutes, and checking if your stomach really is crumbling.

"If you were truly hungry, you might still feel a stomach pang, whereas if you were just thirsty, you'll feel satisfied," the Polycystic Kidney Disease Foundation said.

If you're not a big fan of water, you can dress up your drink by adding lemon juice into your glass. That's a cheap, doctor-recommended hack to help prevent kidney stone formation.

No need to fuss too much over the colour of your urine, either. As long as it's not a super-dark yellow or amber colour, you're doing well.