Here’s one factor to consider: Some diets, such as intermittent fasting and the ketogenic diet, are more likely than others to cause dehydration. Given that we need water to survive, health experts suggest making that part of the equation when you weigh the pros and cons of any diet.

When choosing a new diet, you’ll want to consider how effective it will be at helping you achieve your health goals, whatever they may be — and you’ll want to be sure you’re vetting its potential health risks.

Water helps all cells, tissues, and organs survive, per the Mayo Clinic, so you don’t want to skimp on hydration.

The National Academy of Sciences recommends getting about 15 cups of fluids a day if you’re a man and 11 cups a day if you’re a woman. (That said, around 20 percent of that recommendation should come from water-rich foods, like fruit and vegetables; 13 cups of fluid for men and 9 cups a day for women are usually enough for people who eat a balanced diet.)

“Any diet that is restrictive may cause dehydration,” says Keri Gans, RDN, a New York City–based registered dietitian nutritionist and the author of The Small Change Diet. “Most people don’t drink enough water to begin with, so we look for other ways for them to get water” – for example, through hydrating fruit. When diets eliminate fruit or other entire food groups, the risk of dehydration rises, Gans says.

Most diets don’t explicitly forbid water, Gans says, and “ideally, no diet should cause dehydration.” But some will require you to pay special attention to how much you’re drinking throughout the day to make sure you’re adequately hydrated. You should also learn to recognise the signs and symptoms of dehydration to watch out for, which according to MedlinePlus include:

  • Feeling thirsty
  • Dry mouth
  • Urinating less than usual
  • Sweating less than usual
  • Dry skin
  • Dizziness
  • Fatigue
  • Dark-coloured urine

Here are five diets that could lead to dehydration:

1. High-Protein Diets

High-protein diets, such as the Dukan diet and paleo diet, have become increasingly popular ways to lose weight. While the U.S. Department of Agriculture’s Dietary Guidelines for Americans recommend that 10 to 35 percent of daily calories come from protein, these plans call for more.

The downside, experts suggest, is that high-protein diets could lead to dehydration.

Nitrogen is found in the amino acids that comprise protein. When you consume large amounts of protein, your body flushes out excess nitrogen with fluids and water.

In this case, potential signs of dehydration can be subtle, says Lisa R. Young, PhD, RDN, an adjunct professor of nutrition at New York University in New York City. “It’s not like you ate something salty and feel thirsty, or you ate Chinese food and are so thirsty. You don’t realise it.”

One small study compared the hydration levels of five endurance athletes as they consumed low, moderate, and high amounts of protein. The researchers found that “as the amount of protein consumed went up, the degree of hydration progressively went down.”

The takeaway, they noted, is that if you’re on a high-protein diet, it’s important to drink more to prevent dehydration, even if you don’t feel thirsty.

2. Ketogenic Diet

You may be interested in the popular high-fat, low-carb keto diet because you’ve heard it can lead to fast weight loss through a metabolic state called ketosis. Ketosis leads your body to burn fat in the absence of enough carbs.

“When you cut carbs, you end up releasing water,” Dr. Young says. “The body is going into its glycogen storage state to break down the carbs, so you end up losing more water from a diet like that.” Indeed, this loss of water weight is often why keto is helpful for quick weight loss – at least temporarily.

Regardless of whether you’re just starting keto or have been on the plan for a while, take steps to stay hydrated every day. This includes drinking when you wake up and before meals, and consider keeping track of hydration with a smartphone app.

There are lots of options: Young likes Aqualert and Daily Water Tracker Reminder, both of which send reminders and notifications, making it “nearly impossible to forget to drink,” she says.

3. Intermittent Fasting

Intermittent fasting is a dietary approach whereby you’ll alternate between fasting and eating throughout the day, or from one day to the next. There are different ways to follow it: Some people opt for the 5:2 approach, which allows you to eat normally five days of the week and then restrict your calories on the other two days. Others prefer the 16:8 plan, which means fasting for 16 hours of the day. Whatever your approach though, you stick to predetermined eating times for all meals and snacks.

You’re allowed to drink water if you’re intermittent fasting, even outside of your eating times. But the problem, Gans says, is that some people forget. “You’re sitting down to less meals,” she points out – and mealtime is a natural opportunity to have a glass of water.

That’s why, if you’re fasting, it’s important to pay extra attention to how much you’re drinking and to make it a priority to keep a water bottle with you or include hydrating fruit and vegetables as part of your meals during allocated eating times.

4. Dry Fasting

Dry fasting is a version of intermittent fasting that requires followers to restrict both food and drink. During the fasting period, you can’t have any type of liquid: water, broth, tea, coffee, and all other beverages are off-limits.

Some people practice dry fasting for religious reasons – for example, Muslims fast from dawn to dusk during Ramadan each year. Other proponents of dry fasting believe it promotes weight loss or slows down the ageing process. Dry Fasting has emerged as a fad diet, in part because of Ramadan. One study has found that after Ramadan, participants’ body weight and body mass index decreased.

At the very least, you’re very likely to end up dehydrated when following this type of plan, which can lead to other problems over a longer period of time. Per the National Kidney Foundation, these may include kidney stones and urinary tract infections.

“I’m not a fan of dry fasting,” Young says, adding that it’s not the right choice for most people looking for a diet plan.

5. Atkins Diet

The Atkins diet, a popular low-carb diet (though one that isn’t as low-carb as keto), could put its followers at risk of dehydration, Gans says.

One reason: It eliminates many food groups, such as starchy vegetables and most most fruit, per the Atkins website. During phase one, which lasts two weeks or more, fruit is not permitted at all (though lox-carb fruit such as cherries and cantaloupe may be added back into the diet in later phases). Fruit juice is also discouraged.

“If you’re eliminating fruit and vegetables, which are hydrating foods, you’re putting yourself at higher risk of dehydration,” Gans says. To help compensate, pay extra attention to how much you’re drinking throughout the day, and don’t skimp on water consumption (since hydration is encouraged on the Atkins diet).