Here's What to Know Before You Start a Liquid Diet

Whether you're on a doctor-prescribed liquid diet or you're following one in an effort to lose weight, we'll break down what a liquid diet is, which foods are included, the risks and when it might be worth trying.

A liquid diet is one where you only "eat" foods that are liquid, or become liquid at room temperature (think: ice pops).

Look a little deeper and you'll see there are two versions of liquid diets.

"One is prescribed in the hospital for people who have health issues and can't eat solid food," says DJ Blatner, RDN, author of ‌The Superfood Swap‌. (For people on a medically prescribed liquid diet, you're either consuming a clear liquid or a so-called full liquid diet. More on that below.) "There's another version that people put themselves on with juices or smoothies, aka juice cleanses," Blatner adds.

What you can and can't eat on a liquid diet depends on which type of liquid diet you are following.

If your liquid diet is prescribed by a doctor, he or she will advise either a clear liquid or a full liquid diet.

According to the U.S. National Library of Medicine, a clear liquid diet includes:

• Clear broth
• Tea
• Cranberry juice
• Jell-O
• Popsicles

It's common to be prescribed a clear liquid diet before some medical tests or procedures. You might also need to follow a clear liquid diet leading up to surgery, and almost always after surgery until your stomach and intestines recover back to their normal function.

This is a diet you should only follow for a few days (three to four, per the U.S. National Library of Medicine).

A full liquid diet contains a bit more variety. Per the U.S. National Library of Medicine, you can have:

• Everything allowed on a clear liquid diet
• Strained creamy soups
• Ice cream
• Milkshakes
• Pudding
• Juices, including those with pulp
• Drinks like Ensure and Boost

Similar to a clear liquid diet, a full liquid diet may be prescribed before a medical test, procedure or surgery, and also after surgery.

Sometimes a full liquid diet is a stepping stone between a clear liquid diet and your normal diet. A full liquid diet might also be advised if you are having any swallowing or chewing problems, and if that's the case, you'll receive more specific guidance from a health professional.

The duration of a full liquid diet depends on the reason you're following it in the first place, so it may last anywhere from a few hours to indefinitely if swallowing is a concern.

If you're following a juice cleanse, you're likely only drinking juices or smoothies throughout the day, or a combination of the two. Because there isn't a single definition for a juice cleanse, what you can and can't have on a juice cleanse will depend on the plan you're following.

When it's not medically prescribed, people often go on a liquid diet to "jumpstart" their weight loss.

Following a low-calorie, all-liquid diet — whether it's prescribed or self-induced — can, in fact, lead to weight loss, per an August 2018 study in ‌Obesity Surgery‌. In the study, participants were instructed to drink a very low-calorie liquid diet before bariatric surgery, and they lost about 8 to 10 pounds over the course of a week or two.

Following a liquid diet can help you lose weight initially, but there are more sustainable ways to achieve those goals. Plus, any weight you'll lose is potentially only "modest," and sticking to this type of diet is challenging, found a September 2018 study in ‌Healthcare‌.

"Liquid diets and juice cleanses are ‌not‌ a magic bullet," Blatner says. "What you do for a few days will not change your health."

This is especially true if you return to the same eating habits you had before you started the cleanse. The long-term trajectory of your health is dictated by your usual habits.

"It's what you do consistently for the other 362 days that matters most," Blatner says.

For example, if you drink green juice for three days and then go back to eating fast food, it's unlikely you'll keep off the weight you lost over those three days of juice.

That said, if you're healthy, following a liquid diet for a few days likely won't lead to any long-term problems.

In the short-term, however, severe calorie restriction could leave you irritable and possibly even depressed; you may have trouble concentrating and/or feel restless, according to the National Centre for Eating Disorders.

If you have diabetes, heart disease, kidney disease, digestive issues or are pregnant or elderly, however, an extreme change to your diet can lead to anything from dizziness and fainting to entering a coma, since an all-liquid diet affects the body's electrolytes and blood sugar balance.

"Additionally, anyone with a history of disordered eating or eating disorders should not do liquid-type diets since they can trigger a restriction, deprivation or diet mindset," Blatner says.

If your doctor prescribed a liquid diet — whether it's a clear or full liquid version — it's safe to follow. Be sure to contact your doctor or medical professional, however, to share and discuss any changes or if you have any concerns.

If, for nonmedical reasons, you want to follow a liquid diet, it's safe to consider for a short period of time. "Up to three days," Blatner says. "Otherwise, I do not recommend liquid diets."

If you're thinking about a liquid diet to lose weight, know that there are other (and healthier!) ways to go about losing weight. The Mediterranean Diet, for example, is a well-regarded, healthy way of eating that's also fairly easy to start and stick to. The weight you'll lose will be steady, and you're more likely to keep off what you shed, per an April 2018 study in ‌Nutrition & Diabetes‌.

Other research (published in that September 2018 study in ‌Healthcare‌) suggests that following a so-called "high-quality diet" — one that is low in added sugars and processed foods and high in produce and whole grains — helps adults with overweight and obesity to lose weight.

So, if weight loss is your goal, consider the Mediterranean way of eating (or another healthy diet) first before you launch into a highly restrictive, hard-to-follow liquid diet.