What is considered a liquid diet?

Liquid diets promise weight loss, detoxing and cleansing. From protein shakes to cold-pressed juices, they claim to have a solution—albeit an expensive one—to your health worries and woes. But they may not actually be the answer. Should you try a liquid diet? Here we break down what a liquid diet include, any potential benefits and many of the downsides.

What Is a Liquid Diet?

A liquid diet consists only of liquids instead of solid food. This includes homemade or store-bought juices and smoothies, homemade protein shakes, premade protein shakes and store-bought liquid meal replacements. You can replace all meals and snacks with liquids or do a partial liquid diet, eating some solid foods as well.

Some companies have specific "juice cleanses" with different phases you can buy. Others offer a variety of liquid meal replacements to choose from based on your goals. These, however, can be expensive and usually must be purchased and mailed to you.

Reasons for Going on a Liquid Diet

Liquid Diet for Medical Reasons

Some people go on a short-term liquid diet for medical reasons, such as difficulty swallowing or an intestinal issue.

"It's difficult to make the case for a liquid diet in most cases," says Ayla Barmmer, M.S., RDN, LDN, CLT, an integrative and functional dietitian in Boston. "However, the one exception would be when treating small intestinal bacterial overgrowth (SIBO), which is an increasingly common condition given widespread use of PPIs [proton-pump inhibitor medications for heartburn], chronic stress, antibiotic use and more."

Not everyone with SIBO needs to follow a liquid diet, she notes, but if it is recommended, it should be done with the supervision of a health care professional such as a physician or dietitian.

Other Reasons to Try a Liquid Diet

The more popular reasons for a liquid diet are weight loss and "detoxes." Liquid meal replacements provide a convenience factor—grab your shake and go. Plus, calories and portion size are controlled, so it is easier to stay within calorie goals if you're trying to lose weight.

Juice cleanses and detoxes have seen a surge in popularity in recent years but remain controversial in the nutrition world. Juices pressed from fruits and vegetables deliver a healthy dose of vitamins, minerals and antioxidants, but their claims to detox the body are not backed by science.

Liquid diets have pros and cons, regardless of your reason for doing them.

What Are the Benefits of a Liquid Diet?

three glasses of Green Smoothie on white counter

Liquid diets can help you lose weight-at least in the short term.

"Sometimes people can lose a few pounds," says Isabel Smith, M.S., RD, CDN, dietitian nutritionist and founder of Isabel Smith Nutrition. But, "they can also gain them back quickly, too," she says.

One study found that obese patients who replaced two meals a day with diet shakes lost more weight over a four-year maintenance period than those who ate calorie-controlled meals. This may have been due to the lack of variety in their diets. The greater the variety of food that is present, the more people tend to eat.

Liquid meal replacements also provide structure. Following a structured meal plan might lead to greater weight loss than a standard nutrition program.

The benefits of a juice cleanse are increased vitamin, mineral and antioxidant intake because of the amount of fruits and vegetables it takes to extract the juice.

"There are certainly studies that show benefits of juice on antioxidant concentration and anti-inflammatory mechanisms in the human body," says Rachele Pojednic, Ph.D., M.Ed., assistant professor of nutrition at Simmons College, "but it's generally in the presence of a healthy diet (or other solid foods). The biggest problem is that people think they are 'detoxing' their organs, which just isn't how your liver, or kidneys, or any other organ works."

What Are the Risks of a Liquid Diet?

• Feeling light-headed or dizzy
• Too few calories
• Lack of important nutrients
• Not sustainable long-term
• Lack of satiety
• Expensive

"There are very few rewards of going on a liquid diet," Pojednic says. "You may lose a little weight in the short term due to water loss, and perhaps a couple of pounds in the longer term due to a massive calorie deficit. But achieving these results is not typical because the diet is so challenging and makes you feel pretty terrible."

Most people can't last more than a few days before giving in to everything they were restricting, which just leads to overeating, guilt and gaining back the weight you lost.

In addition to feeling hangry, you might be missing important nutrients, too. Juices have vitamins and minerals, but they don't have fiber, fat or protein. Drinking juice alone can lead to "debilitating headaches, overwhelming hunger and diarrhea," Pojednic says. "Despite the hype that you feel this way because your body is 'detoxing,' these symptoms are actually because your calorie intake is so low, your blood sugar in between 'meals' is tanking, your body is responding to never feeling satiated, and there's nothing in your gut to bulk up your stool."

Rest assured that your body takes care of the cleansing for you.

"Your body operates on very tightly regulated signaling mechanisms to keep you upright, functioning and clearing out molecules that it doesn't need," Pojednic says. This is why you don't overdose on aspirin. "Your liver has very specific enzymes to 'detoxify' your body. Some foods can influence these enzymes, but flooding your body with liquid isn't going to dramatically change those mechanisms or 'flush out your system,'" she says.

One final downside? Cost. Subsisting on liquids alone gets expensive.

Differences in Nutrient Absorption

There is a difference in how your body absorbs liquids and solids. Solids come with an extra step in the digestion process: chewing. Chewing your food increases your fullness factor. Fiber also slows down digestion, helping you stay full longer, but juices lack this key ingredient.

"The sugars (glucose and fructose) in the juice will cross the intestinal wall much more quickly without the soluble fiber present in whole fruit, because that fiber barrier will be missing," Pojednic says. And while you are getting a concentrated dose of vitamins and minerals (and sugar) from juice, you might not absorb them all. Vitamins A, D, E and K require fat for absorption.

Can You Do a Liquid Diet Yourself?

You can follow a liquid diet on your own, but check with your doctor or dietitian before doing it. You want to ensure you are getting proper nutrients.

Liquid diets could also be dangerous if you are pregnant, on certain medications, have had a recent procedure, or have intestinal or digestive issues.

Not sure if a liquid diet is right for you? Talk to a dietitian, who can guide you through the pros and cons based on your goals. If you choose to go for it, choose beverages that have protein, carbohydrates and fat to help you stay full. Swapping juices for smoothies can help. Consider having one liquid meal per day instead of all three. And don't stay on the liquid diet for long.

"You probably won't do much damage if you keep it to less than three to seven days," Pojednic says. "In the meantime, though, prepare to feel like crap."