AUTHORITY NUTRITION

Are Liquid Diets a Good Idea for Weight Loss?

Written by Grant Tinsley, PhD on November 28, 2017

Losing weight is a very common goal.

Whether for health or appearance, many are searching for the ideal weight loss program.

One category of weight loss diets emphasizes the consumption of liquids, rather than solid foods.

Some programs simply replace certain meals with liquids, while others replace all solid foods with liquids.

This article discusses several types of liquid diets and whether they are recommended for weight loss.

Woman Juicing

Liquid diets are nutrition programs that require you to get either some, most or all of your daily calories from liquids, rather than solid foods.

While there are many liquid diets, most can be grouped into one of the following categories.

Meal Replacements

Some liquid diets involve meal replacement shakes, which are consumed in place of solid foods. Numerous companies sell these shakes for weight loss purposes.

Meal replacement shakes are often lower in calories than typical meals. They can replace one or multiple meals each day (1).

They are designed to contain all the nutrients your body needs to function, including macronutrients (protein, carbs and fat) and micronutrients (vitamins and minerals) (2).

Some weight loss programs use these shakes to account for your entire calorie intake for up to several months (3).

Detox Diets and Cleanses

Other liquid diets include detox diets or cleanses, which require the consumption of certain juices or drinks that supposedly remove toxic substances from your body (4).

Examples of these diets include the Master Cleanse, long-term water fasting and various juicing programs.

Unlike meal replacement shakes, these programs typically rely on a few natural ingredients like juices from certain fruits and vegetables and other botanical ingredients.

Because of this, these diets may not contain all the nutrients your body needs.

Medically Prescribed Liquid Diets

Clear liquid and full liquid diets are examples of diets that are medically prescribed for specific health reasons.

As the name implies, clear liquid diets only allow the consumption of clear liquids, such as water, apple juice, tea, certain sports drinks and broths (5).

These diets may be prescribed before or after certain surgeries or if you have digestive problems.

Full liquid diets are prescribed for similar reasons, but they are less restrictive than clear liquid diets.

They allow most beverages, as well as foods that become liquid at room temperature, such as popsicles, Jell-O, pudding, syrups and some shakes (6).

Summary Liquid diets replace some or all food with beverages. There are several types, including meal replacement programs, cleanses and medically prescribed liquid diets.

Liquid diets often contain fewer calories than diets consisting of solid foods.

For a liquid meal replacement diet, the total number of daily calories may range from 500–1,500 (7, 8).

However, these diets are often just one phase of an overall weight loss program.

For instance, one weight loss study in 24 obese people involved a 30-day period in which participants consumed 700 calories per day from meal replacements but no solid foods (9).

Over the next 150 days, solid foods were gradually reintroduced. Daily calorie intake increased gradually from 700 to 1,200 calories.

This program was effective for weight loss and reduced body fat from 33% to 26%.

In studies of liquid meal replacement diets, it is common to use this pattern of reintroducing solid foods after a liquid diet has been followed for one to three months (3, 9).

Research has shown that both low-calorie (1,200–1,500 calories per day) and very low-calorie (500 calories per day) diets using liquid meal replacements can be effective for weight loss.

While very low-calorie diets can lead to greater weight loss, they may also lead to greater risks, such as an increased risk of gallstones in some individuals (7).

It is important to note that people participating in studies on low-calorie liquid diets are typically monitored closely by medical personnel.

What’s more, many of these programs are not meant to be followed in the long term.

Certain liquid diets don’t allow any solid foods and thus may not contain all the beneficial nutrients found in whole foods like fruits and vegetables (10).

However, replacing just one or two meals per day with a low-calorie meal replacement shake may be a practical long-term strategy as a complement to eating healthy, solid foods.

Summary Some liquid diets consist of prepackaged meal replacements, which provide 500–1,500 calories per day. These diets are often just one phase of an overall weight loss program that gradually reintroduces solid foods.

Although liquid diets are often associated with weight loss programs, there are other reasons why you may follow one.

For example, clear liquids are typically easy to digest and do not leave much undigested material in your intestines (11).

As a result, your physician may prescribe a clear liquid diet before certain surgeries, such as colonoscopies and bariatric surgery.

They may also be prescribed after certain surgeries, such as gallbladder removal and bariatric surgery (12).

Additionally, liquid diets are advised for those who have digestive problems, including diarrhea and vomiting.

However, some evidence suggests that solid food diets that leave minimal undigested materials may be superior to liquid diets (13).

Summary Liquid diets are used for more than just weight loss. Your physician may prescribe a liquid diet before or after certain surgical procedures or if you have particular digestive problems.

Many studies have been conducted on programs that replace some or all meals with liquid meal replacements (2, 3, 14).

An eight-year study including over 8,000 obese people looked at whether liquid meal replacements promoted weight loss and weight maintenance (3).

The program consisted of a 12-week period during which participants consumed only 800 calories per day of liquid meal replacements.

After the weight loss period, the participants were prescribed a weight maintenance program that gradually reintroduced solid foods.

After one year, women lost 43 pounds (19.6 kg) on average, while men lost 57 pounds (26 kg).

While these results are impressive, it is important to remember that the participants completed a very intensive program under medical supervision.

Another study including over 9,000 overweight and obese adults examined the effects of a 500-calorie liquid formula on weight loss (14).

The liquid formula was the only source of calories for 6–10 weeks, followed by a 9-month weight loss maintenance period.

After one year, those using the liquid formula lost 25 pounds (11.4 kg), which was more than those who ate solid foods. However, this was likely because they ate fewer calories than the solid-food group.

Research directly comparing low-calorie diets consisting of either food or liquids has found both diets to be equally effective when they contain the same number of calories (15).

Summary Replacing some or all meals with liquid meal replacements can promote weight loss. However, this is due to a reduced calorie intake. Both food-based and liquid-based diets are equally effective when they contain the same number of calories.

Liquid diets that only allow you to drink certain juices, teas or other beverages are not good long-term weight loss strategies.

Solid foods contain many necessary nutrients. Therefore, it is not recommended to stay on a diet consisting of liquids alone in the long term.

Even in studies showing impressive results from liquid meal replacements, solid foods were reintroduced after several weeks or months (3, 14).

Medically prescribed liquid diets like the clear liquid diet or full liquid diet are not meant to be followed in the long term.

Similarly, cleanse and detox programs may involve periods during which only certain juice mixtures are consumed for days or weeks.

For example, the Master Cleanse consists of 3–10 days of only consuming a special beverage made of lemon juice, maple syrup, cayenne pepper and water (4).

Drinking this beverage in place of eating food will reduce your calorie intake, but 3–10 days of low calorie intake will do very little in terms of long-term weight loss if you simply return to your normal diet afterward.

Short-term, low-calorie diets can cause you to lose body weight quickly due to the loss of carbs and water, both of which are normally stored in your liver and muscles (16).

What’s more, the Master Cleanse and similar programs recommend the use of laxatives, which could further contribute to the temporary weight loss (4).

Thus, much of the weight you lose during these short-term liquid diets may not be due to fat loss (17).

Once you resume a normal diet, you will likely regain much or all of the weight that you lost as your carbohydrate and water stores are replenished (18).

Short-term crash diets don’t typically lead to lasting weight loss because they don’t do anything to change your permanent eating habits (19).

For these reasons, overly restrictive diets that don’t allow any solid foods are not generally recommended.

A more appropriate goal is to incorporate simple strategies that you can use every day for a long period of time, rather than short-term quick fixes that fall short on their promises (19).

Summary Diets that contain solely juices or special beverages are not good long-term strategies. These programs may lead to some rapid weight loss but will probably not lead to lasting fat loss. Focusing on sustainable, long-term dietary changes is a better strategy.

While it is possible to find success with some liquid diets, such as those that use meal replacements, these programs aren’t ideal for everyone.

Some people may find that replacing some solid foods with liquid meal replacements is a practical way to reduce their calorie intake (2).

Nevertheless, others find this pattern of eating challenging.

If you find that substituting lower calorie liquids for solid foods allows you to eat fewer calories while still feeling satisfied, it may be a worthwhile weight loss strategy.

However, if you feel hungrier when you consume liquid meal replacements rather than a snack or small meal, this strategy may not be good for you (20).

For example, you may be considering swapping your normal lunch with a liquid meal replacement.

If you typically go out to eat for lunch or have high-calorie leftovers from last night’s dinner, you may reduce your calorie intake substantially by using a meal replacement.

However, if you typically eat a light healthy lunch, you may not reap any benefit from switching to a liquid meal replacement.

Several groups of people should not consider a liquid diet, such as pregnant or nursing women, children and adolescents and those who are underweight (21, 22).

Not to mention, there are financial considerations. Commercial meal replacement shakes can often be more expensive than traditional solid foods.

Summary Some people find emphasizing liquids to be an easy way to reduce calorie intake, while others find it difficult. First, consider whether replacing foods with liquids will help you reduce your calories and if it's a sustainable diet strategy for you.

The safety of liquid diets depends on the type of diet and the duration of the program.

Diets that replace one or several meals per day with meal replacement shakes are generally considered safe in the long term (3, 14).

Most meal replacement shakes are designed to contain the nutrients needed by the human body, including carbs, fats, protein, vitamins and minerals.

Yet, replacing only some meals with liquids ensures that you still get nutrients from solid foods as well.

One side effect of a liquid diet is constipation, which may be due to the low fiber content of most liquids (23).

Additionally, very low-calorie diets (500 calories per day) may lead to a higher risk of gallstones than low-calorie diets (1,2001,500 calories per day) (7).

However, there is a low incidence of side effects overall with weight loss programs that include low-calorie meal replacement liquids (3, 8, 9, 14).

Meanwhile, medically prescribed liquid diets are considered safe for short-term use, but they are typically ordered by a physician (5, 6).

If this type of diet was not prescribed to you by a medical professional, it is probably unnecessary.

Following a liquid diet over the long term could increase your risk of nutrient deficiencies, particularly if you are only consuming juices or other beverages that do not contain all essential nutrients (4).

Overall, it is probably a good idea to include some healthy solid foods in your diet, even if you are considering emphasizing liquids.

Summary The safety of liquid diets depends on the specific diet and how long you follow it. Substituting balanced meal replacement shakes for some solid foods is likely safe in the long term. However, it's not recommended to consume liquids alone long term.

Liquid diets replace some or all meals with liquids.

They're often low calorie and may be used for weight loss.

Some use nutritionally balanced meal replacement shakes, while others only allow juices or beverages that may be low in nutrients.

Liquid meal replacements can aid weight loss but are often just one part of a program that incorporates solid food.

What's more, they’re only recommended for weight loss if they’re a feasible strategy for you.

There is no “one size fits all” diet program. Choosing something that fits with your preferences will increase your chances of long-term weight loss success.

An evidence-based nutrition article from our experts at Authority Nutrition.

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