Is a Liquid Diet for Weight Loss a Good Idea?

David Levine

It's the most wonderful time of year -- especially for gaining weight. While the holiday party scene will be less active this year because of COVID-19, most of us are still likely to enjoy our favorite holiday treats, and most likely to excess. When New Year's Eve rolls around, weight loss resolutions will once again be plentiful.

There are, of course, many eating plans that proclaim weight-loss benefits. One particularly harsh plan includes no eating at all. The liquid diet, as its name indicates, provides all (or most) of your calories, vitamins and nutrients in liquid form. There are variations on this theme -- clear liquids, smoothies, power shakes, fruit juice cleanses -- and some may allow for one or two small meals, but all of them have one thing in common: Most nutrition experts warn against trying them for more than a day or two.

[READ: Best Soups for Weight Loss.]

Liquid Diet Specifics

There are times when a doctor will prescribe a liquid diet. The Mayo Clinic says that a clear liquid diet is often needed the day before certain tests, procedures or surgeries, like a colonoscopy, that require the stomach or intestines to be empty of food. A clear liquid diet may also be recommended short-term to help relieve digestive problems, such as nausea, vomiting or diarrhea, or after certain types of surgery, including bariatric surgery. These clear liquids, such as water, clear broth and plain gelatin, are easily digested and leave no undigested waste products in your intestinal tract. But these extreme diets do not include enough calories and nutrients to sustain you for more than a day or two. They are certainly not recommended in attempts to lose weight.

Liquid diets for weight loss go beyond clear liquids and allow foods that are liquified or will melt while being eaten. They include foods that have more nutritional value, such as:

-- Dairy products.

-- Strained or pureed soups and whole foods.

-- Juices, gelatin, broth and tea.

-- Shakes and smoothies, often boosted with nutritional supplements.

-- Frozen juice- or dairy-based products.

-- Nut butters.

Depending on how strict you want to be, you can also modify a liquid diet with one or two small meals, typically breakfast or lunch, to make this a more satiating and satisfying eating plan.

"There are liquid, or better to call them meal replacement, shakes that can be utilized to create an effective weight loss approach," says Elizabeth DeRobertis, a registered dietitian and certified diabetes educator with Scarsdale Medical Group, an affiliate of White Plains Hospital in New York. A meal replacement should contain adequate amounts of protein and macronutrients and micronutrients. And it should have enough calories to meet the body's needs. "A very low-calorie diet is considered to be in the 400 to 800 calorie range. This is extremely low, and it is hard to meet nutrient needs when someone is in this range. There is more research to support meal replacement plans that are in the 900 to 1200 calorie range," she says. "There have been programs around for many years including Optavia, Optifast and SlimFast, that have clinical data to support the efficacy."

[See: The 9 Best Diets for Fast Weight Loss.]

Will It Work?

The short answer is, yes. "It is restrictive (of calories), so you will lose weight," says Wesley McWhorter, the director of culinary nutrition for the Nourish Program at the Center for Healthy Living at The University of Texas Health Science Center at Houston School of Public Health. In general, weight loss is basic math: Consume fewer calories than you burn, and you lose weight. That's why this -- and any restrictive, low-calorie diet -- will work short-term.

But that comes with a caveat: "Is it sustainable? Absolutely not. Is it healthy? Absolutely not," McWhorter quickly adds. He is far from alone in that belief. "Following a liquid diet is not a good long-term strategy for weight loss," says Kristen Smith, a registered dietitian, bariatric surgery coordinator for Piedmont Healthcare in Atlanta and author of a blog that promotes healthful eating.

Here are three main issues, according to Smith:

1. Liquid diets do not teach you how to maintain healthy eating habits for the long-haul, because they "take the guesswork out of making food selections and portion control."

2. Liquid diets are often not satisfying, so they are not maintainable for long periods of time.

3. Liquid diets could be void of essential vitamins and minerals your body needs. "Not all liquid diet plans offer adequate macro- or micronutrients," says Smith, a spokesperson for the Academy of Nutrition and Dietetics.

For example, when you juice fruits and vegetables, "you remove a lot of the good parts, like fiber that feeds our gut bacteria," says McWhorter, a professional chef who teaches hands-on nutrition and cooking classes. "We don't know everything else that's being removed."

McWhorter also asks you to consider the psychosocial aspects of eating. "It is important to note that eating is a very social behavior. That's really important in this time of COVID, because we are separated from other people. When you go into just drinking liquids, you take away the human element of eating. If you are just drinking, that whole part is gone," he points out. "I strongly advise against things like that," especially now, as we are all isolated from loved ones.

[See: 10 Lessons From Extreme Dieting.]

The Right and Wrong Ways

Nevertheless, many people will be persuaded to try a liquid diet anyway. Here are a few tips to do so safely.

-- If you decide to follow a liquid diet for more than a few days, consult your physician. "Most liquid diets offer a significantly lower number of calories and require regular medical monitoring," Smith warns.

-- Aim to drink a liquid meal replacement every few hours while awake. "If you go more than a few hours without drinking a liquid meal replacement you may have challenges controlling your hunger later in the day," Smith says.

-- Ensure adequate hydration. Make sure you drink plenty of low-calorie beverages in between drinking liquid meal replacements.

-- Have a plan to wean off the liquid diet. "If someone starts a meal replacement program without acknowledging the importance of a proper transition, they will be more likely to gain the weight back, as they may return to poor eating habits," DeRobertis says. "If they do the right transition, this is key to keeping the weight off."

-- Consider replacing just a few meals with liquid meal replacements, not all of them. "I think it is important to have a least one meal per day. The idea here is for people to make changes that will have a long-term benefit," DeRobertis says.

-- Join a nutrition or weight loss support group, or seek the guidance of a registered dietitian nutritionist. "The dangers would be if someone selected a program that was not properly fortified, and was too low in calories and macronutrients, DeRobertis warns. "Other dangers include wasting money and wasting time if someone has not done the right research on a safe approach, and also an approach they feel will be effective for them."

DeRobertis says she has used meal replacements as part of her practice for many years, and has had patients lose "significant amounts of weight using meal replacements. I do believe that this can be an effective tool for weight loss, but it is certainly not for everyone," she says.

Better yet, McWhorter says, simply focus more on what is in your meals. Look at healthier options like the Blue Zone and Mediterranean eating plans, which he says encourage "enjoying foods. It's not drudgery, it's a lifestyle, not just about losing 10 or 15 pounds by the end of the year. We call this 'small nudges,' not massive changes to your diet." That's the way to long-term, healthy and, yes, enjoyable weight loss.