- Clear Liquid Diets|
- Full Liquid Diet|
- Liquid Diet Hazards|
- Losing Weight|
- When a Liquid Diet Makes Sense|
We’ll start this article by emphasizing the most important information you should remember after reading it: not all liquid diets are the same – and some of them are dangerous to follow on your own.
If you’ve undergone abdominal surgery, or have had to prepare for medical procedures like colonoscopies, you might think you know what a liquid diet is. But you may only have experienced the most extreme form.
Clear Liquid Diets
On the clear liquid diet prescribed ahead of a procedure or after some surgeries, your choices are extremely limited. You’re only able to drink water, tea, clear juices like cranberry or apple juice, sports drinks like Gatorade, bouillon and broth; you can also “eat” Jell-O, fruit ices and plain popsicles, or suck on hard candy. Those liquids are easy to digest and provide a small amount of water, electrolytes and calories, sufficient until you can progress to a “soft diet.” 
Under a doctor’s supervision, a clear liquid diet is medically useful. It leaves the digestive system empty (for surgeons who are going to be performing procedures) and doesn’t put a lot of strain on the system (for patients recovering from surgery). You’ll probably lose a little weight, too, but clear liquids don’t provide enough nutrients or calories for the body to remain healthy over the long term.
In short, a clear liquid diet is not what responsible experts (or “experts”) are referring to, when discussing the types of diets that can help you lose weight.
The diet option a health professional may suggest, or that you may consider after online research, is a full liquid diet. It’s a lot less restrictive, and somewhat healthier to follow. But a full liquid diet can still be medically problematic if you stay on it for long periods of time.
Here’s what you need to know.
What Is a Full Liquid Diet?
There’s no set of firm guidelines for a full liquid diet. Some versions require you to simply replace all meals with liquid foods, and some suggest (or supply) somewhat-nutritious shakes, smoothies, or clear fruit juices or vegetable juices as meal replacements. Others let you eat a regular dinner, with the liquids just replacing breakfast and lunch. We’ll look at those different types of liquid diet shortly.
However, these diets all have one basic thing in common: they only allow you to consume liquids or foods which will become liquid at room temperature (in other words, melt). In more specific terms, most full liquid diets allow you to eat everything that’s allowed on a clear liquid diet, with the addition of more substantial foods. 
Depending on the version of the diet you’ve chosen or been prescribed, you may be able to consume things like puréed fruits and veggies, hot cereals such as cream of wheat and oatmeal (if strained), dairy products including milk, ice cream and milkshakes (ingredients like blended peanut butter are OK), sherbet, eggnog, pudding and custard, consommé and strained cream soups, mashed avocado, smooth grits, yogurt, baby food (if you’re adventurous) – and a key to many full liquid diets designed for weight loss, smoothies or high-protein drinks.
If your diet is medically supervised or designed by a registered dietitian, you’ll be given a complete “do-and-don’t eat” list. It will be designed to provide you with the best possible nutrition while you’re avoiding solid foods, and may include additional “almost liquid” meals like puréed meats and mashed potatoes.
You’re really playing with fire if you try to follow a full liquid diet on your own, however. Drastically limiting calorie intake, failing to properly balance carbs, proteins and fats, and/or not getting enough minerals and vitamins, can quickly lead to a number of health problems even worse than being overweight.
Perhaps surprisingly, paid or subscription programs which provide protein shakes for most or all of your meals can be a healthier choice than DIY full liquid diets, since the best programs are designed to give you at least some of the nutrients you need on a daily basis.
In any case, a liquid diet can become a dangerous choice if you follow it for too long.
Potential Hazards of a Liquid Diet
The biggest problem you can experience when trying to follow a full liquid diet is the one we’ve already mentioned: not getting enough calories and nutrients, and a poor balance of fats, carbs and protein. Even if you balance the diet well (or have a nutritionist do it for you), you run into the very real possibility of not getting enough vitamin A, vitamin B12 and iron.
Some of the medical conditions that can eventually develop if you spend too much time on an unbalanced liquid diet are electrolyte imbalance, fatigue and dizziness, gallstones, hair loss and even heart damage. A liquid diet usually doesn’t contain much fiber, so you can also be at risk for constipation or other gastrointestinal problems.
Nutritional supplements are usually required, in order to avoid the serious risks of consuming all liquid meals; they should contain your entire daily recommended amount of vitamins and minerals. You should also be sure to get at least 25 grams of fat and 60 grams of protein each day.
There’s another risk. Consuming fewer than 800-1000 calories per day often causes the body to enter what’s called “starvation mode,” slowing down its metabolism. That can lead not only to feeling tired and lethargic, but also a slowing of brain function, immune system problems and in worst cases, heart arrhythmias. (It should be noted, however, that at least one study has found that a well-done very-low calorie diet can be effective. )
In addition, sticking to a liquid diet has been shown in some studies to negatively affect mental outlook and the ability to stay on the diet, although there are other studies showing the opposite.  We’re all accustomed to the satisfaction of eating a meal, and for nearly everyone, drinking 500 calories isn’t going to be as satisfying as eating a hamburger. That can be mentally wearing, put you into a bad mood – and increase the risk that you’ll be reaching for that burger sooner rather than later.
That all sounds pretty bleak. Is the potential weight loss worth it?
Can You Lose Weight on a Liquid Diet?
Yes, you can lose weight on a full liquid diet, and it will happen quickly if you follow the diet rigorously. It’s not uncommon to drop five to ten pounds in the first week.
Here’s the problem, though: that lost weight is almost all water. The body stores a lot of the fat we eat in the muscles and liver as a substance called glycogen, which is known to bond to large volumes of water. A liquid diet forces the body to look for immediate sources of energy – and the easiest available source is glycogen. The body burns the fat, the water is released and excreted in urine, and you lose a noticeable amount of water weight very rapidly.
After that? Some people don’t stay on a liquid diet for longer than a couple of weeks (as many as one-third may drop out, according to a survey of study results ), because it’s very hard to stay motivated and because it’s bad for them. And as soon as they go back to eating solid food, poof! Back comes the glycogen, back comes the water, and back comes the weight.
It’s true that those who do manage to stay on the diet for a longer period of time will start to burn fat and lose some of the excess weight they’ve been carrying around. Unfortunately, at the same time the body is burning fat cells, it’s also burning muscle. And muscle mass is extremely hard to regain once it’s been lost.
Finally, a liquid diet isn’t going to go on indefinitely. What happens to most people once they switch back to real food, sadly, is that they end up overeating. That’s not just because they’ve missed food so much, but because their body craves the calories and nutrients it’s been deprived of. In most cases, people put all of the weight they’ve lost back on. Some end up even heavier than when they tried the miracle liquid diet.
Put simply, you can definitely lose weight on a full liquid diet. Just don’t expect it to stay off.
Does that mean no one should ever try a liquid diet?
When a Liquid Diet Makes Sense
We’ve already addressed the clear liquid diets which are medically indicated for patients who are either preparing for medical procedures or recovering from them.
There are other times when a full liquid diet is not only sensible, but prescribed.
- Patients preparing for bariatric weight-loss surgery are often put onto a medically-supervised liquid diet so they can lose some weight before the surgery.
- People who suffer from Crohn’s disease are sometimes able to ease their painful abdominal symptoms by temporarily following a high-calorie liquid diet, which gives the inflammation in their gastrointestinal system time to subside. A similar approach is also taken with some patients suffering from pancreatitis.
- Those recovering from face or jaw injuries, or dental surgery, are usually put onto a liquid diet for obvious reasons.
Opinions vary on the advisability of the “hybrid” liquid diets that we mentioned earlier. Those are the legitimate options like Slim-Fast (but not the fad Instant Breakfast diet) which involve commercially-prepared shakes or smoothies, combined with one healthy meal per day.
Many physicians say well-constructed programs which include nutritionally-balanced shakes and supplements, are effective for those who don’t want to bother with calorie counting or portion control. Others say that while these diets aren’t overly harmful, they’re not as effective as a sensible diet plan which doesn’t rely on meal replacement. 
Opinions on DIY liquid diets to lose weight, however, are pretty much unanimous: the weight loss is only temporary, and not worth the risk.