This article was taken from chapter 28 of the book 'Healthy Weight Loss --> Healthy Life: The essential guide to long-term healthy weight loss for Australian adults' (Read More....)
Very Low Calorie Diets (VLCD's)
Meal replacement milkshake programs involve adding a small sachet of powdered ingredients (usually comprising of calcium caseinate and milk solids fortified with a few vitamins and minerals) to water to make a "shake", which you consume instead of your usual meals. They are among the most popular commercial weight loss methods available, promoting themselves as a type of Very Low Calorie Diet (VLCD)
In clinical terms, VLCD's do not have to use meal replacements; it is simply a term to describe a diet which typically provides between 400 to 800 Calories per day, whereas those classified as Low Calorie Diets (LCD's) provide between 800-1200 Calories per day or thereabouts. The interesting thing which studies have found however (as reviewed in the November 2001 supplement issue of Obesity Research  ) is that after several months, people on VLCD's 400 Calories daily lose no more weight than those on the 800 Calorie per day diets. In other words, even if you were intent on following a VLCD, there would be no point in following one that provided less than 800 Calories per day, especially as the lower Calorie diets have more uncomfortable side effects. Additionally, whilst VLCD's might result in a greater weight loss in the first couple of weeks (due to fluid loss, not fat loss) people who begin a VLCD for several weeks and who then shift to a LCD for maintenance (which even the commercial meal replacement schemes advise) do not seem to lose any more weight after several months than those who followed a LCD the whole time.
The only real difference with VLCD's, however, are the uncomfortable side effects. The most common side effects people using VLCD's have reported include: dry mouth, headache, dizziness/orthostatic hypotension, fatigue, cold intolerance, dry skin, menstrual irregularities, hair loss (especially when continued long-term) and constipation (it depends on the fibre content of the diet, though if it were from a replacement shake, the fibre intake will be minimal). A few cases of far more severe complications have been reported such as gall bladder problems, gout and even psychosis.
It seems that the lower the Caloric intake, the greater the likelihood of these side effects, though they seem to occur to a lesser extent even in VLCD's providing 800 Calories per day. Now consider that the daily Calorie contribution of the meal replacement shake programs is usually well below 800 Calories per day.
Furthermore, studies have found that about 25% of total weight lost on these types of diets will be from muscle tissue, and even more so if the diet does not include a bare minimum of at least 50g of protein per day. Muscle strengthening exercises may help minimize this effect, but only a little. 
Proponents of these diets (as well as others that result in short term weight loss) will often cite studies which have also shown that they provide improvements in markers of cardiovascular disease such as lower fasting glucose levels, triglycerides and LDL cholesterol. These markers will generally always improve in obese people once they start losing weight, and are simply indicative of their fat loss, not due to the healthfulness of the foods they are eating, as the same initial improvements have been shown using just about any weight loss method. Surely there are healthier ways to do this!
Whether or not these radically different diets can realistically be sustained long term is doubtful.
Most studies have found that after several years, people who have been placed on these extreme diets generally tend to put the weight back on, and then some. For example, researchers at the University of Pennsylvania published a study in 1989 in the International Journal of Obesity, which found that placing obese women on a VLCD for 2 months and then shifting into a LCD for 4 months resulted in an average loss of 13 kg. Some of the women in the study received behavioural therapy (nutritional counselling) during this time (to teach them how to make healthier food choices) whereas the others did not. After one year, 32% of the women who received both treatments had managed to maintain their weight comparison with only 5% who had received only the VLCD. Not surprisingly, even the additional counselling was not enough to help these women maintain their extreme dietary makeovers for much longer than that, as 5 years later, most women in both groups had put all their lost weight back on, and over half had actually put on more than what they did to begin with.
The only other study which examined the success rate after 5 years was published in July 1997 issue of Archives of Internal Medicine, which found that after 5 years, both subjects who had been placed on a VLCD in combination with Behavioural Therapy as well as those given Behavioural Therapy alone (with no dietary prescription) had put on a significant amount of weight since they lost it in the initial 16 week intervention period. The subjects given both treatments however had put back on less than those with the Behavioural Therapy alone did. The major problem however was that more than twice as many people prescribed the VLCD could not comply with it for the whole 16 week intervention period and consequently dropped out of the study.
It's difficult to interpret the significant differences between these results, though it would probably depend very much upon how different the VLCD's were from their usual diet, as well as the quality of the Behavioural Therapy. For example, whilst there are plenty of competent dietitians out there who you can feel comfortable with and therefore be more willing to follow their advice, I'm sure that there are plenty of incompetent, ones out there who many people wouldn't feel comfortable with at all. Consequently, not all behavioural therapy will be the same.
Several things are clear however. The first is that with professional dietary behavioural therapy (nutritional counselling) the chances of putting all the weight back on are much lower than if you try to adopt a prescribed diet on your own. The second thing is that VLCD's are difficult to follow, especially in the long term once the initial motivation has worn off. Given that they are no more effective that LCD's and usually involve unpleasant side effects, why would you bother?
Keep in mind however that these VLCD studies used real food, not meal replacement shakes, and the behavioural therapy was individualized and conducted by a dietetic professional, not by an employee of a pharmacy or commercial scheme. So why is this significant?
As I mentioned previously, meal replacement schemes are a popular method that many people try. A 1993 survey in the United States found that 15% of women and 13% of men trying to lose weight were using them. Given the increase in popularity of meal replacement schemes commercially available in pharmacies of late, I would suspect that the prevalence is even higher now in this country. But do they work?
The answer, according to a review published by C.S.I.R.O. researchers in the August 2005 issue of Obesity Reviews, is basically - yes.  The most encouraging results to come from the meal replacement scheme trials was that subjects seemed to have less difficulty in adhering to them than what they did doing so to prescribed diets of the same Caloric contributions, and that they reported feeling like it was easier to use them than to follow dietary prescriptions.
This is no surprise, firstly because most of these studies provided the meal replacements to the subjects (whereas the others had to go and buy their own food) but secondly because of the fact that meal replacements require so little effort, thought and motivation; it's a classic no-brainer! You don't have to worry about Calorie counting or label reading, you just drink the damn shake, not needing to even think about it. After all, why bother thinking when someone else can think for you?
But what about in the long run? I've already mentioned that when subjects of a study are told to continue their dietary prescriptions on their own, they generally put a lot of weight back on within a few years if left to their own devices. This is not because their bodies' biochemistry changed, it's because their food choosing becomes lazy and their motivation to make the right food choices simply fades away. Funnily enough, this does not seem to be the case with the no-brainer approach, and after all, why should it? If the problem is the motivation to continue making healthy choices, then taking the choice away altogether is an almost guaranteed solution.
For example, the longest study like this was published in the August 2000 issue of Obesity Research, and found that after 4 years of patients having a meal replacement for 1 meal and 1 snack per day; subjects were still about 8 kg lighter than what they were to begin with. Well I guess that's settled right? Meal replacements are the way to go, because you don't have to make so many choices, and giving someone the chance to make a choice may mean that they could easily make the wrong choice.
That would be the conclusion one might easily reach after reading the review paper by the CSIRO researchers, though admittedly, a commercial meal replacement company paid them to write it, and the same researchers had been responsible for conducting one of the trials they reviewed. So perhaps I should fill you in on the downside to meal replacement schemes.
Firstly, it is not at all surprising that people given a meal replacement would find it easier to stick to their instructions than those who were told which foods to go out and eat, as there's less thought involved. The thing is however, the studies have found that using a single food is just as successful in short term weight loss.
For example, a study published in the November 1998 issue of the British Medical Journal  found that subjects told to replace all their meals by drinking only milk, lost more weight (9.4 kg over 4 months) than those prescribed a standard diet of the same energy value. Furthermore, subjects found it easier to stick to the milk diet than they did the conventional low Calorie diet (which presumably consisted of a reasonably balanced diet containing a variety of food groups).
In another study published in the December 2002 issue of the Journal of the American College of Nutrition,  subjects were told to replace two of their regular meals with a particular brand of cereal (the cereal was assigned to them), whilst another group was told to eat from a variety of different cereals. After several weeks, the group who used the cereal as a meal replacement has lost almost twice as much weight as those who had to make their own choices.
These results (plus a bit of common sense) provide fairly convincing evidence that the reason why meal replacements are successful is that they are simple, require little or no thought, are easy to follow, though the actual replacement used (whether it be a food or a shake) seems arbitrary. Consequently, if you really were going to replace most of your meals with a single food source, wouldn't it make more sense to do so with a healthier, nutritious food than doing so with a nutritionally poor sachet added to water?
That brings up a few other problems with these meal replacement schemes. Another issue is that they are a relatively poor source of nutrition. They are made basically from milk protein, and have added vitamins and minerals in there to prevent a micronutrient deficiency. Basically, they contain the very bare essentials you need to stay alive, and that's it. Most of them contain little or no fibre (which is why constipation can be a problem) and they contain little or none of the beneficial Omega 3 fatty acids. They contain no disease-fighting phytochemicals found in abundance in fruits, veggies and whole grains. Basically, they have a nutritional quality even poorer than that of baby formula.
This is significant because we know that there is an abundance of evidence to show that babies raised exclusively on formula are much more likely to have a plethora of health problems later on in life compared to those who receive adequate amounts of breast milk. This is presumably because breast milk contains an abundance of nutrients (some essential but many probably non-essential but beneficial anyway) while formula does not. With formula, they basically throw in everything which current science tells us is essential for life. Unfortunately, current science does not know everything, and it is more than likely that we have not even discovered many of the beneficial substances found in breast milk, just as we have not been able to isolate the precise substances found in plant foods which are responsible for the lower risk of cancer and heart disease found among people with higher intakes. (When I was a baby, scientists did not even know about the importance of Omega 3 fatty acids and lactic acid bacteria found in breast milk. In recent years they have become aware of this, which is why modern day formula has them added in. I wonder what other substances newborn babies need which will take scientists another 20 years to discover before they add that to the formula as well.)
Basically, you would not want to rely exclusively on these meal replacements, and you would certainly not want to do so for more than a few years. In the case of the people who were still having 1 meal replacement per day, they would want to make sure that the rest of their diet contained plenty of fibre and disease combating, phytochemical-rich plant sources, because they sure as hell wouldn't be getting any from the meal replacements.
Having mentioned this, most commercial meal replacement schemes are not intended to be followed long term. In fact, most of them recommend that after you lose the desired weight, you go onto some kind of maintenance plan which advises you to follow a healthier low Calorie diet. Now comes the really concerning part.
The only study which has found relatively successful weight management over several years using meal replacements did so among people who were still using them after all that time, the health implications of which are unknown.  Because most commercial schemes are (rightfully) not meant to be followed this long, we don't know what kind of success the subjects would have had having to make food choices if they ceased using the meal replacements altogether.
And that brings up the other problem with these studies; were controlled, and not observational. This means that the people being studied (the subjects) were aware that they were part of a clinical trial. An observational study would have involved contacting people who have already chosen their own weigh loss methods and getting them to report their own results. Although there are advantages and disadvantages of both methodologies, the major problem with controlled trials is that people don't always do things that same way when they know they are being studied as apposed to when they are doing it of their own accord out in the real world so to speak.
To date there have been no observational studies that I am ware of which have looked at what success certain diet schemes have had in the long run among people who have chosen to follow them on their own as apposed to those who have been recruited and studied for a trial. So why is this significant?
I have worked for pharmacies who have sold meal replacement shakes and have been employed to consult with their customers to do their weigh ins and given them dietary advice. I would often ask the customers how they thought hey were going to manage once they went off the shakes and had to go back to choosing their own foods once again. They would usually tell me that once they had lost the desired weight and achieved the weight they wanted to be, they would then start to adopt a healthy eating regime. That sounds good in theory, and I know they even believed it themselves, but here's the problem.
If they have been so unmotivated and lazy that the only way they can lose weight is by resorting to a no-brainer meal replacement shake program which takes the necessarily choices away from them, what on earth makes them think that once they are back in the real world of choosing their own foods, that they are going to be able to maintain healthy eating practices, especially given that during the meal replacement phase, they have not learnt any new motivational or food choosing skills? Realistically, if they did have the motivation and the skills to be able to maintain a healthy eating regime, then quite simply, they would have done so already and wouldn't have had to resort to meal replacements.
As I mentioned previously when comparing VLCD's and LCD's; after a few weeks, you don't seem to lose weight any quicker by having less than 800 Calories per day, and after a few months, you won't have lost any more than if you were on a typical 800 – 1,200 LCD. Consequently, if you've been feeling very hungry in between your shakes (not to mention the other uncomfortable side effects from VLCD's like headaches, constipation and even hair loss) whilst being careful to limit yourself to the 500 Calories or so they provide, then you're doing so unnecessarily. Even if you wanted to follow a VLCD and use meal replacements to do so, you could probably have closer to 5 or 6 per day and still lose just as much weight. (I think that the reason why commercial schemes use such extremely low Calorie shakes is because the customers will notice a rapid drop in their weight within the first few weeks. As I explained earlier, this is essentially due to dehydration from the exhaustion of carbohydrate stores, though the customer will inevitably be impressed by the quick results, and therefore be more likely to continue buying them expecting the same rapid results to continue.
Replace food with food
One of the silliest things I find about these meal replacement products is this: instead of replacing a high Calorie meal with a low Calorie, nutritionally pathetic powder, why not just replace the high Calorie meal with a low Calorie nutritious meal instead? For example, remember the dinner I mentioned in chapter 16; the one with the meat, pasta and veggies? Even a well balanced wholesome and nutritious meal like that provides only 180 Calories. You might as well replace your usual three meals a day with three of them instead! At 540 Calories per day, you'd still be well and truly within the VLCD range; in fact, you could have 4 or 5 a day and still lose weight just as much weight over several months, and you wouldn't even have to think about choosing your food (which is after all, the sole reason why meal replacements are successful).
So, given the nutritional uselessness of meal replacement shakes compared to the nutritional superiority of healthy foods, if you are really into the whole "replacement", no-brainer way of dieting, why not just "replace" your usual high Calorie meals with a few of the following low Calorie ones, which are far more nutritious than those silly shakes though they provide about the same number of Calories. (Check chapter 14 for serving sizes)
2 – 3 pieces of fruit
1 serve of spaghetti or bakes beans
1 ½ serves of most soups (or 1 serve of the more fatty ones)
1 big bowl of bran cereal
1 medium bowl of Muesli
1 slice of pizza
4-5 fish fingers
1 large fruit salad
2 cans of tuna
1 large muesli bar
1 salad sandwich
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