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               LIQUID DIETS
                                                         SAFE AND EFFECTIVE?

Elizabeth Hemphill


1) INTRODUCTION                                                                               6) HARMFUL CONSEQUENCES
2) PURPOSE OF TREATMENT                                                7) SCIENTIIC RESEARCH
3) HOW DOES IT WORK?                                                      8) CONCLUSION
4) SUPPORTING CLAIMS                                                       9) REFERENCES

Obesity is one of the most common problems faced by people today.  Since thirty-four million Americans are estimated to be obese, one out of every three Americans must live with this disorder.  Obesity is defined as a body weight consisting of 20% or more above the standard ideal weight (  In order to reduce obesity, most invest in diet and exercise programs.  Recently, liquid diets have been positively modified, thus rising in popularity since their fall out during the late 1970’s.  Out of the twenty million dieters, about one billion dollars will be spent this year on either medically sponsored liquid diets or over-the-counter liquid diet products (…ve/health/Library/CAD/abstract13110.html).  Even though many companies claim their diet produces safe and effective weight loss, many medical researches express their concern for various health risk consequences.
The main purpose of liquid diets is weight loss.  Many people have a low self-esteem concerning their looks and feel that weight loss would improve their outer appearance.  Losing weight tends to boost self confidence by giving a feeling of accomplishment which is an incentive to lose more.  Most of the over the counter liquid diets are invested by people who are not necessarily obese, but interested in taking off the excess weight.

Liquid diets are also widely used to improve health conditions.  Dieting results in weight loss which indirectly can decrease health risks. "If all Americans were to achieve a normal body weight, it has been estimated that there would be a 3 year increase in life expectancy, 25% less coronary heart disease, and 35% less congestive heart failure and stroke (  Obesity has been related to high blood pressure, heart disease, respiratory problems, gallstones, insomnia, and some cancers ( Some doctors prescribe liquid diets to patients unable to digest solid foods; however, the majority of liquid diets are used for the purpose of losing weight.

Since a reduction of 3,500 calories is needed to lose a pound, most of the liquid diets consist of a very low calorie intake of 400-800 calories a day (http://www.webcom/!lewrose/brochures/diet.html).  Most liquid diets consist of a high protein shake instead of eating meals.  Since the diet lacks the excess calories and fat calories, the body can directly start to burn the already digested fat.  The main reason these liquid diets are effective is because of their "complete removal of patients from the food environment" (  These diets usually cause a decrease in energy which results in a rapid weight loss of about 3-4 pounds a week.
Some of the new liquid diet programs such as Optifast, Medifast, and HMR consist of a 3 month fasting period (420-800 calories a day in liquid shakes), a "refeeding" stage (sensible meals), and a maintenance stage (patients eat sensibly on their own).  This three step diet method is performed in conjunction with an exercise program and support groups.  These types of liquid diet programs help the patient understand the importance of long-term dietary change, exercise, and behavioral modification (…ve/health/Library/CAD/abstract13110.html).

Liquid diets have drastically improved since the 1970’s.  Today, liquid diets claim to contain complete protein, carbohydrate, fat, vitamin, and mineral supplements.  A few of the most popular liquid diets are the Slender Now Thick Shake, ToppFast Diet Plan, Slim Fast, Medifast, and Optifast.  Many companies declare that their diets give "delicious, nutritious, and filling shakes" that are so convenient to make and drink instead of preparing a meal (  36% of the recommended amount of fiber needed each day is guaranteed.  Fiber tends to be an extremely important nutrient in weight loss because it cleanses the digestive tract, aids in the absorption of fats, and provides a content feeling of fullness.  Also, these diets provide 18 of the 23 amino acids including the 8 essential ones as well as proteolytic enzymes which aid in protein digestion.  These products affirm an overall improvement in health and nutrition as well as weight loss.

 The Fasting Center International claims that sustained fasting (juice fasting) is one hundred percent safe and when combined with therapeutics will "treat virtually every disease, from cardiovascular and digestive disorders to rheumatic and skin conditions" (  The people on the FCI programs lose one pound per day for the first 20 days on average.  The juice fasting will rejuvenate and detoxify the body.

 Liquid diets are not for everyone; they may be successful for some and not for others.  Any kind of dieting requires a highly motivated and disciplined person.  Many people on the medically supervised liquid diets started showing vast improvements in health after only a few weeks of dieting.  This effectiveness was tested by electrocardiograms as well as weekly blood tests which measured the levels of sodium, potassium, and other blood nutrients (  Reduction in their blood lipids, blood sugars, and blood pressure were shown to occur.  Some patients with diabetes, high blood pressure, or high cholesterol can reduce their medications due to the health benefits from their diet (  In addition to improving health, many disciplined people lose considerable amounts of weight.  The more obese the person is, the more weight is lost.  The problem with liquid diets is not losing the weight but keeping it off.  It has been predicted that for every 100 people who lose weight, 95 will gain it back (…ve/health/Library/CAD/abstract10275.html).  The diets proved most effective, Optifast, Medifast, and HMR, are the ones combining liquid diets with exercise and behavioral modification classes.  Without support classes, people will revert back to their old habits and regain their weight when they are finished dieting (…ve/health/Library/CAD/abstract13110.html).  Dieting without learning how to make it a long term change in eating behavior will lead to the everlasting gaining and losing weight which causes the yo-yo effect.  A prospective cohort study divided 59 patients with an average weight of 133 kg into two groups: 1st- had both a liquid diet and behavioral therapy; 2nd- had just the behavioral therapy.  This study observed these two groups for five years to determine if behavior modification improved weight loss.  56% of the 1st group dropped out while only 28% of the 2nd group dropped out.  However, the group with the combination of liquid diet and behavioral treatment proved the most effective concerning maintaining weight loss (

 Many of the sources from which this information was found on the world wide web are advertisements for companies.  Since they are trying to sell the product, they make their product seem unbelievably perfect.  Most of the articles found were not scientifically researched, but were instead a few accounts expressing the product’s amazing results.
Even though liquid diets may have instructions and limitations on usage, critics claim that these diets have a large potential for misuse.  Health risks may rise from lack of medical supervision or from people with only mild obesity on the diet.  Many weight loss experts claim that liquid diets causing rapid weight loss tend to over use lean muscle and slow the metabolism, thus, making it even more difficult for weight loss to be maintained.  Eventually, liquid diets can lead to the development of muscle cramps, anemia, dizziness, menstrual abnormality, and constipation.  The people who are only mildly obese lose too much lean body mass which increases their chance of cardiac dysfunctions (http:www/…ve/health/Library/CAD/abstract12030.html).  The intensity of protein in the liquid diets can cause an electrolyte imbalance which results in irregular heart beats (  Studies show that 25% of the people on liquid diets develop gallstones due to their inability to contract bile.  In addition, liquid diets have even been known to cause deaths.  During the 1970’s, 58 deaths were linked to the inadequate nutrition and too little calories in liquid diets (…ve/health/Library/CAD/abstract13110.html).

Ultra Slim-Fast
 A staff of doctors at the UCLA School of Medicine did a study to determine if the continued use of the Slim Fast products as meal replacements would result in an initial weight loss followed by a long-term maintenance (Heber 608-614).  The goals of the study were to determine the extent of weight loss, the changes in plasma lipids, and the rate to which people complied to the weight loss program.  Six centers chose individuals with mild to medium obesity to be subjects for the study.  Even though these centers were not supplied with nutrition or obesity knowledge, they were experienced in recruiting people for scientific testings.

There were 301 patients chosen, 71 males and 230 females, each who received $25 a week to participate in this study.  Instructions on the Slim Fast package insert concerning the diet were given to the subjects.  They were told to drink two of the Ultra Slim-Fast shakes to replace meals, one shake for a snack, and a low-fat meal for either lunch or dinner.  The calorie intake adds up to be about 1000-1200 kcal/day.  For the first 12 weeks, the subjects were accurately weighed on a calibrated doctor’s scale, and afterwards, they were weighed every other week.  Besides measuring weight loss, plasma samples were also tested.  The samples determined the cholesterol, triglycerides, and high density lipoprotein cholesterol levels.

After the 12 weeks of dieting, men lost an average 18.6 lbs. while females lost 14 lbs.  The second phase of the study was to determine the long-term effects of the diet.  35 of the subjects who completed phase one did not participate in phase two due to their unaccountable weight loss.  After a year, 41% maintained their weight below their weight at 12 weeks while 36% maintained 80% of their weight loss.  After 2 years, 22.8% weighed lower than their weight at 12 weeks while 39% maintained 80% of their weight lost.  This does not meant that all of the subjects maintained their weight, some did gain back their weight and more, but these percents are on average.  The changes is the plasma cholesterol levels, plasma triglycerides levels, and plasma high-density lipoprotein cholesterol were few.  The level usually decreased when there was a drop in weight but usually averaged back up by the end of 12 weeks.  In addition to those tests, the subjects’ opinions concerning the overall perception of the diet program was collected.  The ones that rated the diet program as excellent were the one that had lost the most weight.

From this study, the doctors concluded that taking Ultra Slim-Fast for two meal replacements combined with a low fat meal is safe and effective over a 12 week duration.  Since most of the obese people are only mildly or fairly obese, then Slim-Fast is considered a good way to take off a few of the unnecessary pounds which reduces the health hazards of being obese.  Since Slim-Fast is so widely available and inexpensive, some suggest that medical doctors should send slightly obese patients to purchase these commercially available products that are just as safe and effective as the expensive medical ones.  However, many fear that commercially sold products are abused which leads to many dangerous side effects.  Although this study was proved safe and effective for 12 weeks, this does not mean that this diet is safe when taken to the extreme such as one shake a day for 24 weeks.  In order to diet safely, people must follow the different guidelines concerning each diet.

I.  VLCDs relation to changes in EKGs
During the 1970’s very low calorie diets (VLCD) became very popular (Seim 817-819).  However, concerns rose about the safety of these VLCDs when EKG levels varied and suddenly deaths occurred.  The EKG levels of those who suddenly died while on the VLCDs were similar to the EKGs of starving individuals.  They both had prolonged QT intervals.  The early VLCDs contained a poor quality of protein and did not contain enough vitamins and minerals; therefore, they were basically starving the people.  Due to the results of the early VLCDs, new diets were created hoping to be safe and effective.  The purpose of this study is to determine if obese individuals have abnormal EKGs before, during, or after participating in VLCDs.  The product used in this study is called Optifast-800.  It is a 800 kcal/d diet consisting of 100g/d carbohydrate, 13 g/d fat, and an adequate supply of vitamins and minerals.

 One hundred and ninety-three women participated in the 26 week long diet program which consisted of drinking Optifast combined with group therapy.  For the first 12 weeks, the women’s diet consists of Optifast shakes and non-caloric beverages.  After the first 12 weeks, food was introduced again back into the diet in small amounts while the protein supplement (Optifast) was decreased.  This phase lasted for 6 weeks.  During the diet as well as 3 months afterwards, all of the subjects attended counseling groups which taught them about eating behaviors, the importance of changing one’s lifestyle, and strategies for maintaining their weight loss long-term.  EKGs were taken before the diet (baseline), 3 months after the diet began, and 3 months after the diet had been completed.

Of the 193 subjects, only the results for 126 of the subjects were analyzed.  Thirty-four out of the 126 women had normal readings on all three of the EKG tests.  Those that had an abnormal reading on at least one EKG had minor ST-T wave abnormalities, sinus bradycardia, prolonged QTc, or sinus tachycardia.  None of the changes in EKGs correlated with the diet; therefore, the VLCD did not have any effect on the women’s change in EKG levels.  Since the earlier VLCDs caused prolonged QTc on EKGs, these eight people were further studied.  Four  out of the 8 showed prolonged QTc before the diet even started.  Two subjects developed QTc prolongation after 3 months of the diet while two others developed it by the 6 month EKG reading.  There were no cardiac complications reported during or after the diet.  Since 33 subjects did drop out of the study, the possibility that they may have dropped out due to abnormal EKGs had to been considered.  The body mass indexes (BMI) was calculated on all 193 subjects.  Since the BMIs of all of the subjects (even those who dropped out) were normal and there were no significant differences discovered in the QTc prolongation of those who dropped out, then none of the subjects withdrew from the study due to EKGs.  Thus, the results should hold true.
 By measuring the patients’ EKG levels frequently, a close watch of any abnormalities was noted.  Since prolonged QTc intervals on the EKG have been known to cause ventricular arhythmias, torsade de pointes, and sudden death, the doctors were especially interested to see if there was any correlation of these prolonged QTc intervals to the Optifast diet plan.  These prolonged QTc intervals have also been found to be more likely found in obese people.  Only two of the subjects (1.6%) were found to have more than 2 s.d. above average QTc intervals while 2.5% of the population has QTc intervals greater than 2 s.d ; therefore, VLCDs cannot be connected to a risk of prolonged QTc intervals.  Thus, this study concludes that VLCDs are safe and have no relation to abnormal EKG readings.  The modern VLCDs have improved their quality of protein and have added sufficient vitamins and minerals to where they do not  cause abnormal EKGs if followed correctly.

II.  Effectiveness of Optifast
Another study was done to evaluate very low calorie diets (Walsh 231-235).  This study was led by Michael Walsh, MD and Thomas Flunn, MD.  Like the study above, patients consumed the liquid formula Optifast for 12 weeks, were reintroduced to food for 6 weeks, and then ate a regular diet of 1200 to 1400 kcal a day.  Once a week the patients attended a support meeting where behavioral modification, nutrition, and exercise training was taught.  Sixty-one % of the patients stayed in the program until at least 19 weeks when they were no longer drinking liquid shakes.  The average weight loss for men was 27.2 kg and 19.3 kg for women.  After 54 months of the program, most patients maintained a loss of 5.1 kg which was 4.3 % of their original weight.  As more time passed, the patients gained more weight back.  However, those that regularly exercised maintained an average of 9.6 kg compared with 1.3 kg for those who did not exercise.  This study proved that VLCDs have restricted long-term success.  Continued exercise and longer program attendance usually lead to better results in maintaining the weight lost.

I.  Determining Relationship between weight loss and development of gallstones
 Severely obese individuals tend to develop changes in their hepatoliliary system such as fatty liver, increased blood concentrations of hepatic enzymes, and an increased risk for cholelithiasis (gallstones).  Weight loss improved all of these health hazards of the obese except for the development of gallstones.  In fact, two studies actually show an increased development of gallstones with weight loss.

 The purpose of this study was to determine if VLCDs were related to the hepatic changes and the development of gallstones in people. The 73 qualified subjects were first instructed to eat a low-energy diet plan with men receiving 1200 kcal and women 1000 kcal for two weeks prior to the beginning of the formula diet.  The subjects were then randomly assigned to liquid formula A (Equiline 840 kcal) or liquid formula B (Ultrafast 800 kcal).  Formula A provided 23.4 g fat/d while Formula B contained 13.5 g fat/d.  The formula phase of the diet lasted 10 weeks.  Patients were instructed to drink all of the formula in 3-6 servings per day in replacement for meals.  A few specific food items were allowed during this phase as well as over 1920 mL of water.  Then the subjects were switched to regular food for 4 weeks.  All subjects attended a group program weekly to learn about nutrition and behavior modification strategies.

 During the course of the diet, the subjects were tested regularly to insure progress and safety.  They were weighed and had waist and hip measurements once a week.  Blood tests were completed before the diet, at 2, 6, and 10 weeks during the formula diet, and at 2 weeks after returning to solid foods.  The blood studies consisted of the normal tests as well as electrolyte and lipid analyses.  Specific liver tests were also performed as well as ultra sonograms of the gallbladder before and after the 10 week formula diet.

 Out of the 73 subjects, 59 had normal gallbladders and 14 had previous gallstones.  Only 69 were included in the analysis because 4 subjects had to drop out.  Two out of the 53 patients that repeated the gallbladder ultrasound after the 10 week formula diet were found to have asymptotic gallstones.  The subjects that developed gallstones were discovered to be taller and with larger waist-hip measurements than the other subjects.  They also showed a more rapid decline in weight than the other patients.  The serum cholesterol levels overall declined throughout the study, but there was no significant difference between the levels of those who developed gallstones and those who did not.  The serum bilirubin concentrations did not relate much to weight loss, but the patients who developed gallstones had a higher bilirubin during the study.  The SAP and the LDH declined greatly during the course of the study.  The AST and ALT levels rose in the patients who developed gallstones.

 The study verified that changes in liver tests and development of gallstones occurred in some obese patients consuming a formula diet over 10 weeks.  However, these risks are much lower than with those patients consuming very-low-energy or low-fat formula diets.  Since only 2 out of 53 (3.8%) patients developed gallstones, this is greatly lower than the 10-37% who developed gallstones on earlier studies.  The two formulas (A and B) used in this study contain more energy and fat which is healthier for the body, but also slows the weight loss.  There is not much difference in weight loss between the patients who developed gallstones and those who did not.  Therefore,  the researchers believed that there may be a correlation between the total energy and fat intake and developing gallstones.  Other studies have showed that in order for the gallbladder to contract fully, more than 7 grams of fat must be consumed in a single meal.  The amount and rate of weight lost also contributes to the development of gallstones.  The more weight lost at a faster rate, the higher the risk for gallstones.  This gives support that "total energy, degree of negative energy balance, and rate of weight loss are closely interrelated and are correlated with the degree of bile cholesterol saturation and/or frequency of gallbladder emptying" (253).  This study proved that any liquid diet is apt to cause the development of gallstones; however, diets with more fat grams are less likely to cause gallstones.  Therefore, Equiline and Ultrafast formulas which provide between 13.5 and 23.4 g fat/d are less likely to cause gallstones in patients than other commercially sold products containing 1 g fat/d.

II.  Effectiveness of VLCDs
A study done by Anne Shovic and other nutritionist consultants wanted to determine the effectiveness and dropout rate of VLCDs (Shovic 583-584).  They also found that VLCDs are very effective for inital weight loss and decrease in blood pressure and cholesterol values.  However, they also determined that all of the patients who hadn't started regaining weight did so after one and a half years.   This VLCD resulted in a high dropout rate.  Twenty-two of the 72 patients (31%) dropped out of the program before phase one, (the consumption of liquid shake) was complete.  There are many reasons patients may drop out: too difficult physically or emotionally, high costs, inconvenient, and abnormal health conditions.

III.  Determining relationship between VLCDs and cognitive effects
 "Cognitive effects of long-term weigh reducing diet" is a study completed by Kretsch to determine if there is a connection between food restriction and cognitive impairments (Kretsch 14-20).   It is already known that people suffering from eating disorders have impairments with short term memory, attentional focus, and spatial reasoning.  This study was to discover if long-term calorie restriction (not starving oneself) would have an effect on cognitive functions.  The results proved that short-term and long-term calorie restriction both caused a slowing of reaction time.  A focused attention and immediate memory were shown to become impaired with a short-term calorie restriction program but went back to normal with long-term calorie restriction.  Kretsch claimed that further study is needed to determine the significance of a slowed reaction time with restricted calorie intake.

For obese patients, liquid diets can definitely cause a large amount of weight loss as well as an improvement in health.  However, if there is no medical supervision, liquid diet programs can get misused and lead to health risks.  Many mild obese patients without medical attention tend to test out various diets trying to find one more successful.  However, the more one diets, the slower one’s metabolism becomes; therefore, one must eat less in order to maintain one’s weight.  Since the safety and effectiveness of different products claim various results, it is important for all dieters to seek medical help before starting a liquid diet.  Questions concerning effectiveness, commitment, health risks, cost, and more should be asked (http://www.webcom/!lewrose/brochures/diet.html).  Many advertizing companies fail to provide information concerning the dropout rate, the regaining of weight, and the risks that are involved with the diet program.
Scientific research provided information concerning Slim Fast, Optifast, and VLCDs in general.  All diets were effective in initial weight loss.  Slim Fast was proved to be safe and effective for the 12 week program which took off unecessary pounds of obese patients.  Since a long term study was not completed, the overall effectiveness cannot be determined.  Even though Slim Fast may be mostly safe, if the diet program is abused, then dangerous side effects may occur.  Optifast was also proved to be safe and effective.  Even though earlier VLCDs had been known to affect EKG levels and the development of gallstones, modern VLCDs have improved their quality.  However, this does not mean that VLCDs will not cause gallstones to develop. Modern VLCDs are not as strongly related to the harmful consequences due to their increase in fat grams and mineral and vitamin supplements.


Heber, D., JM Ashley, HJ. Wang, and RM. Elashoff.  "Clinical evaluation of a minimal
intervention meal replacement regimen for weight reduction."  Journal of the American College Nutrition.  13(6):608-14, 1994 Dec.

Hoy, MK., S. Heshka, DB. Allison, E. Grasset, R. Blank, M. Abiri, and SB. Heymsfield.
"Reduced risk of liver-formation-test abnormalities and new gallstone formation with weight loss on 3350-kJ (800-kcal) formula diets."  American Journal of Clinical Nutrition.  60(2):249-54, 1994 Aug.

Kretsch, MJ., MW Green, AK Fong, NA Elliman, and HL Johnson.  "Cognitive effects of
a long-term weight reducing diet."  International Journal of Obesity & Related Metabolic Disorders.  21(1):14-21, 1997 Jan.

Seim, HC., JE. Mitchell, C. Pomeroy, and M. de Zwaan.  "Electrocardiographic findings
associated with very low calorie dieting."  International Journal of Obesity & Related Metabolic Disorders.  19(11):817-9, 1995 Nov.
Shovic, Anne Caprio, PhD, Susan Adams, Jane Dubitzky, and Melody Anacker.
"Effectiveness and dropout rate of a very low calorie diet program."  Journal of the American Dietetic Association.  93(5):583-4, 1993 May.
Walsh, MF and TJ Flynn.  "A 54-month evaluation of a popular very low calorie diet
program."  Journal of Family Practice.  41(3):231-6, 1995 Sep.


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