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To Fast or Not to Fast?

Susan Thompson

Welcome! Decide for yourself…to fast or not to fast!?


or  ?…



"Rapid weight loss", "quick and easy weight loss", "preventative", "therapeutic" and "low cost"; with these guarantees, who would not want to attempt a seemingly unchallenging fasting diet!? According to a report on the Food and Drug Administration (FDA) web site, as of 1995, tens of millions of Americans are dieting at any given time, in the process spending more than $33 billion annually on weight-reduction products. Are you playing the weight loss game? Here I will identify weight-loss programs advertised on the internet, discuss their claims to success, highlight specific fallacious claims, and report on findings of both the FDA and various medical studies.

  What’s on the Web?

A collection of "easy" fasting or very low-calorie weight loss plans advertised on the world wide web includes the following: California Dreaming, The Wellness Center of Alaska’s "weight loss on-the-web", Medifast, Optifast, 4 Season Weight Control Center’s "medically supervised weight loss program", Liquid Fasting Diet, All-natural Aspen Spa diet program, and various methods compiled by Fasting Center International.

As an example of programs guaranteeing a quick fix to weight problems, I will focus on both the Medifast and Fasting Center International (FCI) methods and claims concerning weight loss.


According to the Shape Up America web site, a supporter of the Medifast product, it is a "physician-supervised very low-calorie diet program of fortified meal replacements providing 450-500 calories per day". ( The purpose of Medifast is to promote quick and healthy weight loss to its customers by creating a great deficit between the number of calories used per day and the number of calories taken into the body. The fasting and weight-loss phase of the program lasts 16 weeks, followed by only 6 weeks of "realimentation", or transition back to regular foods. To qualify for the very low-calorie plan, a client must be at least 30 percent above ideal body weight and have a relatively stable medical history. However, the 860 calorie-per-day program is open to all clients.

The Medifast program, in collaboration with both the Shape Up America and Wellness Center of Alaska web sites, makes a number of intriguing claims. The first web site claims that average weight loss is three to five pounds per week. You "must rely on Medifast products during the weight-loss phase", says Shape Up America, and then you will see that the low-calorie level of the program promotes fast weight loss.

"Start now, lose 25 lbs. in Six Weeks", reads the heading of the Wellness Center of Alaska Medifast information page. ( Using Medifast, the company claims that they have created "a unique R.N. supervised weight loss and maintenance program suited for individuals who do not have the time to visit a weight loss center weekly..."; in bold print, the claim reads on: "You can reach your goal weight without ever leaving your home!" The supposed benefits of this plan include: no groceries or additional foods to buy, high energy and rapid weight loss. In addition, The Wellness Center of Alaska reports that the program provides the essential protein needed to ensure the preservation of muscle tissue while fat stores are reduced. As in the first Medifast advertisement, approximate client weight loss can be expected at a rate of three to five pounds per week.

As the Shape Up America site combines product cost with physician consultations, the cost per week is approximately $65-$85. While the Wellness Center of Alaska introduces the product as a "unique R.N. supervised...program", they proceed to make their fasting products available without medical consultation at approximately $2 per serving.

Neither Medifast program offers specific evidence to support their claims; therefore, we must ask, "Do these liquid fasting programs really work?" and "How safe are they?" I will address these questions in combination with those posed by the fasting strategies of Fasting Center International, which follows.

  Fasting Center International

Fasting Center International (FCI) makes further claims about the supposed benefits of fasting and very low-calorie diets. ( Reported claims include: "...fasting actively guards against physical and mental fatigue or exhaustion", "while fasting, the patient improves her or his physical health and gains much", "fasting cures...psychosomatic disturbances and states of exhaustion including bulimic disturbances of eating habits, and depressive moods...", and, "marvelously, it decomposes and burns all cells and tissue that are aged, damaged, diseased, weakened or dead".

Moreover, as the Medifast supporters explain that dietary protein is essential to retain lean muscle mass while dieting, FCI, relying on studies by the late Otto Buchinger, M.D., of Germany, claims that the need for protein diminishes during the fast. Likewise, according to FCI, energy levels increase, not decrease, during prolonged juice fasting.

In short, FCI makes the following statement: "Prolonged, scientific fasting has proved itself, over millennia, as humanity’s oldest, fastest, safest and the most effective weight-loss, detoxification, healing and longevity-enhancing modality known to our species".

  Too good to be true?: The FDA

Reports on the Food and Drug Administration web site clearly indicate that the FDA does not support extremely low-calorie fad diets as a healthy and successful manner of weight loss and long-term weight maintenance. ( What sounds too good to be true more than likely is too good to be true; or, says Dr. Victor Herbert, a member of the board of directors of the National Council Against Health Fraud, "If a weight loss claim is sensational, it is not true; if it is true, it is not sensational".

In a web site copy of a 1996 report in the FDA Consumer, the FDA recommends that to lose weight "sensibly and safely requires a multifaceted approach that includes setting reasonable weight-loss goals, changing eating habits, and getting adequate exercise". Moderation, variety and balance are key concepts in a healthy weight-loss plan. The report recommends avoiding low-calorie fad diets that promote weight loss through the exclusion of entire food categories, such as carbohydrates (bread and pasta).

A related FDA web site report, titled "Never Say Diet?", states that diets that aim to restrict food intake are pathways to failure. While food restriction and low-calorie diets may at first be both profitable for the weight-loss industry and easy for clients as they watch the pounds quickly drop, weight maintenance is the sometimes impossible feat. Estimates by the FDA indicate that as many as 85 percent of dieters regain the weight within two years of initial weight loss. As this happens, the dieting industry simply makes more money as dieters jump back on their weight loss plans for the second, third, fourth...or twentieth time.

One conclusion of "Never Say Diet?" is that exercise is the key. Web site author Ruth Papazian states: "Rather than severely restricting caloric intake and depressing metabolic activity as a result, weight-loss specialists now advise moderate exercise as a means of achieving weight control".

To fast or not to fast? The question is, "What does medical research say about the effects, good and bad, of fasting or starvation on the body?!"

  To fast or not to fast: what medical research says...

Let us consider and investigate the findings of medical studies that indicate the good and bad results of a fasting, or starvation, diet.


A. G. Dulloo, in "Human pattern of food intake...: a theory of autoregulation of body composition", reviews studies of the manner in which the body autoregulates itself after a period of starvation. From several experiments, including one in Greenland and one in Switzerland, Dulloo concluded that, as humans are subjected to a unrestricted refeeding process following starvation, they tend to over-compensate for lost energy and overshoot their pre-starvation body weight. (Dulloo, 25) As both body fat and lean tissue decrease in a period of starvation, body fat returns much faster than lean body mass (LBM) as the subject again eats normally. This is shown in the Greenland Expedition Case Study:

•After a ski expedition through Greenland, a 59-year-old man returned in a state of semi-starvation. 2-3 weeks later, the man’s food intake, unrestricted by scientists, was 1.5 MJ/day above habitual food intake, although his body weight and body fat were back to pre-starvation levels; his LBM, however, was still 1 kg below his normal level. 4 months post-expedition, while his lean body mass was still not fully recovered, his overall weight was 1.2 kg above pre-expedition levels, and his body fat had increased to 2.5 kg above the starting figure. (Dulloo, 28)

As similar results were found in a study of 700 persons between 1941 and 1946 who underwent food rationing in Switzerland, as well as in other related studies, we can draw a conclusion that the restoration of lean tissue is a rather slow process, allowing in the meantime for a fast restoration of body fat and overall body weight. (Dulloo, 25) Results of these studies indicate that the degree of energy over-compensation is a factor dependent on the amount of lean body tissue lost in the initial starvation period. As further evidence, on page 30, Dulloo cites the following: "Debray et al. (1946) noted that the early increase in the weight of prisoners transferred from German concentration camps to a Paris hospital in a condition of severe starvation was largely due to the accumulation of fat rather than to the rebuilding of muscles".



I. A. Macdonald and J. Webber, in their study titled "Feeding, fasting and starvation: factors affecting fuel utilization", examine the role of a decrease in the metabolic rate during a period of bodily starvation. Their conclusion reads: " the early stages of starvation there is a small rise in resting energy expenditure, but this reverts to a decreased energy expenditure after 72 h without food". (Macdonald & Webber, 273) This fall in resting and total energy expenditure during starvation or underfeeding is the body’s adaptive response, allowing it to hold on to energy sources within the body with greater efficiency.

Keys et al. (1950) and Grande et al. (1958) found that, with prolonged underfeeding of a week or more in previously healthy females, they showed a 16 percent fall in resting energy expenditure per unit body cell mass. (Macdonald & Webber, 270) This reduction in metabolic rate, in turn, supports the unwanted return of body fat at the end of the fast.

Schwartz, Dallman and Woods, in "Hypothalamic responses to starvation", similarly found that, as a result of hormonal changes interacting with the central nervous system during starvation, the following occurs: "....the classical peripheral effects of starvation are accompanied by increased drive to eat and decreased energy expenditure, reciprocal changes that enable caloric intake during refeeding to correct the energy deficit and return fat stores to their regulated level". (p 950)

Finally, the findings of Schwartz and Seeley further support the belief that a lowered metabolic rate, and thus relatively fast weight gain at refeeding, are results of food deprivation. They state: "The inability to consume enough calories to meet energy requirements is a common threat to survival. To meet this danger, animals retard their fuel depletion by lowering their metabolic rate and changing fuel substrates. They also stimulate their feeding behavior..." (Schwartz & Seeley, 1802)



According to a study by Edward J. Masoro (1995), scientists do not have enough evidence to either affirm or deny the validity of claims that fasting, or undernutrition, will lengthen the human lifespan. So far, only rodents have been thoroughly studied concerning this issue.

In the final section of his article, Masoro writes: "Does [dietary restriction] have anti-aging actions in other mammalian species, including humans? This question cannot be answered at this time because the cost in time and other resources to test this action in species longer lived than rodents is so great that up to now such studies have not been done". (Masoro, 662)


Several of the claims made by the Shape Up America, Wellness Center of Alaska and Fasting Center International web sites can not be substantiated by the results of scientific medical studies.

While Medifast may indeed offer quick weight loss, the weight loss does not, according to research, appear to be necessarily healthy or long-lasting.

As the Medifast diet offers weight loss without ever leaving home, it does not advocate an exercise plan to aid in upholding the metabolic rate or preventing loss of lean muscle mass.

While each program claims a high energy level while dieting, I found no evidence to support this statement; instead, I believe that the energy level would most likely drop as the body has a lack of incoming nutrients and a lowered metabolic rate.

I found no evidence to support FCI’s claim that fasting "decomposes and burns all cells and tissue that are aged, damaged, diseased, weakened or dead". On the contrary, I found that, without proper nutrition, the body will instead "decompose" important lean muscle mass. (Dulloo, 25)

It seems that the best diet for prolonged weight loss and healthy living is the plan recommended by the Food and Drug Administration. An eating program of moderation, variety and balance, accompanied by exercise, eliminates the processes of starvation and refeeding, which inevitably lead to an increase in body fat.


Dulloo, A. G. Human pattern of food intake and fuel-partitioning during weight recovery after starvation: a theory of autoregulation of body composition. Proceedings of the Nutrition Society. 56: 25-40, 1997.

Macdonald, I. A. and J. Webber. Feeding, fasting and starvation: factors affecting fuel utilization. Proceedings of the Nutrition Society. 54: 267-274, 1995.

Masoro, Edward J. McCay’s hypothesis: undernutrition and longevity. Proceedings of the Nutrition Society. 54: 657-664, 1995.

Schwartz, Michael W. and Randy J. Seeley. Neuroendocrine responses to starvation and weight loss. The New England Journal of Medicine. 336(25): 1802-1811, 1997.

Schwartz, Michael W., Dallman, Mary F., and Stephen C. Woods. Hypothalamic response to starvation: implications for the study of wasting disorders. American Journal of Physiology. 269: R949-57, 1995.






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