Fitness and fads
Quick weight loss: sorting fad from fact
David C K Roberts
MJA 2001; 175: 637-640
How to recognise a fad diet -
Why fad diets "work" -
Our metabolic flexibility has limits -
Low carbohydrate diets -
High carbohydrate, very low fat diets -
Other types of fad diets -
How to advise patients -
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Current contents list -
More articles on Nutrition
- This article reviews popular diets for their ability to produce
effective weight loss.
- Most of the "evidence" for fad diets is based on anecdotal findings,
theories and testimonials of short term results.
- The most prominent elements of fad diets are those of ritual
and sacrifice. These diets offer quick and painless weight
loss while allowing consumption of favourite or tasty foods, but
place severe restrictions on certain other foods or food categories.
- Fad diets often work in the short term because they are low-kilojoule
diets in disguise; that is, energy intake as a result of the diet is
lower than the person's requirements.
- Successful long term weight loss depends on the consumption over a
long period of time of less energy than is expended. The ideal approach
is to increase physical activity while modifying eating behaviour to
achieve a nutritionally balanced intake.
As the desire for instant thinness continues to be a feature of our
society, so is the appearance of new and not-so-new fad diets. The
Journal published an article in 1999 reviewing substances used in
weight loss; the authors concluded that most had no evidence to
support their action.1 An excellent review of
popular weight-loss diets has been published elsewhere by Anderson
and co-workers.2 In this article, I review
popular diets for their ability to produce effective weight loss, and
provide additional information to assist practitioners in
distinguishing fad from fact.
As a nation, we are fat. According to the latest National Nutrition
Survey,3 64% of Australian men and 47%
of women are overweight or obese. The situation is getting worse
rather than better — the proportion of overweight or obese adults has
increased since 19834 by about 52% for men and 34%
Personal efforts to address the overweight problem, while common,
are apparently not working. One in three Australians claim they are on
some type of "diet",3 yet energy intake has
increased and physical activity levels have decreased.5 Mathematical
modelling suggests that weight loss is a simple matter, with limited
inputs and outputs to be controlled.6 Yet most people who
successfully lose weight return to their old eating habits, and
within two years regain most of the lost weight.7 The methodology
and design of reported weight-loss studies have been
questioned,8 especially in studies
involving long term follow-up. Weight loss can be a treatment effect
(weight loss to improve diabetes control) or it can be an outcome of
some other treatment (medication used to produce weight loss),
making randomised controlled trials difficult to interpret.
The lure of rapid weight loss promised by each new popular diet is
undoubtedly compelling. A survey in the United States found that more
than one in five dieters used fad diets.9 Fad diets feed into the
psyche of people who seek to look better and feel better with the
minimum of effort.
Sensible eating for weight loss often does not appeal to people who
feel they are already doing the best they can. However, very simple
dietary changes, followed diligently, can often produce effective
weight loss at a rate that can be maintained over the longer
term.10 Conversely, when weight
loss is too fast, changes in body composition, especially the loss of
lean body mass, can compound the problem of overweight in the longer
term. One large study reported an overall increased risk of major
weight gain in the long term (at 6 and 15 years) in those who undertook
weight-loss attempts (dieting) at baseline.11 However, these findings
do not rule out the potential success and benefit of weight-loss
programs which aim to encourage permanent changes in behaviour.
To the aware practitioner, fad diets are relatively easy to spot (Box
1), but they can be quite convincing to the lay person. They offer a
quick solution to a long term problem. The author or promoter presents
what appear to be scientifically valid explanations or references to
support the dieting theory. The promoter may be tertiary educated,
although frequently has no formal nutrition or dietetic
qualifications.12 The theory behind the
weight loss approach is often explained using scientific
terminology that simplifies or expands upon the biochemical and
physiological facts that provide the evidence to support the claims.
However, the validity of the scientific support is often
questionable. Most of the "evidence" for fad diets is based on
anecdotal findings, theories and testimonials of short term
The most prominent elements of fad diets are those of ritual
and sacrifice. The ritual aspect is to always include, say,
grapefruit daily but never add sugar to your beverage (sacrifice).
These diets offer quick and painless weight loss while allowing
consumption of favourite or tasty foods, but severely restrict
certain other foods or food categories.
Fad diets often work in the short term because they are low kilojoule
diets in disguise (Box 2); that is, energy intake as a result of the diet
is lower than the person's requirements.
This is the only way to lose weight — to consume less energy than the
body needs. No magic ingredients, strange food combinations or
pseudoscientific formulas will alter this metabolic fact. The rate
of weight loss (which reflects shifts in water equilibrium as well)
varies depending on the relative proportions of the three major
nutrients in the diet — carbohydrate, fat and protein. The
macronutrient composition can also affect appetite: high-protein
diets can suppress appetite, as can ketosis, which results from
severe carbohydrate restriction.7
Because energy from food comes only from these nutrients (and
alcohol), the number of dietary permutations and combinations is
limited. Thus, most diets can be categorised into three main
- low carbohydrate with the emphasis on high
- low carbohydrate with the emphasis on high fat; and
- high carbohydrate with an emphasis on low fat.
To complete the picture, some fad diets promote one food or a very
limited range of foods, while others may be based on individual
characteristics such as blood type or personality, or on an unproven
physiological concept (such as cleansing "toxins" from the body).
Fad diets are generally nutritionally unbalanced and lack essential
nutrients.13 They have the potential
for health risks. A major problem is that the unfounded nutritional
theories espoused with these diets undermine sound nutrition
education and public awareness of the importance of healthy long term
eating combined with regular physical activity.
The primary objective in effective weight loss is to lose fat and not
lean body mass (muscle). From a biochemical point of view, this means
encouraging the body to use fatty acids for energy with minimal
reliance on glucose as an energy source, except for those tissues with
an obligate requirement for glucose, such as red blood cells.
With limited carbohydrate in the diet, once carbohydrate (glycogen)
stores have been used the only source of glucose available to the body
is that derived from the carbon skeletons of amino acids. In this
situation, and in the absence of sufficient dietary protein, body
protein (lean body mass) is catabolised to provide glucose. Muscle
mass will therefore decline markedly on a very low carbohydrate,
restricted protein diet. The ideal weight-loss diet should provide
enough carbohydrate to prevent net protein catabolism, enough good
quality protein to meet the normal needs of protein turnover, and
enough fat to meet essential fatty acid requirements.
Low carbohydrate diets have a long history. The Greek Olympians are
said to have eaten high meat, low vegetable diets to improve athletic
performance.7 The modern popularity of low
carbohydrate diets has been influenced by the seeming "failure" of
low fat diets because of a misunderstanding that energy intake is not
important and that you can eat as much low fat food as you like and still
lose weight.12 Furthermore, low
carbohydrate diets appear to work, as they produce rapid weight loss
in the first week.7
Because the body's demand for glucose is constant, body glycogen
stores are mobilised in the early phases of a low carbohydrate diet,
and for each gram of glycogen lost two to four grams of intracellular
water are lost (intracellular water maintains isotonicity).
Consequently, there is greater water and hence weight loss in the
early days of this type of diet. Water equilibrium is re-established
in the second and subsequent weeks, so that, in the longer term, weight
loss simply reflects the energy deficit. Energy-nitrogen balance
studies have demonstrated that the greater weight loss on a low
carbohydrate, high fat diet is accounted for by losses in body
If carbohydrate restriction is severe (for example, less than 60 g),
ketosis can result, which decreases appetite and causes nausea, but
can also cause hyperuricaemia as ketones compete with uric acid for
renal tubular excretion.7
Popular low carbohydrate, high protein diets include the Zone
Diet,14 the Carbohydrate
Addict's Diet,15 and the Sugar Busters!
diet.16 A popular low
carbohydrate, high fat diet that has been around since the 1970s is the
Dr Atkins diet.17
Low carbohydrate, high protein diets
As with other low carbohydrate diets, high protein diets result in
initially rapid weight loss. If continued, they produce weight loss
because they are also low kilojoule diets.
There is also evidence that higher-protein diets are more satiating.
People feel fuller and eat less after a meal with a high protein content
(31%-54% energy).18-20 A low fat,
higher-protein diet (25% of energy) has also been found to produce a
significantly reduced energy intake and greater weight and fat loss
over six months compared with a low fat diet with 12% energy from
protein.21 However, energy
restriction is responsible for the weight loss.
An additional problem of high protein diets is the extra solute load
placed on the kidneys owing to greater production of nitrogen waste
products, particularly in situations of high water loss from
perspiration or inadequate fluid intake contributing to
dehydration.7 In the long term, very high
protein diets may increase the risk of osteoporosis in people with
inadequate calcium intake by increasing calcium
Low carbohydrate, high fat diets
Popular for many years, the Dr Atkins diet17 allows protein-rich
foods such as meats, fish, chicken and eggs, but also encourages fatty
foods like butter, cream, fats, oils and salad dressings in large
amounts. The key principle of the diet is to develop ketosis, which is
seen as a dieting advantage because loss of ketones in the urine is
regarded as wasting "usable" energy. The early stage of the diet
restricts carbohydrate to no more than 20 g per day to achieve this.
However, the actual energy value of urinary ketone losses is
insignificant compared with the energy deficit of around 30 MJ
required to lose one kilogram of fat. The daily loss of energy from
ketones rarely exceeds 2%-3% of the total energy
requirement.23 After ketosis is
established, small amounts of carbohydrate (up to 60 g per day) are
allowed back into the diet, provided urinary ketone losses are
Common consequences of following this type of diet include
dehydration, diarrhoea, weakness, headaches, dizziness and bad
breath. Over the longer term, such a diet can increase the risk of
atherosclerosis — one study has shown that this diet increases serum
cholesterol levels and may increase the risk of coronary heart
disease by more than 50% with long term use.2
This type of diet also does not include sufficient fruits and
vegetables for good health and promotes the misconception that
energy intake is not important.
High carbohydrate diets for weight loss can be consistent with
healthy eating if they recommend high fibre intakes and provide
sufficient essential fatty acids and fat-soluble vitamins.
However, if lean meat and fish and low fat dairy products are allowed
only in tiny amounts (eg, as "condiments" only), there is the risk of
inadequate intakes of calcium, iron, zinc and high quality protein.
The Pritikin diet,24 for instance, recommends
that fat intake be less than 10% of energy intake, which is likely to be
unpalatable for many people used to a Western diet and is close to the
lower limit of our requirement for essential fatty acids. The
Pritikin diet is also quite low in protein in one of its forms (Maximum
Wt Loss), so the quality of any protein present becomes important.
A US study of popular diets has demonstrated that diet quality
(measured by dietary variety and intake of five food groups, fat,
saturated fat and sodium) is higher in high carbohydrate diets and
lowest in low carbohydrate diets.25 The same study showed body
mass index is lower in people following high carbohydrate diets and
highest in people on low carbohydrate diets.
Over the years, an array of "one food" diets have been promoted, such as
the rice diet, banana diet, and the grapefruit diet. These types of
diet are potentially dangerous, nutritionally unbalanced and
unscientific, and encourage poor eating habits and food faddism.
Some diets base their theories on unproven information about
physiology and metabolism, such as that which suggests that blood
type influences the best food pattern for you,26 and diets that suggest
excess weight is caused by liver dysfunction and not energy
Successful long term weight loss depends on the consumption over a
long period of time of less energy than is expended (Box 3). The ideal
approach is to increase physical activity while modifying eating
behaviour to achieve a nutritionally balanced intake.10
Energy needs for weight loss are best established by determining the
energy needs of the person at their desired weight and then providing
for a weekly energy deficit of about 30 MJ, or 4.2 MJ (1000 kcals) per
day. This usually means a suggested energy intake of around 5 MJ (1200
kcals) per day for a woman and up to 8 MJ (1900 kcals) per day for a man.
All foods should be allowed, with an emphasis on fibre-rich
carbohydrate foods (cereals, breads, fruit and vegetables), fish
and other seafood, lean meat and low fat dairy foods, with small
amounts of unsaturated fat as oil or margarine. Behaviour
modification to help control impulsive eating is also useful.
The eating plan should be based on the principles of the Australian
Guide to Healthy Eating.28 Increased and regular
physical activity adds substantially to the success of weight loss
programs, so regular physical activity should be
I wish to thank Ms Toni Irwin (APD), Dietitian/Nutritionist, for her
help and assistance in the preparation of this article.
(Received 4 Oct, accepted 31 Oct, 2001)
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non-prescription weight loss supplements. Med J Aust 1999;
Anderson JW, Konz EC, Jenkins DJ. Health advantages and
disadvantages of weight-reducing diets: a computer analysis and
critical review. J Am Coll Nutr 2000; 19: 578-590.
Australian Bureau of Statistics and Commonwealth Department of
Health and Family Services. National nutrition survey: selected
highlights, Australia. Canberra: ABS, 1997. (Catalogue no.
National Heart Foundation of Australia. Risk factor prevalence
study No. 2. Canberra: NHF 1983.
Armstrong T, Bauman A, Davies J. Physical activity patterns of
Australian adults. Results of the 1999 National Physical Activity
Survey. Canberra: Australian Institute of Health and Welfare, 2000.
(Catalogue no. CVD-10.)
Kozusko F. A setpoint based dieting model. Math Comput Model
1999; 29: 1-7.
Denke M. Metabolic effects of high-protein, low-carbohydrate
diets. Am J Cardiol 2001; 88: 59-61.
Lean ME. Is long-term weight loss possible? Br J Nutr 2000;
11 Suppl 1: s103-s111.
Jeffery RW, Folsom AR, Luepker RV, et al. Prevalence of overweight
and weight loss behavior in a metropolitan adult population: the
Minnesota Heart Survey experience. Am J Public Health 1984;
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Korkeila M, Rissanen A, Kaprio J, et al. Weight-loss attempts and
risk of major weight gain: a prospective study in Finnish adults.
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Stein K. High-protein, low-carbohydrate diets: do they work?
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weight-reducing diets. J Am Diet Assoc 1985; 85: 450-454.
Sears B, Lawren B. The Zone — a dietary road map. New York: Harper
Heller RF, Heller RF. The carbohydrate addict's diet. The
lifelong solution to yo-yo dieting. London: Reed International,
Steward HL, Bethea MC, Andrews SS, Balart LA. Sugar Busters!
London: Random House, 1998.
Atkins R. Dr Atkins' new diet revolution. New York: Avon, 1992.
Stubbs RJ. Macronutrient effects on appetite. Int J Obes Relat
Metab Disord 1995; 19 Suppl 5: s11-s19.
Stubbs RJ, Ritz P, Coward WA, Prentice AM. Covert manipulation of
the ratio of dietary fat to carbohydrate and energy density: effect on
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Am J Clin Nutr 1995; 62: 230-237.
Stubbs RJ, Harbron CG, Murgatroyd PR, Prentice AM. Covert
manipulation of dietary fat and energy density: effect on substrate
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weight-loss methods. 1. Diets. Postgrad Med 1982; 72: 73-80.
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Grosset and Dunlap, 1981.
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correlation to health, nutrition, and obesity. J Am Diet Assoc
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School of Health Sciences, University of Newcastle, Newcastle, NSW.
David C K Roberts, BSc, PhD, Foundation Professor of
Nutrition and Dietetics
Reprints will not be available from the author.
Professor D C K Roberts, School of Health Sciences, University of
Newcastle, Newcastle, NSW 2308. david.robertsATnewcastle.edu.au
Readers may print a single copy for personal use. No further
reproduction or distribution of the articles
should proceed without the permission of the publisher. For
permission, contact the
Australasian Medical Publishing Company.
Journalists are welcome to write news stories based on what they read here, but should acknowledge their source as "an article published on the Internet by The Medical Journal of Australia <http://www.mja.com.au>".
© 2001 Medical Journal of Australia.
1: Common features of fad diets
- Promises of rapid weight loss
- Elements of ritual and sacrifice
- Magical food or food combination
- Unlimited foods of some type
- Rigid menus or monotonous food choices
- Jargon and scientific half-truths
- Lack of good scientific evidence
- Lack of acknowledgement of physical activity needs
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2: How to assess weight loss diets — GP checklist
- Does the diet promote a new fact or newly discovered secret?
- Does the diet involve purchase of a commercial product?
- Is there a promise of rapid weight loss?
- Has the diet been independently tested and results published in a reputable journal?
- What are the credentials of the author or promoter?
- Will the diet result in only small quantities of carbohydrate foods being eaten?
- Does the diet promote adequate intakes of the main food groups: fruit and vegetables, cereal foods, low fat dairy foods, lean meats?
- Is there an overemphasis on dietary fat or any one food type?
- Is the energy-balance equation recognised and physical activity promoted as an important part of this?
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3: Features of an appropriate weight-loss diet
- Considers the individual's current habits, preferences and risk factors.
- Sets realistic weight loss targets (0.5-1 kg/week).
- Has a minimum daily intake of 5000 kJ (1200 kcal) for women and 6500 kJ (1500 kcal) for men.
- Has carbohydrate intake in excess of 150 g per day.
- Includes foods from each of the food groups.
- Emphasises dietary fibre.
- Recommends increased physical activity.
- Is based on change of life-long eating habits.
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