Diet imageMany Australians want to lose weight and can improve their health by doing so. Significant proportions of Australian men (64%) women (47%) and children are overweight or obese and may be tempted to try a ‘fad’ diet which promises fast weight loss. However, weight problems develop as a result of long term energy imbalance; consuming more energy than is expended through daily living and physical activity. The only proven way to lose weight is to achieve negative energy balance, that is; to consume less energy than is expended. In the long term it is necessary to maintain a balance between energy intake and expenditure, to ensure lost weight is not regained.
Although there is no scientific evidence that processes such as cleansing or detoxifying certain body organs (e.g. the liver) or eating set combinations of food enhances the weight loss process, ‘fad’ diets are promoted in the media and on the internet. Fad diets are those which make scientifically implausible claims about weight loss and provide no scientific evidence to support their claims. However, they are often marketed in a manner which gives them an air of scientific credibility. For example, the diets may be authored by an individual with health and/or nutrition qualifications and often include scientific jargon and make reference to physiological processes such as digestion and metabolism.
Because of the way fad diets are marketed, you may have trouble distinguishing fad diets from those which support their weight loss claims with sound scientific evidence. Being familiar with the claims of ‘fad’ diets, and aware of scientifically sound diets and the weight loss and other benefits these may have is important for individuals who are attempting to lose weight.

Who uses diets? Why do they use them?

Weight loss is the most common reason for an individual to adhere to a specific diet. Up to one third of Australians report being on some kind of diet at any given time. There is little information about the types of diets most commonly used by Australians. However, a survey from the United States reported that 20% of dieters were following some type of fad diet.
Diets can also be used as treatments for a number of health conditions. For example, there is evidence that adherence to a gluten-free diet benefits individuals with coeliac disease and evidence suggests that children with attention deficit hyperactivity disorder may benefit from adhering to a FAILSAFE diet whilst also using other forms of treatment.
Diets may also be used as treatment for nutrition-related conditions. For example, individuals with high cholesterol levels may benefit from adhering to a cholesterol lowering diet, while those with metabolic syndrome may benefit from a Mediterranean style diet.

Distinguishing fad from fact

Fad diets are those which make unrealistic weight loss promises. Most commonly they claim to produce very rapid weight loss, often with minimal effort on the part of the dieter. For example, they may allow the dieter to eat their favourite fatty, unhealthy foods. Claims are usually backed up by individual testimonies or success stories, rather than the results of rigorous scientific studies.
Fad diets all incorporate elements of ritual (e.g. drinking supplements or eating specific foods at particular times) and sacrifice (e.g. dietary restrictions). Many of the diets incorporate severe restrictions on certain types of foods (e.g. carbohydrate rich foods) with a lax approach to the consumption of ‘favourite’, and often unhealthy, foods.
When attempting to distinguish a fad diet from a diet based on scientific fact, bear in mind that fad diets often:

  • Promise rapid weight loss without acknowledging the energy balance equation (the need to consume less energy than is expended) or the need to increase physical activity in addition to restricting energy intake. Fad diets may even claim to be based on a new weight loss ‘secret’;
  • Promote magic tonics/supplements or combinations of food as weight loss enhancers. In some cases the magic components of the diet are commercially available and must be purchased by individuals wishing to follow the diet;
  • Over emphasise one or certain types of foods at the expense of promoting adequate intake from all the food groups. Fad diets may allow unlimited consumption of some food types but typically provide a monotonous and rigid diet. They are usually nutritionally imbalanced;
  • Use scientific jargon which gives an air of credibility but is not supported by scientific evidence from independently conducted studies published in scientific journals;
  • Are promoted by an individual with limited or no relevant qualifications.

On the contrary, scientifically sound diets:

  • Promise realistic and healthy weight loss targets of up to 1 kg per week;
  • Set a minimum limit for overall energy intake;
  • Include appropriate amounts of food from all food groups, including at least 150 grams of carbohydrate foods per day and adequate dietary fibre;
  • Aim to change eating habits in the long term;
  • Factor physical activity into the energy balance equation and aim to increase physical activity.

In addition to the right dietary plan, most dieters will need to carefully monitor their nutritional intake and physical activity levels and receive frequent dietary counselling and professional support to succeed in their weight loss attempt. Ensure you are well informed about your daily energy requirements as well as the energy values of different types of foods if you are attempting to lose weight. In addition, obtaining information about energy expenditure and how much energy is expended by performing different types of physical activity may assist you in developing an eating and exercise regime with a negative energy balance.

Types of diet and supporting evidence

Types of diet imageDiets may be classified as those which claim some sort of cleansing or detoxifying effect in addition to weight loss and those which are promoted as weight loss strategies alone. Creating a negative energy balance, either by restricting energy intake or increasing energy expenditure is the only scientifically proven way to lose weight. Many fad diets, including “detox” and cleansing diets are calorie restricted. While these diets may affect short term weight loss, it is due to their low calorie content, rather than any purported claims made of certain combinations of food and/or supplements (e.g. that detoxifying supplements ‘speed-up’ the weight loss process).
It is scientifically implausible that the weight loss process can somehow be enhanced by eating particular combinations of foods without calorie restriction. The eating patterns fad diets promote are often unsustainable and there is little evidence that fad diets affect long-term weight loss. One of the major barriers to reversing the epidemic of overweight and obesity is the tendency for individuals to regain weight within 2 years of the initial weight loss. Thus a truly effective diet needs to develop eating habits which can sustain weight loss in the long term. It should also promote minimum levels of physical activity as a component of the energy balance equation.

Cleansing and detoxifying diets

Cleansing or detoxifying diets claim that the nutritional regimens they promote lead to the elimination of toxins which have accumulated in the body, and in doing so restore optimal biochemical and enzymatic functioning and enhance the weight loss process.

Liver cleansing diets

Liver cleansing diets are a type of detoxification diet that claim to remove toxins from the liver and in doing so purport to increase the efficiency of liver functioning and enhance weight loss. Nutritional intake for these diets is a combination of healthy food and detoxifying supplements.
Liver cleansing diets are based on the premise that the liver requires detoxification to function efficiently, and that detoxifying the liver assists in weight loss. However, there is no scientific evidence to suggest that dietary measures can cleanse the liver, nor that the liver functions to control weight. While the liver cleansing diet has been associated with weight loss, evidence suggests these effects occur due to the low calorie content, rather than the liver cleansing effect of the diet.

Colon cleansing diets

Colon cleansing diets aim to clear the colon and eradicate toxins. They are typically based on a combination of fibre rich foods and fruit and vegetables. Individuals on the diet often also take colon cleansing supplements. Some dieters also include ritual colonic irrigation (the flushing of the bowel with large quantities of water).
Proponents of colon cleansing diets claim that without the assistance of dietary measures and/or irrigation, the colon can harbor toxins which might poison the body. There is no evidence to support the claims upon which colon cleansing diets are promoted, that is, that the bowel harbours waste products that may poison the body. While the nutritional content of the diet (whole grains, fruits and vegetables) is healthy and could plausibly induce weight loss, the practice of bowel irrigation which is often incorporated into the diet is associated with numerous health risks, including serious conditions such as kidney disorders, bowel perforation or blockage and heart failure.
Low fibre, clear fluid diets are a specific type of colon cleansing diet which may be prescribed to individuals who require colonoscopy, for example those with Crohn’s disease or ulcerative colitis. However, the aim of the pre-colonoscopy diet is to clear the bowel of solid matter, rather than to eradicate toxins.

Other organ cleansing diets

Some diets also purport to detoxify the kidneys. Like other cleansing diets they often promote detoxification by withdrawal of certain foods which are replaced by supplements, often containing pre-digested forms of protein. Some also encourage the use of bowel-purging laxatives. There is no scientific evidence to support the use of other organ cleansing diets.

Raw food diets
Raw food diet image

Raw food diets are diets in which unprocessed and uncooked foods are consumed predominately (>70% of intake) or exclusively. The diets are based on fruits, vegetables, nuts, seeds and sprouted beans and grains, and sometimes also include raw fish or meat. They are based on the premise that eating predominately raw foods preserves digestive enzymes and facilitates the absorption of nutrients.
There are numerous raw food diet ‘brands’ including the ‘hallelujah’ diet, the living food diet and more rigid diets such as the grape mono diet. Some claim to have a detoxifying effect which produces health benefits. For example, the grape mono diet claims to detoxify and in doing so improve overall health by preventing and curing illness. Proponents of the diet claim that grapes have a magical or yet undiscovered element with therapeutic qualities. There is no evidence to support these claims.
Raw food diets typically exclude carbohydrate sources. However, surprisingly, the macronutrient ratio of the diet is similar to the ratio of a healthy balanced diet incorporating adequate intake from all food groups, including carbohydrates. One study reported that individuals adhering to the diet obtained approximately 58% of energy from carbohydrates, 9% from protein and 33% from fat. The fat content of the diet, while similar to the proportion of total energy recommended for healthy nutrition, was markedly lower than the fat content of the average western diet.
In the largest study of raw food diets to date, long term adherence to the diet was reported to lower total cholesterol levels but not to improve the low density lipoprotein/high density lipoprotein (LDL/HDL) level. In terms of cardiovascular risk, improving the LDL/HDL ratio and particularly reducing HDL levels is more important than lowering total cholesterol. In the raw food diet study 46% of the study group had low HDL levels (<1.1 mmol/L men, <1.3 mmol/L women) and HDL levels declined significantly and in a dose dependent manner with increasing consumption of raw foods. In addition the study reported that almost half the participants were deficient in vitamin B12 and low vitamin B12 levels were associated with elevated homocysteine levels. Evidence shows that increasing HDL levels reduces cardio vascular risk, and that even mildly elevated homocysteine levels increase the risk of cardiovascular disease. This evidence suggests that raw food diets are associated with high levels of cardiovascular health risk.

 Nutrition for lowering cholesterol levels picture For more information about the effects of cholesterol on health and how to maintain healthy cholesterol levels, see Nutrition for Lowering Cholesterol Levels. 

Alkaline diets

Alkaline diets are those which promote the consumption of a combination of foods which collectively have a similar pH value to that of human blood (7.35–7.45). Proponents of the diet claim that the consumption of acidic foods destroys the body’s equilibrium, increases the loss of essential minerals and makes individuals more prone to illness. These diets are based on the consumption of large quantities of fruit and vegetables and the avoidance of acidic foods including meat, fish and cheese.
There is no rigorous evidence detailing the effect of the alkaline diet on weight loss, pH equilibrium or mineral loss, nor is there evidence to support claims that achieving pH equilibrium assists weight loss. While the diet is likely to produce weight loss due to its relatively low energy content, the diet may create health risks for some people. Individuals with chronic or acute kidney failure, heart disease and those using medications which affect potassium levels should consult their doctor before starting an alkaline diet.

Anti-inflammatory diets

Anti-inflammatory diets promote the avoidance of pro-inflammatory foods (mainly fatty and sugary foods but also plant foods containing a chemical alkaloid solanine which is known to have inflammatory effects) and consumption of foods with known anti-inflammatory effects (e.g. omega 3 fatty acids and fruits such as berries which contain anti-inflammatory phytochemicals. Proponents of the diet claim that avoiding these foods can reduce systemic inflammation. Inflammation is associated with a range of nutrition-related conditions including obesity and type 2 diabetes mellitus. However, there is no evidence that avoiding inflammatory foods induces weight loss; these diets can only induce weight loss if energy intake is restricted to create negative energy balance.

Candida diet

The candida diet is based on avoidance of foods which some believe can encourage the growth of candida (yeast) in the gastrointestinal tract. These foods include sugars, yeast-containing foods, caffeinated beverages and many processed foods. There is no rigorous evidence regarding the detoxifying, weight loss or other effects of adhering to a candida diet.

Weight loss diets

Low carbohydrate diets
Low carb diets image

Low carbohydrate diets are calorie controlled diets in which a low proportion (~5%) of total energy is consumed as carbohydrates and fat is the largest source of energy (~60%). Sometimes fat intake is restricted in favour of a high protein intake. The Dr Atkins diet is the best know low carbohydrate/high fat diet. Other names which low carbohydrate diets are promoted under include the Zone Diet, Carbohydrate Addict’s Diet, and the Sugar Busters Diet. The specific carbohydrate diet, a strict carbohydrate limiting nutritional regimen, is based on the premise that residues from unabsorbed carbohydrates encourage the growth of pathogenic (disease causing) microbes in the gastrointestinal system which disrupts gut integrity.
Low carbohydrate diets have been shown to produce similar weight loss to low fat diets, although they are contrary to traditional health messages which encourage people to eat low fat diets and base their meals on whole grain carbohydrates. In one study participants lost an average of 14.5 kg after following a low “carb” diet for 1 year. In the initial stages of the diet weight loss can occur very rapidly, however weight loss occurs due to loss of water from the body, rather than due to loss of fat. After the first week of the diet water equilibrium is re-established and weight loss is moderated to reflect energy balance.
In addition to producing similar weight loss, compared with low fat diets, low carbohydrate diets appear to have favourable effects on triglyceride levels (levels of stored body fat) in the short term and may offer some benefit to obese individuals with insulin resistance and/or metabolic syndrome after 1 year. It should be noted, however, that these benefits are modest in comparison to the cardiovascular benefits of weight loss which occur from either low-fat or low-carbohydrate diets. In addition, it is important to be aware that these diets are associated with elevated LDL cholesterol which is known to increase cardiovascular risk. Individuals who wish to try a low carbohydrate diet should consult their doctor about the need to monitor LDL cholesterol levels whilst adhering to the diet.

Low fat diets

Low fat diets are calorie controlled diets in which fat intake is restricted to 30% of total energy and carbohydrates are the largest energy source (~45%). This energy ratio is similar to that achieved with healthy eating based on adequate intake from each food group. However, some low fat diets prescribe markedly greater fat restrictions. For example, the Pritikin diet restricts fat consumption to 10% of total energy and also advocates low protein intake.
While low fat diets are promoted for healthy nutrition and weight management and are backed by scientific evidence showing that negative energy balance can be achieved by adhering to the diet, many individuals who attempt the diet fail to lose adequate weight. This appears to result from lack of understanding amongst dieters that overall energy intake, as well as fat intake, needs to be limited as part of the diet. It is important for individuals attempting a low fat diet to be aware that even low fat healthy foods contain energy and need to be consumed in moderation. Ensure you monitor your overall energy intake as well as your fat intake if you choose to lose weight with a low fat diet.
It is also important to choose high-fibre carbohydrates and consume adequately from all food groups, including fats. While consuming too much fat is associated with unhealthy weight and numerous chronic health conditions, the body requires some fat. Very low fat diets like the Pritikin diet which restricts fat intake to 10% as well as restricting protein intake may result in deficiencies, for example in fatty acids, zinc and calcium.

Meal replacement diets

Meal replacement diets are those in which one or more daily meals are replaced with nutrient rich beverages or snacks. Overall calorie intake is restricted. As the meal replacements are calorie and portion controlled they are a convenient means for individuals who have difficulty accessing appropriate healthy meals.
Meal replacement diets have been assessed by scientific studies and found to be an effective means of achieving weight loss. For example, one Australian study reported individuals on a meal replacement diet lost similar amounts of weight to those adhering to other structured weight loss programs. However, meal replacement diets are difficult to sustain in the long term. It is recommended that they are implemented alongside nutritional and behavioural changes which have the potential to reduce energy intake and increase energy expenditure in the long term.

Mediterranean diet

Mediterranean diet imageA Mediterranean diet is one based on the traditional eating habits typical of inhabitants of the Mediterranean region. It incorporates predominately whole grains, fresh fruit and vegetables, with moderate amounts of protein and the consumption of low fat dairy and omega-3 fatty acids. It is important to note that the combination of foods, rather than the component parts of the diets, must be consumed for the weight loss and health benefits of the diet to be realised.
Calorie-restricted Mediterranean diets have been demonstrated effective in inducing weight-loss. Scientific studies have reported greater weight loss in patients assigned to a Mediterranean diet compared to those assigned to a low-fat diet. Adherence to a Mediterranean diet has also been shown to produce health benefits over and above those which arise from lowering weight. These benefits include:

    • Lower risk of mortality, with increasing adherence to the combination of foods promoted in the Mediterranean diet;
    • Reduced cardiovascular risk of up to 70% after 27 months adherence to the diet, including a reduced risk of heart attack, stroke and unstable angina;
    • Reduced risk of insulin resistance, metabolic syndrome, and type 2 diabetes mellitus.

Risks associated with fad diets

While weight loss has considerable health benefits for overweight or obese individuals, some fad diets are associated with health risks which may undermine the health-promoting effects of weight loss.

Nutritional deficiencies

Many detox and cleansing diets are nutritionally imbalanced. Over time lack of certain nutrients can cause health conditions. For example raw food diets which almost universally exclude dairy products are associated with depleted bone mass. Low carbohydrate, low fat diets which do not contain sufficient fruit and vegetables are associated with high cholesterol levels and increased risk of cardiovascular problems including atherosclerosis (hardening of the arteries) and coronary heart disease. Diets which promote consumption of only one type of food (e.g. grapefruit) are the most likely to be nutritionally imbalanced.

Unhealthy body composition changes and further weight gain in the long term

Fad diets which promise rapid weight loss often achieve reduced weight in the short term; however it may not be healthy weight loss. Evidence suggests that when weight is lost too quickly, body composition also changes. Specifically, there is a loss of lean body mass. In the long term, data show that the loss of lean body mass associated with fad dieting increases the risk of major weight gain in the future.

Undermine attempts to promote evidence-based healthy eating

The promotion of scientifically unsound diets such as cleansing diets, undermines public health attempts to promote healthy nutrition which can be sustained in the long term to maintain healthy weight. The promotion of misleading information about metabolism and physiology (e.g. that liver problems rather than energy imbalance causes weight gain) causes misunderstanding about the reasons for overweight and obesity and the ability of diets to induce weight loss. Diets which incorporate unhealthy eating patterns (e.g. consumption of only a single food) contribute to the development of poor eating patterns which reduce the chance that weight loss will be maintained.


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