As a dietitian, I’ve often wondered what makes Australians embrace fad diets with such zeal.

Of course, the lure of instant success and the so-called “science” behind such diets can sound very convincing. And with a growing number of people overweight, it’s little wonder record numbers have attempted some kind of diet at some stage.

The simplest way to lose weight is to eat less and move more. But that’s not a very exciting message and we don’t tend to hear Hollywood stars claiming it to be the secret of their triumph.

Instead, we hear about the Dukan, South Beach and Atkins diets, to name just a few.

What these diets have in common is the exclusion of some critical dietary component as the key success. The current craze, for instance, is the exclusion of the protein gluten usually found in grain foods – just ask Miley Cyrus.

The practice ranges from regular fasting through avoiding whole food groups (such as vegetarianism), to exclusion of what’s perceived as a harmful component of food (such as gluten), to exclusion of a single food.

While there are some well-founded medical reasons underpinning food exclusion for certain people, most of what is done in the name of dieting has no such basis.

Eliminating in the ‘70s

Two examples of the more extreme forms of food exclusion date back to the 1970s.

The Israeli Army diet (that the army had no knowledge of) is followed for eight days. Only four foods are eaten and only one food at a time. Apples followed by cheese, then chicken, then salad.

Weight loss is assured as consumption is self-limiting (only a small numbers of calories are consumed), but once you start eating normally again, you’re most likely to regain lost weight fast.

rob patrick

Quite different is another diet that’s also very limiting in range of foods allowed but was developed for medical reasons. The “salicylate elimination” diet is used to diagnose and treat food intolerance.

It requires excluding all sources of dietary salicylates (many fruits and vegetables) for two to six weeks. Those on the diet are then “challenged” with a capsule form of the excluded dietary chemical (salicylate) to assess symptoms and identify if it was indeed causing the problem.

Many parents of affected children and adults undergoing the dietary therapy attest to the success of this treatment. But, the Medical Journal of Australia recently published a paper (paywalled) by a group of paediatric immunologists questioning the safety of the diet for children.

And an accompanying commentary (also paywalled, but here’s an article about both papers) noted the importance of ongoing medical and dietetic input to prevent unwanted side effects, including nutritional deficiencies.

The importance of variety

Even people who are not overweight or have medical problems are interested in diets that exclude certain foods.

Vegans, for instance, remove all animal-based food and food products from their diet. But their philosophy is about how we should treat animal life and about food production that uses less land, less energy and produces fewer gas emissions.

Perhaps the desire to exclude foods has its origins in religion, as well as perceived health benefits. Exclusion of certain food groups is a feature of many leading religions such as Muslims fasting during Ramadan, the vegetarianism of Seventh Day Adventists, and the avoidance of pork and shellfish by Jews.

I don’t have the training to fully explore the sociological reasons for exclusion diets – perhaps dietary prohibition demonstrates superiority or signals membership to an elite group – but I am qualified to tell you people following such diets may be placing themselves at nutritional risk by excluding core food groups.

One of the foundations of dietitians’ advice is to eat a variety of foods and there are two good reasons for this.

First, many foods have natural or introduced toxicants. Potatoes, for instance, can be high in solanine poison so that a diet of only potatoes is more likely to lead to harmful levels of intake.

The other reason to eat a variety of food is to get all the macronutrients and vitamins and minerals your body needs for healthy functioning. You get these from all the basic food groups so excluding an entire food group is likely to place you at risk of nutritional deficiency.