A very restrictive detox diet would show quick results - even if much of the weight loss was just water.
"When it comes packaged nicely with anecdotes from people who have tried it and lost weight, that's seductive ... much more than someone like me saying eat five-plus a day, go for a walk for 30 minutes."
The fact that people have often paid an upfront cost for the detox diet plan also makes them more likely to stick at it in the short-term, Wall says. But the benefits would not be lasting because the diets were too restrictive.
"They might stick to it for however many days [but] it's much harder to change behaviours that are ingrained and not going to go away."
And a lot of the changes that happen to your body on a detox diet are not all that desirable. Many include regular doses of laxatives. Though this might make you feel lighter, generally it just leads to fluid loss and dehydration, rather than any real loss of fat.
When it comes to purifying toxins, there are not many better systems than the one your body already has. The liver breaks down harmful chemicals, which are then processed by your kidneys. This process is not helped by detox plans.
"The detox diet idea is nonsense," said Nigel Denby, a British dietitian who worked on a detox experiment for a TV programme aired a couple of years ago.
"Our research has confirmed what medics have long suspected: That our bodies are extremely efficient machines for doing all the detoxing needed and they don't need much extra help."
Many people doing detoxes report increased energy and better skin but experts say the energy boost is a natural response to fasting. Clearer skin can be attributed to the increased water intake that goes with many detox diets, and the emphasis on avoiding fatty foods.
A heavily restricted diet could lead to vitamin deficiencies, muscle breakdown because of a lack of protein, blood sugar problems, potassium and sodium deficiencies. Wall said it was also dangerous for anyone who did not have much body fat to undergo a detox. A detox plan generally lacks a lot of the nutrients that the body needs. "Long-term, you could become deficient," Wall said.
She said none of the detox diets presented a lasting change. "At the end of the day, you can't survive on it, you can't live for the rest of your life on a detox. When you are back on your regular diet, the weight will come back on and more."
Cleansing programmes are big business. It has been reported that herbal cleansing products generated US$28 million ($35.3 million) in sales worldwide in 2009.
Part of their success is because people are drawn to the idea of undoing years of bad habits with a couple of days or weeks of a strict eating programme.
But Wall said if people had got into bad habits, or thought they were likely to over-indulge at Christmas, it was much better to start the new year with an improved diet, reducing alcohol intake and increasing exercise, than to starve themselves for a week. "That will be better that something like the Lemon Detox Diet. It's better long term."
Wall said people should be sceptical of anything that was promising a quick fix or miracle.
"There is no evidence of detox plans having any benefit at all."
She acknowledged that some cultures advised fasting for religious reasons but she said there was no scientific evidence that detoxes or fasts had any health benefit.
"People would be better to practice moderation and improve their overall lifestyle and behaviour if they want long-term success."
Three detox diets to avoid:
Lemon Detox/Master Cleanse
Cited by Beyonce as the reason for her dramatic weight loss for the movie Dreamgirls, the Lemon Detox Diet has been around in various forms since the 1950s. It is claimed that dieters can lose a kilogram a day. The basis of the diet is that you consume a drink made up of lemon juice, cayenne pepper and syrup, followed by regular flushes of salt water. No solid food is consumed. The diet is really low in calories, so you lose weight, and the salt water has an extreme laxative effect, which means you lose water as well. Long term, this diet could cause liver, heart and kidney problems.
The Cabbage Soup Diet
The Cabbage Soup Diet claims to help weight loss by flushing out your system with lots of vegetables. The idea is to eat as much cabbage soup as you like, and very little else. Weight loss of about 5kg a week is promised. The soup, made up of vegetables including cabbage, tomatoes, capsicum, celery, carrots and onions, is a good dose of vitamins but can be quite high in salt, and provides no protein or carbohydrates. Doing this diet for a week is unlikely to cause health problems but most of the weight lost will be water.
Juice Diet
Consuming nothing but fruit and vegetable juice for seven days is another popular way of "detoxifying" the body. There is no fibre in juice, so juice fasters often have to take laxatives as well. The idea is that because your body is not busy digesting solid food, it can get on with expelling "toxins" from your system. There is no scientific evidence to back this up. Weight loss will be because of a dramatic reduction in calories. Fasting is not recommended for anyone who is underweight or pregnant.
