Revealed: Which fad diets actually work


EXCLUSIVE: The popular 5 and 2 fasting diet has been disowned by the professor whose research underpins it.

Sydney University Professor of Medicine and Nutrition Luigi Fontana, whose research showed the longevity benefits of fasting, said too many people using the diet eat junk food for five days and think fasting for two days solves their health problems.

He still backed fasting but said the latest research showed we were making ourselves unhealthy by eating too much protein and instead needed to eat healthy all the time even when we aren't fasting.

Two in three Australians are overweight or obese and as they struggle to keep their New Year's resolution to lose weight a News Corp investigation into the science behind fad diets has found conflicts continue over the best way to lose weight.

News Corp asked leading dietitian and nutritionist Dr Rosemary Stanton to review the best and worst fad diets.

Amy Devereux from Melbourne who lost weight on the Total Wellbeing Diet.
Amy Devereux from Melbourne who lost weight on the Total Wellbeing Diet.

Dr Stanton, who helped develop the National Health and Medical Council's dietary guidelines, gave the 5 and 2 Diet eight out of 10 if followed properly.

She scored the Mediterranean Diet and CSIRO Gut Diet - both which encourage a higher carbohydrate model - 10 out of 10.

Conversely, she gave the popular Keto Diet - which pushes extreme low carbohydrate and high fat consumption - just one out of 10.

Professor Fontana said he never backed the now famous 5 and 2 Diet, which promotes eating normally for five days and restricting calorie intake to between 500 and 600 calories on two non- sequential fasting days, even though it was inspired by his research.

"They took some real information and they dressed it up and put it together with recipes that people like and people think it's a magic bullet, sorry that doesn't exist," he said.

Professor Fontana said while you can lose weight by restricting food types, not all calories are equal.

Research from Washington University has shown when people eat too much protein their insulin resistance does not improve putting them at risk of diabetes, cancer and accelerated ageing.

To achieve health benefits it is important to restrict protein intake to 0.8 grams per kilogram of body weight but most Australians consume 1.3 grams of protein per kilogram of body weight, Professor Fontana said

Dr Stanton backs that recommendation.

Professor Fontana's research found intermittent fasting helps fight ageing by flicking cells into maintenance mode so they produce fewer waste products, grow and divide more slowly and the body repairs itself better.

Karen Mudge successfully lost weight twice on the Total Wellbeing Diet. Picture: Supplied
Karen Mudge successfully lost weight twice on the Total Wellbeing Diet. Picture: Supplied

The healthiest diet is similar to the Mediterranean diet with plenty of wholegrains, legumes, vegetables, nuts, seeds and fruit, fish two to three times per week and free range meat once a week, he said.

His latest diet advice is to eat a healthy high carbohydrate low protein diet four to five days a week and fast for one or two days eating only non starchy vegetables and two tablespoons of olive oil.

Pennie McCoy, Accredited Practicing Dietician at the CSIRO Total Wellbeing Diet said the problem with fad diets is they lasted for only a few weeks but to sustain weight loss a complete lifelong change in eating habits is required.

The higher protein content of the Total Wellbeing Diet helps control appetite and improve metabolism, she said.

It does not restrict any food groups, produces a half a kilo per week weight loss and allows a daily treat like a glass of wine or chocolate or chips. On average those who followed the diet lost 6.2 per cent of their body weight.

One in 10 Australians bought the CSIRO diet book and 60,000 people have subscribed to the online diet platform where they log in and record their weight loss in return for receiving back the money they spend on the diet.

Dr Stanton's said "any diet that cuts kilojoules below what you normally consume will lead to weight loss. However, "the ideal diet is one you can follow for life" which provides the nutrients your body needs and healthy gut bacteria.


The Keto diet scored the worst.
The Keto diet scored the worst.

The Keto Diet - 1/10.

A Keto Diet causes the body to switch from using glucose as its primary fuel to using fatty acids. It aims for 70-90 per cent of kilojoules to come from fat. This means eating foods such as butter (recommended for use in coffee), avocado, coconut, any kind of oil or fat, bacon, cream, cheese and some nuts. Modest amounts of high protein foods can be included but no grains, milk, yoghurt, fruit (apart from a few berries), legumes, potatoes or any vegetables with more than minimal carbohydrate. Small, short term studies show good weight loss, but there's no evidence of long-term maintenance of weight lost.

The diet is used in children with a particular type of epilepsy but a review of 11 studies reports constipation and other disturbances in gastrointestinal function, as well as longer-term risks for cardiovascular disease and reduction in bone mineral density. A 2019 study found adverse changes in gut bacteria, with good gut microbes decreasing and those associated with adverse health increasing.


Most people find the Paleo diet hard to follow.
Most people find the Paleo diet hard to follow.


The Paleo Diet - 2/10

The 'modern' Paleo Diet is nothing like the diet our ancestors consumed before agriculture with wild animals and plants quite different from those available today. Nor was there any single food pattern because people in different parts of the world ate whatever was available. The current Paleo diet permits all meats, fish, poultry, eggs, nuts and fats from meat, avocado and coconut as well as most vegetables. All grains, legumes, peanuts, dairy products, sugars, salt, coffee, processed foods and potatoes are forbidden.

The restrictions produce a very low carbohydrate diet which does lead to weight loss. Problems include a high content of saturated fat and a low intake of calcium. The types of dietary fibre are also limited and this is likely to have adverse effects on healthy gut bacteria.

Most people find the diet hard to follow and we have no long-term studies showing any benefits.

The 5:2 Diet - 8/10 if followed properly.

The original book carrying this title was written by Dr Michael Mosely. While the diet said eat normally for five days and restrict yourself to a close to fasting level 500 calories (2100 kJ) on two separate days of the week, Dr Mosely also counselled people to eat sensibly from the main food groups on the five days. The advantages of this diet include its flexibility. It also helps those who eat so often or so much that they don't really know what hunger pangs feel like that when they experience feelings of true stomach rumbling hunger on their 'fast' days, that these were bearable. Studies show that people who follow a 5 and 2 diet lose pretty much the same amount of weight as those who follow a more structured low kilojoule diet. If you prefer the 5 and 2 version, it is therefore a good choice for you.


Book cover of the CSIRO Complete Recipe Collection. For Daniela Ongaro. Supplied
Book cover of the CSIRO Complete Recipe Collection. For Daniela Ongaro. Supplied

The CSIRO Total Wellbeing Diet - 9/10

This diet is based on choosing healthy protein foods, mainly unsaturated fats and carbohydrate foods that have a low glycaemic index. If foods are chosen as directed in the 12 week program - which comes with meal suggestions and recipes - the diet will meet nutritional requirements, as you would expect from a program devised by CSIRO's dietitians. It is available in 4 different kilojoule levels designed to suit people of different sizes and activity levels. All participants are encouraged to exercise.

The downside is that the 12 week online program costs $199. However, this is refundable if the dieter meets certain terms and conditions. My only reason for deducting a point is that successful weight loss is for life, although hopefully this 12 week program will encourage healthy eating and exercise habits that will last much longer than the initial 12 weeks.

The CSIRO Healthy Gut Diet by Dr Tony Bird, Dr Michael Conlon and Pennie Taylor.
The CSIRO Healthy Gut Diet by Dr Tony Bird, Dr Michael Conlon and Pennie Taylor.

The CSIRO Healthy Gut - 10/10

This diet concentrates on healthy eating to establish and maintain healthy gut bacteria. It is not designed specifically for weight loss but it can start those following it onto a pattern of eating that should help control weight. Evidence is emerging that healthy gut bacteria may help control weight, although much more research is needed to confirm this aspect of health. Designed by CSIRO's dietitians and nutritionists researching healthy gut bacteria, the book has 85 recipes and daily meal plans designed to increase the many types of dietary fibre needed for healthy gut bacteria. Like all advice from CSIRO, the meals feature healthy plant sources of dietary fibre and resistant starch as well as sources of fat that are predominantly unsaturated. The book also explains why healthy gut bacteria are important. It should definitely be read by anyone following keto, paleo or other low carb diets.

The DASH Diet (Dietary Approaches to Stop Hypertension) - 8/10

Designed as a lifelong diet to stop blood pressure rising, DASH is well-balanced, featuring plenty of vegetables and fruit plus whole grains, fish, poultry and legumes. Low fat and low salt dairy products are included, as are small quantities of unsalted nuts and lean meats. Added sugars, fats, alcohol and any foods with extra salt are limited. Although designed to help curb high blood pressure, studies also show that DASH is likely to lead to weight loss. I give it a lower rating than the Mediterranean Diet because its rules are somewhat more stringent and so it may be a little less easy to follow for life.

The Mediterranean Diet 10/10

This follows the principles of the traditional diets in Mediterranean countries and is a diet for life. There is no single Mediterranean diet but the term represents the diets of different countries around the Mediterranean which feature a wide range of vegetables (always present in two meals each day, and often all three meals), legumes, fruit, nuts and seeds, herbs and spices, grains (usually mainly wholegrains such as wheat or barley (in tabouli or other cracked wheat dishes or breads), fish and other seafood, cheese and yoghurt (both fermented dairy products with unique nutritional benefits), eggs, and olive oil as the main fat. Meat is included, but not every day. Rich foods and sugary items are kept for feasts and special occasions.