Dr Kieron Rooney

Effectiveness of different modes of fasting

Dr Kieron Rooney
3 min read

Is it time to eat yet?

One of the most common questions I get asked when attending community talks is – what do you think about fasting for weight loss? Which is then almost always followed up with – what is the best fasting regimen to follow?

One of the greatest difficulties in answering this question is the scant amount of scientific evidence that compares, head-to-head, one style of fasting to another. As such, when I came across a paper conducting a meta-analysis comparing the effectiveness of different modes of fasting it is an understatement to say I was keen to read it.

First things first – what is a Meta-analysis?

A meta-analysis is where someone takes a whole heap of individual studies that have asked a similar question, and have measured similar things, but in different groups of people, and then puts them all together to pretend it was one large study. The authors of a meta-analysis quantitatively combine the results in the individual studies to come up with an overall combined result.

In the example of this paper, the authors went searching to find as many studies as they could that had compared the effectiveness of intermittent fasting for people trying to lose weight. They found 24 highly controlled studies. The smallest individual study was conducted in 16 people, the largest of the 24 studies was conducted in 332 people, and when the authors combined all 24 studies, they had data from a total of 1768 people that had undergone some form of intermittent fasting.

Importantly, these 1768 people did not all do the same type of intermittent fasting.

In this study there were people that had been in studies investigating alternate day fasting (0 calories or restricted calories one day, eat what you like the next); or they may have been following the 5:2 diet (0 calories or restricted calories two days a week, eat what you like the other 5); or they may have been following a time-restricted eating diet (you can eat everyday … but only in discrete windows of time such as 4-12 hours).

By including all these study designs, the authors were able to do some fancy statistical analyses to compare different types of fasting to each other, without having to run a study of their own that directly compared them.

Sounds neat right?

However, what this does mean is that this is secondary data, being analysed for a purpose not originally designed. So, while the maths is fancy and powerful we do need to keep in mind that it is a statistical study and at no point still, did we have the same person testing different types of fasting to see which worked best for weight loss.

Regardless, what does this study teach us?

First, if you perform any type of intermittent fasting for up to 3 months, you will lose weight compared to simply eating whatever you want whenever you want. However, you can achieve a similar amount of weight loss (up to 12% of body weight in some studies) by simply eating less everyday and not having to fast at all.


Where do we go from here?

Unfortunately, despite the impressive use of 1768 individual data points, we need to appreciate that there were only 24 studies included and not all of them tested the same fasting type – there were 12 studies that looked at alternate day fasting; 8 studies that looked at the 5:2 diet and only 4 that looked at time-restricted feeding. Further, the individuals studied were either overweight or obese, yet did not have any other metabolic condition such as diabetes or metabolic syndrome, so how well we can rely on this for individual advice is very limited. Regardless, we do see here some good mathematical evidence for alternate day fasting as the most effective approach to intermittent fasting for weight loss.

So to answer our first two questions – I think intermittent fasting is a method for weight loss in which the scientific evidence is building to support it as an effective method just as good as trying to reduce how much you eat everyday. And for those of us that like strict rules, intermittent fasting is a viable and a relatively easy method to comply with.

Which method of fasting is the best? I don’t know – but it looks like we have some points in the corner for alternate day fasting here.

Dr Kieron Rooney is a nationally recognised expert in nutrition research and translation into policy and practice.

To date, his novel research has focussed on how high sugar and/or high fat diets impact metabolic health.

He has been a vocal advocate for improved labelling of manufactured products with a number of successful campaigns related to junk foods marketed to children.

Kieron is part of the Good Mood Dudes network of experts available to support your wellbeing program. If you want to soundboard your wellbeing plan or hear how we’d get your program up and running, get in touch with our team for a complimentary strategy call today. 

The NOVA Food Classification System Explained

NOVA is a system by which foods (and food products) are classified by their degree of processing and the purpose for processing, into one of four groups. It is not an acronym, it is just a name. So we thankfully don’t have to try and remember what it stands for.

How does NOVA classify foods?

Group 1 represents the unprocessed or minimally processed foods and includes edible parts of plants and animals which are either eaten directly after removal from nature (raw) or have had some minor level of processing performed to make them edible such as roasting, boiling, and pasteurisation. 

Group 2 refers to processed culinary ingredients – think oils, syrups, preserves and butter – these are substances obtained from Group 1, but with higher degrees of processing to make products that are used in the kitchen to cook with. The general recommendation then is to make Group 1 foods the basis of your diet using Group 2 foods in small amounts for seasoning and cooking.

As we increase the level of processing towards Groups 3 and 4 however we enter troubled waters. 

Group 3 are plain and simple – processed foods. These will be made from a collection of Group 1 and 2 foods. They contain a handful of ingredients but the process employed is for the purpose of increasing the durability and sensory qualities of the Group 1 and 2 foods. Here we are thinking smoked or cured meats, canned fruits and vegetables, cheeses and breads – and for those waiting to see where beer wine and ciders sit – they are right here as products of fermentation.

Group 4 are the ultra-processed products. A subtle note here that the word “food” is intentionally dropped from the group heading by the NOVA creators. These are industrial formulations typically with 5 or more ingredients. The ingredient list might look like there are Group 1 foods present, but they no longer represent anything like the way nature intended. The ingredients list here reads like a who’s who of chemistry’s rich and famous. Additives whose main purpose is to either mimic the qualities of Group 1 foods or to disguise the bitter taste the many “preservatives”, “emulsifiers” and “humectants” (whatever they are!?) that have been packed into the product possess. Some of the more common Group 4 product examples are supermarket breads, breakfast cereals, muesli bars and packet sauces and many of the frozen reheat meal options.

Which groups of foods should we be consuming? 

The general recommendation in regard to these groups is to consume Group 3 sparingly. They can be consumed in small amounts and as part of a meal based around Groups 1 and 2 but only on occasion. Group 4 however, are to be avoided. That’s it. Just avoid them.

Can ultra-processed foods be healthy?

The avoidance of processed products is far more easily said than done. For the most part, well over a third of our diet comes from products in this group. And more concerning is that many of the Group 4 products can be found with a healthy-looking 5 stars, low GI, tick of approval! These products are aggressively marketed, displace Group 1 foods from our daily diets and have a huge negative impact on our health. In a recent analysis of over 100,000 French adults, compared to those that reported consuming at least one-fifth of their diet from Group 4, overall cancer risk was increased in those consuming higher amounts of Group 4 products.

Progressively, nutritionists around the world are beginning to re-frame their understanding of healthy diets in the context of NOVA classifications. The good news is, we do not have to completely re-invent wheels here. We can look to a number of very popular dietary patterns in the community today as examples that are fundamentally built on diets of Group 1 and 2 foods.

Further reading:

NOVA. The star shines bright. World Nutrition Volume 7, Number 1-3, January-March 2016 [PDF]


Dr. Kieron Rooney completed his PhD in the Department of Biochemistry, within the Faculty of Science at the University of Sydney. Kieron’s primary interest focuses on conducting research and using this research to educate others on how what we eat, influences our metabolism. 

When Did Eating A Healthy Diet Become So Hard?

According to the Australian Bureau of Statistics, only 1 in every 20 Australians consumes the minimum serving of vegetables per day. While over a third of our diet comes from packaged junk food. Nutrition based public education campaigns don’t work. Sure, most of us know what we are supposed to be doing – 5 serves of vegetables, 2 serves of fruit, some protein but not too much, and go easy on the fats – and so to some extent, the message has got through. But they haven’t worked in affecting change or establishing good routine behaviours.

What does the Government have to say?

Governments, past and present, say it is the individuals’ fault for ignoring some 40 years of public awareness campaigns. More than one former Prime Minister and/or Federal Health Minister have proudly proclaimed that the only person that should tell them what to eat is themselves and Governments have no place in restricting food choices. But it is not the fault of the individual. It is a consequence of the food environment in which education must compete against marketing practices that overwhelm the senses and fatigue even the most committed shopper. Messaging in both public health campaigns and marketing practices seem to be widely varied and misinforming in many cases. With some 2 in every 3 Australians overweight or obese, we need a more authorative and thorough approach to public health messaging than just being told what is good for us.

Why are we all so confused on what to eat?

Over the past 40 years there has been and continues to be a fundamental shift in our understanding of nutritional science. In the early days, a reductionist approach was embraced in which foods were identified by their individual nutrients. Such as, did they contain saturated fat or unsaturated fat? Are they high protein or low protein? The result of this approach was a re-conceptualising of food, not as food. But rather as a vehicle of specific nutrients resulting in what is termed nutrient based criteria. Foods were quickly classified good or bad for you on the basis of perhaps only one ingredient. With the most consumed products being made up of three or more ingredients today, this approach can skew the validity of what is healthy and what is not.

The Health Star Rating System

The popular Health Star Rating System (HSR) is derived from this more reductionist approach. Where the apparent health of a food is determined by an algorithm incorporating component ratios of certain ingredients and correction factors for different food categories. While this system relies on science and a few calculations, in no living system, has the accuracy of the star ratings been tested, examined and shown to be true. Controversially, in some studies where interventions were supposed to improve the health of participants, incidence of disease increased. There are many examples of where the HSR fails to meet its lofty advocacy as a universal indicator for healthy choices. Not least the automatic allocation of 5 stars to fruit juice which the World Health Organisation arguably classifies as a sugar sweetened beverage and recommends we avoid. However, if adequately explained, consumers may still be able to find some use in the HSR.

The Glycemic Index or GI

An alternative approach to understanding the healthfulness of some foods has been to focus on the carbohydrate content, both the quantity and quality. The early steps in this approach saw the creation and development of the glycemic index. In brief, members of the community would be asked to eat small portions of a test food and their blood glucose response would be monitored. On another day an equivalent portion of white bread or some other comparative food would be consumed and the relative difference in blood glucose response would be used to calculate the GI. The general belief being – the lower the GI the healthier it is for you.

Over the past 20 or so years, millions of dollars and hours of effort have gone into validating this tool as an indicator of the healthfulness of a product. At the same time however, shortcomings in the methodology and high variability between individuals has chipped away at confidence in this commonly advocated front of pack label.

What do we do now?

If the two most immediately recognisable and advocated front of pack labels for helping consumers make informed choices are of limited use – where does that leave us? Well one of the first things we need to recognise with approaches such as the HSR and the GI, is that they focus only on some of the components in a product. And not necessarily the food, in the context of our daily lives and how we eat. Food is greater than the sum of its individual parts.

When we look beyond our borders we see a vastly different approach to “dietary guidelines”. For example in Brazil, there is no singling out of saturated fat, carbohydrates or even alcohol. Rather there are steps towards a healthy diet focussing on the avoidance of ultra-processed foods. They encourage planning, developing and sharing cooking skills and eating in social contexts. It is out of Brazil that the NOVA food classification was borne. A system that has both excited nutritional science in providing a whole new scope of data to play with but more importantly has provided community members and public health advocates with a simple enough guide to improving diets – focussing on food processing.

The systems and messaging in place in our modern society that were designed to aid in making healthy lifestyle changes when it comes to our diet are confusing and outdated. The government needs to take a new approach in advocating healthy lifestyle changes, like Brazil’s NOVA classification, where emphasis is put onto advocating for healthy food choices according to food proccessing standards without isolating a particular food group.

Further reading:

The NOVA Food Classification System Explained


Dr. Kieron Rooney completed his PhD in the Department of Biochemistry, within the Faculty of Science at the University of Sydney. Kieron’s primary interest focuses on conducting research and using this research to educate others on how what we eat, influences our metabolism.

Research Review: The Effect Of Sleep On Diet

Keiron - Sleep and Diet

In this article, our expert Dr. Kieron Rooney – reviews: Effect of sleep duration on dietary intake, desire to eat, measures of food intake and metabolic hormones: A systematic review of clinical trials, led by  Samira Soltanieh From the Department of clinical nutrition and dietetics, Faculty of Nutrition and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran.


1) What was the high-level summary of the research? 

Individuals that have their sleep disrupted or who report naturally shorter sleep duration are more likely to also eat more. It is difficult to pinpoint exactly what they eat more of, but in general, adults seem to snack on foods with higher fat content and teenagers on higher glycemic index (GI) sweet foods.  

2) What did the study try to measure? 

This study sought out as many studies as possible in which a person’s sleep duration and dietary habits were investigated. They then explored if there was any association between what people ate with how long they slept. 

3) How was the study undertaken? 

This study is referred to as a systematic review. The authors themselves did not implement a study in which they collected data from individuals with disturbed sleep. Instead, they searched for, identified, and synthesised studies that met their inclusion criteria, which had already been conducted by other investigators. 

The authors found over 700 studies and ended up identifying 50 studies that reported both food intake and sleep duration; 43 of these studies were on adults. Once the review authors had found these studies, they looked at the dietary data to see what the individuals in those studies were eating, and, how long they slept for. They also looked for any studies that reported on hunger and/or appetite and any studies that may have measured hormones believed to influence what humans eat.

4) What did the study find? 

The main result the authors focused on here was total energy intake. This was reported in 30 of the 50 studies they found. Most studies – 19 of the 30 – associated short sleep duration with a tendency to overeat. While some studies showed this was a result of eating larger meals other studies reported that it was a result of more snacks being eaten throughout the day. There was no clear indicator of which – larger meals or more snacks – was likely to be common in specific people.

There was also no clear indication as to which macronutrients – fat, protein, or carbohydrate – may have been contributing to the excess energy being consumed. The authors summarised the studies and suggested the extra energy was coming from either fat or protein rather than carbohydrates, yet the results were very much 50/50 on this. A big reason for the lack of clarity here is that the review included studies that induced sleep deprivation from as short as 1 night by keeping people awake with entertainment and keeping lights on all night compared to other studies in which sleep was restricted for over a month to only 6 hours a night.

5) Is there any other research out there that supports these findings or contradicts it? 

Absolutely, a 2017 systematic review was published that looked only at studies in which sleep was partially disturbed with reduced hours in bed. That review contained only 17 studies but they were so similar in design that the authors performed a meta-analysis. This is where the individual study results from each study are mathematically combined for each intervention, rather than simply being summarised such as in the present study. The smaller but more mathematically robust systematic review reported that even just partial sleep reduction of a couple of hours a night resulted in much greater energy intake with no effect on energy expenditure which was then concluded to lead to weight gain.

6) How much weight should we give this research?

This study is interesting and contains nearly three times the number of studies as the 2017 paper. However, the results of these studies are summarised rather than analysed and as such are very much open to interpretation. Despite this, this study provides a great resource for the complete repository of studies investigating the association between our diets and our sleep duration.

7) What does this mean for your work/research/industry? 

For me, I think this is interesting in the context of understanding why some people may find themselves eating more processed snacks than others. The big question that still needs answering is whether or not it is the disrupted sleep that promotes individuals to snack and eat more, or it’s the eating more that then disrupts sleep.

8) What’s the key takeaway for us to take from this research?

If you are looking for simple ways to cut your intake of processed high-energy snacks – get more than 6 hours of sleep a night! 

9) Will you be doing anything differently because of this research? 

Not so much differently – but perhaps I will start taking more sleep history surveys in my diet intervention studies.


Dr. Kieron Rooney completed his PhD in the Department of Biochemistry, within the Faculty of Science at the University of Sydney. Kieron’s primary interest focuses on conducting research and using this research to educate others on how what we eat, influences our metabolism. 

Research Review: Ultra-Processed Food and Mortality

In this article, our expert Dr Kieron Rooney – Associates Professor at The University of Sydney & nationally recognised expert in nutrition research – reviews Ultra-processed food intake and all-cause mortality: DRECE cohort study by Ferreiro et al. 2021, and breaks it down to give us the vital parts we need to know. 


1) What was the high-level summary of the research?

The risk of dying increases with the amount of ultra-processed food products in one’s diet.


2) What did the study try to measure?

This study monitored the risk of what is referred to as “all-cause mortality” (death from any cause) during the 26 years that spanned 1991 – 2017 in Spain. The authors wanted to see if this risk was influenced by what people ate.


3) How was the study undertaken?

The study design described in this paper is called a longitudinal cohort survey. This simply means following the same group of people over a long period of time. Practically speaking, the authors gained access to a diet survey that was completed by 4679 individuals living in Spain in 1991. The survey is what is called a food frequency questionnaire and asked individuals to estimate over the previous 12 months how often they may or may not have eaten over 100 different foods.

Once the authors had this survey data, they classified the food items according to degree of “processing” as described by the NOVA classification.

The NOVA classification allocates foods into 1 of 4 groups depending on the level of processing the food has undergone. Group 1 for example are fruits and vegetables; Group 2 are culinary ingredients such as salts and oils; Group 3 are processed products with 3-4 ingredients while Group 4 are ultra-processed foods with multiple, highly refined ingredients and additives.

The authors then reviewed the National Institute of Statistics in Spain to see how many, if any, of these 4679 participants had died during the 26 years between completing the survey in 1991 and December 31, 2017.

Once they had both the diet and the incidence of death data, they used statistics to see if there was any increased risk of likelihood of dying in the 26-year period with the foods reported being eaten in 1991.


4) What did the study find?

The average age of individuals in the study was 30 years, and on average, this group of participants were eating about a quarter of their total daily energy from Group 4 ultra-processed foods products such as sugar sweetened beverages, milkshakes, meat and meat products like sausages and deli meats, dairy products, cakes pastries, sweets and cookies.

Of the 4679 individuals that completed the food frequency questionnaire in 1991, 450 had died by December 31, 2017.

And…. the higher the amount of Group 4 ultra-processed food products in the diet, the higher the risk of being one of those 450 individuals.

The actual risk reported by the study was a 15% increased likelihood of all-cause mortality for every 10% increase in the proportion of energy in the diet from group 4 products.

The authors also made some changes to the diet survey responses to see if the risk of all-cause mortality could be reduced and found that replacing Group 4 ultra-processed foods with Group 1 foods (fruits and veges) resulted in a statistically significant improvement and a reduced risk of all-cause mortality.


5) Is there any other research out there that supports these findings or contradicts it?

Absolutely, very similar studies have been completed on population data in France, the USA and Italy. Some of these studies have been completed in larger cohorts with the French study completed in over 100 000 individuals looking at cancer incidence in the first 8 years following diet survey. Each of these cohort studies are singing the same song – the higher the proportion of energy in your diet that comes from Group 4 ultra-processed food products. The higher the risk of health problems and disease.

To date, there are no studies that contradict this outcome.


6) How much weight should we give this research?

This study is interesting, and the statistical analysis is strong. Importantly it confirms data coming out of Europe and America that are generally telling us the same thing – the rise of ultra-processed foods is dangerous for our health. However, the sample size is relatively small, and there was only 1 diet survey completed in 1991 and how representative that was of each participant’s diet for the next 26 years is obviously a stretch.


7) What does this mean for your work/research/industry?

What this does for me is add strength to the need to continue to unpack the role of ultra-processed foods in the development of disease and empower individuals to make changes towards reducing the consumption of these foods.


8) What’s the key takeaway for us to take from this research?

If you can find the motivation and capacity to switch out an ultra-processed food product for its minimally processed equivalent – do it!


9) Will you be doing anything differently because of this research?

Not so much differently, but perhaps with more vigour, as it confirms the need for more current prospective studies in which we actively remove these group 4 foods from people’s diets and see if it improves their health as predicted.


Dr Kieron Rooney is a biochemist, nutritionist and exercise physiologist from the University of Sydney whose research focuses on how what we eat, influences our metabolism. 


Expert Q&A: Introducing Dr Kieron Rooney

1) Could you tell us a little about your career and areas of expertise/interest? 

My day job entails conducting research and teaching on how what we eat, influences our metabolism. This work includes investigating for example, the influence of lower carbohydrate and higher fat diets in diabetes and obesity as well as on measures of performance in normal healthy individuals. I’ve also completed work on the role of high sugar diets in altering health status and the potential for non-nutritive sweeteners to assist recovery in diets focused on lowering sugar intake. I completed a PhD in Biochemistry in 2003 and since then have been an academic at the University of Sydney.


2) What drew you to this line of work/research in the first place? 

To be honest, it was the only thing I was good at at University. I squandered most of my first year enjoying the freedoms that University Student life brought. However, by second and third year I found myself intrigued by metabolic biochemistry and the way in which our entire system is integrated to utilise the energy of food we eat and how our behaviors may change to seek out specific foods. Through the course of my PhD and then academic life, the relationship between what we eat, how we eat it and our health fascinated me.


3) How do you look after your own physical and mental wellbeing?

I wax and wane. Periods of control and periods of laziness. I like to convince myself it is all by design. But to be honest sometimes I have all the energy in the world to commit to health and sometimes sleeping in, having an extra drink and getting take away feels like the right thing to do. When I am committed, there are 3 – 4, 7km runs a fortnight interspersed with some weights on alternate days and more often than not there are 10-11 home cooked dinners in that fortnight with leftovers for lunches. I typically avoid sugar sweetened beverages, and opt for extra veges over “passenger carbs” like bread and pasta 


4) Do you have a favourite post-workout cafe?

Not really, since most of my runs and weights workouts are at home. But if you are in the Balmain / Birchgrove area The Gladstone Corner store does a great long black.


5) What is one thing you wish people knew about wellbeing? 

It takes a conscious effort to find it, grow it and keep it. And a subconscious effort to lose it.


6) What is one of the most ridiculous things you’ve read or seen about wellbeing that you know to be untrue?

That you have to cut the fat off your meat to make it healthy.


7) Do you have any favourite books, podcasts or websites on health or wellbeing that you’d recommend?

I really enjoyed “the art and science of low carb living” and “The case against sugar” otherwise I am somewhat of an online itinerant.


8) What is your top tip for living a healthy and happy life? 

Every sugary drink is doing you harm