It’s been a year since Chris van Tulleken set his twin brother, Xand, a challenge to help him quit his addiction to junk food. Xand had to eat an 80% ultra-processed food (UPF) diet while learning about its health impact. It worked and by the end Xand rejected all those foods he’d previously adored, including his beloved Chinese dumplings. The experiment had an aversion effect, just as Chris had hoped.

But something else happened during the experiment, Chris also had a conversion experience. A podcast about food addiction transformed into a podcast about the twins’ relationship and how best to help someone you love.

In this episode, the twins reflect on their conversion experiences – are they eating better and more importantly, are they getting on better?

Chris speaks to obesity expert Professor Rachel Batterham who tells him how the scientific discourse about UPF has developed since the end of series 1. And the twins go to see philosopher Barry Smith whose professional life has been affected by the twins’ experiment and he tells them why he’s now refusing to work with major food companies as a sensory consultant.

When Xand pops round for tea one evening, Chris’s five-year-old daughter shares some home truths about her dad and uncle’s relationship and it prompts the twins to consider what else they need to improve in their lives.

Presented by Drs Chris and Xand Van Tulleken

A Loftus Media and van Tulleken Brothers Ltd production for BBC Radio 4.

With thanks to Voltage TV for use of their archive.

Chris and Xand are doctors, scientists and identical twins. Well, not quite identical. Xand is 20kg heavier, clinically obese, and has a Covid induced heart condition.

Chris believes that the reason Xand is overweight is the same reason that most of us in the UK are overweight - Ultra Processed Food or UPF. It’s the main thing that we now eat and feed to our children, but most of us have never heard of it. It’s addictive, highly profitable and the main cause of the global obesity pandemic. It’s destroying our bodies, our brains and the environment.

In this series, recorded during the first coronavirus lockdown of 2020, Chris wants to help his brother quit UPF and get his health back. So, he has a plan. In an attempt to turn Xand's life around, Chris persuades his brother to eat a diet comprising 80% Ultra-processed food while learning about every aspect of it. By doing this, Chris tests two theories - that Xand is addicted to UPF, and that eating more of the stuff while learning about it, will help him quit.

In episode 6 - Building an ultra processed world – finishing the experiment, Xand explains that he has had a ‘conversion experience’. Recognising the dangers of UPF, not only to his own health and wellbeing, but to the health and wellbeing of society, he concludes that he no longer has any desire to eat UPF.

Chris and Xand talk to the American Academic and former professor of nutrition, food studies and public health at New York University, Marion Nestle, who explains how UPF is not just a public health issue, it's an environmental disaster. Marion considers and recommends what needs to be done to combat the rocketing levels of obesity – especially in children - while ensuring sustainable healthy food production.

Presented by Drs Chris and Xand Van Tulleken

Chris and Xand are doctors, scientists and identical twins. Well, not quite identical. Xand is 20kg heavier, clinically obese, and has a Covid induced heart condition.

Chris believes that the reason Xand is overweight is the same reason that most of us in the UK are overweight - Ultra Processed Food or UPF. It’s the main thing that we now eat and feed to our children, but most of us have never heard of it. It’s addictive, highly profitable and the main cause of the global obesity pandemic. It’s destroying our bodies, our brains and the environment.

In this series, recorded during the first coronavirus lockdown of 2020, Chris wants to help his brother quit UPF and get his health back. So, he has a plan. In an attempt to turn Xand's life around, Chris persuades his brother to eat a diet comprising 80% Ultra-processed food while learning about every aspect of it. By doing this, Chris tests two theories - that Xand is addicted to UPF, and that eating more of the stuff while learning about it, will help him quit.

In episode five - Building an ultra-processed mind - Xand continues the experiment eating 80% UPF, becoming more aware of what he is eating, and how it is effecting his mind and body. Xand also speaks to Dr Nicole Avena, a food addiction neurologist, about how our brains are affected by UPF in relation to other addictive behaviour. Both Chris and Xand go on to speak to sensory expert, Professor Barry Smith from the University of London, about how all of our senses are targeted by companies when we consume their UPF products.

Presented by Drs Chris and Xand Van Tulleken

Chris and Xand are doctors, scientists and identical twins. Well, not quite identical. Xand is 20kg heavier, clinically obese, and has a Covid induced heart condition.

Chris believes that the reason Xand is overweight is the same reason that most of us in the UK are overweight - Ultra Processed Food or UPF. It’s the main thing that we now eat and feed to our children, but most of us have never heard of it. It’s addictive, highly profitable and the main cause of the global obesity pandemic. It’s destroying our bodies, our brains and the environment.

In this series, recorded during the first coronavirus lockdown of 2020, Chris wants to help his brother quit UPF and get his health back. So, he has a plan. In an attempt to turn Xand's life around, Chris persuades his brother to eat a diet comprising 80% Ultra-processed food while learning about every aspect of it. By doing this, Chris tests two theories - that Xand is addicted to UPF, and that eating more of the stuff while learning about it, will help him quit.

In episode four - Building an ultra-processed body - Xand starts the diet, eating 80% UPF while continuing to learn about it. Chris thinks the diet will work because he’s done it, subsisting on a junk food diet for four weeks while investigating the causes of childhood obesity in a BBC TV documentary. In order to understand the direct effect UPF is having on his body - appetite, hormones and weight - Xand speaks to obesity expert, Dr Janine Makaronidis from University College London. Xand also interviews Dr Kevin Hall from the National Institute of Health in the US about his ground-breaking research into the consumption of UPF. Kevin was the first scientist to prove that UPF causes weight gain.

Presented by Drs Chris and Xand Van Tulleken

Chris and Xand are doctors, scientists and identical twins. Well, not quite identical. Xand is 20kg heavier, clinically obese, and has a Covid induced heart condition.

Chris believes that the reason Xand is overweight is the same reason that most of us in the UK are overweight - Ultra Processed Food or UPF. It’s the main thing that we now eat and feed to our children, but most of us have never heard of it. It’s addictive, highly profitable and the main cause of the global obesity pandemic. It’s destroying our bodies, our brains and the environment.

In this series, recorded during the first coronavirus lockdown of 2020, Chris wants to help his brother quit UPF and get his health back. So, he has a plan. In an attempt to turn Xand's life around, Chris persuades his brother to eat a diet comprising 80% Ultra-processed food while learning about every aspect of it. By doing this, Chris tests two theories - that Xand is addicted to UPF, and that eating more of the stuff while learning about it, will help him quit.

In episode three - How to change? Let it go… - Chris and Xand have an emotional conversation about why this project is important and hard for both of them to undertake. They speak separately to Alasdair Cant, a behaviour change expert, about how we decide to become different people. Alasdair also speaks to Chris about how he, like many family members, may be holding Xand back from making the necessary changes in his life to get healthier.

Presented by Drs Chris and Xand Van Tulleken

Chris and Xand are doctors, scientists and identical twins. Well, not quite identical. Xand is 20kg heavier, clinically obese, and has a Covid induced heart condition.

Chris believes that the reason Xand is overweight is the same reason that most of us in the UK are overweight - Ultra Processed Food or UPF. It’s the main thing that we now eat and feed to our children, but most of us have never heard of it. It’s addictive, highly profitable and the main cause of the global obesity pandemic. It’s destroying our bodies, our brains and the environment.

In this series, recorded during the first coronavirus lockdown of 2020, Chris wants to help his brother quit UPF and get his health back. So, he has a plan. In an attempt to turn Xand's life around, Chris persuades his brother to eat a diet comprising 80% Ultra-processed food while learning about every aspect of it. By doing this, Chris tests two theories - that Xand is addicted to UPF, and that eating more of the stuff while learning about it, will help him quit.

In episode 2 – UPF is not food - Chris and Xand meet Professor of Chemistry Andrea Sella to try to understand some of the more complex ingredients in Ultra Processed Food and the lies they tell us about when we are full and satisfied. Dr Fernanda Rauber was on the team who "discovered" UPF, and explains why it exists and that perhaps we are thinking about it in the wrong way - that it’s not food, it's an industrial formulation of chemicals.

Presented by Drs Chris and Xand Van Tulleken

Chris and Xand are doctors, scientists and identical twins. Well, not quite identical. Xand is 20kg heavier, clinically obese, and has a Covid induced heart condition.

Chris believes that the reason Xand is overweight is the same reason that most of us in the UK are overweight - Ultra Processed Food or UPF. It’s the main thing that we now eat and feed to our children, but most of us have never heard of it. It’s addictive, highly profitable and the main cause of the global obesity pandemic. It’s destroying our bodies, our brains and the environment.

In this series, recorded during the first coronavirus lockdown of 2020, Chris wants to help his brother quit UPF and get his health back. So, he has a plan. In an attempt to turn Xand's life around, Chris persuades his brother to eat a diet comprising 80% Ultra-processed food while learning about every aspect of it. By doing this, Chris tests two theories - that Xand is addicted to UPF, and that eating more of the stuff while learning about it, will help him quit.

In episode 1 - How did we get so different? - Chris and Xand speak to Cambridge University geneticist Dr Giles Yeo to begin to understand the origins of Xand's (and everyone else's) size, learning about the role our food environments play in our susceptibility to UPF. How much is destiny, how much might we be able to control?

Presented by Drs Chris and Xand Van Tulleken

Chris van Tulleken is on a mission to get his twin, Xand, to quit ultra-processed food.

There’s a growing global addiction to ultra-processed food aka UPF. Chris thinks UPF is driving Xand’s (and everyone else's) weight problem. So, he proposes a simple experiment - that Xand goes on a final week-long UPF binge whilst interviewing the world's leading experts on addiction, food, nutrition and weight. It's the nutritional equivalent of smoking 100 cigarettes whilst going on a quit smoking course. Simple right? Well, it turns out to be far stranger and more emotional than either of them ever imagined...