Obesity and Twin Psychology

“Nature versus nurture,” otherwise known as “heredity versus environment,” is a conversation starter in almost any field of knowledge. But no matter where someone stands with respect to the relative importance of those two factors, almost anyone would agree that identical twins are clones.

This is, incidentally, also the assumption on which specially bred laboratory animals are sold. They are supposed to all start out the same, so the researchers can eliminate the constants and focus on the variants, and recognize causes and effects. The ability to take that sameness for granted is vital to the whole enterprise.

Xand and Chris van Tulleken are identical twins, born and raised in Britain, and both doctors, so how did it get to where they were 42 years old and Xand outweighed Chris by 30 pounds? As previously mentioned, Xand had moved to the United States for educational purposes, and an unplanned pregnancy brought unexpected responsibility. He told The Atlantic that eating is his go-to stress response:

I remember eating almost continuously. So it was stress, and the food environment in America is different. Portions are bigger, and the ingredients are different as well.

These twins shared the same genetic material and were brought up in the same home environment. It would seem reasonable to expect both to be stress eaters (or neither), but Chris says that is not so:

The collision of genes and environment is terribly complicated… My response to stress is just entirely stopping eating.

The history of which twin was heavier at which life stages, and why, is a bit confusing. At some point, they set some kind of record by having the biggest weight difference recorded by a King’s College longitudinal study of twins, and that was 30 pounds. Another anecdote brings up questions. Chris says,

Once, Xand was in Sudan, eating a junky diet and probably gaining weight in basically the hottest place on Earth. I went to the Arctic for three months and lost four stone.

Four stone is 56 pounds, which is a lot to lose, whether intentionally or inadvertently. If Chris is the brother who does not stress-eat, where had so much weight come from? At any rate, it is no doubt possible to trace every wrinkle of their unusual situation, because the Drs. van Tulleken tell the world about it in hopes that others might be helped.

On the physical side, the twins have “all the major known genetic risk factors for obesity.” But that is the least of the problems. Chris confesses that they enable each other in binge behavior. (If we were all honest with ourselves, it would be evident that far too many relationships are based on that paradigm.) Apparently, the brothers have always encouraged each other to be disordered and transgressive.

There are philosophical differences and a whole lot of head trips and complicated psychological sibling rivalry nuttiness. This is interesting because it shows that relationships are complicated and varied, and some solutions don’t work for everybody.

The origin story of their podcast is that Chris wanted to start it to encourage Xand to face up to his overeating tendency, but a therapist “made Chris realize that Xand wasn’t the only one who had a problem,” wrote journalist Helen Lewis. The various media projects give the two doctors plenty of scope to air their personal differences, recognize their various blind spots, and work on their control issues. A quotation from Xand relates how his brother stopped nagging, and instead…

[…] Chris spent thousands of pounds on [making] a podcast to change the way I eat, got therapists and scientists from all over the world, and has completely changed what’s in my fridge. All in a way that I feel I took charge of it. Maybe you just have to be clever about the way you manipulate your family.

Your responses and feedback are welcome!

Source: “‘The Revelation Was That I Was the Problem’,” TheAtlantic.com, 08/07/21
Image by PitchVision/CC BY-ND 2.0

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About Dr. Robert A. Pretlow

Dr. Robert A. Pretlow is a pediatrician and childhood obesity specialist. He has been researching and spreading awareness on the childhood obesity epidemic in the US for more than a decade.
You can contact Dr. Pretlow at:


Dr. Pretlow’s invited presentation at the American Society of Animal Science 2020 Conference
What’s Causing Obesity in Companion Animals and What Can We Do About It

Dr. Pretlow’s invited presentation at the World Obesity Federation 2019 Conference:
Food/Eating Addiction and the Displacement Mechanism

Dr. Pretlow’s Multi-Center Clinical Trial Kick-off Speech 2018:
Obesity: Tackling the Root Cause

Dr. Pretlow’s 2017 Workshop on
Treatment of Obesity Using the Addiction Model

Dr. Pretlow’s invited presentation for
TEC and UNC 2016

Dr. Pretlow’s invited presentation at the 2015 Obesity Summit in London, UK.

Dr. Pretlow’s invited keynote at the 2014 European Childhood Obesity Group Congress in Salzburg, Austria.

Dr. Pretlow’s presentation at the 2013 European Congress on Obesity in Liverpool, UK.

Dr. Pretlow’s presentation at the 2011 International Conference on Childhood Obesity in Lisbon, Portugal.

Dr. Pretlow’s presentation at the 2010 Uniting Against Childhood Obesity Conference in Houston, TX.

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