Guest Essay by Kip Hansen

Dr. Kevin Hall, at the U.S. National Institutes of Health (NIH), has  recently been conducting “randomized clinical trials to study how diets high in ultra-processed food may cause obesity and other chronic diseases”, and was the lead author of a study,  Hall et al. (2019)  titled “Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake”.

That study is almost always cited in other studies about Ultra-processed Foods (UPFs) as being “…the first and only to show us how ultra-processed diets drive people to consume about 500 extra calories per day, without even realizing it.”   As published in Cell Metabolism the results of the study were summarized as:

“Highlights

•  20 inpatient adults received ultra-processed and unprocessed diets for 14 days each

•  Diets were matched for presented calories, sugar, fat, fiber, and macronutrients

•  Ad libitum intake was ∼500 kcal/day more on the ultra-processed versus unprocessed diet

•  Body weight changes were highly correlated with diet differences in energy intake”

This was a very small study – 20 participants – and it showed that over a two-week period participant, who were restricted to the hospital, those eating the so-called UPF diet gained an average of about 2 lbs (1 kg) in the first six days, then their weight held steady (no further increase).  Those on the unprocessed menu immediately began to lose weight and continued to do so throughout the 2-week period. (Photographs of the foods actually served are included in the full study report supplement – pdf download here. )

The papers title is false.  “Ultra-Processed Diets Cause Excess Calorie Intake” – ‘Ultra-processed diets’ are not a cause in and of themselves – so this is mis-stated at best.  It does appear that the participants preferred the UPF offerings and ate a bit more of them taking in “extra” calories but notice that the weight gain halted after day six after which their weights remained level.  However, for the unprocessed diet, weight loss continued in a linear fashion.

I emailed Dr. Hall and asked him if he thought this weight loss was a problem.  Most hospitalists (the doctors generally responsible for patients in a hospital) would be concerned by continued weight loss of their patients.  Dr. Hall replied: “Body weight loss on the minimally processed diet was not a concern, especially given that the average body mass index of the study participants was 27 kg/m^2 which is in the overweight range.” 

I have issues with the study conclusions – but we will let that go for now.  The point being that Dr. Kevin Hall is an anti-UPF advocate.  So much so, that he decided to prove that UPFs were addictive.

That meme – “UPFs are addictive” – is ubiquitous in the literature on so-called UPFs.  So much so that there are published studies claiming that “14% of adults and 15% of youths” are addicted to UPFs.  The mechanism suggested for this “addiction” is:  “UPFs triggers addiction-like biological (e.g., dopaminergic sensitization) and behavioral (e.g., withdrawal, use despite consequences) responses”

Dr. Kevin Hall and a group at the National Institutes of Health set out to prove that addictiveness of UPFs by showing that feeding subjects a UPF would produce a dopamine spike, just like additive drugs do.

The study is “Brain dopamine responses to ultra-processed milkshakes are highly variable and not significantly related to adiposity in humans”.  Dr. Hall is the lead contact for the paper.

For this study, the journal Cell Metabolism again summarizes:

“Highlights

•  PET scans found no significant mean dopamine response to ultra-processed milkshakes

•  Individual brain dopamine responses were not significantly related to adiposity

•  Greater brain dopamine responses were correlated with fasting hunger levels

•  Ad libitum cookie intake was correlated with brain dopamine responses”

Try not to be confused by the reference to “Ad libitum cookie intake”, I’ll explain later.

The study abstract states this more clearly:

“Surprisingly, milkshake consumption did not result in significant postingestive dopamine response in the striatum (p=0.62) nor any striatal subregion (p>0.33) and the highly variable interindividual responses were not significantly related to adiposity (BMI: r=0.076, p=0.51; %body fat: r=0.16, p=0.28). Thus, postingestive striatal dopamine responses to an ultra-processed milkshake were likely substantially smaller than many addictive drugs and below the limits of detection using standard PET methods.”

As an image:

Let’s see if we can put this a little more bluntly:

Paraphrasing editorially: “Dang, our super-duper, purpose-made exemplar of a UPF didn’t produce any dopamine response that we could see. “

But, afterwards, when subjects were offered snacks as part of their post-study lunch, the subjects whose test showed those that liked sweets ate a few more delicious  Chips Ahoy! chocolate chip cookies.

In a more detailed discussion later in the paper, the authors say:

“In other words, despite expecting the high fat and sugar formulation of the ultra-processed milkshake to produce a synergistic effect on striatal dopaminergic activity (DiFeliceantonio, Coppin et al. 2018, McDougle, de Araujo et al. 2024), our data suggest that any extracellular dopamine responses following milkshake consumption were smaller than those following ingestion of drugs of abuse. Thus, the narrative that ultra-processed foods high in fat and sugar can be as addictive as drugs of abuse based on their potential to elicit an outsized dopamine response in brain reward regions was not supported by our data.”

Bottom Line:

UPFs are not addictive — they do not produce dopamine spikes that consumers seek to repeat as seen with addictive drugs.

(but they may be delicious!)

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Author’s Comment:

Kudos to Dr. Hall and his group for publishing a “negative result” paper.  They expected and desired to show the UPFs were just addictive as opioids and other drugs of abuse but found that they were not.  In fact, they did not produce measurable amounts of dopamine.

I extend these kudos even if the paper was published as a matter of policy – registered NIH studies completed must be written up and published – I’m pretty sure of this (not positive).

I suspect that the War on Food will not end now despite that fact that the battle against “addictive UPFs produced by nasty evil international corporations” has been dealt a death blow by real science.

This is not to say that some foods are not “habit forming” – humans like pleasant experiences – they like things that taste good and can form unhealthy repetitive eating habits.    Think of those eating giant bags of chips, guzzling orange soda, while binge watching years of old Star Trek episodes. (No, I don’t mean you.)

Thanks for reading.

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