Junk food inflammation and bad behaviour link

Monkeys fed a Western diet for 15 months behaved badly and showed signs of persistent inflammation...
18 October 2021

Interview with 

Tom Register, Wake Forest School of Medicine


A few burgers on a table


The western diet gets a bad rap - especially if it’s the extra large duck with hoisin sauce, extra salt and no salad option. In contrast, epidemiologists repeatedly point to the cuisine enjoyed around the Mediterranean as the healthier “gold standard” diet consistent with the greatest lifespan and least ill health. But what underpins this effect? As he explains to Chris Smith, Tom Register has been studying the immune systems of monkeys eating either junk food or more Mediterranean-type diets to try to find out…

Tom - Western diets, such as eating hamburgers and cheeseburgers and French fries and Cokes and a high sugar, high fat diets is associated with chronic diseases. And one of the ideas is that the immune system is involved and we were interested in the idea that Western diets would influence circulating cells and promote disease through those.

Chris - So what was it you actually measured? What did you do? How did you do these experiments? Tell us about the study.

Tom - The study, basically, involved developing two diets, which were matched in protein, fat and carbohydrate percentages, but different in their composition. One matching the Western-like diet, cheeseburger-like diet, and the other matching Mediterranean-like diet. We fed the diet to cynomolgus macaques, which are a good model for human diseases. And these were female cynomolgus macaques of reproductive age.

Chris - And did you cross the diets over? Was this a sort of crossover thing? You feed them one diet for a period of time, then you switch it.

Tom - This was not a crossover study. That would be useful for answering selected questions that were actually raised by this study. This was a 15-month study where the monkeys consumed this diet the whole time prior to their randomization, they were eating just a child diet. And so at 15 months we isolated their blood cells and we looked at the gene expression profiles in those cells and compared between diets.

Chris - And tell me about the differences that you saw.

Tom - We saw a very marked difference between gene expression in the two diets. 40% of the genes were actually differentially regulated and the Western diet promoted a pro-inflammatory gene expression profile.

Chris - Could it be accounted for on any other basis? Did the animals change weight? Did the fat distribution in the animals change that could be causing this? So it's not the diet that's doing this. It's the second effect of the diet. What do you think is doing it?

Tom - That's a great question. And the body weights in subsets of the Western group did change, did increase over time. Their fatness increased over time, but that didn't account for the gene expression changes that we saw that was a separate kind of characteristic.

Chris - Did you make any measurements on what was living in their intestines? Because one thing that's also emerged in recent years is very important in respect of diets is that microbiome diversity is very dependent on the sort of food we eat. Did you look at that?

Tom - That's another excellent question. And yes we did. And we did find that the Mediterranean diet consumers had a greater biodiversity in their microbiome, in their gut.

Chris - So do you think then it's the microbiome that is changing what the immune system's doing or do you think that actually it's a whole raft of things that are all changing and we're going to now have to try and pick through what it is that then causes the inflammatory state in response to the Western diet?

Tom - Obviously we can't lay blame on one thing or another: it's a multifactorial. The microbiome has effects on the monocyte blood cell populations that we're studying and the microbiome has effects throughout the body, on the brain, on the heart. So yes, very definitely.

Chris - And with that in mind, were the effects just immunological or biochemical, or were there other knock-on effects of eating these diets, did the animal's behaviour change? Were there any other manifestations that went along with eating 15 months of cheeseburger-like food?

Tom - Yes. It was very interesting that we did find that diet dramatically altered behaviour. The Western fed monkeys were more anxious and less socially integrated. And we also observe relationships between the behavioural changes in gene expression, which suggests there's an interaction between diet, the central nervous system activity and circulating cell gene expression.

Chris - And is this reversible?

Tom - That's another great question. And it calls for a crossover trial. We did not do that specific study, but it's well-known that you can change your diet and you can change your risk profiles. So if you stop eating cheeseburgers and move to a more healthy diet, you can improve your health for sure.


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