Food and Behaviour Research

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This Is Your Brain on Junk Food

by Scott C. Anderson

Junk food

We can’t change the genes we were born with, but we can change our microbial genes. That provides a powerful lever to lift our health and our mood.


This blog article from the 'Psychology Today' website is written in a style accessible to non-specialist audiences.

Possibly for that reason, the author didn't use the term 'ultra-processed' to refer to the kinds of foods that the article is discussing.  Ultra-processed foods (UPF) come closest to what most people mean or understand by 'junk food' - and they are also the kinds of 'highly processed' foods that
  • contain artificial additives, and
  • have been firmly linked with numerous physical and mental health disorders.

Related research article:

For further information please see:

See also:

    • In this webinar, leading international researchers Professor John Stein and Dr Alex Richardson summarise the latest scientific evidence and answer questions on:

      • why what we eat has such a powerful influence on how we feel, think, and behave – via its effects on our brains and nervous systems
      • how changing diets really can change minds, for better or for worse – and the practical implications of this for health and education professionals, policymakers, and the general public
17/10/23 - Psychology Today


Many highly processed foods are potentially dangerous, partly because they disregard the fate of gut microbes. It is pure folly to ignore those microbes, especially since they are so crucial to our physical and mental health. How important?
A new study from Tufts University, supported by the Rockefeller Foundation, says that better diets “could avert approximately 1.6 million hospitalizations and result in an estimated net savings of $13.6 billion in health care costs in the first year alone.”
The microbes in your gut differ from mine, and they vary daily. The diversity of gut microbes gives rise to an astonishing number of genes, outnumbering our genes by a factor of 100.
Good bacteria produce nourishing substances that feed and heal the cells lining your gut. If you don’t support those good bacteria, your gut cells may become hungry and disease-prone. Your gut may become leaky enough to allow bacteria and toxins to pass through.
Once bacteria breach the gut lining, the heart will pump them to every organ in your body, including your brain. This can lead to depression, anxiety, paranoia, psychosis, cognitive difficulties, and dementia.

What Is Processed Food?

The term “processed” as applied to food can be confusing. A lot of processed foods are perfectly healthy. Shelled nuts, for instance, are processed to remove an inedible shell.
Other foods are so highly processed that it’s difficult to identify the source material. Think of cheese puffs, twinkies, or vegan burgers. Delicious, yes, but what are they made of?
These foodstuffs can be problematic since one of the first steps in processing them is to remove the fiber. After all, the thinking goes, fiber is indigestible and makes products brown. Take the fiber out, and you have beautiful white foods that are easy to color any way you wish.
But fiber, an important macronutrient, is meant for your gut microbes, not you. That single elimination may be the worst thing that has happened to our diet over the last 60 years. Our gut microbes are changing composition, and some species are even becoming extinct.
There’s more: Processed foods often contain emulsifiers, which improve texture, extend shelf life, and keep ingredients mixed. Some of them, like carboxymethylcellulose and polysorbate 80, can significantly impact intestinal microbiota and lead to gut inflammation. Modern diets are failing us.

Major Macronutrients

There are thousands of nutrients in food that are good for you, but we can classify them into four broad categories. Let’s imagine a food called EquiStuff made with equal amounts of each macronutrient:
  • Fiber 25 percent
  • Fat 25 percent
  • Protein 25 percent
  • Carbs 25 percent
Now take out the fiber to improve taste and texture:
  • Fat 33 percent
  • Protein 33 percent
  • Carbs 33 percent
Notice what just happened. By the magic of math, the fat and carb content went from 25 percent of the food to 33 percent. Let’s keep going and take the fat out of EquiStuff. Now we have:
  • Protein 50 percent
  • Carbs 50 percent
Again, we didn’t set out to do this, but the carbs in EquiStuff have gone from 25 percent to 50 percent. By taking out two macronutrients, we doubled the carbs.
Thus, you don’t need to add carbs like sugar to make something sweeter. Remove the fat and fiber, and the job is done for you. But sadly, sugar is not good for a balanced gut microbiome.

Effects on Your Brain

Your diet and intestines have a clear connection, but how does that affect your brain?
Amazingly, bacteria in your gut can produce neurotransmitters, including dopamine and serotonin. These can communicate with your brain via the vagus nerve.
These neurotransmitters are the same ones targeted by psychoactive drugs, so these microbes may be just as effective as Prozac but without the side effects.
On the downside, a leaky gut caused by sugar-pumped pathogens can lead to systemic inflammation. Over time, that can adversely affect our cognition and mood.
There are several more channels of communication between the gut and the brain, but these two are extremely important from a dietary point of view.

What You Can Do

The good news is that you can fix gut-brain problems by cutting back on processed food and replacing it with fiber-filled veggies, like onions, broccoli, artichokes, and beans. Good fiber and beneficial bacteria sources can be found in ferments like sauerkraut, kimchee, kefir, and yogurt. If you can’t flip the script, try probiotic or prebiotic fiber supplements to give you a concentrated dose of the good stuff.
This isn’t an all-or-none life change. But every step you take toward increasing fiber in your diet is a step toward rejuvenating your gut bacteria. Your microbes will make you feel better in return.
We can’t change the genes we were born with, but we can change our microbial genes. That provides a powerful lever to lift our health and our mood.