The Impact of Ultra-Processed Foods on the Brain

By Mauro Proença — Apr 02, 2024
Discovering the truth about the impact of ultra-processed foods on our brains can be like navigating a maze of conflicting information. In a recent article published by The Wall Street Journal, the spotlight was once again cast on this controversial topic.
Image by David Sánchez-Medina Calderón from Pixabay

Earlier this month, The Wall Street Journal published an article on the impact of ultra-processed foods on our brains. I initially presumed it was yet another article asserting the detrimental effects of ultra-processed foods, blaming the food industry's intentions to promote obesity and hinder access to nutritional foods.

While the article raises intriguing points, it's crucial to acknowledge that the studies the WSJ referenced did not exclusively target ultra-processed foods. Instead, they primarily examined products characterized by high sugar and saturated fats. Products with such compositions poses significant concerns for at least two reasons:

  • They exhibit a high caloric density, signifying an elevated concentration of calories per gram. Excessive consumption of these products can consequently contribute to weight gain.
  • They are categorized as hyper-palatable foods, inducing heightened pleasure upon consumption. They typically contain two of the following three ingredients: salt, sugar, and fat.

The WSJ boosted viewership, deliberately or unintentionally, by vilifying ultra-processed products without adequately considering their nutritional composition.

Another aspect that greatly perturbed me was the assertion made by Ashley Gearhardt, a psychology professor at the University of Michigan and co-creator of the Food Addiction Scale.

Initially, Gearhardt builds upon a widely accepted scientific premise: ultra-processed foods swiftly influence the brain and exert a potent effect on the reward system, which regulates pleasure, motivation, and learning. However, rather than concluding at this point, she proceeds to make the following assertion:

"Those effects are similar to ones when people use nicotine, alcohol, and other addictive drugs."

While I can comprehend this as a metaphor or hyperbole, equating ultra-processed foods to nicotine seems like an exaggeration – especially considering that I've never observed someone resort to stealing to purchase instant noodles or a donut.

What defines a food as ultra-processed?

This definition is established by NOVA, an internationally recognized and validated tool for research, public policies, and actions in nutrition and health.

The NOVA classificationis a system that categorizes foods based on their processing rather than their nutritional content. Essentially, it considers the various processes foods undergo before being consumed or utilized in meal preparation:

  • Unprocessed or minimally processed foods: These foods remain in their natural state or undergo minimal alterations. Examples include fruits, eggs, whole grains, and flour.
  • "Ingredients": Substances extracted from nature and used for seasoning or culinary preparations, such as oils, fats, sugar, and salt.
  • Processed products: These are made by adding salt or sugar to unprocessed or minimally processed foods. Examples include canned vegetables, fruit in syrup, cheese, and bread.
  • Ultra-processed products: These undergo multiple stages of processing and contain various industrially derived ingredients like flavorings, colorings, and additives. Examples include soft drinks and filled cookies.

While hyperpalatability is a predominant characteristic of ultra-processed foods, it is not exclusive to ultra-processed products nor arises solely from processing but rather from the ingredients incorporated during manufacturing.

This highlights a flaw in the NOVA system; within the category of "ultra-processed" foods, there exists a range of products with varying nutritional densities. However, the prevailing perception surrounding this category often leads to all these products being uniformly avoided with equal intensity.

Ultra-processed Foods and the Reward System:

In the first study referenced by the Wall Street Journal, 49 healthy volunteers with a normal BMI were involved. Participants maintained their usual diets for eigh tweeks but were randomly assigned to an intervention receiving a yogurt rich in saturated fat and sugar (HF/HS) or a control group that received a yogurt with low saturated fat and sugar content (LF/LS), twice daily. Both snacks were isocaloric.

The researchers sought to determine whether consuming these snacks would influence preferences for fat, the neural responses during exposure to tasty foods, and thei mpact on learning tasks.

Both groups had marginal increases in BMI, Fat Mass Index (FMI), and leptin levels. At the same time, no significant changes were noted in body weight or other metabolic parameters such as insulin resistance and lipid profile.

In analyzing images obtained through fMRI, researchers observed increased neural responses in some brain regions, playing a fundamental role in sensory and motor control pathways and areas processing emotional and physiological responses.

The researchers found that exposure to HF/HS foods:

  • Diminishes preference for low-fat foods
  • Significantly influences anticipation and consumption of highly palatable and energy-dense foods
  • Exerts a widespread effect on associative learning, independentof food rewards.

“Hence, changing the food environment and reducing the availability ofenergy-dense HF/HS food items is pivotal to combating the obesity pandemic.”

While the findings of this current study are concerning, we have addressed them previously, and they fall short of constituting conclusive evidence of the detrimental effects of ultra-processed foods on learning.

  • The study's sample size of only 49 volunteers may be deemed small, potentially limiting the generalizability of the findings.
  • Participants were required to meet two significant inclusion criteria: possessing a healthy BMI and rating the milkshake and yogurt as at least moderately desirable. This latter criterion raises whether it unconsciously selected individuals with a stronger affinity for these foods. It's a possibility worth considering, especially as the authors acknowledge that these results may not apply to individuals who lack interest in consuming these foods.
  • An even more critical variable is the participants' overall diet quality. The study did not verify the quality of their diets beyond the intervention’s snacks.  Participants' diets could have included foods high in saturated fat, sugar, and sodium, among other components.
  • Additionally, it's challenging to determine whether other hyperpalatable snacks would produce similar results. This consideration is crucial, particularly given that the composition was HF/HS; a conventional cheeseburger might not elicit the same outcomes.
  • The study was not double-blind, introducing the possibility of the researcher’s reporting bias - suppressing data that could impede publication or highlighting data or conclusions that facilitate publication.

These factors could influence the outcomes or create a false impression that the dietary intervention was effective.

How does the Western diet impact our brains?

The second referenced "study" investigated whether a four-day transition to a diet high in saturated fat and sugar among a sample of healthy, lean Young adults accustomed to a nutritionally adequate diet (characterized by low saturated fat and sugar intake) would lead to:

  • Impaired performance on hippocampal-dependent learning and memory (HDLM) tests without alterations in measures unrelated to the hippocampus.
  • Reduction in hunger and satiety sensitivity.
  • Changes in biological markers such as blood glucose and lipid profile
  • Changes in dietary habits outside the laboratory, i.e., whether there would be compensation.

The final sample consisted of 102 participants with a BMI below 25, not currently engaged in dieting, randomly assigned to an intervention group that received a high-saturated fat and sugar breakfast or a control group that received a low-saturated fat and sugar breakfast. The groups differed slightly concerning BMI, waist circumference, and dietary habits. The intervention group:

  • Required more energy intake, approximately 70 calories, to transition from hunger to satiety, indicating decreased sensitivity to satiety cues
  • Exhibited poorer performance on components of the HDLM tests, specifically verbal learning, compared to the control group. The researchers proposed that the high-saturated fat and sugar breakfast may directly impair memory retention, as evidenced by elevated blood glucose levels throughout breakfast and their relationship with changes in verbal learning performance over the trial. But logical memory was not impacted at all.

The study made use of food diaries and self-reports of eating habits. While valuable, these tools aren't reliable – participants might underestimate consumption, especially of "unhealthy" foods, or forget what they ate.

Please, don’t spoil my dessert:

Despite the intriguing nature of the data in both studies, it's crucial to recognize that these findings are preliminary investigations. They require replication and confirmation before being considered definitive or even a consensus.

Until we have more concrete evidence on this topic, I suggest that If you indulge in foods rich in sugar and saturated fat, do so in moderation.

Source: The New Science on What Ultra-Processed Food Does to Your Brain Wall Street Journal

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