As tempting as it may be to reach for high-calorie, ultra-processed foods when we’re feeling stressed or just looking to kick back and enjoy ourselves, new research reveals that even short periods of indulgence can change our brains for the worse.
In a study, published in the journal Nature and cited in Psychology Today, researchers at the University of Tübingen in Germany demonstrated that even just five days of eating junk food can alter our brain’s insulin sensitivity, mirroring the patterns seen in obese people, even though study participants did not gain weight.
What’s more, the insensitivity to insulin persisted after participants returned to their regular diet. This has implications for appetite regulation, which insulin helps with, and for the body’s ability to use sugar (glucose) for energy.
To study the effects of junk food on the brain, researchers recruited 29 healthy young men and split them into two groups. One maintained their regular diets while the other added an extra 1,500 calories per day for five days, most of which came from ultra-processed, high-fat, high-sugar foods. Functional MRI scans were taken before the diet change, immediately after the five days, and one week later, to measure participants’ brain activity when stimulated by insulin administered via a nasal spray.
[See more: Ultra-processed foods need tobacco-style warnings, says top nutrionist]
After five days on the altered diet, the junk food group showed increased activity in the regions of the brain involved in food reward and dietary changes, similar to the patterns seen in individuals experiencing obesity and insulin resistance.
One week after returning to their regular diet, they were scanned again and still showed worse results compared to the group that maintained a regular diet throughout. They also showed higher levels of liver fat accumulation, commonly associated with excess weight, than the control group and reduced activity in brain regions linked to memory and visual food cues.
The study suggests that short-term changes in our diets can disrupt brain insulin sensitivity even in the absence of weight gain. Whether or how long these effects persist is unknown, given the limited time frame of the study. The generalizability of the results is also quite limited, given the small number of participants and the fact that only men were studied. Earlier studies have shown sex-specific findings of insulin on appetite, metabolism and memory, dependent in part on hormonal fluctuations associated with the menstrual cycle.
Additionally, while the effect on the brain is persistent, that doesn’t mean it’s permanent. Previous research has demonstrated that exercising regularly for a specific amount of time can restore brain insulin sensitivity in overweight and obese people, and the same is likely true of healthy weight people.
