Just Five Days of Junk Food Can Throw Off Your Brain’s Metabolism | The occasional splurge can have long-lasting consequences.

OK so let's start with Nature Metabolism because that's the big one here. Nature is one of the number one scientific journals to get published in. They are so big they have a portfolio dedicated for different fields. This is one of them. This tells me you are not familiar with the field. Getting published in Nature alone is impressive and tells us this article did go through a rigorous peer review process.

Secondly, the effects mentioned in the news article align with similar research I am familiar with, and in science consensus is usually a good sign for the findings being valid.

I haven't had time to look through the actual published article yet but I'm inclined to believe this. Regarding the sample size, yes it's smallish, but you can't judge it on its own. You have to look at the stats to see if it was sufficient or not. The larger the effect the smaller the sample size you need to show it. Liver fat went from like 1.5-2.5% which is a huge difference. I have definitely seen legitimate studies before with similar sample sizes.

Imma assign this weight heavier than the average study you come across, though less groundbreaking.

Source: neuroscience PhD student.

So fast food is healthy? Thank god.

When you literally don't have the money to buy groceries or the time to prepare food, yep. Or the education to truly understand the impacts of eating that food all the time... This is why poor people in America are overweight.

I mean, junk food diets tend to be more calorie dense

the issue is volume though. ~3500 calories of “healthy” foods will be physically harder to consume than 2000 calories of healthy foods and 1500 calories of calorically dense food.