What just 5 days of overeating can do to your brain and liver

I’ve been treating metabolic disorders like Type 2 diabetes, heart disease, and obesity for decades.

That means I often work with patients who are aware of the dangers of a poor diet. They’ve seen firsthand what sugar and processed foods can do to the body.

But I also see another type of patient…

They have no weight problems, no diagnosed conditions, and no real reason (in their minds) to question what they’re putting on their plate.

And quite honestly? They’re the hardest to convince that food influences health.

So, no matter where you fall on that spectrum, here’s a little reality check…

Five days of damage

In a small study, researchers observed how a few days of overeating affected the health of 29 young volunteers.

In addition to their normal meals, participants consumed an extra 1,500 calories per day of ultra-processed snacks.

After “just” FIVE days, researchers observed the following:

• A significant increase in liver fat
• Altered insulin activity in multiple regions of the brain

Notably, these were young, healthy volunteers. Meaning their bodies haven’t yet endured decades of poor lifestyle habits.

Yet, they still experienced these detrimental effects.

And while there were no changes in body weight, inflammatory markers, or peripheral insulin sensitivity in that short period of time, the fact that liver fat and brain insulin signaling were altered so rapidly—and those effect lingered—is quite concerning.

In fact, even after returning to a regular diet, researchers observed some parts of the brain did NOT return to baseline, especially in the reward and punishment centers.

The brain-body connection

I’ve talked a lot about insulin resistance over the years.

It means your body stops reacting to insulin normally. As a result, blood sugar levels begin to skyrocket, paving the way to metabolic syndrome and diabetes.

Plus, when the brain’s ability to respond to insulin becomes impaired, it leads to poor appetite control, increased fat storage (especially around the mid-section), a sluggish metabolism, and difficulty keeping weight off—even with healthy lifestyle changes.

And this study just highlights that even before weight gain sets in, the brain is already reacting to your food choices. It adapts quickly—and not in your favor.

This is why I always tell you to take your diet seriously, even if you’re “naturally slim.”

After all, your brain and liver may still be under strain from your dietary choices.

Hear me when I say that what you eat today affects how your body functions tomorrow—and perhaps for much longer than you think.

So, as always, ditch the junk food. Adopt a healthy, balanced diet full of fresh, whole foods—like lean protein, healthy fats, and organic produce.