This Study Changed How I See Junk Food

Comfort food. No one can eat just one. Give me a break, give me a break. Ba ba ba ba, I'm loving it. These aren't just slogans. These are psychological hooks designed by marketing geniuses to make you want to indulge, to hear that whisper in your ear that you deserve a treat. And when you eventually cave, you know what happens, right? Some fat gain from caloric overload and maybe a temporary stomachache. But what if I told you the real damage goes far deeper? Because a single junk food binge doesn't just hit your waistline, it leaves a metabolic scar, and in the last place you want that—your brain. I just read a new human-controlled trial that you need to understand, and once you do, I promise you, the next time fast food or junk food calls the same, you'll hear it a little bit differently. Let's begin. Calories. Eating candy. Junk food. Something way more dangerous was happening. That signal gets lost. The brain was alarming. That's okay. That's good, in fact. It's so interconnected, complex. Let that— The calories don't tell the full story. I want to jump straight into the study. The only thing I want to call out first is if you watch this video and then want extra nuances, details, all the references, or early access to content like this, check out the associated Stay Curious Metabolism newsletter. Anyway, with that self-promo over, let's get into the study. This was a controlled human trial published earlier this year in Nature Metabolism. It involved 29 young healthy men with normal BMIs between 19 and 25. They were all healthy and free of disease. Then what the researchers did is they split them into two groups. One consumed a "high calorie diet"—very heavy air quotes there— They were instructed to eat 1,500 calories more than their estimated caloric needs, and the other continued on the normal diet. The high-calorie diet lasted for 5 days, and during this time the researchers measured all sorts of things: body weight, body fat, insulin sensitivity, even brain blood flow and brain-specific insulin sensitivity. Now here's the first twist. The high-calorie diet participants did eat a lot more, But what happened to their weight? Despite eating significantly more, there was no significant increase in total body weight in the high-calorie group compared to controls. There wasn't even a trend towards weight gain. In fact, if you take the group averages as gospel, the control group actually gained 0.2 pounds more weight than the high-calorie group. So, #caloriefails for the first time. So, if the weight didn't budge, was everything good? Not even close. Something way more dangerous was happening under the surface. The high-calorie diet participants still developed much more liver fat, with a striking 64% increase in percent liver fat between baseline and the 1-week follow-up, and this was not seen in the controls. The absolute increase was 1.55% to 2.54%, so relative increase 64% to be clear. We'll return to this fact shortly when we talk about the brain findings, so put a pin in that for now. And interestingly— this was odd— there was no difference in general insulin sensitivity using standard measures of like whole body insulin sensitivity. Maybe that's not surprising, it was only 5 days, right? But what happened in the brain was alarming, and this is the big twist. At the 2-week follow-up mark, about a week after the high-calorie phase had already completed, there was decreased blood flow to critical brain regions like the hippocampus and the fusiform gyrus. Now you don't need to know what these brain regions are exactly, there's no anatomy test, but at a high level, they're important for memory, learning, and self-control. They're parts of your brain involved in the "put on the brakes" on impulsive eating. So when they go quiet or are turned down, as with decreased blood flow, willpower effectively weakens. And yes, if there are any neuroscientists watching, I'm oversimplifying, but you get the point. Anyway, this is what I alluded to earlier when I said the diet left a metabolic scar on the brain. And it didn't stop there. The high-calorie diet participants also developed brain-specific insulin resistance, which you can assess using intranasal insulin—up the nose. And recall, this was independent of any changes in body weight or peripheral, rest of the body insulin resistance, as compared to control participants. This was brain-specific insulin resistance from 5 days of high-calorie feeding. Why does that matter though? Well, normally insulin helps reduce appetite when it signals to the brain, but when the brain becomes insulin resistant, that signal gets lost, meaning you crave more and make worse food choices. So the punchline is clear: a short-term high-calorie binge can leave a lasting mark, a scar on the brain, one that makes you more likely to overeat in the future. Or, to quote the authors themselves, "These data suggest a short-term high-calorie diet rich in sugar and saturated fat"— I will caveat that, but that's what they said— "has prolonged effects on the brain that outlast the time frame of its consumption." But we're still not done, because there are critical nuances to unpack. So let's start with the most basic question that I've heretofore failed to answer: What was the source of the extra calories? Well, according to the study's methods, a nutritionist prepared 5 days' worth of snacking packages totaling 1,500 additional calories per day, and these came from Snickers, brownies, and chips, with a roughly equal split between fat and carb calories. Now, hear me, let me be very clear, the participants were not eating calories. They were eating candy, junk food, refined carbohydrates. They were consuming biomolecules that our bodies process, cleaving covalent bonds, pushing molecules through biochemical pathways—glycolysis, oxidative phosphorylation—that directly generate ATP or reduced electron carriers, which ultimately fuel oxidative phosphorylation in the mitochondrial electron transport chain. I can go on and on with jargon. The jargon is not the point. Jargon aside, The participants, humans, didn't just eat calories, they ate food. Calories are not a physical thing you consume, they're a measurement, a number derived from the energy released not by our biochemical processes, but when we measure it by taking that food, putting it in a bomb calorimeter, and blowing it up, and measuring the amount of heat that's released in surrounding water. And I hope you see how different those things are. Measuring calories and what our body actually does to process the molecules we eat into energy to fuel our bodies. That difference matters a ton. Hi, future Nick here. Now, before I finish up this video and prove to you that the source of calories matter and how eating 5,800 calories on a low-carb keto diet produces drastically different effects than the same number of calories on a high-carb diet, I want to tell you about a product that I'm taking for brain health including brain insulin sensitivity. It's called Lysovita. Now, here's the deal. Most omega-3 supplements use a form called triglyceride that tends to get stored in body fat and struggles to get through the blood-brain barrier. That's why Lysovita was engineered to fix this problem. It contains a concentrated form of omega-3 called lysophosphatidylcholine DHA, which is transported directly into the brain through a specialized pathway. What you need to know is that in preclinical studies, this form has been shown to raise brain omega-3, brain DHA levels far more efficiently and boost levels of BDNF, a key molecule for memory and cognition. Now, I'll admit, this is a premium product. It's the one I use personally because I want to invest in my long-term brain health, and because of my own genetic predisposition to Alzheimer's disease, a disease I'm determined to avoid. Others in the community have had great experiences with this new product as well, which is why I wanted to share it here. And to make it slightly more accessible, I've partnered with Phoenix Health to offer a 20% discount code on what I use with the code STAYCURIOUS. If you want more details, I've linked far more science below, including a detailed explanation, because I want you to know this isn't just another shallow product plug that you'll generally find, but something I genuinely use that I want to explain to you and that I wanted to share for your consideration. Now, with that, back to your main content. Because this was a two-arm study, we don't know what would happen if those same number of additional calories came from different foods. The question is, would eating an extra 1,500 calories of steak and eggs have the same effect as eating 1,500 additional calories from Snickers and chips? I don't think so. But this nuance, this metabolic fact in fact, is completely obscured by our culture's pathological obsession with calories. It's not just a flaw in the paper, although I think it is in the discussion, but it's a flaw in nutrition science and culture at large. To double down on this point though, I want to now consider a fascinating case report involving a young man who voluntarily increased his caloric intake to 5,800 calories per day, but cycled through different diets for 3 weeks at a time without changing his activity level. He had a low-carb diet, 6% calories from carbs, during which he consumed 121,674 calories over 3 weeks, so 58,000 calories per day. He only gained 1.3 kilograms and actually his waist circumference decreased by 3 centimeters. Then, during the low-fat phase, calorie-controlled, with 64% of his calories from carbs, his caloric intake was identical at 121,653 calories, yet he gained much more weight, 7.1 kilograms, and his waist circumference, get this, —increased by 9.25 cm. These aren't small differences, they're huge. And while this is an n=1 study, the findings are consistent with controlled human trial data we reviewed earlier. The point is, you can uncouple factors like liver fat and waist circumference from overall weight change. #CalorieFail. The scale, the calories don't tell the full story. Or if you want a cute analogy, Calories are like a misleading trailer. They're trying to sell you the greatest action movie you've ever seen while actually delivering two dudes sword fighting with PVC pipes. It's disappointing. But let's return to our main scientific story. Even in this controlled study, there was an association between liver fat gain in the high-calorie group and changes in brain insulin action. Now, while it's incredibly difficult to draw causal conclusions in human studies, we can look to other literature. That provides a very plausible biological basis for, say, a liver-brain connection. So, for instance, an unhealthy liver spits off different hormones and releases packages called small extracellular vesicles, which can carry molecules that are instructions to the brain through the blood-brain barrier and influence brain activity and brain insulin resistance. We've discussed this sort of thing previously, and I'll link more information below if you want to dive into that. But the point here is not to obsess over the exact pathway. What I really want to drive home is this: the quality of the food we eat profoundly shapes how energy and nutrients are handled by our body, influencing variables that go far beyond a number on the scale— liver fat percent, brain insulin sensitivity. We're talking about how organs and cells in our body communicate with one another, how the liver talks to the nervous system, how fat cells communicate with the heart, how metabolic health orchestrates a delicate, dynamic conversation across your entire physiology. It's not simple arithmetic. It's not simple calories. It's a complex symphony. And while humans love simplicity, simplicity is comforting. We want to hear the "it's just calories, stupid." This narrative is also profoundly misleading. So what I'm challenging you to do here is to lean into the complexity of nutrition and biology. Let yourself be a little overwhelmed. That's okay. That's good, in fact. It's so interconnected, complex. Let that humble you because when you do so, something beautiful happens. Your knowledge base expands. Your relationship with your body and your health transforms. It stops feeling like a chore to take care of your body and learn about your body and starts to feel like what it is, a gift, an exploration that we as a species can share and build knowledge like we're doing here. And that we as individuals can then experiment with that knowledge in the context of our own n=1 journey, that's miraculous. That's something to be deeply grateful for. That's something that when I recount it gives me goosebumps every time. So with that, I want to wrap up. I'd love to hear from you. What stood out? What questions do you still have? What did I get right? What did I get wrong? Stay curious and thanks.