We do it to ourselves by eating the wrong stuff!

And unfortunately, although I'm working on it, I'm guilty as anyone else.

If you love so-called “junk food”, and feel like you can’t stop eating it, you’re not alone, bad, or weird. However, our ancestors weren’t exactly dialing in for delivery. They had to bust their butts with daily activity such as stalking, searching, gathering, and digging, even for minor rewards like a meal of turtle and tubers. Today, of course, high-fat foods aren’t nutrient-rich animal organs or blubber that we had to work nine hours to get; they’re Frappucinos, donuts, pizza, and double cheeseburgers with fries that we bought while seated in our car to tote back to our home or office.

Evolution’s gifts now work against us. This is your brain on processed food. Our taste-buds loooooove processed foods. But our bodies don’t. These overly enchanting and semi-addictive foods aren’t nutritious. They have more energy than we need, with little to no nutrients: no  protein, vitamins, minerals, phytonutrients, essential fatty acids, and fiber. That’s why we don’t feel full or satisfied when we eat them.

After a while, our brain forgets about its natural “stop” signals in favor of getting more of that delicious “hit” from food rewards. Our hedonic pleasure system starts bullying our homeostatic energy and health balancing system.

Over time, if we eat a lot of these foods consistently, we might even injure and inflame the parts of our brain and body that regulate our food intake and energy output. Now our homeostatic regulation isn’t just getting pushed around, it’s also on fire. We’re not sure exactly why this happens.

Getting too much energy from foods, and especially these foods, seems to injure our brain’s neurons, particularly in the hypothalamus. When we are injured, we normally release inflammatory cytokines (aka cell signals). This happens in the brain as well (since the brain is part of our body), causing hypothalamic inflammation.

There is also evidence that significant consumption of these energy-dense foods changes the populations of the bacteria in our gut. Which affects the gut-to-brain pathway and also causes hypothalamic inflammation. Hypothalamic inflammation then leads to leptin resistance.

Disrupting the leptin feedback loop:  You might have heard of insulin resistance, the condition where people’s cells stop “hearing” insulin signals, and slowly lose the ability to control their blood sugar levels. The same thing can happen with leptin: Your brain can start to ignore or “tune out” the leptin, even if you’re eating enough, and have plenty of energy stored in your body fat. In insulin resistance, the pancreas can simply pump out more insulin to keep blood sugar under control (at least for a while). Since body fat is our main leptin factory, to make more leptin, we need more body fat.

You see where this is going, right? When you’re leptin resistant, your brain thinks it doesn’t have enough leptin. The brain needs the leptin factory (i.e. body fat) to get bigger and produce more leptin.Operation Add Adiposity (FAT) begins. You feel hungry. Regular portion sizes are no longer satisfying; it’s harder to feel satiated and you want to keep eating, and eat more often. You gain fat. Mission accomplished, or so your brain thinks.

Here’s what the leptin feedback loop looks like now, in this disrupted scenario:

The leptin feedback loop can be disrupted by inflammation and neuron injury, sometimes caused by eating too many processed foods. This, combined with other genetic and environmental factors, can lead to leptin resistance and increasing body fat.

As if that weren’t enough, it seems this inflammation and resulting leptin resistance might even cause our bodies to defend our increased weight. This seems to be because the brain now views this higher level of leptin and body fat as its new normal. In this case, our body fights even harder than normal to stop us losing fat. Scientists are still researching exactly how and why our bodies do this.