I've been doing intermittent fasting for quite some time now. And going long stretches without eating doesn't bother me much anymore. This experience has given me the opportunity to find out firsthand, how food types affect me.
One thing I've noticed repeatedly is that what I eat first matters a great deal.
If my first meal is something simple, eggs, fruit, yogurt, oatmeal, something recognizable as actual food, I can go hours without thinking about food again.
But if that first meal comes from a packet, a bar, crackers, or something sweet and processed (and no, not all packaged foods are ultra-processed), my day usually looks different. I'm back in the kitchen not long after, feeling peckish and looking for the next thing.
For a long time I thought those were just "off days."
They weren't.
Ultra-processed foods trigger cravings in ways real food doesn't. I talk more about why these foods are engineered to keep you eating in Why Can't I Stop Eating Junk Food?
Ultra-processed foods are designed to hit the brain's reward system hard.
The combination of sugar, refined carbohydrates, salt, and fat creates a strong dopamine response. Dopamine is the brain chemical tied to motivation and desire. When something produces a large spike, the brain remembers it and wants to repeat the experience.
Whole foods trigger dopamine too, just at normal levels.
An apple with peanut butter or a bowl of oatmeal tastes good. You feel satisfied, the signal fades, and you go about your day.
Ultra-processed foods, on the other hand, push that signal much higher. Instead of "that was satisfying," your brain registers something closer to "again."
Many ultra-processed foods rely heavily on refined carbohydrates.
Refined carbs digest quickly and move into the bloodstream as glucose. Blood sugar rises quickly, insulin rises to deal with it, and levels often fall again not long after.
When blood sugar drops quickly, the body interprets that change as hunger. Even if you ate recently, the brain reads the signal as a reason to eat again.
This is also where ghrelin comes in.
Ghrelin is the hormone that signals hunger, and blood sugar crashes tend to trigger it.
Meanwhile, leptin, the hormone that signals fullness, doesn't get much of a chance to catch up.
The result is that your body is chemically telling you to eat again while you're still digesting your last meal.
Whole foods come with built-in brakes that help regulate appetite.
Fiber slows digestion.
Protein activates hormones that signal fullness.
Water adds volume in the stomach.
These things work together, and when they're present in a meal, your body gets a clear message that it's done.
Many ultra-processed foods strip most of those elements away. They can contain plenty of calories but very little fiber, water, or protein to help trigger fullness signals.
Without those signals, the body never gets a strong message that it's satisfied.
Real food naturally becomes less appealing as you eat more of it.
This phenomenon is called sensory-specific satiety. The first few bites of a plain baked potato taste great. By the end, it mostly just tastes like potato.
That gradual drop in interest is your body nudging you toward variety and away from overeating any one thing.
Ultra-processed foods, on the other hand, are designed to avoid that effect.
The ratios of salt, fat, sugar, and flavor compounds are carefully calibrated so the food stays rewarding bite after bite.
Your interest doesn't drop. The bag doesn't get boring. That's not an accident.
Texture also plays a role.
Many snack foods are designed to break apart or dissolve quickly in the mouth. Chips, puffs, crackers, and similar products deliver strong flavor but very little chewing resistance.
Because they disappear so quickly, the body doesn't always register them as substantial food. The stomach and brain receive weaker signals that something meaningful was eaten.
That makes it easy to consume a large number of calories without feeling satisfied.
Your gut contains trillions of bacteria that help digest food and interact with appetite signals in the body.
Different microbes thrive on different foods. Some prefer fiber from plants, while others thrive on simple sugars and refined carbohydrates.
When a diet contains a lot of ultra-processed foods, microbes that prefer sugar and refined carbs tend to grow more dominant.
Those microbes can influence hunger signals and even the types of foods you crave.
It's not instant, and it's not irreversible.
When whole foods become more regular in your diet, the balance shifts too. But it does mean that the longer a craving pattern has been running, the more layers there are to it.
When you stack all of that together:
A dopamine spike that wants repeating
Blood sugar swinging up and crashing back down
No fiber or protein to trigger fullness
Flavor engineered to stay interesting
Textures that vanish before your body registers them
And a gut environment shaped by weeks or months of the same pattern
...cravings stop looking like a character flaw. Which means beating yourself up was never going to fix it.
That reframe matters. Because if cravings are a predictable outcome of a specific input, then changing the input changes the outcome.
Not immediately, and not without some discomfort while your gut microbiome and blood sugar patterns reset. But the direction of travel is clear.
I've seen it enough times now that it's not even a theory for me anymore. Is this something you have noticed too?