Why Calories‑In vs. Calories‑Out May Not Tell the Whole Weight Loss Story

In 2023, I lost nearly 50 pounds of fat by eating a caloric-restrictive diet. I maintained a high-protein, 1,700-calorie/day diet for months. And it worked. Until it didn’t.

I got down to about 185, then the weight loss stopped. I’ve read that restricting calories too much can eventually backfire. But then I learned something fascinating. And the more research I did, the more I realized that there was something else going on, too.

I’m mildly resistant to insulin, which complicates the calorie-in vs. calorie-out equation.

The deeper I got, the more interesting it became.

What Is Calories-in vs. Calories-Out?

For decades, the dominant narrative around weight loss has been simple: if you burn more calories than you consume, you’ll lose weight.

It’s the “calories‑in vs. calories‑out” model, often abbreviated as CICO.

On paper, it makes perfect sense.

Energy balance is a fundamental law of physics—consume less energy than your body expends, and the difference has to come from somewhere, usually stored fat.

But here’s the catch: while calorie restriction works for most people in the short term, it often stops working as effectively over time. And for certain individuals—especially those who are insulin resistant—the story is far more complicated.

In fact, for them, eating more calories can sometimes unlock weight loss, because the body stops behaving as if it’s under siege.

The Basics: Why Calorie Restriction Works… to a Point

When someone first cuts calories, the results are usually encouraging. A person eating 2,500 calories a day who drops to 2,000 will almost always lose weight initially. The body taps into stored energy, fat cells shrink, and the scale moves.

This is why nearly every diet, whether low‑carb, low‑fat, intermittent fasting, or even fad cleanses, works in the short term. They all create a calorie deficit, whether directly (by restricting food) or indirectly (by limiting food choices so you naturally eat less).

But here’s where things get tricky: the body is not a static machine. It adapts.

Metabolic Adaptation: The Body’s Defense Mechanism

When you restrict calories for too long, your body interprets it as a potential threat. Evolution trained us to survive famine, not thrive in it.

So the body responds with metabolic adaptation:

• Lowered resting metabolic rate. Your body burns fewer calories at rest.
• Reduced non‑exercise activity. You fidget less, move less, and unconsciously conserve energy.
• Increased hunger signals. Hormones like ghrelin ramp up, making you feel hungrier.
• Decreased satiety signals. Hormones like leptin drop, so you feel less satisfied after meals.

The result? That initial 500‑calorie deficit shrinks over time. What once produced steady weight loss now produces a plateau. Studies like the CALERIE trial confirm that long‑term calorie restriction triggers measurable metabolic adaptations.

Let’s now talk about why all this flies out the window with certain people.

Why Insulin Resistance Changes the Game

Insulin resistance has entered the conversation…a condition where the body’s cells don’t respond properly to insulin. Insulin is the hormone that helps shuttle glucose (from carbs) into cells for energy. When cells resist insulin, glucose lingers in the bloodstream, prompting the body to produce more insulin.

High insulin levels make fat loss harder for several reasons:

• Insulin is a storage hormone. Elevated insulin signals the body to store energy rather than burn it.
• Fat cells become “sticky.” They hold onto stored fat more tightly.
• Energy feels locked away. Even if you’re carrying extra fat, your body struggles to access it for fuel.

For insulin‑resistant individuals, simply cutting calories doesn’t always work. The body is stuck in “storage mode,” and the deficit feels more like deprivation than liberation.

Research shows insulin‑resistant adults often lose more weight on low‑carb diets compared to low‑fat diets, highlighting how biology changes the equation.

Why Eating More Can Sometimes Help

Here’s the paradox: for insulin‑resistant people, eating more—or at least eating differently—can sometimes unlock weight loss.

How?

1. Lowering insulin through food choices. When you eat fewer refined carbs and more protein, fiber, and healthy fats, insulin levels drop. This shift allows fat cells to release stored energy.
2. Convincing the body it’s not starving. If the body constantly feels deprived, it clings to fat. But when you provide adequate calories from nutrient‑dense foods, the body relaxes. It stops hoarding energy and starts burning it.
3. Restoring metabolic rate. Eating more can reverse some of the metabolic slowdown caused by chronic restriction. Your resting metabolic rate increases, and you naturally burn more calories.

Beyond Calories: Other Factors That Matter

Calories matter, but they’re not the whole story. Other key players include:

• Hormones: Insulin, leptin, ghrelin, cortisol, thyroid hormones all influence weight regulation.
• Sleep: Poor sleep raises cortisol and disrupts hunger hormones, making weight loss harder.
• Stress: Chronic stress keeps cortisol high, which promotes belly fat storage.
• Muscle mass: More muscle means higher metabolism. Strength training can offset metabolic adaptation.
• Food quality: 500 calories of donuts is not the same as 500 calories of salmon. Nutrient density affects satiety, hormones, and energy.

The Balanced Approach

So what’s the takeaway? Calories matter, but they’re not the only lever. Sustainable weight loss requires a broader view:

1. Start with a modest deficit. Don’t slash calories too aggressively. Aim for slow, steady progress.
2. Prioritize protein. It supports muscle, boosts satiety, and stabilizes blood sugar.
3. Choose quality carbs. Fiber‑rich sources like vegetables, beans, and whole grains keep insulin in check.
4. Strength train. Muscle is your metabolic engine. Build it, and you burn more even at rest.
5. Manage stress and sleep. These are silent saboteurs of weight loss.
6. Listen to your body. If you feel constantly drained, hungry, or stuck, it may be time to adjust, not double down on restriction.

Final Thought

The CICO model is not wrong. It’s just incomplete.

It explains the physics but ignores the biology. It treats the body like a calculator when in reality it’s more like a thermostat, constantly adjusting to maintain balance.

For most people, calorie restriction works until the body adapts. For insulin‑resistant individuals, restriction can backfire, keeping them stuck in storage mode. In both cases, success comes from understanding the bigger picture: hormones, metabolism, psychology, and lifestyle.

Weight loss is not just about eating less—it’s about teaching your body to trust you. When you fuel it properly, manage stress, sleep well, and move consistently, the body stops fighting back. It releases stored energy because it no longer feels threatened.

So yes, calories matter. But if you’ve ever felt like the math doesn’t add up, you’re not crazy. The story is bigger than calories‑in vs. calories‑out. And once you understand that, you can stop fighting your body and start working with it.