How weight loss actually works: calories, energy balance, and hormones

You know how we always hear about calories in and calories out when it comes to losing weight? Like if you just eat less than you burn you win the game and your jeans magically fit again.

Well… that is part of the story, but if you have ever been on that calorie‑counting treadmill and felt like your body just kept swaying back toward the same weight… you are not imagining it. Weight loss is deeper than a math problem.

It’s a conversation between your body’s energy balance and its hormones… and sometimes your biology is as stubborn as that one friend who always orders dessert even when they are full.

If you are like me and you’ve felt overwhelmed, confused, or tired of oversimplified advice… let’s have a real talk about what’s happening inside your body, how calories work biologically, how hormones play their part, and why all of this matters for your journey.

Let’s Start With Calories and Energy Balance

Calories are units of energy in the food we eat. Your body needs energy just to keep you alive… to breathe… to keep your heart beating… and to digest your coffee in the morning. Scientists often talk about energy balance, which is basically this simple equation: calories eaten minus calories used equals change in body energy stores.

If you consistently take in more energy than your body uses, that extra gets stored… often as fat.

Eat less than you use and your body will tap into stored energy, shrinking those fat stores.

That basic law of physics does hold true inside us. But our bodies aren’t simple machines… they are smart adaptive organisms that try hard to keep you within a certain energy range.

When you eat fewer calories your body often responds by slowing down how many calories it uses just to survive. Researchers call this adaptive thermogenesis… and it’s part of why weight loss can feel slow or plateau after a while.

When that happens it feels like your body is saying “OK… let’s be efficient… we don’t want to starve.” This is normal biology not personal failure.

Why Your Body Doesn’t Just Do CICO and Call It a Day

If calories were the whole story we would all lose weight simply by eating less. But your body has systems that defend against weight change because for most of human history survival meant keeping weight up during famine. This leads to your body adjusting hunger and metabolism when you reduce intake.

Some scientists talk about a set point that your body gravitates toward. If you dip below it your hunger increases and your metabolism slows… as if your body is gently tugging your weight back toward familiar ground.

This is not a personal flaw. It’s biology designed to protect you. In our modern world of abundant food and stress we often feel pulled in two directions… our environment pushes toward eating more while our internal systems push toward holding on to energy.

Hormones: The Chemical Messengers That Shape Appetite and Storage

If energy balance is the math part, hormones are the conversation part. They tell your brain when you are hungry, when you are full, when it is time to store energy, and when it is safe to burn energy.

Ghrelin Hormone

Ghrelin is sometimes called the hunger hormone. It rises before meals and drops after eating… telling your brain you are ready to eat again. Life gets tricky when dieting raises ghrelin levels and makes you feel hungrier than you expect.

Insulin Hormone

Insulin manages blood sugar and also influences how your body stores energy. When insulin is high or your cells become resistant to its signal, your body tends to store more energy as fat and might make it harder to use fat for energy.

Leptin Hormone

Leptin is produced by your fat cells and tells your brain how much energy is stored. When fat stores fall, leptin drops and your brain senses energy scarcity… which can ramp up appetite and slow energy use. This feedback loop is part of why long-term weight loss can feel like a biological tug‑of‑war rather than a straight line.

Thyroid Hormone

Thyroid hormones influence how fast your metabolism runs at rest. If these are low, your calories burned at rest drop too, making weight loss feel slower.

Cortisol Hormone

Even stress plays a role. Cortisol can rise in chronic stress and make your body crave high‑energy foods and store more fat around your belly.

And for women… fluctuations in hormones across the menstrual cycle can influence appetite, cravings and even energy use from day to day.

So What Does This Mean For You?

First be gentle with yourself. Your body is trying to keep you safe… not sabotage your goals. When you feel hungrier after cutting calories or your energy slows down it is not a moral failing. It is biology.

Second it means your approach needs compassion not punishment. Eating nutritious balanced meals, focusing on sleep, managing stress, and moving your body in ways that feel good supports hormone balance and energy regulation… not just calorie burning. Getting enough protein and fiber helps hormones that make you feel full work better. Sleep routines help leptin and ghrelin stay in better balance. Stress practices calm cortisol so you don’t feel driven to eat.

Finally… progress matters more than perfection. Your biology might push back sometimes. You might plateau. That is normal and not the end of your journey. Your body is adapting because it wants you to stay healthy. You adjust and keep going.

Weight loss isn’t a single number or a straight slope. It is calling in the math of energy balance and the messengers of hormones and saying “I am doing my best.” That is enough.