Dr. Ahmed Sometimes, even with strict dieting, hunger increases, energy decreases, and it feels like the rules of the game have changed.
If “calories in vs. calories out” were the whole context, your effort would equal your results. Your lived experience says: it is not that easy.
“Calories in vs. calories out” is part of the truth and not the complete story. While energy balance is indeed important, your body is not a calculator.
Your body has the ability to adapt; it sends strong hunger and fullness signals, it responds to our sleep habits, our stress levels, medications, our genetics, and the entire food environment.
These factors influence what, when, and how much you eat, often well before any willpower and the decisions of whether to eat or not come into play.
Here’s the bigger picture: obesity is a complex, chronic condition influenced by biology, and it is much more than just simply managing calories.
Why does the Simple Calories in and out formula stick around?
“Calories in vs. calories out” persists because it is mathematically true. Your body stores energy when more comes in than goes out and loses stored energy when the opposite happens. That part is physics.
The issue is not the equation; it’s everything the equation leaves out. The slogan misses how your body automatically adjusts appetite and energy use, how hormones influence hunger, and how environment and stress change the choices you can make. It explains balance, not behavior.
Here’s how hormones, genes, and environment can impact your body weight:
Metabolism learns and adapts
Metabolism is the set of processes that keep you alive: turning food into usable energy, powering your organs, and maintaining body temperature.
Resting energy expenditure is the energy your body uses when you are not moving, just to run basic systems.
When you lose weight, that baseline often drops. This is a metabolic adaptation. Your body becomes more efficient and uses fewer calories to do the same tasks, like a car getting better mileage.
This adaptation helps people survive famine, but it frustrates modern weight loss. After weeks of cutting calories, your body may burn less and signal you to eat more.
Hunger hormones rise, fullness signals drop, and you feel driven to replace what you lost. You didn’t “fail.” Your biology did exactly what it evolved to do: defend against weight loss.
Hormones shape hunger and fullness
Hunger and fullness are not just about willpower. They are guided by hormones—chemical messengers that carry instructions through the blood.
Ghrelin is often called the “hunger hormone.” It rises before meals and nudges you to eat. Leptin signals that you have enough stored fat and helps curb appetite.
Insulin helps move sugar from the blood into cells and, when levels stay high, can promote energy storage.
When sleep drops short, ghrelin tends to climb and leptin tends to fall. You feel hungrier and less satisfied after eating.
Chronic stress pushes up cortisol, a stress hormone that can increase cravings for quick energy foods and make it harder to regulate appetite.
Insulin can also become less effective over time in some people, a state called insulin resistance, which can tilt the body toward storing more energy in fat tissue.
None of this means you are powerless. It means your hunger is influenced by signals you did not choose.
Genetics and biology play a big part
Genes do not create a single destiny, but they create a playing field. Some people are unlucky in that when they inherit certain traits, it means their bodies will intentionally defend a higher weight; this includes feeling hungrier after meals, expending less energy at rest, or both.
Researchers often talk about a “set point” or “settling point”, which is the range of weight your body defends and works to maintain.
It’s not an exact number, and it changes over time, to be sure. But it does help explain why two people can eat roughly the same foods and be moderately active, and one will gain weight while the other does not. The same plan does not end the same way in different bodies.
Medications and medical conditions matter
Several common medications affect weight. Some antidepressants and antipsychotics can increase appetite.
Steroids can change where you store fat and promote hunger. Some diabetes medications or insulin cause weight gain, while other medications may promote weight loss.
Moreover, thyroid problems, especially hypothyroidism, can reduce energy utilization. Polycystic ovary syndrome (PCOS) can cause changes in hormones that influence appetite and insulin signaling. The hormonal changes that occur with menopause, perimenopause, or postpartum bring their own disturbances. If weight changes feel out of proportion to your habits, a conversation with a clinician can be helpful.
The microbiome
Your gut is home to trillions of microbes—bacteria, viruses, and fungi—that help digest food and produce compounds that talk to your brain and immune system. This community is called the microbiome.
Early research suggests it can influence how many calories you extract from food and how full you feel. That said, it is not a switch you can flip.
Probiotics or a single “superfood” will not solve obesity. A varied, fiber-rich diet can support a healthier microbiome, but it’s one contributor among many.
The food environment
We do not eat in a vacuum. Food is everywhere: in checkout lanes, on apps, and in break rooms. Portions have grown over time, and marketing pushes combinations of sugar, fat, and salt designed to be intensely rewarding.
Ultra-processed foods are products made from refined ingredients and additives that change flavor and texture.
They are convenient and shelf-stable, but they often digest quickly and can be easy to overeat. When large portions are cheap and available at all hours, eating “just the right amount” becomes a constant negotiation. It’s not about blame; it’s about the field you’re playing on.
Movement beyond the gym
Exercise is important for health, but other daily movements outside of workouts are also a part of energy use called non-exercise activity thermogenesis, or NEAT for short. NEAT consists of walking to the bus, standing while you work, doing chores, and simply fidgeting.
Desk jobs and daily commutes can drastically reduce the amount of NEAT you engage in without you realizing it.
Small additions to your day, like more steps on walk’n talks, a short afternoon walk after lunch, or carrying groceries home, can compound over time.
You don’t have to crush a workout to reap some benefit. Gentle, frequent movement can help keep energy flowing as well as assist with mood and sleep.
Why “Just Eat Less” Often Backfires?
When advice is oversimplified, people try extreme cuts. At first, weight drops. Then the body pushes back: hunger intensifies, cravings sharpen, and energy dips. The brain becomes preoccupied with food.
Eventually, you eat more, often more than before, which feels like failure. Shame then drives more restriction, and the cycle repeats.
This is not a character flaw; it is a predictable response to deprivation. Sustainable changes work better because they align with how bodies regulate energy and how minds handle effort over time.
A More Helpful Way Forward
Start by making meals more satisfying so you are not fighting hunger all day. You can still eat foods you enjoy; anchor them with protein and fiber so your body gets the signals it needs to stop naturally.
Protect your sleep like it’s part of your plan, because it is. Aim for a consistent schedule and a cool, dark room. Even a one-hour improvement can lower next-day cravings and make it easier to notice fullness.
Build stress outlets that you can repeat on busy days. Short walks, breathing exercises, a few pages in a journal, or a call with a friend all help turn down the internal “alarm.”
Lower stress does not just feel better; it makes it easier to choose foods and portions that suit your goals.
Move in ways you enjoy and can repeat. If the gym helps, great. If not, start with brisk walks, beginner strength exercises at home, or dancing to a few songs after dinner.
The routine you like is the routine that lasts. As consistency builds, you can add intensity or duration.
Conclusion
Energy balance is real, but the path to it is not simple. Bodies adapt, hormones influence appetite, genes set the stage, and the world you live in shapes your choices. Obesity is not a personal failure; it is a condition with many drivers that add up over time.
You can still make meaningful progress by aligning with how your body works: eat in ways that satisfy, sleep as consistently as you can, move in ways that fit your life, reduce stress where possible, and ask for support when you need it.
You are not broken. With compassionate, realistic steps, you can move toward health without fighting yourself at every turn.
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