Calories in, calories out — the version with asterisks

If you spend any time on fitness internet, you'll see CICO — calories in, calories out — defended like religion and dismissed like a hoax, often within the same comment thread. The truth is less dramatic and more useful.

Energy balance is real. It is also more elastic, more variable, and more annoying to apply than people who shout "it's just CICO!" want it to be.

What CICO actually says

The first law of thermodynamics, applied to a human body, says: if you take in more energy than you spend, you store the difference. If you spend more than you take in, you draw it from storage. The body's preferred storage medium is fat, with smaller buffers in glycogen and (under stress) lean tissue.

That's it. That's the law. It's not in dispute among physiologists.

The asterisks

Asterisk one: "calories in" is not a fixed number. You don't absorb 100% of every calorie you eat. Whole almonds give you about 25% fewer net calories than the label says, because some of the fat passes through undigested. Resistant starch (cooled potatoes, green bananas, certain legumes) is partially fermented in the colon rather than absorbed. Cooking method matters too — a steak cooked to 145°F gives you slightly more usable energy than one cooked to 125°F.

Asterisk two: "calories out" is a dynamic system, not a setpoint. Your basal metabolic rate is not a constant. It adapts — sometimes meaningfully — to chronic energy intake. Cut for long enough and your body will quietly throttle thyroid output, fidgeting (NEAT), and mitochondrial efficiency. This isn't "starvation mode" mysticism. It's measurable, and it's why month four of a diet feels different than month one.

Asterisk three: hormones are not a CICO loophole, but they are an enforcement mechanism. Insulin sensitivity, leptin, ghrelin, GLP-1 — none of these violate energy balance, but they massively influence the psychology of energy balance. They decide whether you feel hungry at 3pm, whether you sleep through the night, whether you have the willpower to skip the pastry. Two diets at identical calories can produce wildly different lived experiences.

Asterisk four: the scale is not your bank account. Body weight is the sum of fat, lean tissue, water, glycogen, food in transit, and (occasionally) sodium drama. Weight can move three pounds in a day with zero change in stored energy. People who treat the scale as a real-time CICO feedback loop go insane within two weeks.

So what do you do with this?

One: track your inputs honestly. Even if the absolute calorie number is plus or minus 10%, trends are still meaningful. If your tracker says 2,400 calories on Monday and 2,400 calories on Friday, you ate roughly the same amount.

Two: pick a window long enough to see the signal. Energy balance is like compound interest: it works on the time scale of weeks, not hours. Look at the seven-day rolling average of your weight and your intake, not yesterday's number.

Three: design the diet you'll actually do. Adherence beats optimality, every time.

A quick mental model

Think of CICO like the tide and the wind. The tide (energy balance) decides where the boat ends up. The wind (your specific food choices, sleep, stress, training) determines how rough the ride is. Both are real. The tide always wins on long enough timescales.

CICO is the law. The asterisks are the practice.

Where tracking fits

Calorie tracking is a tool for calibration, not a tool for control. The point is not to live inside a spreadsheet. The point is to spend three weeks being honest with yourself, learn what 2,200 calories actually looks like on your plate, and then mostly not need the app anymore.

Yes, CICO is real. Yes, the math is more complicated than the slogan. No, hormones don't get you out of it. And yes, the only sustainable way to apply it is with a tool you'll actually open seven days a week. That's the whole post. Eat well.