Calories & energy balance

Energy balance is the least controversial idea in nutrition and the most frequently misunderstood one. Fat loss requires eating less energy than you spend. That is a physical constraint, not a diet philosophy, and no arrangement of foods gets around it.

What it does not tell you is how large the gap should be, how to find your starting point, or why the scale refuses to cooperate for weeks at a time. Those are the parts worth reading about.

Start from maintenance, not from a number

Almost every failed diet starts with a calorie target someone read somewhere — 1,200, 1,500, 2,000 — with no relationship to the person eating it.

Your maintenance level depends on your size, your muscle mass, your training and how much you move outside of it. Two people of the same weight can differ by several hundred calories a day. The TDEE calculator gives you an estimate for you, which is the only number worth subtracting from.

Twenty percent is the useful default

A deficit of roughly 20 percent below maintenance suits most people. On a 2,500 calorie maintenance that is 500 a day, and about half a kilogram of fat loss a week.

Larger deficits are tempting and mostly counterproductive. Below about 25 percent you start losing meaningfully more lean mass, training quality drops, hunger becomes the dominant fact of your day, and adherence — the thing that actually determines outcomes — collapses.

Two adjustments. If you are already lean, drop to 10 to 15 percent, because there is less fat available to fund the deficit and more risk to muscle. If you are carrying a lot of fat, you can tolerate the upper end comfortably.

The estimate is a hypothesis

Every maintenance calculation carries roughly 10 percent of error. On 2,500 calories that is a ±250 band, which is half your deficit.

So treat the number as a starting point to be corrected. Eat at it for two weeks. Weigh yourself daily under the same conditions — first thing, after the bathroom, before eating — and use the weekly average, because daily readings swing by a kilogram or more on water and gut contents alone.

If the average dropped roughly as expected, the estimate was good. If nothing moved, cut another 150 to 200 and repeat. After a month you have a maintenance figure measured on the actual person, which no equation can give you.

Why the scale stalls when you are doing everything right

This is the single most common reason people quit a diet that was working.

Fat loss is steady; scale weight is not. Glycogen binds water at roughly three grams of water per gram of glycogen, so a higher-carb day adds a kilogram overnight that has nothing to do with fat. A new training programme causes inflammation and water retention that can mask two weeks of genuine progress. Salt, sleep, menstrual cycle and travel all move the number.

The fat loss is still happening underneath. Track the four-week trend, your waist measurement, and photographs in the same light — not Tuesday’s reading against Monday’s.

Tracking is less accurate than you think

Studies that compare self-reported intake against measured intake find under-reporting is close to universal, and often by several hundred calories a day. Not through dishonesty — through cooking oil, eyeballed portions, the handful of something while making dinner, and the systematic error in packaging labels.

You do not need to track forever. You do need to track accurately for a few weeks to learn what portions actually contain, which is the skill that survives after you stop.

Calories decide the direction, protein decides the outcome

The deficit determines whether you lose weight. Protein and resistance training determine whether that weight comes from fat or from muscle.

That is why the macro calculator sets protein first, and why cutting on low protein produces a smaller version of the same body rather than a leaner one. Get the deficit right, then go and read the protein guide.