The repair material. Every time you train you damage muscle fibres slightly, and protein is what rebuilds them thicker. It also keeps you full longer than anything else you can eat.

Dietary protein is broken into amino acids, nine of which are essential because the body cannot synthesise them. Those amino acids feed muscle protein synthesis, driven largely by leucine crossing a concentration threshold at each meal — which is why spreading protein across the day beats one large serving. Protein also has the highest thermic effect of the three macronutrients: roughly 20–30% of its calories are spent digesting it, against 5–10% for carbohydrate and 0–3% for fat.

This is why the plan sets protein first and refuses to move it. Everything else negotiates around it.

Your fastest fuel, and the one your brain and hard training actually prefer. Cutting them does not burn more fat, it just makes training feel worse.

Carbohydrate is digested to glucose and either burned immediately or stored as glycogen in muscle and liver. To release energy, glucose enters glycolysis — a catabolic pathway that splits it into pyruvate and yields ATP, the cell’s actual energy currency. With oxygen present, pyruvate continues into the citric acid cycle and oxidative phosphorylation, producing far more ATP per molecule. Muscle glycogen is the limiting fuel for repeated high-intensity effort, which is why a low-carb day and a heavy lifting session are a bad pairing.

This is why carbohydrate is set last: it fills whatever calories remain, and it gets pushed toward your training window.

Not the enemy, and not optional. Fat runs your hormones and lets you absorb whole categories of vitamins. Cut it too low for too long and you feel it.

Dietary fat provides essential fatty acids the body cannot make, and is the substrate for steroid hormone synthesis including testosterone and oestrogen. Vitamins A, D, E and K are fat-soluble: without dietary fat present in the same meal, absorption drops sharply. At 9 kcal per gram it is more than twice as energy dense as protein or carbohydrate, which is why it is the easiest macro to overshoot without noticing.

This is why we hold a floor of roughly 22% of calories from fat, even on an aggressive cut.

Plant material your body cannot break down. It passes through largely intact — which is exactly what makes it useful.

Fibre is carbohydrate whose bonds human digestive enzymes cannot cleave, because we lack the enzymes to hydrolyse beta-glycosidic linkages. Soluble fibre forms a gel that slows gastric emptying and blunts the glucose response of a meal. Insoluble fibre adds bulk and speeds transit. Neither is absorbed as energy by you — but gut bacteria ferment some soluble fibre into short-chain fatty acids like butyrate, which the cells lining your colon use as fuel. Most adults get around 15g a day against a 25–38g recommendation.

This is why fibre is a direct input to the fullness score. High-fibre foods: black beans, lentils, raspberries, chia, oats, broccoli, avocado, artichoke, split peas, pears with the skin on.

Two meals with the same calories can be wildly different amounts of food. The bigger one usually wins, because your stomach responds to how much is in it, not how many calories.

Gastric stretch receptors signal fullness by physical distension, largely independent of energy content. Water and fibre add weight and bulk without calories, lowering energy density. Barbara Rolls’ work on volumetrics repeatedly found that people eat a fairly consistent weight of food day to day, so lowering energy density reduces intake without a conscious effort to eat less.

This is why the volume score is simply kcal per gram, and why swaps get biased toward it.

The equation predicts an average person with your height, weight, age and sex. You are not the average person. Treat the number as a starting point and adjust from what the scale actually does.

Mifflin–St Jeor predicts resting energy expenditure within about 10% for most healthy adults, but individual variation in lean mass, thyroid function and non-exercise activity thermogenesis (NEAT) is substantial. NEAT alone — fidgeting, posture, spontaneous movement — can vary by several hundred calories a day between two similar people. The activity multiplier is the largest source of error in the whole calculation, not the equation.

This is why we show you the working rather than presenting one confident number.

Most supplements do very little. A short list has real evidence behind it, and it is shorter than the industry would like.

Creatine monohydrate (3–5g daily) is among the most studied sports supplements, with consistent effects on strength and lean mass; timing is irrelevant. Vitamin D3 matters if you are deficient, which is common at higher latitudes and in winter — test rather than guess. Whey or casein protein is food, not magic: useful only for hitting a protein target you would otherwise miss. Caffeine (3–6 mg/kg) reliably improves performance and perceived exertion. Omega-3 is worth it if you rarely eat oily fish. Nearly everything else — fat burners, BCAAs alongside adequate protein, testosterone boosters — does not survive controlled trials.

We will never sell you any of these. This section exists so you can stop buying the rest.