How should you split your macros?

Most macro advice starts with a ratio: 40/30/30, or 50/30/20, or whatever the current fashion is. That is the wrong end of the problem. A ratio tells you nothing until you know your calorie total, and it quietly hides the fact that the three numbers are not equally important.

A more useful way to think about it is as a sequence of decisions, each constrained by the one before:

1. Protein, from your body weight. Set in grams per kilogram, because the amount you need tracks how much of you there is, not how much you happen to be eating.
2. Fat, as a share of calories. Set as a percentage so that it scales with intake and does not fall to an impractical level when calories are low.
3. Carbohydrate, whatever is left. Not a demotion. Carbohydrate is the flexible one, which makes it the right thing to absorb the remainder.

FitQuota's Macro Calculator runs exactly that sequence, and shows each step, so you can see which decision produced which number.

Protein is the one macronutrient with a defensible target rather than a convention. A 2018 meta-analysis pooling 49 studies found that gains in muscle and strength from resistance training stopped improving above about 1.62 g per kilogram of body weight per day. That gives a real number to aim at, which neither fat nor carbohydrate has.

It also has the most to lose from being set last. In a calorie deficit, adequate protein helps preserve lean tissue that would otherwise go along with the fat, and it is the most satiating of the three per calorie. Deciding it first means it never gets squeezed by whatever is left over. There is more detail in how much protein you need per day.

Fat is set as a share of calories for a practical reason. A fixed gram target that is sensible at 2,500 kcal becomes a large fraction of the plate at 1,600, and one that is sensible at 1,600 leaves an unnecessarily restrictive diet at 2,500. A percentage scales.

FitQuota offers 20%, 25% and 30%, with 25% as the default. Those are a reasonable convention rather than a published equation, and the site says so plainly on the calculator page rather than attaching a citation that does not actually support the numbers. The lower end is deliberately not zero: fat carries the fat-soluble vitamins and essential fatty acids, and very low fat intakes tend to be unpleasant to sustain.

The honest summary is that anywhere in that range works, and the choice is mostly about which foods you want to keep.

Whatever remains after protein and fat becomes carbohydrate. For the worked example used across this site, a 2,540 kcal target at 70 kg with the default settings:

Notice that this lands at roughly 18/25/57, which is not one of the famous splits. It was not chosen to be. It is simply what falls out of setting protein and fat sensibly, which is rather the point.

This has been tested directly, more than once, at a scale that is hard to argue with.

The POUNDS LOST trial assigned 811 overweight adults to four diets with deliberately different fat, protein and carbohydrate targets and followed them for two years. Weight loss was similar across all four.

The DIETFITS trial went further, comparing a healthy low-fat diet against a healthy low-carbohydrate one in 609 adults over 12 months. The groups ended up genuinely different in composition, 48% versus 30% carbohydrate and 29% versus 45% fat. Weight change was 5.3 kg against 6.0 kg, a difference of 0.7 kg that was not statistically significant.

That trial also tested something people still sell courses about: whether your genotype or your insulin secretion predicts which diet suits you. Neither did.

Two large randomized trials, roughly 1,400 people between them, both finding that the split is not where the difference lives. The calorie total does the work, and adherence decides whether you hit it.

Three situations, and none of them is general weight loss:

• Hard training. Carbohydrate fuels high-intensity work. If you are training heavily and feeling flat, taking carbohydrate down to make room for fat is usually the wrong trade.
• Very low calorie targets. The lower the total, the harder protein and fat minimums squeeze everything else, and the more the ordering above actually binds.
• Medical conditions. Diabetes, kidney disease and several others change the calculation entirely. That is a conversation with a doctor or a registered dietitian, not a calculator.

Outside those, the best split is the one you will actually follow for months. If you prefer bread, eat more carbohydrate. If you prefer olive oil and eggs, eat more fat. Hit your protein, hit your calorie total, and stop optimising the part that two trials could not find a difference in.