Zone
What it is
A commercial programme that fixes the split of every meal at forty percent of energy from carbohydrate, thirty from protein and thirty from fat, measured in "blocks", with a theory that this ratio keeps insulin and certain signalling molecules in a favourable "zone". The ratio itself sits inside the acceptable ranges for a healthy diet; the theory is the programme's own.
How it works in practice
Every meal composed to the ratio: a palm of lean protein, roughly twice that volume in vegetables and fruit, a small amount of fat. Bread, pasta and sugar largely go, not by rule but because they make the ratio hard to hit. The protein share is generous — about a third of energy — which is where most of the programme's actual effect lives.
What the evidence shows
In the network meta-analysis of named programmes, Zone sits among the moderate-macronutrient programmes, which lost somewhat less at six months than the low-carbohydrate and low-fat ones, with differences that were small and uncertain — and by twelve months the differences between all the named diets had faded to small, mostly non-significant amounts. Nothing in the trials supports the hormonal theory as a mechanism for weight; what the programme does that works is hold protein high and cut the densest carbohydrates, which the higher-protein page covers on its own evidence.
Who it tends to suit
People who like a fixed formula and are willing to compose meals to it; people who do well with a high protein share and moderate carbohydrate without going low.
How it most often fails
On the composing — weighing and ratio-matching every meal is the kind of effort most people keep for a month — and on the theory, which promises a metabolic effect the ratio does not deliver, so that a plateau is read as a failure of precision rather than of the deficit.
What to watch
Total energy, which the ratio says nothing about — a 40/30/30 day at maintenance loses nothing; and fibre, which the programme's carbohydrate share can carry if it comes from vegetables and fruit rather than from bars.
In the app
The app's balanced policy checks protein and fat against ranges over the day, not a fixed split per meal, so Zone is not something the planner verifies; the protein share it prescribes is roughly what every generated menu is checked for anyway.