Portion control
What it is
The oldest method there is: eat what you already eat, less of it. No food is excluded, no composition changes; the deficit comes from amounts. It is here as a "way of eating" because for many people it is the whole answer, and because the evidence on portion size is better than its unglamorous reputation suggests.
How it works in practice
Smaller plates and bowls; serving at the stove rather than from dishes on the table; a hand as the measure — a palm of protein, a fist of carbohydrate, a thumb of fat — or, better, a scale for a week to learn what the usual portions actually weigh; smaller packages, since people eat what the package holds; and, at restaurants, sharing, starters as mains, and leaving food. The tracking step is the same method with numbers.
What the evidence shows
A Cochrane review of fifty-eight studies on portion, package and tableware size found a consistent effect: larger sizes lead people to select and eat more, in a sitting and over a day, and the effect is not small. The review's authors estimated that eliminating the largest portion sizes from the diet could reduce adults' daily energy intake by around a tenth or more — an estimate from a model, which the review is careful to present as such. What the review does not measure is weight over a year on a portion-control programme, so this page has no twelve-month figure. The mechanism is solid; the long-term outcome is inferred from the arithmetic.
Who it tends to suit
People who like what they eat and do not want to change it; people who eat family meals and cannot run a separate menu; people who have tried named diets and found the rules worse than the hunger. And everyone, as the layer under every other pattern.
How it most often fails
Portion creep — the plate gets a little fuller each month, invisibly; family-style serving, where nobody knows what a portion was; and protein, which shrinks with everything else unless it is protected. The method has no rule to hide behind, which is its strength and its weakness.
What to watch
Protein per meal; the slow drift of portions, which a scale week every few months catches; and, for anyone with a history of restriction, the honesty to notice whether "less" is a method or a compulsion.
In the app
This is the app's default rather than a policy: every generated menu is quantity-planned to the day's target, and logging a meal "as planned" is portion control with the arithmetic already done. Adjusting quantities is checked against the day's floors, never silently.