Vegetarian eating
What it is
Eating without meat or fish, keeping eggs and dairy — the lacto-ovo form that most people mean by "vegetarian". Usually chosen for reasons that have nothing to do with weight, and worth understanding on its own terms before asking what it does to the scale.
How it works in practice
Legumes, eggs, dairy, soy, grains, nuts, vegetables and fruit. The protein has to be deliberate: a plate of pasta and salad is vegetarian and contains almost none, while lentils, beans, eggs, yoghurt and tofu contain plenty. Iron and vitamin B12 need attention — B12 comes from eggs and dairy in this form, so it is a vegan problem more than a vegetarian one, but iron from plants is absorbed less well and menstruating women in particular should keep an eye on it.
What the evidence shows
A meta-analysis of twelve randomised trials, with a median length of eighteen weeks, found vegetarian diets losing about two kilograms more than comparison diets, with a larger effect when energy was restricted and in the vegan arms. The review's own reading is that the mechanism is energy density and fibre — a diet built on vegetables, legumes and grains is bulkier per calorie — rather than anything about meat itself. The trials are short and the comparison diets varied; two kilograms over four months is a real but modest signal, and it says nothing about keeping the weight off.
Who it tends to suit
People who already want to eat this way for other reasons and are asking whether it conflicts with losing weight (it does not); people who like legumes; households where one person's choice has to fit everyone's table.
How it most often fails
By becoming bread, cheese and pasta — vegetarian and energy-dense, with little protein — and by treating "vegetarian" as automatically "light". Cheese, nuts, oil and pastry are all vegetarian and all dense. The deficit still has to be built.
What to watch
Protein, per meal, until the habit is set; iron; and total energy from the dense vegetarian foods. The protein calculator gives the daily figure; the harder part is getting it from legumes and eggs rather than cheese.
In the app
The vegetarian policy code exists and the planner takes it into account, but its revision has no documented review yet, so the app treats it as context rather than a verified rule. The site says the same and will change the day the app can verify it.