Low-fat eating
What it is
The diet that public-health advice recommended for decades and that most "sensible eating" still resembles: fat held to roughly a fifth to a third of energy, with grains, legumes, vegetables, fruit and lean protein filling the plate. The acceptable range in the reference intakes is 20 to 35 percent of energy from fat; "low-fat" in the trials means the lower part of that band, and going below 20 percent brings its own problems with essential fats and fat-soluble vitamins.
How it works in practice
Fat carries nine kilocalories a gram, more than twice carbohydrate or protein, so cutting it is the quickest way to cut energy density: the same volume of food with less energy in it. Grilling and steaming instead of frying, less oil in cooking, lower-fat dairy, lean cuts, sauces made without cream. What it does not mean is "low-fat" packaged products, which often replace the fat with sugar and end up with the same energy.
What the evidence shows
Low-fat is the pattern the others are most often compared against, and the comparisons are consistent. In a year-long trial assigning healthy low-fat or healthy low-carbohydrate eating, the groups lost 5.3 and 6.0 kilograms respectively — no significant difference. In a two-year trial assigning four different macronutrient compositions with the same foods, all four lost similar weight, with adherence to the assigned targets low in every arm. The network meta-analysis of named programmes places low-fat programmes at roughly four to five kilograms more loss than usual diet at six months, about level with low-carbohydrate, with the differences between named diets small by a year. The reading is that low-fat works exactly as well as the deficit it produces, and no better.
Who it tends to suit
People who like bread, rice, potatoes and fruit and would rather give up oil and fried food than carbohydrate; people who cook at home; people for whom volume on the plate is what keeps hunger manageable.
How it most often fails
Through "low-fat" products that are not low in energy; through carbohydrate portions that grow to fill the space fat left, without the satiety fat and protein bring; and through eating out, where almost everything is cooked in fat and the low-fat version has to be requested.
What to watch
Protein, which is easy to under-eat on a grain-heavy plate; essential fats, if fat is pushed far below a fifth of energy; and the sugar content of anything sold as "light".
In the app
The app's macro policy sets a fat minimum of 20 percent of energy for every plan and no fat ceiling, so a low-fat preference is currently a matter of the foods you list as preferred and disliked rather than a policy the planner verifies.