When people with excess body fat eat very few carbs and more fats, their blood ketone levels rise quickly within two weeks, showing their body has switched to burning fat for fuel.

If a woman who is overweight but otherwise healthy eats very few carbs for three months, her body starts making more of a fuel called beta-hydroxybutyrate — this means her body is switching to burning fat for energy instead of carbs.

Eating mostly fats and very few carbs for 3 months helps overweight people lose fat and weight, on average about 5% body fat and 3.5 kg.