In mice.

BBC NEWS | Health | Low-carb diets ‘damage arteries’

The low-carb diet did not affect cholesterol levels, but there was a significant difference on the impact on atherosclerosis – the build-up of fatty plaque deposits in the arteries that can lead to heart attacks or strokes.

After 12 weeks, the mice eating the low-carb diet had gained less weight, but developed 15% more atherosclerosis than those on the standard mice food. For the western diet group there was 9% more atherosclerosis.