New Zealanders are heeding the health message to eat less dairy fat - partly at the expense of a vitamin that is important for healthy vision and disease resistance.
In 12 years, vitamin A intake shrank by 21 per cent for men and 14 per cent for women, the latest Adult Nutrition Survey shows.
Conducted in 2008-09 and now made public, it compares New Zealanders' eating habits and body size with how we were in a 1997 survey.
One of the key findings is that our average weight has increased by 5 per cent, to 85.1kg for men and 72.6kg for women. Twenty-eight per cent are obese, up from 17 per cent.
Looking at micro-nutrients, the survey estimated 17 per cent of adults have an inadequate intake of vitamin A.
Sources are liver, milk, butter, cheese, egg yolk, some fatty fish and margarine (which is usually fortified with vitamin A). Carrots, pumpkin, dark-green leafy vegetables and orange-coloured fruits contain carotenoids, which the body converts to vitamin A.
One of the survey report's authors, Winsome Parnell, an associate professor of nutrition at Otago University, said: "You have to ask what has changed in people's eating habits.
"People are choosing to eat lower-fat dairy products, but of course it's the fat in the dairy products which provides the vitamin A.
"You can balance that out by having a good intake of coloured fruits and vegetables, but what's happening is we're not making up that shortfall."
For several decades, health advice has urged New Zealanders to eat less saturated fat by cutting down on butter and cheese, switching to green-top milk and avoiding meat fat - in order to help reduce "bad" cholesterol and thus reduce our risk of heart disease and stroke.
The latest survey shows a reduction in saturated fat intake - to 13 per cent of total energy intake, from 15 per cent - and blood cholesterol levels have improved.
Butter comprises up to 55 per cent saturated fat; margarines are 17 per cent or less.
The survey shows the top sources of saturated fats in the adult diet are butter and margarines - counted together - at 8.5 per cent; milk comprises 7.6 per cent; bread-based dishes 6.4 per cent; cheese 6.3 per cent; potatoes, kumara and taro 5.8 per cent; and cakes and muffins 5.1 per cent.
WHAT IT DOES
Vitamin A is important for:
* Eye function.
* Immunity against infections, especially in children.
* Healthy skin.
* Reproduction and growth.