Teenage girls have the unhealthiest diets in the UK, with fewer than one in 10 eating the recommended five portions of fruit and vegetables a day.
Half are not getting enough iron, according to the National Diet and Nutrition Survey.
Boys fare slightly better, eating on average more than three portions of fruit or vegetable every day – half a portion more than girls of the same age. Young children, aged between 18 months and three years, eat the most fruit and vegetables of any age group.
The vast majority of teens and adults ate no oily fish during the four-day diary period, despite recent efforts to promote its health benefits.
The findings are taken from two years of data which analysed the diets of 2,216 randomly selected adults and children from across the UK. Food diaries and interviews were combined with urine, blood and weight analysis. The survey is funded by the Department of Health and the Food Standards Agency.
Health experts are worried that people of all ages were continuing to eat too much saturated fat, which increases the risk of obesity, stroke, heart disease and several cancers. High quantities of these fats are found in red meat, dairy products, processed foods and ready-made meals.
The study group ate a third more meat and meat products (such as pies and pasties) than 10 years ago. The country's most senior public health expert said the crisis needed "industrial-sized solutions".
The popularity of supplements, such as vitamins and cod liver oil, has burgeoned over the past two decades, despite expert advice that good nutrition is best obtained from a healthy, mixed diet.
Paul Burstow, junior Health Minister, said: "Over the last 10 years, we have not seen the improvements we should have."