US Health Secretary Robert F Kennedy Jr has unveiled new dietary guidelines that urge Americans to eat more protein while limiting highly processed foods and added sugar.

The guidelines, which are released every five years by the agriculture department and the Department of Health and Human Services, also suggest three servings of full-fat dairy products a day and loosen restrictions on alcoholic beverages.

The guidelines provide the foundation for federal nutrition programmes, including school meal programmes, and the new ones have received mixed reviews from experts.

"My message is clear: eat real food," said Kennedy at a news conference at the White House on Wednesday.

Overall, the recommendations call for eating protein, full-fat dairy, fiber-rich whole grains, and fruit and vegetables, while avoiding sugars and highly processed foods, including prepackaged snacks such as chips, cookies and candy.