The Advertising Standards Authority has upheld two complaints against the Soil Association for describing organic as "healthy" and "more humane to animals".
Organic food's health benefits are disputed
The claims were made in a leaflet last year, but could not be substantiated scientifically, the ASA said.
Sales of organic food have increased tenfold in the last decade, driven in part by perceived health benefits and concern over animal welfare.
The Soil Association told the BBC it still thinks organic food is healthier.
It says it has recently submitted new evidence to the ASA which means it can now legitimately state that no other food has higher amounts of beneficial minerals and vitamins.
And it argues no other system of farming has higher levels of animal welfare standards.
The ASA was responding to a complaint about the leaflet.
Organic food is produced in a way that minimises the use of artificial pesticides and fertilisers, and is usually more expensive than conventionally produced food.
The Soil Association is the main UK body which certifies food and farming as organic, and also campaigns on the issue.
A debate has raged within the scientific community for the last few years over whether organic food can be said to be healthier.
A recent study on rats found those fed on organic fruit and vegetables were slimmer, slept better and had stronger immune systems.
And another showed organic milk had higher levels of vitamin E, omega 3 essential fatty acids and antioxidants, which help beat infections.
But many dispute the claims, saying there is insufficient evidence of any health benefits over ordinary food.