The firm has been told to ensure any general health claims in their ads are supported by authorised health claims and that they are "obvious" to shoppers after a complaint was upheld.
A TV ad for Special K porridge claimed that "our new five grain super porridge is full of goodness" while a Kellogg website stated "our unique Nutri K recipe makes a nutritious ... start to your day."
A complaint was made to the Advertising Standards Authority (ASA) challenging whether the claims were subject to regulations on nutrition and health.
Kellogg believed the claim "full of goodness" was a general health claim for the purposes of the regulation and, therefore, they were required to support such a claim with a specific authorised health claim.
Kellogg believed that use of the word "nutritious" was not a claim that would suggest a health benefit. They felt the term highlighted the product's generic nutritional credentials and as such, it was removed from general health claims such as "goodness", which did imply a positive benefit to health.
The ASA found the two ads both to be in breach of rules regarding food, food supplements and associated health or nutrition claims.
An ASA spokesman said: "We shared Kellogg's view that the claim 'full of goodness' was a reference to a general, non-specific health benefit of the product and as such, we agreed that Kellogg was required to accompany it with a specific authorised health claim.
"The authorised health claim - in this case 'contains vitamin B2 which contributes to the maintenance of normal skin' - should be presented in such a way that it was clear that it accompanied that general health claim; it should be made next to or immediately following the general health claim.
"The specific authorised health claim was shown on screen, but we noted it disappeared before the general health claim "full of goodness" was stated in the voice-over.
"We therefore considered the specific health claim did not appear with or immediately following the general health claim 'full of goodness.'
"As such, we considered it did not accompany the general health claim and in that regard, the ad breached the Code."
He added: "The ads must not appear again in their current form.
"We told Kellogg Marketing and Sales (UK) Company Ltd to ensure that relevant authorised health claims accompanied any general health claims that featured in their advertising."