"part of a balanced breakfast / diet" always has been weasel words to the effect of "if you eat healthy foods as well as the product, then your overall diet will be somewhat healthy on balance".
See The McLibel case, 1997 (1) particularly the statement "You could eat a roll of Sellotape as part of a balanced diet" (2)
See The McLibel case, 1997 (1) particularly the statement "You could eat a roll of Sellotape as part of a balanced diet" (2)
1) https://en.wikipedia.org/wiki/McLibel_case
2) https://www.mcspotlight.org/case/trial/story.html