The Advertising Standards Authority received two complaints about the ad from viewers who thought it was misleading because it implied Jaffa Cakes were a healthy snack by focusing on the amount of fat in one small and lightweight cake, while ignoring the percentage of fat in the product.
The advertising watchdog also challenged whether the claim "only one gram of fat" misleadingly suggested Jaffa Cakes were low in fat.
The ad, created by Publicis, showed two women sitting in a garden talking about their friend Michelle who keeps ringing to say she is trapped down a well.
One of the women says to the other: "Don't worry, she's always lying. Attention thing. Last week she said there was only one gram of fat in a McVitie's Jaffa Cake."
The pair both laugh and then a male voiceover says: "Michelle isn't lying. Each delicious McVities Jaffa Cake really does have only one gram of fat."
The ASA upheld its own challenge because it considered that the ad's message was that the amount of fat in a Jaffa Cake was much less than expected.
In light of that context it concluded that the claim "only one gram of fat" was likely to suggest to viewers that a Jaffa Cake was low in fat.
Jaffa Cakes contain 8g of fat per 100g of solid but nutrition regulations state that "a claim that a food is low in fat, and any claim likely to have the same meaning for a consumer, may only be made where the product contains no more than 3g of fat per 100g of solids".
However, the ASA did not uphold the viewers' complaints because it considered that stating the amount of fat in one cake instead of stating the percentage of fat did not in itself suggest the Jaffa Cakes were, overall, a healthy snack.
In a separate adjudication a TV ad for Maltesers was banned for misleadingly implying that it was a low energy product.
The ad, created by Abbott Mead Vickers BBDO, showed two men asleep on a sofa, while two women were watching TV.
One of the women accepts a Malteser from her friend, calling her "naughty", but looks disappointed when she finds out they are less than 11 calories each.
The two women decide to make up for the lack of naughtiness by rearranging the sleeping men on the sofa so that they are snuggling up together.
One viewer challenged whether the claim "less than 11 calories each" misleadingly implied Maltesers are a low energy product. The ASA also challenged whether the claim "The lighter way to enjoy chocolate" misleadingly suggested Maltesers were lower in energy than other similar products.
The viewer's complaint was upheld, but the ASA's challenge was not because it accepted Mars' argument that the strapline is a trademark that has been in use since 2005 and therefore its use in advertising could not currently be in breach of the regulation.