Huel, which is based in Hertfordshire, was founded by Hearn in 2015. It is currently in the process of being bought by French conglomerate Danone.
The market for so-called complete nutrition products, aimed at time-poor, health-conscious consumers, is thought to be worth $5.9bn (£4.4bn).
The ASA received four complaints about the advert, which challenged whether the content was irresponsible. Two of the complainants also challenged whether the health claims in the ad breached the ASA’s advertising code.
The ASA acknowledged in its ruling that the ad “did not explicitly recommend that consumers replace all conventional foods with Huel”, but consumers could nonetheless interpret the anecdote as “an acceptable dietary practice”.
“By presenting exclusive consumption of Huel in that context, the ads suggested that the complete replacement of conventional food with Huel was nutritionally appropriate and presented no barrier to achieving a high level of physical performance,” the ruling said.
The ASA also upheld the complaint regarding the health claims as it ruled Matthews’ anecdote about the ultramarathon athlete “implied a beneficial relationship between consuming Huel and the ability to sustain exceptionally high levels of physical and endurance performance”.
In its response to the complaints, Huel said the advert “unambiguously positioned Huel as part of a balanced diet for occasions when preparing whole food was not practicable”.
The company pointed to Matthews reacting with “extreme scepticism and disbelief” to the idea of a person solely consuming Huel.
“The anecdote was recounted as a remarkable and unexpected occurrence, not as a representative outcome or a recommendation or instruction to consumers to replicate.
“At no point in the ads did either speaker suggest that consumers should adopt a 100% Huel diet.”
It is not the first time that Huel has landed in hot water with the ASA over the use of its products as a replacement for conventional food.
Additionally, some experts have questioned the effectiveness of replacing meals with nutritionally rich drinks.
Huel told News that it had complied with the ASA ruling.
“We do not position Huel as a complete diet replacement or claim that it improves athletic performance,” a spokesperson said.