Vitamin Well Group is merging with EMPWR, the manufacturer of the sports-nutrition firm's Barebells protein bars.
The financial terms of the deal, announced by Cinven, one of Vitamin Well's private-equity backers, were not disclosed.
Under the agreement, EMPWR's owner Waterland Private Equity, will retain a minority stake in the enlarged business.
In a statement, Cinven, which invested in Vitamin Well in 2024, described EMPWR as an "important manufacturing partner" for the business.
Cinven said the deal "unlocks the ability to increase investments in capacity and pursue significant volume growth opportunities".