Your little one shouldn’t gain any more weight than is usual for their growth from consuming a whole milk based infant formula. 50% of the calories in both breast milk and formula come from fat. Fats are an important source of essential fatty acids (EFA), which are used by the body as building blocks for growth, as well as playing a role in the absorption of a number of fat-soluble vitamins like vitamins A, D, E and K.
Mammalian milk fat is far closer to naturally resembling the fat profile of human breast milk than vegetable oils. These fatty acids are absent in vegetable oils (with the exception of coconut and palm oil). So while most brands as using skimmed milk and a mixture of vegetable oils to provide the fats needed, Kendamil uses whole milk in all of our baby formulas, so we don't need a lot of oils to replace the fat missing when produced using skimmed milk. You can read more about the benefits of whole milk here.