Can excess use of garnier fructise hair putty cause considerable hair thinning and hair loss?

No----but. Hair is not like a plant. Nutrition of hair is only from its blood supply. "fortified fruit" is meaningless nonsense. A 20 yr old man with thinning hair is very common, related to genetics & hormones. See a dermatologist, bringing all meds, vitamins, supplements, & hair products.