From Wikipedia:

A variety of different mixes have been used for nutrient enemas throughout history. A paper published in Nature in 1926 stated that because the rectum and lower digestive tractlack digestive enzymes, it is likely that only the end-products of normal digestion such as sugars, amino acids, salt and alcohol, will be absorbed.[8]

Plus I think you’d have no lipid absorption, so you could probably survive longer than starvation, but I’m guessing not “quite some” time.