In adults with severe obesity, continuous nasogastric tube delivery of a protein-sparing modified fast diet for 150 days is associated with significantly lower fasting insulin levels (11.8 mU/L vs. 28.0 mU/L) compared to oral delivery of the same diet.

When protein is delivered continuously into the intestine through a tube, it keeps amino acid levels high in the blood, which tells muscles to build more protein and stop breaking down. At the same time, the lack of carbohydrates prevents blood sugar spikes, so the pancreas releases very little insulin. Low insulin lets fat cells release stored fat and stops the body from making new fat. The combination of high amino acids and low insulin makes the body use insulin more efficiently, lowering fasting insulin levels even when weight loss is the same as with eating by mouth.