In obese adults, a 10-day protein-sparing modified fast delivered via nasogastric tube is associated with reductions in fasting insulin and HOMA-IR, as well as decreases in triglycerides and liver enzymes.

When no carbohydrates are consumed, insulin levels drop sharply, which stops the body from storing fat and starts breaking down stored fat for energy. The liver converts this fat into ketones, which the brain and muscles use as fuel instead of sugar. This shift prevents muscle loss because protein intake provides enough amino acids to rebuild tissues. As fat breaks down, triglycerides in the blood fall, the liver processes less fat so its enzymes return to normal, and the body becomes more responsive to insulin.