Chyle is lymphatic fluid present in the wall of the intestine. It flows trough lymphatic vessels to cisterna chyli and to venous circulation carrying lymphatic fluid, long-chain triglyceride fatty acids and proteins, fatty soluble vitamins and electrolytes. Lymphatic vessels are at risk of damage in pancreatic surgery and especially when there is vein/artery resection and reconstruction at the same time. Chyle leak can be seen in post-operative patients when there is milky substance coming out of the surgical drains and drain fluids triglyceride level is high (\>1,5 mmol/l). Patients with chyle leak are at risk of dehydration, malnutrition, sepsis and prolonged stay at the hospital. Usually treatment of chyle leak is with drains and no-fat diet up to 14 days after surgery. Sometimes combined with somatostatine-analogue-treatment. In this study investigators are randomizing patients with major pancreatic surgery in to two groups. Intervention group will start no-fat diet, including MCT-oil, right after surgery up to 2 weeks. And control group will start the diet if chyle-leak is seen. End goal is to reduce chyle-leaks in post-operative patients and analyze if it has an effect on patients prognosis.