Final answer:
Chronic pancreatitis is the most likely diagnosis given the patient's symptoms, history of alcoholism, and lab results including elevated serum amylase and lipase, and positive fecal fat test.
Step-by-step explanation:
The most likely diagnosis for a 56-year-old man with a history of alcoholism presenting with abdominal pain, indigestion, weight loss, nausea, vomiting, gray colored stools, elevated serum amylase and lipase, decreased trypsinogen, and a positive fecal fat test is chronic pancreatitis. Chronic pancreatitis is a condition of persistent inflammation of the pancreas that can lead to irreversible damage and impair its function.
Key indicators in this case include the patient's alcoholism, which is a known risk factor for chronic pancreatitis, combined with a constellation of symptoms such as abdominal pain, indigestion, and weight loss. The lab results confirm pancreatic dysfunction, shown by elevated serum amylase and lipase, which are pancreatic enzymes, alongside evidence of fat malabsorption as suggested by the fecal fat test.