This is because the amino acid is utilized to synthesize the vitamin.For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For niacin labeling purposes 100% of the Daily Value is 16 mg. Prior to 27 May 2016 it was 20 mg, revised to bring it into agreement with the RDA. Compliance with the updated labeling regulations was required by 1 January 2020 for manufacturers with US$10 million or more in annual food sales, and by 1 January 2021 for manufacturers with lower volume food sales. A table of the old and new adult daily values is provided at Reference Daily Intake. Sources
Niacin is found in a variety of whole and processed foods, including fortified packaged foods, meat from various animal sources, seafoods, and spices. In general, animal-sourced foods provide about 5–10 mg niacin per serving, although dairy foods and eggs have little. Some plant-sourced foods such as nuts, legumes and grains provide about 2–5 mg niacin per serving, although in some grain products this naturally present niacin is largely bound to polysaccharides and glycopeptides, making it only about 30% bioavailable. Fortified food ingredients such as wheat flour have niacin added, which is bioavailable. Among whole food sources with the highest niacin content per 100 grams:

Vegetarian and vegan diets can provide adequate amounts if products such as nutritional yeast, peanuts, peanut butter, tahini, brown rice, mushrooms, avocado and sunflower seeds are included.
Gastric distention is the enlargement of the stomach, and can be due to a number of causes.Physiologic (normal) gastric distension occurs when eating. Distension of the upper stomach stimulates the secretion of stomach acid, while distension of the lower stomach stimulates gastrin secretion. Distension of the stomach also stimulates the secretion of ghrelin.Other causes include:

binge eating associated with bulimia nervosa
tumors causing obstruction
diabetic neuropathy
scarring due to pyloric gastritis
delayed gastric emptyingTo identify the cause of gastric distention, an upper endoscopy or barium upper GI imaging should be done. == References ==