David S. Ludwig (born December 24, 1957) is an American endocrinologist and low-carbohydrate diet advocate in Boston, Massachusetts.

[6] Ludwig is co-director of the New Balance Foundation Obesity Prevention Center Boston Children's Hospital.

[3] Ludwig is the author of the low-carbohydrate diet book Always Hungry?, Always Delicious, Retrain Your Fat Cells, and Lose Weight Permanently, published in 2016.

has been criticized for relying heavily on a pilot study that tested his low-carbohydrate diet that ran for only 16 weeks.

Ludwig has since commented that the pilot study "was never intended as proof", however, his book cited weight loss "success stories" from the pilot participants to make very specific claims about his diet and weight loss.