Principles of Nutrition and Nutritive Value of Food published.
Date: 1904
Published by Dr. Wilbur Olin Atwater, this early nutrition guide recommends variety in diet, enforcing "correct" proportions, moderation, measuring calories, and a diet focused on nutrient-dense foods and less fat, sugar, and starch.
However, the guide doesn't include an understanding of individual vitamins as being a component of nutrition, as these won't be identified until 1910.