Many of these studies were severely criticized by Osborne and Mendel because, when rats were employed as experimental animals no accurate records were kept to show the exact amounts of food consumed by each individual. They pointed to the great differences in amount of food eaten by different rats as evidence that there must, in this kind of work, be a correlation between food consumption and growth. Osborne and Mendel were able by using large amounts of fat to convert their foods into a paste, which could be placed in a glass tube provided with a rod acting as a plunger. Each rat was kept in an individual cage. Food was from time to time expelled from this device into the feeding dish. Employing this device in all their experiments they were able to furnish figures for food consumption.

McCollum was not able to secure a quantitative record of food intake in his animals (rats) until about 1915, for he and his co-workers employed diets in the form of finely ground powders. These consisted of either purified food substances, or of natural foods with certain additions of salts, fats, etc.