This study aimed to evaluate the nutritional behavior and some immunological criteria (encapsulation index and phenoloxidase – PO activity, the key enzyme for melanization) as well as to study the effect of protein to fat (P : F) diets on hypopharyngeal gland (HPG) protein content. Bees were restricted to consuming specific P : F diets varying in fat ratio under laboratory conditions. These diets included 25 : 1, 10 : 1, 5 : 1 (low-fat diet, LFD); 1 : 1 (equal-fat diet); 1 : 5, 1 : 10 (high-fat diet, HFD), and 1 : 0 (zero-fat diet) as a control. Bees preferred low-fat diets over high-fat diets, where it was 11.27 ± 0.68 μl · day–1 bee in 10 : 1 P : F, while it was 4.99 ± 0.67 μl · day–1 bee in 1 : 10 P : F. However, sucrose consumption was higher in high-fat diets where it was 25.83 ± 1.69 μl · day ^–1 bee in 10 : 1 P: F, while it was 30.66 ± 0.9 μl · day–1 bee in 1 : 10 P : F. The encapsulation index and phenoloxidase activity of bees were positively linked with the fat level they consumed during all 10 days. The maximum percentage of encapsulation index was 74.6 ± 7.2% in bees fed a high-fat diet, whereas the minimum percentage was 16.5 ± 3.6% in bees which consumed a lowfat diet. Similarly, phenoloxidase activity increased in the haemolymph with increasing fat consumed by bees (0.001 ± 0.0001 and 0.005 ± 0.0003 mM · min ^–1 · mg ^–1 at 25 : 1 and 1 : 10 P : F, respectively). The protein content of hypopharyngeal glands in bees which consumed HFD was double that of LFD. Overall results suggest a connection between a fat diet and bee health, indicating that colony losses in some cases can be reduced by providing a certain level of fat supplemental feeding along with sucrose and protein nutrition.