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/bee/day in 10:1 PF, while it was 4.99 ± 0.67 µl/bee/day in 1:10 PF. However, sucrose consumption was higher in high-fat diets where it was 25.83±1.69 µl/bee/day in 10:1 PF, while it was 30.66 ± 0.9 µl/bee/day in 1:10 PF. 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 low-fat 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/mg 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.