Calorie restriction (CR) has been studied as a way to prolong longevity, and CR before chemotherapy can reduce hematological toxicity in cancer patients. We investigated the influence of fasting on immune cells and immature hematopoietic cells. In fasted mice, there was a significant reduction in the hematopoietic stem cell count but no significant difference for progenitor cells. Colony assays showed no difference and the rates of early and late apoptosis were almost identical when comparing fasted and control mice. DNA cell cycle analysis of immature bone marrow (BM) cells showed that CR caused a significant increase in the percentage in the G0/G1 phase and decreases in the S and G2/M phases. We detected a remarkable increase of T cells in the BM of fasted mice. CD44– naïve CD8+ T cells were more numerous in fasted BM, as were naïve CD4+ T cells, and part of those T cells showed less tendency in the G0/G1 phase. Immature hematopoietic cells remained in a relatively quiescent state and retention of colony-forming capacity during CR. The number of naïve T cells in the BM of fasted mice increased. These findings imply immature hematopoietic cells and some lymphoid cells can survive starvation, whilst maintaining their function.