Calorie restriction alone was shown to decrease plasma insulin, and insulin-like growth factor (IGF)-1 levels and increase apoptosis, overall suggesting that calorie-restricted diet may reduce tumour proliferation.114 In another human studies, a 15% caloric reduction over 4 years demonstrated a sustained reduction in plasma growth factors and hormones, which have been associated with increased risk of cancer.114 The cancer cell location and tissue of origin also contributes to the dietary response. This evidence concerns the gene IGF1 and cancer.