The objective of the study was to assess the ranges of phenotypic flexibility as a measurement of health within the apparently healthy population. Therefore, a total of 100 healthy subjects were enrolled (50 males, 50 females) with a range in age (20-70 yrs) and in body fat percentage (low, medium, high), to ensure variation in phenotypic flexibility. Phenotypic flexibility was quantified by measuring in each volunteer the response of 160 markers to the PhenFlex challenge test (PC). The PC is a drink containing high amounts of fat and glucose. We have shown previously that this challenge test is able to quantify the adaptive capacities of most relevant metabolic processes for diet-related health. The markers were selected to monitor the response of the following 4 processes relevant for phenotypic flexibility: glucose metabolism, lipid metabolism, protein metabolism, and low grade chronic stress. The markers were measured in blood samples taken at fasting and 6 time-points (t= 0.5, 1, 2, 4, 6 and 8h) after PC. Next, the range in phenotypic flexibility of the study population was analyzed in the “health-space”, a tool developed at TNO that shows individual phenotypic flexibility in a 4 dimensional space defined by the 4 processes. The health space showed a different adaptation to PC in the extremes of the recruited population: persons of young age with low to normal fat percentage had a significant different response to PC compared to persons of old age with normal to high fat percentage (both genders). Furthermore, the health space allowed the quantification of the individual metabolic health state. Ultimately, visualizing phenotypic flexibility in the health space before and after nutritional interventions will allow the evaluation of individual efficacy of the intervention.