One possible reason for this conclusion is the rare need for a person to perform at their maximum. There is a difference between typical functioning, that is – the normal level of functioning for daily life, and maximal functioning, that is – what cognitive tests observe as our maximum level of functioning. As the maximum cognitive ability that we are able to achieve decreases, it may not actually affect our daily lives, which only require the normal level.Some studies have indicated that childhood hunger might have a protective effect on cognitive decline. One possible explanation is that the onset of age-related changes in the body can be delayed by calorie restriction. Another possible explanation is the selective survival effect, as the study participants who had a childhood with hunger tend to be the healthiest of their era. See also
PASS Theory of Intelligence
Fluid and crystallized intelligence

References
Further reading
Das, J.P.; Naglieri, J.A. ; Kirby, J.R. (1994). Assessment of Cognitive Processes. Needham Heights, MA: Allyn & Bacon. ISBN 0-205-14164-1. Das, J.P. (2002). A better look at intelligence. Current Directions in Psychology, 11, 28–32. Goldstein, Gerald; Beers, Susan, eds (2004). Comprehensive Handbook of Psychological Assessment: Volume I: Intellectual and Neurological Assessment. Hoboken, NJ: John Wiley & Sons. Kaufman, Alan S. (2000). "Chapter 20: Tests of Intelligence". In Sternberg, Robert J. (ed.). Handbook of Intelligence. Cambridge: Cambridge University Press. pp. 445–476. ISBN 978-0-521-59648-0. Naglieri, Jack A.; Otero, Tulio M. (2012). "Chapter 15: The Cognitive Assessment System: From Theory to Practice". In Flanagan, Dawn P.; Harrison, Patti L. (eds.).
Discitis, or diskitis, is an infection in the intervertebral disc space that affects different age groups. In adults, it can lead to severe consequences, such as sepsis or epidural abscess, but it can also spontaneously resolve, especially in children under 8 years of age. Discitis occurs post-surgically in approximately 1–2 percent of patients after spinal surgery. Signs and symptoms
Symptoms include severe back pain, leading to lack of mobility. Some very young children may refuse to walk and arching of the back is possible. In post-operative situations, the symptoms occur within a week and result in severe low back pain or neck pain (depending on the surgical location). If untreated, the discitis may resolve on its own, causing spontaneous fusion of the intervertebral disc space,  cause a chronic low grade infection, or progress to osteomyelitis and possibly even an epidural abscess. In case of concomitant inflammation of one or more vertebrae (in such cases usually involving the areas adjacent to the intervertebral disc spaces) the condition is called spondylodiscitis. Causes
There is debate as to the cause, although hematogenous seeding of the offending organism is favored as well as direct spread. It is important to differentiate between spontaneous discitis which is usually from hematologic spread from a urinary or respiratory infection versus that from a post-operative complication which usually involves skin flora such as staph aureus. It can be caused due to spinal tuberculosis and spread along spinal ligament to involve  the adjacent anterior vertebral bodies, causing angulation of the vertebrae with subsequent kyphosis.