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Nutritional and metabolic adaptation: key points
- The bulk of human evolution occurred in a very different nutritional milieu and the human genotype was selected to be well adapted to that milieu.
- There is a rising incidence of obesity and its associated disorders in both the developed and developing worlds.
- There has been a rapid change in diet and behaviour against the background of a genotype that cannot change rapidly.
- Developmental processes may also contribute to the rising incidence of metabolic mismatch.
Integrated life history responses to developmental cues
If the developing organism predicts a future limited nutritional environment, it might be appropriate to use the mechanisms of plasticity to adjust growth patterns so that later body function is optimised for a limiting nutritional environment. Conversely, if the fetus predicts a later nutritionally luxurious environment, it is appropriate to have metabolic systems set up with different expectations. In the former situation of predicted nutritional threat, an appropriate response would include reduced investment in somatic growth (e.g. reduced muscle mass), a preference for high fat foods, metabolic settings that favour fat deposition in times of energy excess, and altered endocrine, behavioural and vascular controls such that the organism has reduced insulin secretion and sensitivity. Given that evolution is driven by the fitness imperative, anticipation of a threatening environment might be expected to accelerate the timing of maturation and commit more resources to reproduction, perhaps even at a cost to other traits that improve longevity (for instance, by investing less in cellular or DNA repair).