Evolution of Obesity

A recent book “The evolution of obesity” by Power and Schulkin is a very comprehensive survey of the possible causations of this complex problem. It identifies many weight-regulation mechanisms and possible evolutionary reasons for why these can fail. The book uses an evolutionary framework al to analyse a major body of neuroendocrine knowledge about obesity.
They point out that no simple description can be accurate.
Attributing one function to a hormone is attractive, but often wrong. There is a strong correlation of leptin concentrations with body-fat mass, suggesting that leptin limits body weight. But administering leptin to people who are obese does not reduce appetite or weight. Low leptin levels signal the need to seek food, but leptin is only one part of the complex system that regulates eating.
The authors come to similar conclusions for dozens of information molecules that are involved in feeding regulation – including the hormones ghrelin, corticotropin-releasing hormone and cholecystokinin.
The book covers nearly all the main issues in obesity research, the ‘thrifty genotype’ – shaped to store fat to cope with food scarcity , adipose tissue, where fat is stored, as an endocrine organ that secretes at least ten information molecules, and describe the role of cytokines as mediators of the tissue damage associated with abdominal obesity.
The epidemiology of the recent obesity epidemic, a threefold increase in obesity in the United States in just 50 years is discussed.
Power and Schulkin ask why humans eat meals instead of feeding continuously, quoting from explanations from behavioural ecology with the brain mechanisms responsible and with the social functions of sharing meals. They review changes in diet since the Palaeolithic era and the interactions between meat eating and brain evolution.
Other possible contributors to obesity are fructose-based beverages and exercise
The book is reviewed by Randolph Nesse in Nature 2009, vol 40 page 461
Power and Schulkin 2009. The evolution of obesity . John Hopkins University pp 408

Martin Eastwood

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