Obesity: the brain chemistry behind fat
Posted by Charles II on December 5, 2012
A remarkable series of articles on brain chemistry and obesity has been opened to the public by the New York Academy of Sciences.
Kaiser et al. (U. Alabama) give an overview on a hypothesis that, given a perceived deficiency in food availability, the body either adds fat or slows metabolism in a way that lengthens life, depending on whether calories are actually available.
William Banks, VA looks at the role of leptin, a protein that diminishes the desire to eat. In obese people, leptin is, paradoxically, overabundant. This represents a resistance syndrome analogous to insulin resistance. One of the regulators of leptin transport into the brain is triglyceride. In starvation, triglyceride levels rise. Short term fasting increases facilitates leptin transport into the brain, but long-term fasting does the opposite. So fasting can play a positive role in helping to reduce hunger.
Renato Pasquali of Malpighi Hospital in Bologna looks at stress hormones and sex hormones: “stress activates the hypothalamic–pituitary–adrenal (HPA) axis, the sympathetic nervous system (SNS), and the sympathoadrenal system” resulting in the rise of cortisol and catecholamines and an activation of blood pressure elevators like renin and its target, angiotensin. During chronic stress, cortisol elevates lipoprotein lipase, which stores fat especially in the abdomen (perhaps that explains the apple/pear dichotomy, with people with waist fat suffering greater health effects). The term allostatic load refers to the damage inflicted by adapting to adversity. In women, abdominal fat seems to be related to a rise in androgens (male hormones), while in men, to female hormones.
Lucassen et al (NIH and elsewhere) look at the relationship of sleep to obesity. Sleep has declined by over 1.5hr over the last 50 years. Slow wave sleep, which diminishes with age, is probably especially important, though it’s still not clear what’s correlation and what’s causation.
There’s plenty more here.
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