HEALTH
FOOD P
BRAIN ON THE
With obesity levels spiralling out of control, researchers are delving into brain chemistry to understand what happens when people over-eat, Emma Davies reports
art of the challenge with weight loss strategies is understanding the neurocircuitry involved in controlling body weight, says Michael Schwartz, director of the University of Washington’s Medicine Diabetes Institute, US.1 Weight control depends in part on an almond-sized brain region called
the hypothalamus, responsible for regulating crucial processes such as heart rate, temperature, appetite and body weight. Diet-induced obesity can disrupt the hypothalamus, causing inflammation and neuron loss, while defects in this control system are also linked to insulin resistance and Type 2 diabetes. Long-term studies suggest that many people who lose weight eventually put it back on again. The US Diabetes Prevention Programme (DPP), for example, found that participants who lost weight through diet and exercise sharply reduced their risk of diabetes. However, follow-up studies a decade later showed most had regained weight. ‘The question for me becomes: What is it that underlies that predisposition to
biologically defend that elevated level of body fat mass? What happens to the energy homeostasis system?’ asks Schwartz. ‘To answer that question, you have to have a good understanding of what is responsible for energy homeostasis in normal individuals.’
Microglial moves The hormone leptin has long been known to play a key role in letting us know when we have eaten enough. Yet a high-fat diet can stop the brain from acting on leptin signals, says Lynda Williams from the University of Aberdeen, UK. For example, her former colleague Alex Tups, now at the University of Otago, New Zealand, has shown that mice fed a high-fat diet soon lose their sensitivity to leptin. ‘People who become obese also become insensitive to leptin. If you give it to them it has very little effect. The bigger you get, the more leptin you produce, but you stop responding to it,’ says Williams.
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