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Weight Gain New Theory: Blame on leptin, triggered by sugar
– Reported, January 05, 2013
In a fascinating new book, Robert Lustig, a professor of clinical paediatrics at the University of California, expounds a whole new scientific theory.
He argues that the urge to overeat and lounge around doing nothing is not a sign of weakness.
It is, he says, a hormonal issue, eating too much sugar.
He points the finger of blame at the hormone leptin, which acts like an appetite thermostat.
As one of two hunger hormones in the body, leptin works to decrease the appetite (its partner, ghrelin, increases appetite).
When you have had enough to eat, your fat cells release leptin, which effectively dulls the appetite by instructing the brain that its time to stop eating.
But Professor Lustig warns that our sweet tooth is sending this process haywire.
For many years scientists thought obesity could be caused by a shortage of leptin thinking that without adequate levels, overweight people simply never received the message that they were full.
But more recent studies have shown that obese people have plenty of leptin (in fact, the fatter you are, the more of it you appear to have), but are more likely to be leptin-resistant.
This means the cells in the brain that should register leptin no longer read the signals saying the body is full, but instead assume it is starving no matter how much food you continue to eat.
In panic, the brain pumps out instructions to increase energy storage instigating powerful cravings for high-fat, high-sugar foods because these are the easiest and most immediate forms of energy and conserve energy usage, by dampening any urge to get up off the sofa and go for a run.
The food cravings are made even more intense and impossible to resist because leptin is supposed to dampen the feeling of pleasure and enjoyment you get from food by suppressing the release of the brain chemical dopamine, helping to decrease appetite.
But if you are leptin-resistant, food never stops tasting delicious, no matter how much of it you eat.
This, says Professor Lustig, is why many overweight people find it so hard to stop eating, and why diets so often fail.
Scientists have been struggling to work out what causes leptin resistance.
But now Professor Lustig and his team have been able to show in repeated studies on humans that too much sugar in the diet is to blame.
High sugar diets lead to spikes in the hormone.
This is needed to clear sugar out of the blood and into storage as fat.
But repeated insulin spikes, due to a high sugar diet, can lead to a condition called insulin resistance (when the cells have been so bombarded by insulin they no longer respond to it).
Professor Lustig believes insulin resistance triggers leptin resistance, and, crucially, he has discovered that by reducing insulin levels it is possible to improve leptin signalling (the brains ability to read leptin), stop cravings, put the brakes on food consumption and trigger weight loss.
In his new book Fat Chance, Professor Lustig explains that leptin resistance and sugar is at the root of the obesity epidemic.
He believes 1.5 billion overweight or obese people in the world suffer from this condition and is convinced that the problem can be tackled by targeting insulin.
In his studies, many participants took insulin-lowering drugs, but the professor says similar results can be achieved by a few small lifestyle changes notably reducing sugar in your diet.
The professor has a heavyweight background in endocrinology (the study of hormones), as both a medical doctor and academic.
He used organised trials to study the role the brain plays in governing appetite and activity levels and found that patients who had damage to the hypothalamus (the area of the brain that controls energy levels) could not lose weight, but somehow gained weight even when restricted to a near-starving 500 calories a day.
Lustig realised that a similar process could be happening with obese adults and set out to investigate a potential solution.
His studies revealed that the roles of leptin and insulin are intertwined, and bind to cells in the same area of the brain the hypothalamus.
Credit: http://www.dailymail.co.uk/
