Why Are You Still Hungry?It's been less than two hours since your last meal. So, why are you still hungry? If you've ever tried to lose weight, you're probably familiar with that intense sense of hunger, which just won't go away. A recent study, which made front-page news here in the UK, could have the answer you're looking for... In August 2002, endocrinologist Stephen Bloom and colleagues at Imperial College London found that when they injected a hormone called peptide YY3-36 (PYY) into rodents and humans, it decreased hunger for 12 hours or more. Rodents on the peptide also reduced their weight gain, leading some to herald PYY as a potential new anti-obesity drug. However, not all groups have been able to replicate these results, leaving the peptide's promise in the lurch. A former member of Bloom's team, endocrinologist Rachel Batterham of the University College London and colleagues, took another stab, this time from a different angle. Batterham's team first looked at what kind of food best satisfies hunger. They studied nine obese men and 10 normal-weight men. After brief fasts, the men ate different meals. Each of the meals (a high-protein meal, a high-fat meal, and a high-carbohydrate meal) had the same number of calories. All the men said the high-protein meal best satisfied their hunger.Interestingly, the normal-weight men found the high-fat meal more satisfying than the high-carbohydrate meal, while the obese men did not. Measurements showed the high-protein meal triggered the most PYY in all of the men. In the normal-weight men — but not the obese men — the high-fat meal triggered more PYY than the high-carbohydrate meal. Batterham's team also genetically engineered a mouse strain that did not have the PYY gene. These mice ate huge amounts of food, and quickly became obese. Normally, obese mice fed a high-protein diet will eat less and lose weight. But a high-protein diet didn't help the PYY-defective mice lose weight unless they also got PYY treatments. "Increasing the protein content of the diet augments the body's own PYY, helping to reduce hunger and aid weight loss," says lead researcher Dr. Rachel Batterham. "One potential weight loss strategy is therefore to increase the satiating power of the diet and promote weight loss through the addition of dietary protein — harnessing our own satiety system," Batterham says. "Such a diet is perhaps more typical to that of our hunter-gatherer ancestors." However, the research is unlikely to lead to supplements containing PYY as a weight-loss product, says Dr. Batterham. "PYY is a protein so if it is taken in tablet form it is broken down and doesn't pass into the blood. Thus to increase PYY it either has to be given by another route (intravenous, subcutaneous, transdermal, nasally) or we can try and increase the body's own circulating levels by modulation diet," she concludes. So, what does this mean for you?The information that protein helps you lose weight by helping you control your appetite is so old you'll probably catch it on a late night re-run of Starsky and Hutch. Yet this research actually made front-page news here in the UK, with an article in the Daily Express describing it as "ground-breaking." The article also expressed the usual misplaced concerns about safety, with one expert cautioning against protein on the basis that there have been "no long-term studies of high-protein diets," and that high-protein diets "can cause problems with the kidneys and make people feel lethargic." Neither comment is based on any evidence or research that I'm aware of. A number of long-term (12-24 months) studies of high-protein diets (which I'm defining as one that derives around 30% of its total calories from protein) have been completed, and none show any indication of adverse health effects (see The Anatomy of a Balanced Diet for more information). The idea that protein causes "problems with the kidneys" has been around for years, but there's little evidence to show that protein - even at a level twice the current RDA - has any negative effect on renal function in someone with healthy kidneys.
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