Protein can stave off hunger.PunchstockEating a high-protein diet can boost the release of a hunger-suppressing hormone, according to new study on mice. The research suggests that a diet rich in protein may be a good way to lose weight and keep it off.
Mice fed a protein-heavy diet produced higher levels of an appetite-regulating protein called peptide YY (PYY), which has been linked to reduced appetite in human studies. What's more, the high-protein mice put on less fat than mice on a low-protein regime.
The discovery boosts the theory that eating more protein might help to reduce appetite and lead to sustained weight loss, says Rachel Batterham of University College London, who led the research, published in the journal Cell Metabolism1. "All the evidence suggests that it will be beneficial," she says.
The discovery may also shed light on how the notorious Atkins diet, which ditches carbohydrates in favour of protein and saturated fats, might work. Studies have shown that people on this diet can loose weight, though it is unclear why. Batterham thinks she may have the answer: "People on the Atkins diet don't feel as hungry — that's how it works."
But, she cautions, that doesn't mean the Atkins diet is a good idea: "No medical person is going to tell you to have all that saturated fat in your diet and no carbohydrates." In its early stages, the regime causes a condition called ketosis, in which the liver, deprived of glycogen from carbohydrates, switches to its starvation mode and begins to metabolize fatty compounds. "The problem is that it makes you feel terrible," Batterham says.
She now plans to organize a long-term study of the effects of a high-protein diet in humans, which might feature foods such as lean meat, soy, tofu and egg.
Weighty issue
Batterham undertook this study in part to pin down the link between PYY and appetite. Her team first showed that the hormone reduces appetite in humans in a Nature paper2 in 2002, but other researchers said they could not replicate the effect. So her team turned to mice to investigate it in more depth.
In the new study, as well as showing that mice fed lots of protein put on less weight, Batterham and her colleagues also genetically engineered mice to lack functioning PYY. These mice ate more and became fatter, even on a high-protein regime. When these mice were dosed with replacement PYY, they stopped gorging. This proves, says Batterham, that a lack of PYY is directly linked to overeating.
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That might explain why people are growing ever more obese. Since the agricultural revolution, the amount of protein in the average diet has been declining, in favour of carbohydrates from plant crops such as rice and maize. The typical Western diet contains only 16% protein, whereas a prehistoric hunter-gatherer would have consumed twice as much, Batterham claims.
High-protein eating habits such as the 'caveman diet', which can contain up to 35% protein, might therefore be based on some sound principles, Batterham suggests. The PYY system, she points out, has been around for millions of years, and is found in animals ranging from humans right through to primitive fish called lampreys.
Batterham stresses that such diets will still need to be investigated to see if they carry risks of high cholesterol, kidney damage or other problems. "Prehistoric hunter-gatherers did not routinely live to be 80 years old," she points out.
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