Low-Protein Diet May Lead to Overeating By Kristina Fiore, Staff Writer
Explain that lean subjects consuming controlled but disguised macronutrient composition diets took in significantly more calories on a diet containing 10% protein than one containing 15% protein.
Note that most of the excess energy consumed came in the form of snacks, and that those on the 10% protein diet reported more hunger after breakfast than those on a 25% protein diet.
People who ate less protein consumed more fats and carbohydrates, typically in the form of snacks, researchers found.
Study participants' overall energy intake was significantly higher when they ate a diet that was only 10% protein compared with one comprised of 15% of the macronutrient, Alison Gosby, PhD, of the University of Sydney in Australia, and colleagues reported online in PLoS One.
But there was no difference in total energy intake between a 15% and 25% protein diet, they reported.
"Humans have a particularly strong appetite for protein, and when the proportion of protein in the diet is low this appetite can drive excess energy intake," Gosby said in a statement. "Our findings have considerable implications for body weight management in the current nutritional environment, where foods rich in fat and carbohydrates are cheap, palatable, and available to an extent unprecedented in our history."
The "protein leverage" hypothesis proposes that a decline in the ratio of protein to fat and carbohydrates in the diet drives excess energy intake, potentially promoting the development of obesity, according to background material in the article.
To test that idea, the researchers gave 22 lean patients a special diet over three four-day periods. Patients didn't know the macronutrient content of the foods they were eating and were allowed to choose their meals and snacks freely in an inpatient setting.
The diets were comprised of either 10%, 15%, or 25% energy as protein, and carbohydrates were adjusted to comprise 60%, 55%, or 45% of energy, while fat was held constant at 30%.
Gosby and colleagues found that participants took in significantly more energy overall when they ate a 10% protein diet than on the 15% protein diet (P<0.0001).
The majority of that excess energy -- 70% -- came from snacks, not regular meals, they reported (P=0.02). And over half of that energy (57%) was due to increased intake of savory foods (P=0.03).
"This may reflect habitual preferences, or may be an indication of participants seeking protein due to associating savory sensory qualities with protein," they wrote.
However, there was no difference in overall energy intake between the 15% and 25% protein diet, they reported, which may indicate an optimal protein intake.
Hunger levels were generally similar across all diets, although there was a greater increase in hunger score between one and two hours after the 10% protein breakfast compared with the 25% protein breakfast (P=0.005). There was also a trend toward greater hunger after the 15% protein breakfast compared with the 25% one, but it wasn't significant.
They said the findings were consistent with other studies that protein leverage may be a contributory mechanism to the increased energy intake that has gone hand-in-hand with the rising prevalence of obesity.
"Even when the macronutrient composition of foods was disguised and the variety controlled, increased energy intake occurred on diets containing a lower proportion of energy from protein," they wrote, which could potentially "increase the risk that obesity might develop."
The study was supported by the Australian National Health and Medical Research Council.
A co-author reported relationships with Rosemary Conley Diet and Fitness Company.
Primary source: PLoS One
Gosby AK, et al "Testing protein leverage in lean humans: A randomized controlled experimental study" PLoS One 2011; DOI: 10.1371/journal.pone.0025929.
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This makes complete sense! Proteins are very filling yet are not adding too many calories, if lean protein. They also help satisfy your hunger. I love seeing research done on this, thank you for sharing!