Protein Appetite Drives Excess Energy Intake

A new study suggests that calorie intake increases as people eat less protein in proportion to other nutrients such as fat and carbohydrates.

Researchers at the University of Sydney (Australia) collected data from 38 published experimental trials measuring ad libitum intake in subjects confined to menus differing in macronutrient composition. Collectively, the trials encompassed considerable variation in percent protein (spanning 8%–54% of total energy), carbohydrate (1.6%–72%) and fat (11%–66%). The data was used to describe the individual and interactive effects of dietary protein, carbohydrate, and fat on the control of total energy intake.

The results showed that the percent of dietary protein was negatively associated with total energy intake irrespective of whether carbohydrate or fat were the diluents of protein. According to the researchers, the analysis strongly supports a role for protein leverage in lean, overweight, and obese humans, suggesting that the human need for protein is so powerful we are driven to overeat in our search to consume more of it, thus inhibiting the feedback regulation provided by the consumption of carbohydrates and fats. The study was published on October 28, 2013, in the journal Obesity Reviews.

“The strength of our nutritional drive for protein is frightening within our current nutritional environment, where a large number of low-protein, high-calorie foods are consumed on a regular basis,” said lead author Alison Gosby, PhD, of the school of biological sciences. “When the protein becomes ‘diluted’ by the rest of our diet, we may keep eating more and more calories in search of some kind of hard-wired intake target.”

“People on low incomes are particularly at risk of over-weight and obesity, and may have the most trouble affording protein-rich foods,” added Dr. Gosby. “When the proportion of protein in a food is low, it is generally cheaper. This works on two levels to dilute dietary protein: through the food industry and also through the consumer.”

The review found the when people dropped the proportion of calories from protein from 15% to 10%, their overall energy intake shot up by 12%, or about 1,000 kilojoules. But the drive for protein seems to be spread over a one- or two-day period, so not every meal needed to have high protein content. Overall, a woman of average weight needs at least 46 grams of protein each day, while an average man needs at least 64 grams.

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