Scientists discover that “protein hunger” promotes overeating, obesity

The study confirms that processed food is the key to the rise of obesity

‘Protein hunger’ drives overeating, large population study shows.

More and more evidence that they are highly processed and refined food leading associate to rising obesity rates in the Western world was supported by a one-year survey of the eating habits of 9,341 Australians.

The new study, based on the Australian Bureau of Statistics (ABS) National Diet and Physical Activity Survey, continues to support the ‘Protein Impact Hypothesis’. It was conducted by the University of Sydney’s Charles Perkins Center (CPC) and published in the latest issue of the journal Obesity.

First presented in 2005 by Professor Raubenheimer and Stephen Simpson, the protein influence hypothesis claims that people overeat fat and carbohydrates because of the body’s strong appetite for protein, which the body actively favors over everything else. Because so much of the modern diet consists of highly processed and refined foods—which are low in protein—people are forced to consume more energy-dense foods until they meet their protein needs.

Processed foods lack protein and stimulate cravings

“As people consume more junk food or highly processed and refined foods, they dilute their dietary protein and increase their risk of becoming overweight and obese, which we know increases the risk of chronic disease,” said lead author Dr. Amanda Grech, post-doctoral student Research fellow at the CPC and the University School of Life and Environmental Sciences.

“It’s increasingly clear that our bodies eat to meet a protein target,” added Professor David Raubenheimer, the Leonard Ullmann Chair in Nutritional Ecology in the School of Life and Environmental Sciences. “But the problem is that the food in the Western diet has less and less protein. So you have to consume more of it to reach your protein goal, which effectively raises your daily energy intake.

“Humans, like many other species, have a stronger appetite for protein than for major energy-giving nutrients such as fat and carbohydrates. This means that if the protein in our diet is diluted with fat and carbohydrates, we will consume more energy to get the protein our bodies crave.”

Protein is essential for good health

Proteins are the building blocks of life: every cell in the body contains them, and they are used to repair cells or create new ones; and it is estimated that more than one million forms of protein are required for the human body to function. Sources of protein include meat, milk, fish, eggs, soy, legumes, beans, and some grains such as wheat germ and quinoa.

Scientists from the University of Sydney analyzed data from a cross-sectional survey of diet and physical activity in 9,341 adults, known as the National Diet and Physical Activity Survey, which was conducted from May 2011 to June 2012, with an average age of 46.3 years. They found that the average energy intake of the population was 8671 kilojoules (kJ), with the average percentage of energy from protein being only 18.4 percent, compared to 43.5 percent from carbohydrates and 30.9 percent from fat, and only 2 .2 percent from fiber and 4.3 percent from alcohol.

They then plotted energy intake versus time of consumption and found that the pattern matched that predicted by the protein lever hypothesis. Those who consumed less protein in their first meal of the day increased their total food intake at subsequent meals, while those who received the recommended amount of protein did not—and, in fact, decreased their food intake throughout the day.

‘Protein hunger’ has been found to promote overeating

They also found a statistically significant difference between the groups by the third meal of the day: those with a higher proportion of energy from protein at the beginning of the day had a much lower total daily energy intake. Meanwhile, those who consumed the low-protein food at the start of the day continued to increase consumption, indicating that they tended to compensate by consuming more total energy. This is despite the fact that the first meal was the smallest for both groups, with the least energy and food consumed, while the last meal was the largest.

Participants with a lower protein content than recommended in the first meal consumed more discretionary food – energy-rich food with a high content of saturated fat, sugar, salt or alcohol – during the day, and less than the recommended five food groups (cereals, vegetables/legumes; fruit; dairy products and meat). As a result, they had an overall poorer diet at each meal, with protein as a percentage of energy decreasing even as their discretionary food intake increased – an effect scientists call ‘protein dilution’.

An effect seen in other studies

Professor Raubenheimer and colleagues had seen this effect before in other studies over more than a decade, including randomized control trials.

“The problem with randomized controlled trials is that they treat nutrition as a disease, when it’s not,” Dr. Grech said. “Laboratory studies may not be indicative of what people actually eat and do at the population level. So this study is important because it builds on the work, showing that people seek out protein. And this confirms that, at the population level, as the proportion of energy from protein in the diet increases, people eat less fat and carbohydrates.”

Although many factors contribute to weight gain – including dietary patterns, physical activity levels and sleep patterns – University of Sydney scientists argue that the body’s high demand for protein and its lack in highly processed and refined foods is a key driver of energy overconsumption and obesity in the Western world.

An explanation for obesity

“The results support an integrated ecological and mechanistic explanation of obesity, in which a low-protein, highly processed diet leads to higher energy intake in response to a nutrient imbalance driven by a dominant appetite for protein,” Professor Raubenheimer said. “Supports the central role of protein in the obesity epidemic, with significant implications for global health.”

Seeking to understand how proteins drive human nutrition has also taken Professor Raubenheimer to study human nutrition in some of the most remote places, from the Congo to the Himalayas. “The protein mechanism in appetite is a revolutionary insight,” he said. “Obesity, diabetes, cardiovascular disease—they’re all driven by diet, and we need to use what we’re learning to control them.”

The CPC team study was selected by the editors Obesity as one of the five best papers of the year, and the leader of the study, Professor Raubenheimer, has been invited to speak at the Obesity Journal’s annual symposium in San Diego on November 4.

Reference: “Macronutrient (I)imbalance Drives Energy Intake in the Obese Dietary Environment: An Ecological Analysis” Amanda Grech, Zhixian Sui, Anna Rangan, Stephen J. Simpson, Sean CP Coogan, and David Raubenheimer, November 2, 2022. Obesity.
DOI: 10.1002 / may.23578