Highly processed and refined foods are contributing to rising obesity rates in the Western world

Highly processed and refined foods are contributing to rising obesity rates in the Western world

A year-long study of the dietary habits of 9,341 Australians has provided mounting evidence that highly processed and refined foods are the leading cause of rising obesity rates in the Western world.

Professor David Raubenheimer auf seinen Reisen, um die Ernährung der Menschen an einigen der abgelegensten Orte zu studieren, vom Kongo bis zum Himalaya. Bildnachweis: University of Sydney

The new study, published in the latest issue of the journal Obesity by the University of Sydney's Charles Perkins Center (CPC), was based on a national diet and physical activity survey conducted by the Australian Bureau of Statistics (ABS) and supports the 'protein leverage hypothesis'.

The protein leverage hypothesis, first proposed in 2005 by Professors Raubenheimer and Stephen Simpson, argues that people eat too much fat and carbohydrates due to the body's strong appetite for protein, which the body actively prefers over everything else. Because much of the modern diet consists of highly processed and refined foods that are low in protein, people are driven to consume more energy-dense foods until they meet their protein needs.

Processed foods lack protein and promote cravings

"When 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 diseases," said lead author Dr. Amanda Grech, a postdoctoral fellow at CPC and the university's School of Life and Environmental Sciences.

“It is becoming increasingly clear that our bodies eat to achieve a protein goal,” added Professor David Raubenheimer, Leonard Ullmann Chair in Nutritional Ecology in the School of Life and Environmental Sciences. “But the problem is that food in the Western diet contains less and less protein, so you need to consume more of it to reach your protein goal, effectively increasing your daily energy intake.

"Humans, like many other species, have a stronger appetite for protein than for the main sources of energy, fats and carbohydrates. This means that when the protein in our diet is diluted with fats and carbohydrates, we consume more energy to get the protein our bodies crave."

Protein 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 make new ones; and it is estimated that over a million forms of protein are needed for a human body to function. Sources of protein include meat, milk, fish, eggs, soy, legumes, beans and some grains such as wheat germ and quinoa.

The University of Sydney scientists analyzed data from a cross-sectional survey of diet and physical activity in 9,341 adults, known as the National Nutrition and Physical Activity Survey, conducted from May 2011 to June 2012 with a mean age of 46.3 years. They found that the population's average energy intake was 8,671 kilojoules (kJ), with the median energy intake from protein being just 18.4 percent, compared to 43.5 percent from carbohydrates and 30.9 percent from fat, and just 2.2 percent from fiber and 4.3 percent from alcohol.

They then plotted energy intake versus time of expenditure and found that the pattern matched that predicted by the protein leverage hypothesis. Those who ate less protein in their first meal of the day increased their total food intake in subsequent meals, while those who got the recommended amount of protein did not—and actually reduced their food intake throughout the day.

“Protein hunger” has been found to lead to overeating

They also found a statistically significant difference between groups by the third meal of the day: Those with a higher proportion of energy from protein at the start of the day had a much lower total energy intake for the day. Meanwhile, those who ate low-protein foods at the start of the day increased consumption, suggesting they were trying to compensate with higher overall energy expenditure. This is despite the fact that the first meal was the smallest for both groups, with the least energy and food intake, while the last meal was the largest.

Participants with lower than recommended protein at the first meal consumed more of any food throughout the day - energy-dense foods high in saturated fats, sugar, salt or alcohol - and less of the recommended five food groups (grains; vegetables/legumes; fruit; dairy and meat). As a result, they ate worse overall at each meal, with their proportion of protein energy decreasing even as their voluntary food intake increased - an effect the scientists call "protein dilution."

Effect observed in other studies

Professor Raubenheimer and colleagues have observed this effect in other studies, including randomized control trials, for more than a decade.

"The problem with randomized controlled trials is that they treat diet as a disease even though it isn't," said Dr. Greek "Laboratory studies may not be indicative of what people actually eat and do at a population level. So this study is important because it builds on the work showing that people look for protein. And it confirms that at a population level, people eat fewer fats and carbohydrates as the proportion of energy from protein in the diet increases."

While many factors contribute to excess weight gain - including dietary habits, physical activity and sleep habits - the University of Sydney scientists argue that the body's strong need for protein and its lack of highly processed and refined foods is a major driver of energy overconsumption and obesity in the Western world.

Obesity explanation

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

To understand how protein drives human nutrition, Professor Raubenheimer has also sought to study the diets of people in some of the most remote places, from the Congo to the Himalayas.

The protein mechanism in appetite is a revolutionary finding. Obesity, diabetes, cardiovascular disease – they are all driven by diet, and we must apply what we learn to control them.”

Professor David Raubenheimer, Leonard Ullmann Chair of Nutritional Ecology, Faculty of Life and Environmental Sciences

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

Groundbreaking approach to nutrition: Prof. Steve SimpsonPlay

The story behind the protein leverage hypothesis and how it arose from the locust swarms study. Video credit: Australian Academy of Sciences.

Source:

University of Sydney

Reference:

Grech, A., et al. (2022) Macronutrient (im)balance drives energy intake in an obesogenic food environment: An ecological analysis. Obesity. doi.org/10.1002/oby.23578.

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