Obesity is a “growing” issue, so to speak, with no signs of slowing down. A recent Australian study, published in the Journal of Obesity, adds more evidence that an increase in the consumption of refined and highly processed foods due to lack of protein intake are one of the root causes of obesity. 

University of Sydney’s (USYD) Charles Perkins Centre (CPC) researched and used data from the National Nutrition and Physical Activity Survey (NNPAS), acquired from the Australian Bureau of Statistics, to support the “protein leverage hypothesis.” This theory was initially suggested in 2005 by professors David Raubenheimer and Stephen Simpson. The hypothesis hints that our bodies have a strong appetite for protein, but we overeat fats and carbohydrates. As our current diets are full of highly processed foods that are low in protein, people over-consume energy-dense food until their protein demand is met.

Refined Foods Lack Protein and Increase Cravings

Lead author Dr. Amanda Grech, a postdoctoral research fellow at the CPC and the university's School of Life and Environmental Sciences department, believes that dietary protein is watered down by the consumption of highly processed junk food. This raises a person’s risk for being overweight and obese, which may in turn lead to chronic illnesses.

Professor David Raubenheimer, the Leonard Ullmann Chair in Nutritional Ecology at the School of Life and Environmental Sciences, agrees that human bodies are trying to meet a protein target in terms of what they eat. Food in the Western diet has less protein, so we eat more of it to obtain the protein our bodies crave. 

Protein is Vital to Good Health

It’s estimated that over a million different forms of protein are needed for the human body to function. Protein repairs and creates new cells, and is necessary to make hormones, antibodies, and enzymes. Sources of protein include meat, dairy products, eggs, soy, beans, legumes, and some grains including quinoa and wheat germ. 

The data from the NNPAS, which studied the nutrition and physical activity of 9,341 adults with an average age of 46.3 years from May 2011 to June 2012, found that the mean percent of energy from protein was 18.4%. 43.5% of energy came from carbohydrates, 30.9% from fat, 4.3% from alcohol, and only 2.2% from fiber.

The study plotted calorie intake versus the time of consumption. The researchers discovered that those who ate lower amounts of protein in the morning ate more calories at subsequent meals, while those who ate adequate protein declined more food throughout the day. This finding is in line with the “protein leverage hypothesis”.

Hunger for Protein Increases Overeating

By the third meal of the day, there was a statistically significant difference in the two groups of the study. Individuals who consumed more protein earlier in the day had less overall calorie intake. Those who ate lower protein foods at the beginning of the day had higher overall calorie intake, suggesting they were trying to compensate for the lack of protein. This occurred even though both groups had a small initial meal and a large final meal.

Subjects with a lower protein intake than recommended ate more energy-dense foods high in sugar, saturated fat, salt, or alcohol during the day and less of the recommended number of servings of grains, vegetables, legumes, fruit, dairy, and meats. Their diets were of poor quality overall, and the percentage of protein was not met even as discretionary food intake increased. This is known as “protein dilution”.

 Protein Dilution: Not Uncommon

The protein dilution effect has been observed in other studies, including randomized controlled trials. However, the findings of trials have their limitations. "The problem with randomized controlled trials is that it treats diet as a disease when it's not," said Dr. Grech. "Laboratory studies may not be indicative of what people are actually eating and doing at a population level. This study is important as it builds on work, showing that people do seek out protein. And it confirms that, at a population level, as the proportion of energy from protein increases in the diet, people eat less fats and carbohydrates."

Several factors contribute to weight gain including diet habits, physical activity levels, and sleep. The scientists from USYD note that the main driver of calorie overconsumption and obesity in the Western world is related to the body’s demand for protein and the lack of it in highly refined foods.

Rationale for Obesity

Professor Raubenheimer believes these results support an ecological rationale for weight gain. Consumption of highly processed foods results in higher calorie intake due to a nutrient imbalance fueled by the body’s appetite for protein. He believes this has major implications for global health.

Professor Raubenheimer is also interested in studying the diets of people in remote places such as the Congo and Himalayas. As obesity, diabetes, and heart disease are all driven by diet, the protein mechanism may provide more insight into getting these conditions under control. 

By Lisa Andrews, MEd, RD, LD

Reference:

Grech, A., Sui, Z., Rangan, A., Simpson, S. J., Coogan, S. C., & Raubenheimer, D. (2022). Macronutrient (im)balance drives energy intake in an obesogenic food environment: An ecological analysis. Journal of Obesity, 30(11). https://doi.org/10.1002/oby.23578