Obesity is linked to some of the leading causes of preventable, premature death, including heart disease, stroke, type 2 diabetes, and cancer. Between 1999 and 2020, population obesity rates in the United States increased from 30.5% to 41.9%.
First proposed in 2005, the protein leverage hypothesis (PLH) is a theory for the cause of obesity. It states that if the body’s needs for protein consumption are unmet, fat and carbohydrate consumption increases, dampening satiety signals and increasing food intake.
Studies have shown that as the percentage of energy from protein has decreased in American diets, obesity rates have risen.
Another study found that inpatient adults exposed to ultra-processed diets ingested more carbohydrates, fat, and total energy than those on unprocessed diets and consequently gained weight.
Understanding the health effects of highly processed foods and low protein intake could improve obesity prevention strategies.
Recently, researchers analyzed population health data to understand the relationship between protein intake and obesity.
They found a link between lower protein intake during the day’s first meal and higher overall food intake throughout the day.
The study’s findings appear in Obesity.
The researchers analyzed data from the 2011-2012 National Nutrition and Physical Activity Survey from the Australian Bureau of Statistics. They included data from 9,341 people with an average age of 46.3.
Data included:
The average energy intake was 2072 calories, including:
By comparing energy intake and time of consumption, the researchers found that those who consumed lower amounts of protein in their first meal of the day had higher calorie intake in later meals.
The researchers noted that as protein intake decreased, energy from fat, carbohydrates, sugars, and alcohol increased in what is known as “protein dilution.”
They further noted that those who consumed less protein in their first meal consumed more highly-processed foods throughout the day.
“Our study suggests that in free-living humans, eating low protein meals early in the day results, via protein leverage, in energy (fat and carb) over-consumption,” said Prof. David Raubenheimer, a study author and Chair of Nutritional Ecology at the University of Sydney, Australia.
“Even though people who have low-protein breakfasts tend to select higher protein meals thereafter (at lunch and dinner), they don’t quite compensate for the low protein start so that at the end of the day the overall daily diet is lower in protein and higher in fats and/or carbs than people who begin the day with higher protein meals,” Prof. Raubenheimer told Medical News Today.
The researchers noted that many factors might explain why humans are predisposed to consume highly processed foods. These include:
They also noted that umami-flavored, savory snack foods might hijack the body’s protein-seeking responses in what is known as the “protein decoy effect.” They wrote that these products might exacerbate, rather than satisfy, a protein deficiency.
MNT spoke with Dr. Dana Ellis Hunnes Ph.D., MPH, R.D., Assistant Professor at UCLA Fielding School of Public Health, who was not involved in the study. Dr. Hunnes is also the author of “Recipe for Survival: What You Can Do to Live a Healthier and More Environmentally Friendly Life.”
“Protein slows down the rate at which we digest and absorb sugars and carbohydrates from our foods, as does fat. If we eat a breakfast that is full of highly processed or sugary foods, we digest and absorb those foods rapidly.”
– Dr. Hunnes
“This causes our insulin levels to spike very rapidly, causing our cells to take the sugar (glucose) out of our blood very rapidly- assuming we don’t have diabetes,” she noted. “This then leads to a rapid decrease in blood sugar levels that can make us feel hungry again, and stoke that appetite, even if we are not “truly hungry.”
In conversation with MNT, Kristin Kirkpatrick, a registered dietitian nutritionist at the Cleveland Clinic, not involved in the study, added: “If you are hungry, then you are more likely to eat, and if you are experiencing cravings, lack of sleep, near food, smell food- there are so many complex variables here on what one will choose, even your gut microbiota plays a role in the type of food you choose- then you may be more likely to eat.”
A study earlier in the year suggested that diets with less animal protein and higher levels of complex carbohydrates are most beneficial for long-term health and lifespan.
When asked how the findings in the current study suggesting higher levels of protein correspond to these earlier findings, Dr. Hunnes noted that the studies do not contradict each other but “demonstrate the nuance of nutrition and how studies can be misinterpreted.”
Dr. Raubenheimer further explained that the earlier study noted that fiber could be a healthy substitute for high protein levels.
“The [theory that] low protein ‘leverages’ high intakes of fats and carbohydrates applies to diets that have a large proportion of processed foods that are low in both fiber and protein. In those conditions, we over-eat energy to reach our protein target.
However, for people eating diets with high proportions of whole plant foods, which are rich in fiber, the fiber partly replaces protein in providing the feeling of fullness which stops eating.”
– Dr. Raubenheimer
He explained that the advantages of higher fiber intake include reduced protein intake, which has been linked to extended healthspans, and increased levels of micronutrients and other beneficial compounds like antioxidants lost in industrial food processing.
“All these mechanisms likely explain why the diets associated with the longest healthy lifespans (e.g. traditional Okinawa diet, Mediterranean Blue zone, etc.) are low in protein (not much above 10% of energy, vs around 15%-18% for typical USA/Australian diets) and rich in plant foods,” Dr. Raubenheimer noted.
When asked about the study’s limitations, Dr. Hunnes noted that it didn’t differentiate between types of protein and that the findings may glorify protein as a “miracle nutrient when it is not.” She explained that overall diet quality is a better measure and predictor of health, longevity, and disease risk, and it should be taking into account what other nutrients are being incorporated into one’s diet, such as fiber and whole foods.
Kristen Kirkpatrick added: “I often caution my patients that food intake, weight status, and health do not just boil down to one thing. We as humans are complex, and our choices are as well. Environment, social support, genetics, activity, level, even geographic location may all play a role in how we decide and implement a specific dietary pattern.”
Dr. Raubenheimer hopes that his findings will decrease processed food consumption and increase whole, especially plant-based, food consumption. He noted that his message to consumers is to “target foods that come from fields, not factories”.
Noting that this can be difficult as whole foods can often be expensive, he added that governments and industry must also play a role. For governments, he said:
“Develop policy and other interventions that help transform our food environments in directions that enable and encourage healthy food choices. Failing to do so is not only socially irresponsible but also fiscally irresponsible because unhealthy diets are associated with massive costs to productivity and national health systems.”
And to the food industry, he noted: “The science now unequivocally links highly processed industrial foods to obesity and disease. There is no better time to seriously implement transition strategies aligned with public health. Except perhaps yesterday.”
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Overeating and obesity: How curbing 'protein hunger' may help – Medical News Today
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Dec 20, 2022