According to new research, protein restriction is effective in the fight against obesity and diabetes.
According to a study comparing the effects of protein- and calorie-restricted diets in humans, reducing protein intake may help control metabolic syndrome and some of its main symptoms, such as obesity, diabetes and high blood pressure (hypertension). The results of the study were recently published in the journal Nutrients
The term “metabolic syndrome” refers to a group of conditions, including hypertension, high blood sugar, excess fat around the waist, and abnormal cholesterol levels, that increase the risk of diabetes, cardiovascular disease, and stroke.
“The study showed that reducing protein intake to 0.8 g per kg of body weight was sufficient to achieve almost the same clinical results as caloric restriction, but without the need to reduce caloric intake. The results suggest that protein restriction may be one of the key factors leading to the known benefits of dietary restriction. Therefore, a protein-restricted diet may be a more attractive and easier-to-follow nutritional strategy for people with metabolic syndrome,” said Raphael Feraz-Banitz, first author of the paper and currently a postdoctoral fellow at the Joslin Diabetes Center in Harvard Medical School in the United States.
Controlled diet
21 people with metabolic syndrome took part in the study and were followed for 27 days. During the entire period, they were inpatient at the teaching hospital FMRP-USP (Hospital das Clnicas in Ribeiro Preto).
Each participant's daily caloric intake was determined as a function of their baseline metabolic rate (resting energy expenditure). A traditional Western diet of 50% carbohydrates, 20% protein and 30% fat was given to one group, but it contained 25% fewer calories.
Protein intake was reduced to 10% in the second group. Each volunteer's calorie intake was compared to their baseline energy expenditure. Both groups consumed 4 grams of salt daily.
The results showed that both calorie- and protein-restricted groups lost weight by reducing body fat and that symptoms of metabolic syndrome improved. Lower body fat is known to be associated with lower blood sugar and more normal lipid and blood pressure levels.
“After 27 days of monitoring, both groups had similar results in terms of blood sugar reduction, weight loss, blood pressure control, and reduction in triglyceride and cholesterol levels. Both diets improved insulin sensitivity after treatment. Body fat, waist and hip circumference decreased, but without loss of muscle mass,” said Maria Cristina Foz de Freitas, last author of the paper and professor at FMRP-USP.
The obtained results confirmed the results of previous studies involving experiments on mice. “Here, however, we managed to carry out a fully controlled randomized clinical trial lasting 27 days, with a personalized menu designed according to the needs of each patient,” said Foz de Freitas.
Manipulation of dietary macronutrients—proteins, carbohydrates, and fats—is sufficient to produce the beneficial effects of dietary restriction. “We have shown that protein restriction reduces body fat while preserving muscle mass. This is important because weight loss from restrictive diets is often associated with muscle loss,” said Feraz-Banitz.
The study did not investigate the molecular mechanisms that could explain the beneficial effects of protein-restricted diets, but researchers believe that low protein intake caused changes in metabolism or improved the body's energy management, causing it to burn fat to produce energy for cells. “So far we have only hypotheses. One is that molecular pathways are activated to interpret the reduction of essential[{” attribute=””>amino acids as being a signal to reduce food intake while leading to the production of hormones that typically increase when we're fasting,” Mori said. “Studies in animal models have shown the involvement of such pathways in the effects of both protein and calorie restriction, both of which lead to fat loss.”
Despite the promising results of their studies, the researchers point out that the diets involved were personalized. Mori also stressed that they focused on a specific population of patients with metabolic syndrome (obesity, diabetes, hypertension, and abnormal levels of cholesterol).
“Nevertheless, it's tempting to extrapolate the results. We know research has shown vegan diets to be positive for cases of metabolic syndrome. It's also been found that the excessive protein intake common in the standard Western diet can be a problem. Every case should be analyzed on its own merits. We shouldn't forget protein deficiency can lead to severe health problems, as has been well-described in pregnant women, for example,” he added.
Reference: “Dietary Protein Restriction Improves Metabolic Dysfunction in Patients with Metabolic Syndrome in a Randomized, Controlled Trial” by Rafael Ferraz-Bannitz, Rebeca A. Beraldo, A. Augusto Peluso, Morten Dall, Parizad Babaei, Rayana Cardoso Foglietti, Larissa Marfori Martins, Patricia Moreira Gomes, Julio Sergio Marchini, Vivian Marques Miguel Suen, Luiz C. Conti de Freitas, Luiz Carlos Navegantes, Marco Antônio M. Pretti, Mariana Boroni, Jonas T. Treebak, Marcelo A. Mori, Milton Cesar Foss and Maria Cristina Foss-Freitas, 28 June 2022, Nutrients
DOI: 10.3390/nu14132670
The study was funded by the São Paulo Research Foundation. The study also benefited from a FAPESP Thematic Project on strategies for mimicking the effects of dietary restriction, led by Marcelo Mori, a professor at the State University of Campinas (UNICAMP), also in Brazil.
A multidisciplinary team of scientists conducted the study, including researchers affiliated with the University of Copenhagen in Denmark, the University of São Paulo, and the National Cancer Institute (INCA) in Brazil, as well as the Obesity and Comorbidities Research Center (OCRC), a Research, Innovation, and Dissemination Center (RIDC) funded by FAPESP and hosted by UNICAMP.
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