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Lower protein diet may lessen risk for cardiovascular disease

Amino acids are the building blocks of proteins. A subcategory, called sulphur amino acids, including methionine and cysteine, play various roles in metabolism and health. "For decades it has been understood that diets restricting sulphur amino acids were beneficial for longevity in animals," said John Richie, a professor of public health sciences at Penn State College of Medicine. "This study provides the first epidemiologic evidence that excessive dietary intake of sulphur amino acids may be related to chronic disease outcomes in humans."

Richie led a team that examined the diets and blood biomarkers of more than 11,000 participants from a national study and found that participants who ate foods containing fewer sulphur amino acids tended to have a decreased risk for cardiometabolic disease based on their bloodwork.

The team evaluated data from the Third National Examination and Nutritional Health Survey. They compiled a composite cardio-metabolic disease risk score based on the levels of certain biomarkers in participants' blood after a 10-16 hour fast including cholesterol, triglycerides, glucose and insulin.

"These biomarkers are indicative of an individual's risk for disease, just as high cholesterol levels are a risk factor for cardiovascular disease," Richie said. "Many of these levels can be impacted by a person's longer-term dietary habits leading up to the test."

Participants were excluded from the study if they reported having either congestive heart failure, heart attack or a reported change in diet due to a heart disease diagnosis. Individuals were also omitted if they reported a dietary intake of sulphur amino acids below the estimated average requirement of 15 mg/kg/day recommended by the Food and Nutrition Board of the National Academy of Medicine.

For a person weighing 132 pounds, food choices for a day that meet the requirement might include a medium slice of bread, a half an avocado, an egg, a half cup of raw cabbage, six cherry tomatoes, two ounces of chicken breast, a cup of brown rice, three quarters of a cup of zucchini, three tablespoons of butter, a cup of spinach, a medium apple, an eight inch diameter pizza and a tablespoon of almonds. Nutritionists collected information about participants' diets by doing in-person 24-hour recalls. Nutrient intakes were then calculated using the US Department of Agriculture Survey Nutrient Database.

After accounting for body weight, the researchers found that average sulphur amino acid intake was almost two and a half times higher than the estimated average requirement. Xiang Gao, associate professor and director of the nutritional epidemiology lab at the Penn State University and co-author of the study, suggested this may be due to trends in the average diet of a person living in the US.

"Many people in the US consume a diet rich in meat and dairy products and the estimated average requirement is only expected to meet the needs of half of healthy individuals," Gao said. "Therefore, it is not surprising that many are surpassing the average requirement when considering these foods contain higher amounts of sulphur amino acids."

The researchers found that higher sulphur amino acid intake was associated with a higher composite cardiometabolic risk score after accounting for potential confounders like age, sex and history of diabetes and hypertension. They also found that high sulphur amino acid intake was associated with every type of food except grains, vegetables and fruit.

"Meats and other high-protein foods are generally higher in sulphur amino acid content," said Zhen Dong, lead author on the study and College of Medicine graduate. "People who eat lots of plant-based products like fruits and vegetables will consume lower amounts of sulphur amino acids. These results support some of the beneficial health effects observed in those who eat vegan or other plant-based diets."

Dong said that while this study only evaluated dietary intake and cardiometabolic disease risk factors at one point in time, the association between increased sulphur amino acid intake and risk for cardiometabolic disease was strong. She said the data supports the formation of a prospective, longitudinal study evaluating sulphur amino acid intake and health outcomes over time.

"Here we saw an observed association between certain dietary habits and higher levels of blood biomarkers that put a person at risk for cardiometabolic diseases," Richie said. "A longitudinal study would allow us to analyse whether people who eat a certain way do end up developing the diseases these biomarkers indicate a risk for."

Abstract
Background: An average adult American consumes sulfur amino acids (SAA) at levels far above the Estimated Average Requirement (EAR) and recent preclinical data suggest that higher levels of SAA intake may be associated with a variety of aging-related chronic diseases. However, there are little data regarding the relationship between SAA intake and chronic disease risk in humans. The aim of this study was to examine the associations between consumption of SAA and risk factors for cardiometabolic diseases.

Methods: The sample included 11,576 adult participants of the Third National Examination and Nutritional Health Survey (NHANES III) Study (1988–1994). The primary outcome was cardiometabolic disease risk score (composite risk factor based on blood cholesterol, triglycerides, HDL, C-reactive protein (CRP), uric acid, glucose, blood urea nitrogen (BUN), glycated hemoglobin, insulin, and eGFR). Group differences in risk score by quintiles of energy-adjusted total SAA, methionine (Met), and cysteine (Cys) intake were determined by multiple linear regression after adjusting for age, sex, BMI, smoking, alcohol intake, and dietary factors. We further examined for associations between SAA intake and individual risk factors.
Findings: Mean SAA consumption was > 2.5-fold higher than the EAR. After multivariable adjustment, higher intake of SAA, Met, and Cys were associated with significant increases in composite cardiometabolic disease risk scores, independent of protein intake, and with several individual risk factors including serum cholesterol, glucose, uric acid, BUN, and insulin and glycated hemoglobin (p < 0.01).

Interpretation: Overall, our findings suggest that diets lower in SAA (close to the EAR) are associated with reduced risk for cardiometabolic diseases. Low SAA dietary patterns rely on plant-derived protein sources over meat derived foods. Given the high intake of SAA among most adults, our findings may have important public health implications for chronic disease prevention.

Authors
Zhen Dong, Xiang Gao, Vernon M Chinchilli, Raghu Sinha, Joshua Muscat, Renate M Winkels, John P Richie

[link url="https://news.psu.edu/story/606065/2020/02/03/research/lower-protein-diet-may-lessen-risk-cardiovascular-disease"]Penn State University material[/link]

[link url="https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(19)30257-3/fulltext"]EClincal Medicine abstract[/link]

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