Diet alone not the sole culprit: Unraveling the complexities of metabolic disease rise in the U.S.

By Dr. Sanchari Sinha Dutta, Ph.D.Jun 19 2023

In a study published in the journal PharmaNutrition, scientists have explored the long-term impact of Western diet and lifestyle factors on the risk of metabolic disease in the United States.

Study: Trends in nutrition, lifestyle, and metabolic disease in the United States from 1900 onwards. Image Credit: nobeastsofierce / Shutterstock

Background

The prevalence of metabolic syndrome is sharply increasing worldwide. The disease is characterized by high blood glucose (hyperglycemia), abnormal lipid profile (dyslipidemia), high blood pressure (hypertension), and large waist circumference (central obesity). Individuals with metabolic syndrome are at higher risk of developing type 2 diabetes and cardiovascular disease.

Besides genetic risk factors, poor diet and lack of physical activity are the major causes of metabolic syndrome. Excessive intake of high-calorie foods can trigger the onset of this disease by inducing insulin resistance, chronic inflammation, and hormone secretion. Evidence shows that diet, exercise, and body mass index (BMI) can trigger metabolic syndrome by altering gut microbiota composition and function.

In this epidemiological study, scientists have evaluated the trends in diet, lifestyle, and metabolic disease in the United States from 1900 onwards.

Study design

The information on dietary composition and lifestyle factors for adult US residents was collected from published literature and publicly available sources.

Regarding dietary composition, daily intake of protein, fat, carbohydrate, and added sugar was analyzed. Regarding lifestyle factors, percentages of life expectancy, urbanization (proportion of US adults residing in urban regions), and exercise (proportion of US adults performing 150–300 minutes of moderate-intensity or 75–150 minutes of vigorous-intensity activity per week) were analyzed.

Regarding the prevalence of metabolic syndrome, the proportion of US adults having at least three of the major symptoms of the disease (hyperglycemia, dyslipidemia, hypertension, and central obesity) was analyzed. Since metabolic syndrome is developed through a gradual accumulation of symptoms over time, life expectancy was included in the analysis as a proxy for aging.

To calculate the prevalence until 1950, when the term “metabolic syndrome” was not coined, data on related metabolic conditions, including obesity, prediabetes, and diabetes, were included in the analysis.

Important observations

The study findings revealed a significant increase in the intake of protein, fat, carbohydrate, and added sugar between 1900 and 2020. Specifically, the intake of protein, carbohydrates, fat, and added sugar increased by 114%, 116%, 151%, and 343% in 2020, respectively.

A similar increase in lifestyle factors, including urbanization, exercise, and life expectancy, was noticed over time. Urbanization increased from 40% in 1900 to almost 80% in 2020. Similarly, the average life expectancy increased from 48 years in 1900 to 79 years in 2020.

An increase in exercise frequency was observed only in the 21^st century. The proportion of US adults meeting the US guidelines for exercise increased from 15% in 2000 to 23% in 2020.

Considering the current daily recommended intake of macronutrients in the US, the findings revealed that the intake of protein, carbohydrates, and fat remained higher than the recommended values throughout the study period (1900 – 2020). The intake of added sugar was below the recommended value in 1900. However, the intake increased by 2.5 times over the recommended value in 2020.

Comparison between nutrient intake and metabolic disease prevalence

The intake of macronutrients showed a declining or stabilized pattern in recent years (2000 – 2022). However, a sharp increase in the prevalence of metabolic syndrome, obesity, and diabetes was observed throughout the study years. In 2020, the prevalence of metabolic conditions was estimated to be 38%, 52%, and 37%, respectively.

The correlation analysis between studied variables indicated that obesity is not associated with the intake of protein, fat, carbohydrate, and added sugar. In contrast, a significant association was observed between the intake of macronutrients and added sugar and the prevalence of diabetes. The prevalence of metabolic syndrome showed no significant association with protein intake.

While life expectancy showed significant associations with all three metabolic conditions, exercise was found to be associated with metabolic syndrome and obesity.

Study significance

The study finds no significant association between nutrient intake and the prevalence of metabolic disease in the United States, except for diabetes, which shows preliminary correlations with macronutrient and added sugar intake.

Compared to the increase in macronutrients and added sugar intake, a much higher induction in metabolic disease prevalence has been noticed between 1900 and 2020. The scientists suggest that an amplifying factor might be involved in the dose-response relationship between diet and metabolic disease.   

The study also finds some associations between life expectancy and exercise with metabolic disease prevalence. Given the effects of these factors on gut microbiota composition, scientists recommend that future studies investigate to what extent these external factors can influence the development of metabolic disease.