A recent Scientific Reports study explored the association between dietary insulin index (DII) and dietary insulin load (DIL) with metabolic healthy (MH) status and the serum levels of brain-derived neurotrophic factor (BDNF) and adropin among the Iranian adult population.

Background

At present, the global prevalence of obesity and being overweight has increased significantly. Obesity has been associated with several health-related issues, including insulin resistance, hypertension, and hypertriglyceridemia. It must be noted that all obese individuals do not have metabolic abnormalities.

Globally, the prevalence of metabolically healthy adults with obesity is 7.27%, while metabolically unhealthy (MU) adults with normal weight are almost 20%. A recent study estimated the prevalence of metabolically unhealthy normal weight (MUNW) among the adult Iranian population to be 17.2%.

Besides genetic factors, many factors, including cardio-respiratory fitness, lifestyle, chronic stress, and adipose tissue function, play important roles in determining MH status. Insulin resistance that induces chronic inflammation is also linked with MH status. Therefore, diets that increase blood sugar levels elevate the risk of insulin resistance. DII indicates the postprandial insulin secretion after ingestion of common food in comparison to an isoenergetic reference food. DIL provides the DII of each food and its energy.

BDNF belongs to a member of the neurotrophic growth family, which facilitates a reduction in the risk of type 2 diabetes mellitus (T2DM), cardiovascular disease (CVD), obesity, hyperglycemia, metabolic syndrome (MetS), and dyslipidemia. Furthermore, adropin is a short peptide hormone expressed in many organs, including the heart and liver, and has been associated with metabolic disorders. Interestingly, this protein is affected by dietary components.

Previous studies have established the link between DII and DIL with metabolic disorders, including T2DM and obesity. An elevated DIL increases the risk of insulin resistance. No population-based studies have been performed to evaluate how DII and DIL are linked with adropin and serum BDNF with regard to MH among Iranian adults.

About the study

This cross-sectional study invited a total of 600 adults in 2022 from Isfahan, an Iranian city. These participants were selected based on a multistage cluster random sampling method. To select the general adult population with different socioeconomic statuses, adults working in 20 schools, including teachers, principals, assistants, school managers, crews, and other staff were considered.

A total of 527 adults fulfilled the eligibility criteria and were finally considered in this study. Food frequency questionnaires (FFQ) were used to assess the long-term dietary intake of participants. The food insulin index (FII) was used to analyze insulin levels in participants after 2 hours of eating a 1000 kJ meal. FII of every food was obtained from previous investigations.

In this study, participants were divided into two groups, namely, MH and MU. Participants with two or more risk factors that include fasting glucose level ≥ 100 mg/dL, uantidiabetic drugs, abnormal HDL-c and serum triglyceride levels, systolic/diastolic blood pressure ≥ 130/85 mmHg, antihypertensive drugs, and C reactive protein (CRP) level > 90th percentile, were grouped under MU.

Study findings

The mean age of the participants was 42 years, and around 54% were men. Approximately 43% of the cohort was MU. This study observed that adherence to a diet with high DII increased the odds of MU in the study population. However, no significant association between DIL and metabolic health status was observed.

A higher DII was linked with increased blood pressure, while moderate DIL was significantly associated with hypertriglyceridemia. Notably, no significant association between DII and DIL with adropin and serum BDNF was observed. These findings have been attributed to the insulinogenic effects of a diet with high DII and DIL. This diet type could enhance postprandial insulin and insulin resistance. 

Individuals with normal weight or with obesity/overweight are recommended to reduce consumption of food with high DII. This will elevate diet quality and, subsequently, decrease metabolic disease burden and improve quality of life. Consumption of foods, such as refined grains, sugar, potatoes, and desserts, which influence insulin response must be avoided or restricted. 

In line with the results of the current study, a previous study reported a significant association between DII and insulin resistance, and higher DIL was linked with an increased risk of insulin resistance. Contradictory findings of this study with previous studies could be due to differences in participants' age range, study design, meal preparation in different societies, and varied assessment tools used for analysis.

Conclusions

This study also has some limitations, including the use of self-administered FFQ for dietary assessment, which increases the risk of misclassifications and biases. There is a possibility of the presence of unknown or unmeasured confounders that could impact the results. Furthermore, causality could not be determined due to the cross-sectional nature of the study. 

Despite the limitations, this study highlighted the association between DIL and DII with metabolic health status and adropin and BDNF in the Iranian adult population. A greater DII increases the risk of hypertension and MU. Interestingly, no relation was found between DIL and metabolic health. 

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.