Dietary acid load is positively associated with insulin resistance: a population-based study

Diabetes mellitus (DM) and cardiovascular disease (CVD) are among the biggest causes of death and health expenses worldwide. A higher dietary acid load (DAL) is associated with chronic low-grade metabolic acidosis, and may increase the risk of insulin resistance (IR), DM, hypertension, and CVD mortality. However, the association between DAL and IR still lacks population-based studies to confirm laboratory findings.

This is a population-based observational study including a sample of 545 individuals aged 25-64 years from Florianópolis (Southern Brazil) who participated in the EpiFloripa cohort study. All diet variables were obtained through two 24-h Food Recalls adjusted to obtain an estimate of habitual food consumption. DAL was measured by Potential Renal Acid Load (PRAL) and Net Endogenous Acid production (NEAP). Fasting blood samples were obtained from all participants. The primary outcome was IR, which was estimated by HOMA-IR. Secondary outcomes included HOMA-β, glycosylated hemoglobin, and fasting blood glucose and insulin. Multiple linear regression models adjusted for sociodemographics, lifestyle, and clinical variables were used for analysis, with exposure and outcome variables standardized as Z-scores to allow comparability of the results.

The mean PRAL and NEAP in the sample were 16.9 ± 4.8 and 66.1 ± 7.1 mEq/day, respectively. The average HOMA-IR score was 2.4 ± 1.6. In adjusted analyses, PRAL was positively associated with HOMA-IR, fasting insulin, and fasting blood glucose (p-value <0.05 in all cases), but not with HOMA-β or glycated hemoglobin. NEAP also showed a direct-trend relationship with HOMA-IR and fasting insulin, but not with fasting blood glucose or the other outcomes. The strongest association was between PRAL and HOMA-IR (β, 0.20; 95% CI, 0.06-0.35).

A higher DAL was consistently associated with higher IR and insulin levels but not with other glycaemic parameters. Apparently, β-pancreatic cells function is not affected by DAL in this population. This is the first study that describes the DAL in a population-based sample of adults in Latin America and in a middle-income country population. Further longitudinal and interventional studies are required to establish a better causal effect between DAL and IR.