Previous studies have identified a link between metabolic acidosis caused by diet and cardiometabolic conditions like hypertension and type 2 diabetes. A recent study investigated a link between dietary acid load and all-cause mortality. Researchers found that high dietary acid load may impact mortality in a Japanese population.
Chronic illnesses factor significantly into causes of death around the world, and many of these conditions are influenced by modifiable lifestyle factors, such as diet. Acid-base balance is the product of dietary intake; studies have shown that diet-induced metabolic acidosis is linked to cardiometabolic abnormalities, like hypertension and type 2 diabetes. Eating a diet rich in acidogenic foods (meat, fish, cheese) and low in alkaline foods (fruit and vegetables) can cause the body to produce endogenous acid. Potential renal acid load (PRAL) and net endogenous acid production (NEAP), calculated from dietary intake, are values which can be used to estimate dietary acid load. In the study performed by Akter and colleagues published in the American Journal of Clinical Nutrition, the authors examined the link between food intake and acid production and the risk of total mortality. The authors note that this is the first study to examine the association between dietary acid load score and total/cause-specific death in an Asian population.
The Japan Public Health Center-based study was launched in 1990 and 1993, for cohorts I and II, respectively. Cohort I included residents between 40 and 59 years of age from 5 Japanese public health centres, while cohort II included residents between 40 and 69 years of age from another set of 6 public health centres. Researchers conducted self-administered questionnaires at baseline and 5-and 10-year follow up time points. Information collected at these three survey points included: medical history and health-related lifestyle variables, such as, smoking, drinking and dietary habits. The authors found that the questionnaire conducted at the 5 year follow up contained better information on food intake, and therefore used this data as baseline for the analyses. The food-frequency questionnaire (FFQ) assessed average intake of 147 food and beverage items over the previous year, and provided a snapshot of the daily intake of most foods.
PRAL scores were calculated based on intake of the following nutrients: protein, phosphorus, potassium, calcium and magnesium. NEAP scores were calculated using protein and potassium intake. Negative PRAL scores were indicative of alkaline values and positive PRAL scores indicated acidic values. The authors’ initial population set was 102, 366 participants who had completed the second FFQ survey. Of these, 7761 were excluded because they reported a history of cancer, stroke, ischemic heart disease (IHD) or chronic liver disease, either at the baseline or on the second survey. 950 participants with energy intakes at the extremely high or low ranges were also excluded, as were 1177 who had unusual dietary load scores. Analyses were performed on a total of 92, 478 participants.
The results demonstrated that a higher dietary acid load score (using the PRAL and NEAP scores) is associated with the risk of total mortality, cardiovascular disease (CVD) in particular. This risk remained constant even when adjustments were made for BMI, diabetes, hypertension and dyslipidemia, meaning the association could not be fully attributed to these conditions. PRAL values were also associated with cerebrovascular disease. The authors found no association between dietary acid load and cancer mortality in the study population in general, or when accounting for smoking status.
According to the authors, the strengths of the study lay in it’s design: the large number of participants, long follow-up period and the use of a validated FFQ. The fact that there was only a baseline assessment of dietary intake, which may not represent the long-term eating habits of participants was listed as a limitation. Also, the inclusion of individuals with a history of diabetes, hypertension or dyslipidemia, who may have been under medical advice to make dietary changes, may have influenced the study results, although the authors performed the calculations excluding these individuals and the results remained constant. The authors mention an absence of biomarkers to validate the PRAL or NEAP scores as another limitation. Additionally, despite adjusting for factors that may have influenced the scores, they mention that the effects of other existing and unmeasured variables cannot be entirely ruled out and they speculate whether the observed association between dietary acid load and mortality is due to acid-base balance changes or the consumption of nutrients that are linked with dietary acid load. Lastly, the generalizability of the study to the general population may be affected as the study participants were middle-age to older Japanese individuals. The study’s findings that suggest high dietary acid load may impact mortality in this Asian populations may be of importance to those concerned with longevity. Given that longevity may be influenced by an individual’s acid-base balance, people may be able to decrease the risk of death, particularly by CVD, by controlling their dietary acid-base intake.
Written By: Sara Alvarado BSc, MPH