Nut Consumption and Prevention of Non-communicable Diseases: A Global Individual Participant Data Meta-analysis

NCDs account for 74% of global deaths, with 41% of these occurring prematurely in individuals aged 70 years and older. Type 2 diabetes, cardiovascular diseases (CVD), and cancer are among the major chronic diseases that affect people across countries and contribute to premature deaths. Notably, 77% of all NCD deaths and 86% of premature deaths occur in low- and middle-income countries. Reducing premature mortality from NCDs through preventive strategies, especially in low- and middle-income countries, was identified as a target in the Sustainable Development Goals from the World Health Organization. Additionally, as populations age, dementia is gaining recognition as a major public health concern. Dementia is among the leading causes of death and disability, with significant economic implications. Therefore, implementing preventive strategies to maintain cognitive function and delay cognitive decline is essential.

Adhering to a healthy diet is an effective and cost-efficient strategy to reduce NCDs. In fact, unhealthy diets have been linked to over 30% of NCDs and cognitive decline. Nuts are a common food component of several plant-based diets that have shown beneficial effects in preventing NCDs. Nuts are a diverse food group comprising a wide variety of oily kernels with a unique nutritional profile, including high amounts of protein, fiber, unsaturated fatty acids, vitamins, polyphenols, and other phytochemicals. These nutrients may contribute to their beneficial effects, such as antioxidant, anti-inflammatory, antihypertensive, anti-lipidemic, and anti-aging properties, as well as their potential positive influence on gut microbiota modulation.

Prior research has examined the impact of nuts on various health outcomes; however, many of these studies have focused on intermediate outcomes, obtained controversial results, and have been conducted primarily in European countries or the United States. Furthermore, the data has been analyzed using a variety of approaches, the studies were designed in different ways, and different covariates were added to the statistical models, potentially leading to inconsistencies and compromising the reliability of the comparison between studies. These inconsistencies emphasize the need for further research to elucidate the role of total nuts and specific types of nut consumption on the development of highly prevalent NCDs, as well as to allow the generalizability of the results across different countries and ethnicities.

In the NUTPOOL project, the objective is to address these knowledge gaps and provide a thorough assessment of the associations between total nuts and specific types of nuts in relation to a wide range of NCDs and mortality. The results from this global collaborative project will be representative of the worldwide populations, as they include prospective cohort studies from different countries, including not only American and European countries, but also Asian and Oceania. Additionally, the focus is on total and specific types of nuts, along with highly prevalent and relevant outcomes such as type 2 diabetes, cardiovascular disease (CVD), cancer, dementia, and mortality. To ensure consistency and reliability, the analyses will be standardized using Individual Participant Data (IPD) meta-analyses.

The selection of studies will be conducted after the identification of cohorts with data available on nut consumption. This identification process will be based on information comprehensively extracted from recently published systematic reviews and meta-analysis (SRMAs) on the subject, as well as through extensive research network. Invitations will be extended to as many eligible cohorts as possible to mitigate selection bias and ensure comprehensive participation in the study. Studies will be eligible for inclusion if they reported reliable nutrition data from a food frequency questionnaire (FFQ) regarding total nuts and/or specific nuts, along with well-defined data on at least two of the health outcomes. The study population had to be at least 1,000 adults, and the study had to span a minimum of five years or more of median follow-up, enabling time-dependent analyses.