Global and local diet popularity rankings, their secular trends, and seasonal variation in Google Trends data

Objectives: The Internet has become the main source of health-related information including nutrition. The aim of this study was to rank the most popular diets among Google users globally and regionally in addition to secular and seasonal trends in the years 2004 to 2019. Methods: We used Google Trends (GT) to identify and analyze course over time and regional interest of 47 topics related to diets. We analyzed secular trends using the Seasonal Mann-Kendall test and seasonal variation using time-series decomposition. The topic Mediterranean diet (MedD) was used as a benchmark. We calculated the interest of all topics in proportion to the relative search volume (RSV) of MedD. Results: Globally, Google users were particularly interested in veganism (19.54 times higher than MedD), vegetarianism (15.09 times higher than MedD), and gluten-free diet (11.11 times higher than MedD). Veganism was the most frequently searched diet type in 23 countries followed by vegetarianism (14), ketogenic diet (7), and low-carbohydrate diet (7). Whereas an increase of RSV over time was observed for 23 diets, a decrease was noted for 20. The most dynamic increase was found for FODMAP (6.12 RSV/year), gluten-free diet (5.95 RSV/year), and raw veganism (5.72 RSV/year). Sharp declines concerned negative-calorie food (-4.34 RSV/year), macrobiotic diet (-3.89 RSV/year), and cabbage soup diet (-3.50 RSV/year). The interest in most diets falls in December but peaks in January. Conclusion: Veganism, vegetarianism, and gluten-free diet attract the largest public interest globally. Both secular trends and seasonal variation shape the ever-changing landscape of diet popularity. GT holds promise as a valuable tool in local and international nutrition research. (C) 2020 Elsevier Inc. All rights reserved.