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

Google users’ interest in diet

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Global and local diet popularity rankings, their secular trends and seasonal variation in Google Trends data úydecka PhD , ´ Miko laj Kaminski MD , Karolina Skonieczna-Z Jan Krzysztof Nowak PhD , Ewa Stachowska PII: DOI: Reference:

S0899-9007(20)30042-3 https://doi.org/10.1016/j.nut.2020.110759 NUT 110759

To appear in:

Nutrition

Received date: Revised date: Accepted date:

9 October 2019 1 January 2020 10 January 2020

úydecka PhD , ´ Please cite this article as: Miko laj Kaminski MD , Karolina Skonieczna-Z Jan Krzysztof Nowak PhD , Ewa Stachowska , Global and local diet popularity rankings, their secular trends and seasonal variation in Google Trends data, Nutrition (2020), doi: https://doi.org/10.1016/j.nut.2020.110759

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Highlights



Public interest in various diets can be investigated using Google Trends



Vegan, vegetarian and gluten-free diets seem to be most popular at this time



Interest in most diets is subject to mark annual variation



Dynamics of interest in less-established diets are often remarkably high

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

Short title: Google users' interest in diet

Authors (first name, surname) Miko?aj Kami?ski1 MD, Karolina Skonieczna-?ydecka1 PhD, Jan Krzysztof Nowak2 PhD, Ewa Stachowska1 Professor Affiliations 1 Department of Human Nutrition and Metabolomics, Pomeranian Medical University, Szczecin, Poland 2 Department of Pediatric Gastroenterology and Metabolic Diseases, Poznan University of Medical Sciences, Poznan, Poland

ORCID: MK - 0000-0002-4394-0460 KS? - 0000-0002-3430-9079 JKN - 0000-0003-0953-2188 ES- 0000-0002-4009-1977 Corresponding author: Miko?aj Kami?ski Department of Human Nutrition and Metabolomics, Pomeranian Medical University, Broniewskiego 24 71-460 Szczecin, Poland [email protected] phone/fax: +48 (91) 441 4806

Abstract Background The Internet has become the main source of health-related information including nutrition We aimed to rank the most popular diets among Google users globally and locally as well as secular and seasonal trends in the years 2004-2019. Methods We used Google Trends (GT) to identify and analyze course over time and regional interest of (n = 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" (MD) was used as a benchmark. We calculated the interest of all topics in proportion to the Relative Search Volume (RSV) of MD. Results Globally, Google users were particularly interested in "Veganism" (19.54 [times higher than MD]), "Vegetarianism" (15.09), and "Gluten-free diet" (11.11). “Veganism" was the most frequently searched in 23 countries followed by "Vegetarianism" (14), "Ketogenic diet" (7), and "Lowcarbohydrate" 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), "Glutenfree 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. Google Trends holds promise as a valuable tool in local and international nutrition research. Keywords: Google Trends, Internet, diet, veganism, nutrition, ranking

Introduction

Health professionals have long appreciated the role of adequate nutritional patterns in the patient's recovery process and general well-being of a man [1]. Today’s so-called dietary excess era in public health nutrition [2] is intricately linked to superfast socio-cultural and technological changes. It resulted in an unprecedented increase in prevalence of non-communicable diseases, which is paradoxically accompanied by an epidemic of real malnutrition [3,4]. Every year new dietary approaches are being introduced to modulate gut microbiota, reduce blood pressure, control glycemia, diminish the influence of reactive oxygen species, excess energy expenditure, or exert other putatively beneficial influence [1]. Some of them, like the Mediterranean Diet (MD) [5–7], have a strong translational background, whereas other lack it. At the same time, the practice of using dietetic services has just begun to gain popularity around the world, so for the average citizen, the default source of knowledge about nutrition is the Internet [8]. It is estimated that up to 80% of the Internet users perceive the Web health-related information as reliable [9]. Up to 85% of individuals may use the Internet to search for health and/or nutrition information [10]. The personal motivation to seek for diet-related information include 1) an interest in choosing, preparing and cooking healthy meals, 2) an increase in knowledge of a diet recommended by a specialist 3) a need to change the current lifestyle, motivated by personal values and often influenced by trends (e.g., veganism) 4) a necessity of weight reduction, for instance in the pre-holiday period [8]. We must be aware that the diets are subjected to all market rules. Consequently, it means that its popularity may be influenced by values other than merit such as efficient marketing. This raises the question of whether diets with scientifically proven properties are being searched for by potential consumers and whether they can compete with "trendy" diets. The ladder might undergo "evolutionary mimicry" - only apparently changing (e.g., by adopting a new name) thus adapting to the evolution of the market.

We assume that Internet searches associated with diets may reflect the global interest in different nutritional approaches, as well as their rise and fall. Such information is valuable because it allows to investigate the global and local popularity of the diets in order to establish the position of evidence-based diets in the Internet discourse. We aimed to explore Google Trends data to answer two fundamental questions: (1) which diets attract the most public interest globally and locally, (2) whether Internet interest in diets was subject to secular trends and/or seasonal variation in the years 2004-2019.

2. Material & Methods

2.1. Data collection

Google Trends (GT) is an freely accesible tool dedicated to estimating relative search volume (RSV) of queries done in Google search engine (https://trends.google.com/trends/). RSV is an index of search volume adjusted to the number of Google users in a given geographical area. RSV ranges from 0-100, where the value of 100 indicates the peak of popularity (100% of popularity in given period and location) and 0 complete disinterest (0%) [11]. The RSV is adjusted to a number of Google users. The engine enables to analyze a chosen phrase in a selected region and period since January 2004. GT allows to compare up to five terms at the same time. In this case, RSV is adjusted and RSV = 100 represents the highest popularity of one of the chosen phrases. GT may qualify analyzed phrases as "search term" or "topic". Search terms are literally typed words, while topics may be proposed by GT when tool recognizes phrases related to popular queries. Topics enable to easily compare the given term between countries. For example search term "bird" will be analyzed by GT literally thus RSV will be the highest in English-speaking countries, while topic "bird" will include all queries associated with the query in all available languages. We collected the Google data from 1 January 2004 to date of collection (18 July 2019). We identified a total n = 47 topics related to specific diet: "Mediterranean diet", "5:2 diet", "Alkaline diet", "Atkins diet", "Blood type diet", "Cabbage soup diet" , "The Cambridge diet", "Cookie diet", "DASH diet", "Diabetic diet", "FODMAP", "Fruitarianism", "Gluten-free diet", "Grapefruit diet", "Hay diet", "High-protein diet", "Intermittent diet", "Juice fasting", "Ketogenic diet", "Liquid diet", "Low-carbohydrate diet", "Low-fat diet", "Low-fiber diet", "Low-glycemic diet", "Low-protein diet", "Low-sodium diet", "Macrobiotic diet", "Master Cleanse", "Mayo Clinic diet", "Negativecalorie food", "Okinawa diet", "Ovo-lacto vegetarianism", "Ovo-vegetarianism", "Paleolithic diet", "Pescetarianism", "Plant-based diet", "Raw veganism", "South Beach diet", "Specific carbohydrate

diet", "Sport nutrition", "Vegan nutrition", "Veganism" , "Vegetarianism", "Very low-calorie diet", "Volumetrics diet", "Whole30 diet", and "Zone diet". The term "Fermentable Oligo-, Di-, Monosaccharides And Polyols" ("FODMAP") is related to diet with limiting fermentable saccharides and polyols in food thus may correspond the RSV of this dietary pattern ("FODMAP diet" does not exist as a topic). We did not take general topics like “diet" or “healthy diet" into account. We typed all chosen topics separately (non-adjusted data) as well as all compared with the topic "Mediterranean diet" (adjusted data). Only two topics were compared at once. The Mediterranean diet topic was chosen arbitrarily as a benchmark. Firstly, due to good evidence on the beneficial effects of this dietary pattern [6]. Secondly, the ratio of the interest of the others diets to the “Mediterranean diet" topic in the analysis ranged from 0.01 to 20.00. We found that this magnitude of the proportions could be easily understood by a reader. We collected data of interest over time and by region. We excluded countries with low search volumes using GT option. We used modified Nuti et al. protocol template to report in detail search conditions and inputs (Supplementary Table 1) [11].

2.2. Data processing and statistical analysis

We adhered to the data processing protocol previously described in the study analyzing data generated by GT [12]. To fully analyze the data we set "0.5" to all RSV described by GT as "<1%). and "0.1" to all RSV equals "0". We used non-adjusted data on interest over time to analyze the time series (Table 1.). We performed the Seasonal Mann-Kendall test using R 3.6.1 (R Foundation, Vienna, Austria) Kendall package version 2.2 to search for the presence of a significant secular trend of time series [13]. A p-value below 0.05 was considered a significant difference. For all significant secular trends, we performed a univariate linear regression to estimate slope expressed as changes of RSV per year in the analyzed period. To analyze seasonal variation we fitted an exponential smoothing state-space model with Box-Cox transformation, autoregressive-moving average errors, trend and seasonal components (TBATS) to the time trend using forecast package

version 8.9 of R [14]. We extracted the seasonal component of time series using the Seasonal Decomposition of Time Series by Loess (Local Polynomial Regression Fitting). We defined yearly amplitude as the difference between the maximal and minimal seasonal components of time series. We used non-adjusted interest by region data to establish countries with the highest RSV for each topic (Table 1). In this analysis RSV = 100 represents a country with the highest number of generated queries related to a specific diet. In the case of countries with less than five topics with RSV above 0, we shortened the list. We used adjusted data of interest over time to calculate the mean proportion between adjusted RSV of all diets to "Mediterranean diet" (Table 1) in the analyzed period. The topic “Mediterranean diet" is represented by “1.00". The adjusted data of compared break by region represents the proportion between RSV of topics chosen a diet and “Mediterranean diet" in a specific country (Table 1). The sum of both RSV in a given region equals 100. It allows to relatively compare which searches related to the chosen topics are more often typed in the country. We calculated the most frequent diet-related topics for all countries with significant search volume. Since the proportion of the popularity of the topics was always adjusted to the topic "Mediterranean diet" we set RSV of "Mediterranean diet" in a given country to 50. The dataset is available in Mendeley Data [15].

Table 1 Use of data generated by Google Trends. Interest over time

Region Interest by region

Non-adjusted data

Time series analysis: yearly trends, seasonal variation (Table 4, Figures 3A,3B)

Countries with the highest RSV of dietrelated topics (Table 3) Compared breakdown by region

Adjusted data

Proportion of mean RSV to "Mediterranean diet" (Table 2) RSV – Relative Search Volume

List of the most common diet-related topics in a specific country (Figures 1-2, Supplementary Table 2)

3. Results 3.1. Global diet popularity ranking

Globally, Google users were most interested in (data expressed as a proportion to "Mediterranean diet") Veganism (19.54), Vegetarianism (15.09), Gluten-free diet (11.11), Low-carbohydrate diet (9.80), and Ketogenic diet (6.27). (Table 2).

Table 2 Popularity of diet-related topics in proportion to “Mediterranean diet" (adjusted data; Relative Search Volume [RSV] over time).

Rank

Diet

Proportion of mean RSV to Mediterranean diet

1.

Veganism

19.54

2.

Vegetarianism

15.09

3.

Gluten-free diet

11.11

4.

Low-carbohydrate diet

9.80

5.

Ketogenic diet

6.27

6.

Atkins diet

5.86

7.

Paleolithic diet

4.92

8.

Low-fat diet

3.58

9.

South Beach diet

3.30

10.

High-protein diet

2.37

11.

Very low-calorie diet

2.21

12.

Diabetic diet

1.39

13.

Low-glycemic diet

1.24

14.

Alkaline diet

1.16

15.

Macrobiotic diet

1.12

16.

Mediterranean diet

1.00

17.

Cabbage soup diet

0.95

18.

Zone diet

0.95

19.

Master Cleanse

0.92

20.

Low-sodium diet

0.82

21.

Whole30 diet

0.81

22.

Sports nutrition

0.73

23.

Intermittent diet

0.71

24.

Juice fasting

0.68

25.

Blood type diet

0.62

26.

Vegan nutrition

0.58

27.

FODMAP

0.56

28.

Hay diet

0.50

28.

DASH diet

0.50

30.

Specific carbohydrate diet

0.45

31.

Liquid diet

0.42

32.

Plant-based diet

0.35

32.

Pescetarianism

0.35

34.

Low-fiber diet

0.27

35.

Negative-calorie food

0.26

36.

Raw veganism

0.25

37.

Grapefruit diet

0.19

38.

Mayo Clinic diet

0.19

39.

5:2 diet

0.18

40.

Low-protein diet

0.16

41.

Fruitarianism

0.13

42.

Ovo-lacto vegetarianism

0.12

42.

The Cambridge diet

0.12

44.

Cookie diet

0.10

45.

Ovo-vegetarianism

0.06

46.

Volumetrics diet

0.05

47.

Okinawa diet

0.04

RSV – Relative Search Volume

3.2. Local diet popularity ranking

From 250 regions, Google reported 59 countries to have significant search volume. We visualized the most frequently searched diet for all countries (Figure 1,2). "Veganism" was the diet with the highest interest in n = 23 countries, “Vegetarianism" in n = 14, both “Ketogenic" and “Lowcarbohydrate" diets in n = 7, “Gluten-free diet" in n = 2, and , “5:2", “Blood type", “Cabbage soup", “Mediterranean", “Paleolithic" in n =1 country. The five most common diet-related topics in each country are presented in Supplementary Table 2.

Figure 1 World map of the most popular diet-related topics in each country.

Figure 2 Europe map of the most popular diet-related topics in each country.

For all topics, we presented five countries with the highest worldwide RSV (Table 3). "Mediterranean diet" was particularly popular in southern Europe countries. As many as three from five top countries with the highest interest in "Blood type diet" included African countries. "Cabbage soup diet" generated interest mainly in Balkan countries. Information associated with "Cookie", "Gluten-free", "High-protein", "Juice fasting", "Low-fat", "Plant-based", and "Very lowcalorie" diets were mainly searched by Google users from Western English-speaking countries. "FODMAP" was particularly popular in Scandinavian countries and on the Antipodes. "Fruitarianism" was mainly searched by Google users from Central Europe, while "Hay diet" by users from Central and Eastern Europe and the "Low-carbohydrate diet" from Central and Northern Europe. "Low protein diet" was frequently searched by users from Southeast Asian islands.

Table 3

Five countries with the highest non-adjusted RSV by region of all topics related to diet.

Diet Mediterranean diet 5:2 diet Alkaline diet Atkins diet Blood type diet Cabbage soup diet The Cambridge diet Cookie diet DASH diet Diabetic diet FODMAP Fruitarianism Gluten-free diet Grapefruit diet Hay diet High-protein diet Intermittent diet Juice fasting Ketogenic diet Liquid diet Low-carbohydrate diet Low-fat diet Low-fiber diet Low-glycemic diet Low-protein diet Low-sodium diet Macrobiotic diet Master Cleanse

Top five countries with highest RSV (RSV) Italy (100), Greece (90), Cyprus (81), Spain (76), Puerto Rico (63) Sweden (100), Taiwan (60), Norway (44), Australia (42), Macao (40) Hungary (100), Trinidad & Tobago (83), Jamaica (82), Australia (39), Austria (39) Malaysia (100), United States (65), United Kingdom (58), Ireland (46), New Zealand (42) Ghana (100), South Africa (75), Ethiopia (72), Malta (70), Italy (49) Montenegro (100), Serbia (98), South Africa (83), Bosnia & Herzegovina (79), Trinidad & Tobago (63) Isle of Man (100), Czechia (42), Sweden (41), Jersey (35), Slovakia (35) Australia (100), United States (70), Canada (53), United Kingdom (18), New Zealand (15) Croatia (100), Sweden (86), Greece (82), Bosnia & Herzegovina (69), United States (47) Taiwan (100), United States (86), South Africa (80), Puerto Rico (79), Hong Kong (69) Australia (100), Norway (90), New Zealand (84), Finland (64), Denmark (54) Germany (100), Italy (100), Czechia (91), Austria (90), Switzerland (77) Australia (100), New Zealand (100), Canada (83), United States (80), Ireland (64) Malaysia (100), South Africa (95), Ireland (89), United States (80), Singapore (78) Bulgaria (100), Germany (31), Austria (30), Ukraine (20), Moldova (19) Australia (100), South Africa (86), Ireland (79), United Kingdom (75), New Zealand (72) Philippines (100), Singapore (82), United States (75), Canada (74), Australia (70) United States (100), Australia (78), Canada (74), Ireland (67), New Zealand (66) United States (100), Canada (95), Sudan (93), New Zealand (90), Australia (72) United States (100), South Africa (85), Brazil (67), Paraguay (67), Argentina (62) Sweden (100), Norway (59), Finland (36), Germany (30), Austria (26) Ireland (100), United Kingdom (89), Australia (81), Canada (65), United States (61) France (100), Réunion (93), United States (39), Australia (31), Belgium (26) Trinidad & Tobago (100), Canada (67), United States (67), Singapore (43), Austria (36) Taiwan (100), United States (56), Australia (49), Philippines (43), Singapore (41) United States (100), Canada (51), Australia (33), South Korea (28), Ireland (25) Costa Rica (100), Japan (70), Portugal (38), Croatia (34), Czechia (33) United States (100), Jamaica (88), Canada (84), South Africa (42), Philippines

Mayo Clinic diet Negative-calorie food Okinawa diet Ovo-lacto vegetarianism Ovo-vegetarianism

(36) Indonesia (100), United States (15), Romania (13), South Africa (9), Canada (8) United States (100), Australia (92), Canada (91), Singapore (81), New Zealand (77) France (100), Australia (72), Singapore (61), Canada (56), New Zealand (49) Jamaica (100), Finland (63), Uruguay (50), Sweden (43), Australia (38)

Jamaica (100), Sweden (36), Australia (23), Singapore (22), New Zealand (19) Paleolithic diet Hungary (100), New Zealand (94), Australia (91), United States (73), Canada (54) Pescetarianism Jamaica (100), Australia (82), United Kingdom (82), New Zealand (78), United States (78) Plant-based diet United States (100), Canada (81), New Zealand (81), Australia (72), Ireland (47) Raw veganism Romania (100), Iran (58), Australia (24), Slovakia (20), New Zealand (19) South Beach diet United States (100), Poland (57), Canada (56), Netherlands (44), Philippines (31) Specific Trinidad & Tobago (100), Ireland (68), Slovakia (60), Czechia (49), Australia carbohydrate diet (38) Sports nutrition Austria (100), Brazil (26), Spain (25), Ireland (21), Germany (20) Vegan nutrition Réunion (100), Canada (65), France (62), Ireland (50), Italy (50) Veganism Australia (100), Israel (94), New Zealand (86), Canada (83), Austria (80) Vegetarianism Taiwan (100), Singapore (50), Netherlands (32), Austria (29), Germany (29) Very low-calorie Australia (100), United Kingdom (91), United States (88), Ireland (82), New diet Zealand (77) Volumetrics diet Germany (100), United States (96), Canada (62), Switzerland (61), Australia (46) Whole30 diet United States (100), Canada (34), Czechia (22), Australia (15), New Zealand (15) Zone diet Italy (100), Mexico (30), United States (19), Spain (18), Chile (17) RSV – Relative Search Volume

3.3. Time series analysis

Secular trends We observed a diversity of the course over time of analyzed diets. Simultaneously, n = 23 dietrelated topics presented increase over time, while n = 20 topics presented decrease over time. Interest in several topics (5:2 diet, The Cambridge diet, Cookie diet, Juice fasting, Master Cleanse, Paleolithic diet, Raw veganism) presented fad pattern (Table 4, Figures 1A-B). The interest does not change significantly in the case of Low-protein, Low-sodium diets, and Ovo-lacto vegetarianism.

The RSV most dynamically increases over the observational period for topics "FODMAP" (6.12 RSV/year), "Gluten-free diet" (5.95 RSV/year) and "Raw veganism" (5.72 RSV/year), while RSV the most rapidly decreases for "Negative-calorie food" (-4.34 RSV/year), "Macrobiotic diet" (-3.89 RSV/year), and "Cabbage soup diet" (-3.50 RSV/year).

Seasonal variation The interest of all topics except "Fruitarianism" revealed seasonal variation (Table 4). RSV of 31 diet-related topics peaks in January and the lowest number of queries related to 35 diets was observed in December. The highest yearly amplitude was noted for “Very-low calorie" (40.71 RSV), “the Cambridge" (37.37 RSV) and “High-protein" diets, while lowest for “Atkins diet" (4.44 RSV),

“Veganism"

(4.52

RSV),

and

“Ketogenic

diet"

(5.02

RSV).

Table 4 Time series analysis of non-adjusted topics related to diet. Diet

Mediterranean diet 5:2 diet Alkaline diet Atkins diet Blood type diet Cabbage soup diet The Cambridge diet Cookie diet DASH diet Diabetic diet

Seasonal MannKendall test

Slope [RSV/year]

TBATS (seasonality present, period [month])

tau = 0.23; *** tau = 0.41; *** tau = 0.53; *** tau = 0.92; *** tau = 0.74; *** tau = 0.94; *** tau = 0.22; ***

0.64; **

YES, 12

1.88; ***

YES, 12

1.50; ***

YES, 12

-1.32; ***

YES, 12

-2.33; ***

YES, 12

-3.50; ***

YES, 12

-0.72; *

YES, 12

-1.36; ***

YES, 12

0.44; *

YES, 12

-2.96; ***

YES, 12

tau = 0.44; *** tau = 0.15; ** tau = -

Month with the highest seasonal component [RSV] January (9.22) January (4.89) January (4.93) January (2.35) January (7.28) January (14.12) January (13.12)

Month with the lowest seasonal component [RSV]

Seasonal component amplitude [RSV]

December (5.93) December (5.24) December (9.95) December (2.09) December (9.24) December (8.82) December (24.25)

15.15

January (5.81) January (23.09) March

November (3.92) December (5.79) December (-

9.74

10.13 14.88 4.44 16.51 22.94 37.37

28.88 13.06

FODMAP Fruitarianism Gluten-free diet Grapefruit diet Hay diet High-protein diet Intermittent fasting Juice fasting Ketogenic diet Liquid diet Lowcarbohydrate diet Low-fat diet Low-fiber diet Low-glycemic diet Low-protein diet Low-sodium diet Macrobiotic diet Master Cleanse Mayo Clinic diet Negativecalorie food Okinawa diet Ovo-lacto vegetarianism Ovovegetarianism Paleolithic diet Pescetarianism

0.88; *** tau = 0.96; *** tau = 0.36; *** tau = 0.90; *** tau = 0.87; *** tau = 0.85; *** tau = 0.50; *** tau = 0.91; *** tau = 0.30; *** tau = 0.84; *** tau = 0.30; *** tau = 0.60; *** tau = 0.97; *** tau = 0.40; *** tau = 0.91; *** tau = 0.04; NS tau = 0.07; NS tau = 0.96; *** tau = 0.62; *** tau = 0.51; *** tau = 0.94; *** tau = 0.57; *** tau = 0.06; NS tau = 0.56; *** tau = 0.55; *** tau = 0.93;

6.12; ***

YES, 12

1.18; ***

NO, -

5.95; ***

YES, 12

-3.05; ***

YES, 12

-3.00; ***

YES, 12

1.46; ***

YES, 12

3.94; ***

YES, 12

1.93; ***

YES, 12

2.62; ***

YES, 12

0.68; ***

YES, 12

1.86; ***

YES, 12

-3.19; ***

YES, 12

1.07; ***

YES, 12

-2.92; ***

YES, 12

-

YES, 12

-

YES, 12

-3.89; ***

YES, 12

-2.80; ***

YES, 12

-1.68; ***

YES, 12

-4.34; ***

YES, 12

-1.37; ***

YES, 12

-

YES, 12

1.99; ***

YES, 12

4.13; ***

YES, 12

5.24; ***

YES, 12

(4.28) January (1.73) -

8.77) December (4.25) -

December June (-2.67) (3.06) January October ((11.72) 6.83) January December ((9.5) 10.19) January December ((11.57) 22.19) January December ((2.69) 3.67) January November ((8.79) 7.78) January December ((2.78) 2.24) June (4.39) December (8.1) January December ((9.6) 9.66) January (12.64) February (2.83) January (5.32) March (4.37) January (10.98) March (2.91) January (13.46) January (17.48) January (7.34) March (4.93) May (4.39) March (12.71) January (8.39) January

December (9.95) December (10.87) December (6.23) December (8.31) December (9.02) December (5.6) November (8.48) December (7.71) December (7.96) December (4.94) December (5.23) July (-11.06) December (5.76) December (-

5.98 5.73 18.55 19.69 33.76 6.36 16.57 5.02 12.49 19.25

22.6 13.71 11.55 12.69 20.00 8.50 21.94 25.19 15.30 9.87 9.61 23.77 14.16 10.58

Plant-based diet Raw veganism South Beach diet Specific carbohydrate diet Sports nutrition Vegan nutrition Veganism

*** tau = 0.87; *** tau = 0.74; *** tau = 0.93; *** tau = 0.22; ***

3.49; ***

YES, 12

(6.39) July (2.93)

5.72; ***

YES, 12

July (3.08)

-2.06; ***

YES, 12

-0.80; ***

YES, 12

January (3.03) October (3.75)

tau = -2.45; *** YES, 12 April 0.67; *** (2.88) tau = 0.76; 3.63; *** YES, 12 January *** (4.49) tau = 0.96; 5.38; *** YES, 12 December *** (2.4) Vegetarianism tau = 0.55; 1.81; *** YES, 12 January *** (3.96) Very lowtau = 0.14; 0.29; NS YES, 12 January calorie diet * (21.83) Volumetrics tau = -0.89; *** YES, 12 May (5.56) diet 0.70; *** Whole30 diet tau = 0.88; 2.59; *** YES, 12 January *** (12.51) Zone diet tau = -3.41; *** YES, 12 January 0.97; *** (3.83) RSV – Relative Search Volume *** p < 0.001, ** p < 0.01; * p < 0.05; NS - non-significant

4.19) December (2.85) November (5.42) December (2.5) June (-3.25)

5.77 8.50 5.54 7.00

December (9.24) December (5.07) June (-2.12)

12.12

June (-4.68)

8.64

December (18.87) December (2.76) November (4.44) December (5.88)

40.71

9.56 4.52

8.33 16.95 9.71

(3a)

(3b) Figure 3A, 3B Relative Search Volume over time of each analyzed diet-related topics. Non-adjusted data.

4. Discussion

This study employed GT to measure public interest in specific diets globally. The data revealed the highest overall interest in Veganism, Vegetarianism, and Gluten-free diet. There were also some differences in regional interest in diets. Overall, the most dynamic increase was noted for FODMAP diet, and the strongest decrease for Negative-calorie food. Sufficient evidence was also found of a seasonal variation of interest in diets. GT allowed to analyze differences in interest over time proving to be a valuable tool in nutrition research.

Global interest We found that “Veganism" and “Vegetarianism" were of greatest interest to Google users overall. The data on the popularity of diets among the worldwide population is scarce. In 2006 Harris Interactive reported that 1.4% of Americans followed vegan diets [16], but in 2012 the rate increased to 2%. The same year the percentage of vegetarians was 5% [17]. Simultaneously, interest in “Veganism" and “Vegetarianism" rose in the last years. However, search volume might be partially generated by curious Google users without motivation to follow these nutrition approaches. This may explain the relatively low interest in other no-meat diet-related topics such as "Vegan nutrition". We assume that the growing evidence of positive health properties of abovementioned diets [18], and public discourse on animal rights generates the growing interest in diets excluding meat and other animal-derived products [19]. The third most popular diet among Google users was the Gluten-free diet (GFD). Previously, Laszkowska reported that GFD was the most popular search term among different types of diets in the United States in the years 2005-2015 [20]. GFD, originally used only for the treatment of celiac disease, has recently been adapted for non-celiac gluten sensitivity [21,22]. Although the epidemiological data state that celiac disease may affect about 1% of people worldwide [23], the global prevalence of non-celiac gluten sensivity may be as high as 15% [24,25] - hence the increasing interest in this diet is not surprising. A Nielsen survey from 2015 which covered 60 countries reported that 21% of respondents rated products being "gluten-free" as a "very important" product property when making a food purchasing decision [26]. Although GFD was perceived as a fad [27], the visualized trend of RSV of the diet seems to slowly increases to date of collection. Consequently, GFD seems to be an example of the overlap between the epidemiological and partly fashion trend. Popular media have been promoting GFD as a part of the general healthy lifestyle. Meanwhile, when GFD is introduced with no medical reasons it may cause loss of dietary fiber, as well as deficiency of minerals and vitamins and under some circumstances heavy metal exposure [28].

The fourth, fifth, and sixth most popular diet-related topics all over the world were “Lowcarbohydrate", “Ketogenic", and “Atkins" diets which represent the same dietary approach and thus may be an example of “mimicry". The low-carbohydrate diet may serve as an integral part of the treatment of pharmacoresistant epilepsy [29]. Moreover, there is growing evidence on the beneficial effects of diets with the low-carbohydrate rate on weight loss [30,31], type 2 diabetes, polycystic ovary syndrome, and other diseases [32,33]. In the Nielsen report, 24% of the respondents declared that “low/no carbohydrates" food is perceived as “very important" in purchasing decisions [26]. To our best knowledge, there is a lack of data on the prevalence of following the low-carbohydrate diet. The Nielsen report and our results may suggest that the number of consumers may be considerable. Interestingly, low-carbohydrate diet is predominantly searched for in Scandinavia and this has been linked to a conflict between dietitians and health professionals from the National Food Agency [34]. The global interest in the topic “Mediterranean diet" was moderate and the topic was the most commonly searched by Google users from Cyprus. However, the yearly growth of interest was significant but slow. Similar trends were noted for Dietary Approaches to Stop Hypertension (DASH diet). Both diets are recommended due to good properties on cardiovascular risk [6,35,36]. The disparity between good scientific background and the limited interest of Google users suggests that professionals should engage in the promotion of this diet among potential recipients predisposed to benefit from it. The topics: “Blood type", “Cabbage soup", and “Paleolithic" diets were the most commonly searched by Google users from respectively: Ethiopia, Montenegro, and Hungary. Only the paleolithic diet is characterized by a good scientific foundation [37]. The blood type diet does seem scientifically justified to some extent [38], and the cabbage soup diet is based on a non-scientific bestseller [39]. We assume that these diets could be particularly popular in these countries due to local popularization of these diets by media, Internet content and published books. The analysis of the trends from the recent years suggests that we observe emerging interest in ‘FODMAP", “Intermittent diet" as well as topics related with no-meat diets: “Plant-based diet"

and “Pescetarianism". The FODMAP diet was shown to efficiently relieve both inflammatory bowel disease [40] and highly prevalent irritable bowel syndrome symptoms such as abdominal pain and bloating [41], and by this fact it gains popularity among Google users. Intermittent diet (also known as intermittent fasting), which is perceived as anti-aging, has also gained popularity within the last years. It was reported to reduce weight, stabilize lipid concentrations, reduce inflammation and present anti-aging properties [42,43]. Interestingly, besides the pandemia of obesity, hypercholesterolemia, and diabetes the interest in topics “Diabetic", “Low-fat", and “Low-glycemic diet" decreased over the analyzed period. This may be caused by the recent reports of beneficial properties and the popularization of the other types of diets. For his reason, individuals with metabolic syndrome might abandon a classic dietary approach for the new, attractive dietary patterns [44,45]. Surprisingly, the Okinawa diet (OD) principles are not widely searched in the Internet. OD approach is thought to be one of the most effective anti-inflammatory and life-extending diets [46]. We assume that this is an example of a scientific fad - known in the community of health-related professionals, but short-lived in the eyes of the public. We presented the country-level results indicating local interest in diet-related topics. A valid interpretation of these results would require a profound knowledge of local publications, the media coverage and Internet discourse. We would like to expose the value of GT in nutrition research and encourage the readers to consider using it in their own investigations. Course over time Interestingly, RSV of most of the topics peaks in January which might be associated with New Year’s resolutions of weight loss. This hypothesis seems plausible, but this phenomenon was not previously reported. The lowest interest in most of the diet-related topics was observed in December or November. This may be explained by focusing on preparation for Christmas and winter holidays and promises to stop using the Internet during celebration time. As Christmas-

related topics are researched, the relative interest in other fields decreases. Moreover, celebrating may cause to resign from healthy dietary pattern and to feast freely. This results in weight gain after a holiday period [47]. Furthermore, it was reported that diet may reveal seasonal variation: daily caloric intake increases during cold months [48]. The observed seasonal variation of interest in dietrelated topics may reflect changes of general interest in healthy nutrition and require professionals to motivate patients to maintain a healthy diet during November and December [49]. Nevertheless, New Year's resolutions seem to provide an excellent opportunity to influence setting new health goals, including calorie restriction. Nevertheless, the observation and the assumption should be verified in real-world studies. This is the first study analyzing global interest in specific types of diets using GT. We presented relative worldwide popularity of analyzed diets and trends over time. GT seems to provide a unique insight into Google users’ interest in nutrition. We found that diets vary in patterns of interest: some decrease or increase over time, some do not change significantly over time and other are fads. The popularity of diets on the Internet could potentially reflect the real prevalence of specific nutritional approaches in the society. Nevertheless, an association between the Internet traffic and real-world use of diets in a population should be investigated in epidemiological studies. Moreover, it is worth considering that more emphasis is put on the promotion of evidence-based diets in the Internet discourse [50]. The competition with fashionable diets without scientific foundation may require the effort from the professionals to provide the local community reliable nutrition information. Limitations The authors acknowledge several limitations of the study. Firstly, GT did not recognize as topics several important types of diet for instance MIND, Weight Watchers and Flat Belly diets. Therefore we analyzed the limited number of diets. Secondly, the market share of the Google search engine varies between the countries. For instance, in the United States, approximately 60-65% of Internet users seek information on Google while in European countries this rate exceeds 90% [51].

Therefore the results cannot be generalized to the Internet users in each country without a caution. Thirdly, GT allows only to compare up to five search terms simultaneously at the same time. Consequently, we could only compare the relative popularity of the topics. The use of the Mediterranean diet as a comparator was motivated by its stability and appropriate search volume. Fourthly, topics with relative low popularity could be highly sensitive to media clamor which may result in non-seasonal peaks of interest, for instance in the case of Okinawa diet and Ovo-lacto vegetarianism. Previously it was reported that women more frequently use the Internet to search for health-related information than men [52]. Moreover, younger people are more likely to seek information associated with health than older Internet users [53]. Therefore, we assume that interest in each diet might be mostly generated by a young and middle-aged population, mostly females. Because GT does not provide additional characteristics of users such as sex and age we cannot verify this hypothesis in this study In 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. Google Trends holds promise as a valuable tool in local and international nutrition research. Professionals should promote evidence-based diets in Internet discourse.

External funding None Conflict of interest None of authors declared any potential conflict of interests. Authors contribution Concept – MK, Data collection – MK, Statistical analysis – MK, Figures, and Tables – MK, Interpretation – MK, KSŻ, JN, ES, Draft preparation – MK, KSŻ, JN, ES, Critical review and final approval – MK, KSŻ, JN, ES.

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Graphical Abstract