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What is the relationship between adherence to dietary guidelines/recommendations or specific dietary patterns, assessed using an index or score, and risk of type 2 diabetes?

Conclusion

There is limited evidence that adherence to a dietary pattern rich in fruits, vegetables, legumes, cereals/whole grains, nuts, fish, and unsaturated oils, and low in meat and red meat and high-fat dairy, assessed using an index or score, is associated with decreased risk of type 2 diabetes.
 

Grade

III – Limited

 

Key Findings

  • Among  included studies there was variation in the types of indices or scores used, without a preponderance of studies with any one index related to either risk of type 2 diabetes or fasting blood glucose and insulin resistance, making it difficult to draw overarching conclusions related to a specific dietary pattern.
  • The different scores showed varied predictability of incident type 2 diabetes:
    • In European populations, adherence to the MDS was associated with reduced incidence of type 2 diabetes.  Additionally, among women in a U.S. cohort, the AHEI had similar relationships.
    • For other scores considered, such as the Total Diet Score, German Food Pyramid Index, DQI-2005, as well as the MDS in a U.S. population, there was no relationship between diet quality and incidence of type 2 diabetes.
    • One study assessing the DASH score in a U.S. population showed an association in Whites but not in Blacks. A second study showed no association between DQI-2005 and T2D incidence in Black or White young adults.
  • The different scores showed varied association with glucose tolerance and/or insulin resistance:
  • For impaired fasting glucose or insulin resistance, there was some agreement with the MDS and MSDPS being protective for the measures examined.
  • There were mixed findings for Total Diet Score, DQI-2005, and an authors’ a priori score. For the mixed results, the findings differed by sex, type of intermediate outcome examined, and race/ethnicity.

Evidence Summary Overview

Description of the Evidence
A total of 11 studies met the inclusion criteria for this systematic review on dietary patterns and incident type 2 diabetes (T2D). The body of evidence consisted primarily of epidemiological studies, with nine prospective cohort studies and two randomized controlled trials (RCTs). In terms of study quality, nine of the studies were of positive quality and two were of neutral quality. The studies were carried out between the years 2006 and 2013. Sample sizes ranged from 187 to 769 subjects for the RCTs and from 822 to as many as 80,029 participants (1 study <1,000, 4 studies >1,000, 3 studies >10,000 for the prospective cohort studies.). Study duration ranged from 3 months to 1 year for the RCTs, while the prospective cohort study follow-up times ranged from 4.4 to 20 years.
 
Population: The prospective cohort studies were primary prevention studies of general populations; most were conducted with healthy adults who were free of T2D or cardiovascular disease (CVD). The two RCTs were conducted in adults with elevated chronic disease risk: one reported on the Prevencion con Dieta Mediterranea (PREDIMED) trial of older adults at increased CVD risk (Estruch, 2006); the other study reported on men with metabolic syndrome (Jacobs, 2009). In prospective cohort studies with adult participants, age ranges spanned from 18 to 84 years. One study focused on young adults with an age range of 18 to 30 years from the Coronary Artery Risk Development in Young Adults Study (CARDIA) cohort (Zamora, 2011). One of the studies examined only women (Fung, 2007) and one study examined only men (Jacobs, 2009). Some studies that examined men and women assessed health outcomes in men and women separately (Abiemo, 2012; von Ruesten, 2010). Three studies specifically identified the race/ethnic subgroups of their cohort. The CARDIA study examined equal numbers of Black and White young adults (Zamora, 2010); the Multi-Ethnic Study of Atherosclerosis (MESA) examined Black, White, Hispanic, and Chinese adults (Abiemo, 2012); and the Insulin Resistance Atherosclerosis Study (IRAS) examined Blacks and Hispanics separately from Whites (Liese, 2009).
 
Taken together, studies were conducted in the United States, Spain, Norway, Germany, and Australia and included many large, well-characterized cohorts.
  • Five reports were from prospective cohort studies conducted in the United States: the CARDIA study (Zamora, 2010), the Framingham Offspring and Spouse (FOS) study (Rumawas, 2009), the Insulin Resistance Atherosclerosis Study (IRAS) study (Liese, 2009), the MESA study (Abiemo, 2012), and the Nurses’ Health Study (NHS) (Fung, 2007).
  • Two reports were from studies conducted in Spain: the Seguimiento Universidad de Navarra (SUN) Study (Martínez-González, 2008) and the PREDIMED Study (Estruch, 2006).
  • The remaining reports were from countries represented in only one study: Australia (Blue Mountain Eye Study, Russell, 2012), Germany (EPIC-Potsdam, von Ruesten, 2010), and Norway (Oslo Diet and Exercise Study [ODES], Jacobs, 2009).
 
Dietary Exposure: Methodologically, diet exposure was assessed by adherence to a hypothesis-based dietary pattern, defined using a numerical scoring system. Two major categories of a priori dietary patterns were identified: (1) a dietary pattern based on a Mediterranean-style diet and (2) a dietary pattern based on dietary guidelines recommendations. Only one study examined adherence to a DASH diet and one study used the authors’ own a priori diet score.
 
The most common dietary intake assessment method was the use of food frequency questionnaires (FFQs), which were validated for foods in the respective locations of the study population. Many prospective cohort studies assessed dietary intake only at baseline.
  • Four studies examined health outcomes related to adherence to a Mediterranean-style dietary pattern. Of these studies, three used the Mediterranean Diet Score (MDS) of Trichopoulou or a close variant of the MDS (Abiemo, 2012; Estruch, 2006; Martínez-González, 2008) and one study used the Mediterranean-style dietary pattern score (MSDPS) (Rumawas, 2009).
  • Four studies examined health outcomes related to adherence to dietary guidelines recommendations based on the United States, German, or Australian dietary guidelines, including the alternate Healthy Eating Index (AHEI) (Fung, 2007), the Diet Quality Index (DQI)-2005 (Zamora, 2011), the Total Diet Score (Gopinath, 2013), and the German Food Pyramid Index (von Reusten, 2010).
  • One study examined health outcomes related to adherence to a DASH diet (Liese, 2009).
  • One study examined health outcomes associated with the authors’ own a priori diet scores (Jacobs, 2009).

Qualitative Synthesis of the Collected Evidence

Themes and Key Findings 

Health Outcomes: The studies in this body of evidence examined (1) T2D incidence or (2) impaired glucose tolerance or insulin resistance.
Type 2 Diabetes Incidence: This category included studies that assessed T2D incidence as the primary outcome of the study (tables 4-C-I-1 and 4-C-I-2). Subjects who met the American Diabetes Association or World Health Organization criteria for fasting blood glucose or oral glucose tolerance, or were taking hypoglycemic medication, were considered having incident T2D. Eight studies examined the association between adherence to a dietary pattern and T2D incidence (Abiemo, 2012; Fung, 2007; Gopinath, 2013; Liese, 2009; Martínez-González, 2008; Rossi, 2013; von Ruesten, 2010; Zamora, 2011).
 
The results of prospective cohort studies that examined incident T2D outcomes were mixed. Several studies assessed Mediterranean-style diets. One study conducted in Spain with the Seguimiento Universidad de Navarra (SUN) cohort found a favorable association between the Mediterranean Diet Score (MDS), the original Mediterranean diet score of Trichopoulou, and risk of T2D. Overall, a 2-point increase in MDS was associated with a 35 percent reduction in risk of T2D (Martínez-González, 2008). Another study, conducted in Greece with the EPIC-Greece cohort, also assessed the relationship between the MDS and T2D. In this second Mediterranean population, adherence to the MDS was also favorably associated with risk of T2D (Rossi, 2013). Conversely, a study conducted in the United States, using the authors’ MedDiet Score with the Multi-Ethnic Study of Atherosclerosis (MESA) cohort found no association between their MedDiet Score and T2D incidence in the total population, in men or women, or in racial/ethnic subgroups (Abiemo, 2012). Taken together, studies in Mediterranean populations that assessed adherence to the traditional MDS found an inverse association with T2D incidence; however, the one study that examined a multi-ethnic U.S. population, found no association.
 
Studies that assessed a dietary guidelines-related pattern were also mixed. In the United States, a study that assessed adherence to the alternate HEI (AHEI) found a favorable association between AHEI score and risk of incident T2D in women in the Nurses’ Health Study (Fung, 2007). In a second U.S. cohort, Liese and colleagues found adherence to their DASH score was associated with markedly reduced odds of T2D in Whites in the Insulin Resistance Atherosclerosis Study (IRAS), but not in the total population or in the Black and Hispanic subgroup, ~60 percent of IRAS cohort (Liese, 2009). In a third U.S. cohort in the Coronary Artery Risk Development in Young Adults (CARDIA) study, there was no association between DQI-2005 score and T2D incidence in the total population or in Blacks or Whites (Zamora, 2011). Lastly, studies in Australia using a Total Diet score in the Blue Mountains Eye Study (BMES) and Germany using a German Food Pyramid Index with the EPIC-Potsdam cohort found no association between these scores and incident T2D (Gopinah, 2013; von Ruesten, 2010). The AHEI was predictive of T2D risk in a population of U.S. women, and a DASH score was predictive in Whites, but not Blacks or Hispanics in a U.S. population. With regard to incident T2D, the DQI-2005 was not predictive in that there was no association in the total population, Blacks, or Whites in young adults in the United States. Other studies in Australia and Germany, using dietary guidelines-related scores found no association between respective scores and incident T2D.
 
Impaired Glucose Tolerance and/or Insulin Resistance: This category included studies that assessed fasting blood glucose, fasting blood insulin, oral glucose tolerance, or insulin resistance using the Homeostasis Model Assessment–Insulin Resistance (HOMA-IR) equation (tables 4-C-I-1 and 4-C-I-2). These outcomes were measured by standard clinical and laboratory methods. Five studies examined adherence to a dietary pattern and intermediate outcomes related to glucose tolerance and/or insulin resistance: two RCTs (Estruch, 2006; Jacobs, 2009) and three prospective cohort studies (Gopinath, 2013; Rumawas, 2009; Zamora, 2011).
 
The two RCTs were conducted in at-risk populations in Europe. An early report from the PREDIMED trial showed that a Mediterranean diet decreased fasting blood glucose, fasting insulin, and HOMA-IR scores in a Spanish population at-risk for CVD (Estruch, 2006). In the Oslo Diet and Exercise Study (ODES), increased adherence to the authors’ a priori diet score resulted in decreased fasting insulin and insulin after a glucose challenge, but not fasting glucose, in Norwegian men with metabolic syndrome (Jacobs, 2009). Results from prospective cohort studies were consistent in showing a favorable association between diet score and fasting glucose, fasting insulin or HOMA-IR (Rumawas, 2009; Zamora, 2011) with the exception of one study that found the association with fasting glucose only in men (Gopinath, 2013). It is difficult to assess food components across these studies, as numerous different scores were used, without a compelling number of studies using any one score or index.
 

Qualitative Assessment of the Collected Evidence

Quality and Quantity
Quality assessment of the studies included in this systematic review involved determining the validity of each study by examining the scientific soundness of study design and execution, as well as the risk of bias in the findings related to outcomes. The preponderance of the evidence consisted of positive quality studies (9 out of 11 studies). In terms of quantity of studies, there were a moderate number of studies with varied results in T2D outcomes.
 
Consistency
When comparing across the large well-characterized cohorts for incident T2D, the findings were mixed. There were no significant findings from the CARDIA or MESA studies; mixed findings from the IRAS cohort, although a notable T2D risk reduction in Whites; and some protective findings from Nurses’ Health Study (NHS). Overall, it was challenging to synthesize the results because of the number of indices examined, including MDS, variations on MDS, and a large number of unique dietary guidelines-related scores. Overall, there were not a compelling number of studies with any one index. Of the eight studies that examined diabetes incidence, seven different scores were used and only the MDS was used in two studies. Of the five studies that assessed glucose tolerance and insulin resistance, all used different scores.
 
Impact
This body of evidence directly addressed the exposures and health outcomes of interest for the systematic review; eight studies measured the endpoint outcome, incident T2D. When associations were found between a dietary pattern and incident T2D, they were clinically meaningful. However, a number of the included studies did not find association. 
 
Generalizability/External Validity
Overall, the prospective cohort studies on incident T2D were from large, well-characterized cohorts from the United States and Europe, so potentially generalizable if the findings had been consistent. The two RCTs were conducted with at-risk subjects, therefore, not generalizable to the healthy U.S. population, but relevant to the large at-risk population in the United States.
 

Limitations of the Evidence

For several of the studied indices, there was only one analysis, including for the Total Diet Score, German Food Pyramid Index, DQI-2005, AHEI, and DASH. Mediterranean-style scores were the only dietary pattern measures/indices used in more than one study. It was a challenge to compare results across the studies because some of the scores were not validated and used different diet assessment tools. Furthermore, the number of study participants and number of type 2 diabetes cases varied widely. Additionally, sample size was cited by authors who examined racial/ethnic subgroups as a potential limitation in their ability to detect significant associations related to incident T2D in the MESA, CARDIA, and IRAS cohorts.
 

Research Recommendations

Overall, there is a need for more coordinated studies involving multiple U.S. cohorts, all of which examine the same scores or indices assessed in a standardized way. In addition, more analysis of key subpopulation groups, with sufficient sample sizes, would further inform policy in this area.
 

Abbreviations:

Dietary pattern scores: Mediterranean Diet: Mediterranean Diet Score (MDS), Mediterranean Style Dietary Pattern Score (MSDPS), Dietary Guidelines-related: Healthy Eating Index (HEI), Alternate HEI (AHEI), Diet Quality Index (DQI), Dietary Approaches to Stop Hypertension (DASH)
 
Cohorts or Trials:Blue Mountains Eye Study (BMES), Coronary Artery Risk Development in Young Adults (CARDIA), European Prospective Investigation into Cancer and Nutrition (EPIC), Framingham Offspring and Spouse (FOS), Insulin Resistance Atherosclerosis Study (IRAS), Multi-Ethnic Study of Atherosclerosis (MESA), Nurses’ Health Study (NHS), Seguimiento Universidad de Navarra (SUN)
 

Table 4-C-I-1 Summary of Findings
Table 4-C-I-2 Overview Table: Type 2 Diabetes

 

REFERENCES

  1. Abiemo EE, Alonso A, Nettleton JA, Steffen LM, Bertoni AG, Jain A, Lutsey PL. Relationships of the Mediterranean dietary pattern with insulin resistance and diabetes incidence in the Multi-Ethnic Study of Atherosclerosis (MESA). Br J Nutr. 2012 Aug 30:1-8. [Epub ahead of print] PubMed PMID: 22932232.
  2. Estruch R, Martínez-González MA, Corella D, Salas-Salvadó J, Ruiz-Gutiérrez V, Covas MI, Fiol M, Gómez-Gracia E, López-Sabater MC, Vinyoles E, Arós F, Conde M, Lahoz C, Lapetra J, Sáez G, Ros E; PREDIMED Study. Investigators. Effects of a Mediterranean-style diet on cardiovascular risk factors: a randomized trial. Ann Intern Med. 2006 Jul 4;145(1):1-11.
  3. Fung TT, McCullough M, van Dam RM, Hu FB. A prospective study of overall diet quality and risk of type 2 diabetes in women. Diabetes Care. 2007 Jul;30(7):1753-7. Epub 2007 Apr 11. PubMed PMID: 17429059.
  4. Gopinath B, Rochtchina E, Flood VM, Mitchell P. Diet quality is prospectively associated with incident impaired fasting glucose in older adults. Diabet Med. 2013 Jan 10. doi: 10.1111/dme.12109. [Epub ahead of print] PubMed PMID: 23301551.
  5. Jacobs DR Jr, Sluik D, Rokling-Andersen MH, Anderssen SA, Drevon CA. Association of 1-y changes in diet pattern with cardiovascular disease risk factors and adipokines: results from the 1-y randomized Oslo Diet and Exercise Study. Am J Clin Nutr. 2009 Feb;89(2):509-17. Epub 2008 Dec 30. PubMed PMID: 19116328.
  6. Liese AD, Nichols M, Sun X, D'Agostino RB Jr, Haffner SM. Adherence to the DASH Diet is inversely associated with incidence of type 2 diabetes: the insulin resistance atherosclerosis study. Diabetes Care. 2009 Aug;32(8):1434-6. Epub 2009 Jun 1. PubMed PMID: 19487638; PubMed Central PMCID: PMC2713612.
  7. Martínez-González MA, de la Fuente-Arrillaga C, Nunez-Cordoba JM, Basterra-Gortari FJ, Beunza JJ, Vazquez Z, Benito S, Tortosa A, Bes-Rastrollo M. Adherence to Mediterranean diet and risk of developing diabetes: prospective cohort study. BMJ. 2008 Jun 14;336(7657):1348-51. Epub 2008 May 29. PubMed PMID: 18511765; PubMed Central PMCID: PMC2427084.
  8. Rossi M, Turati F, Lagiou P, Trichopoulos D, Augustin LS, La Vecchia C, Trichopoulou A. Mediterranean diet and glycaemic load in relation to incidence of type 2 diabetes: results from the Greek cohort of the population-based European Prospective Investigation into Cancer and Nutrition (EPIC). Diabetologia. 2013 Aug 22. [Epub ahead of print] PMID: 23975324
  9. Rumawas ME, Meigs JB, Dwyer JT, McKeown NM, Jacques PF. Mediterranean-style dietary pattern, reduced risk of metabolic syndrome traits, and incidence in the Framingham Offspring Cohort. Am J Clin Nutr. 2009 Dec;90(6):1608-14. Epub 2009 Oct 14. PubMed PMID: 19828705; PubMed Central PMCID: PMC3152203.
  10. von Ruesten A, Illner AK, Buijsse B, Heidemann C, Boeing H. Adherence to recommendations of the German food pyramid and risk of chronic diseases: results from the EPIC-Potsdam study. Eur J Clin Nutr. 2010 Nov;64(11):1251-9. Epub 2010 Aug 18. PMID: 20717136.
  11. Zamora D, Gordon-Larsen P, He K, Jacobs DR Jr, Shikany JM, Popkin BM. Are the 2005 Dietary Guidelines for Americans Associated With reduced risk of type 2 diabetes and cardiometabolic risk factors? Twenty-year findings from the CARDIA study. Diabetes Care. 2011 May;34(5):1183-5. Epub 2011 Apr 8. PubMed PMID: 21478463; PubMed Central PMCID: PMC3114488.



Research Design and Implementation
For a summary of the Research Design and Implementation results, click here.
Worksheets
Abiemo EE, Alonso A, Nettleton JA, Steffen LM, Bertoni AG, Jain A, Lutsey PL. Relationships of the Mediterranean dietary pattern with insulin resistance and diabetes incidence in the Multi-Ethnic Study of Atherosclerosis (MESA). Br J Nutr. 2012 Aug 30: 1-8.

Estruch R, Martínez-González MA, Corella D, Salas-Salvadó J, Ruiz-Gutiérrez V, Covas MI, Fiol M, Gómez-Gracia E, López-Sabater MC, Vinyoles E, Arós F, Conde M, Lahoz C, Lapetra J, Sáez G, Ros E; PREDIMED Study Investigators. Effects of a Mediterranean-style diet on cardiovascular risk factors: a randomized trial. Ann Intern Med. 2006; 145(1): 1-11.

Fung TT, McCullough M, van Dam RM, Hu FB. A prospective study of overall diet quality and risk of type 2 diabetes in women. Diabetes Care. 2007 Jul; 30(7): 1,753-1,757.

Gopinath B, Rochtchina E, Flood VM, Mitchell P. Diet quality is prospectively associated with incident impaired fasting glucose in older adults. Diabet Med. 2013 Jan 10. doi: 10.1111/dme.12109.

Jacobs DR Jr, Sluik D, Rokling-Andersen MH, Anderssen SA, Drevon CA. Association of one-year changes in diet pattern with cardiovascular disease risk factors and adipokines: Results from the one-year randomized Oslo Diet and Exercise Study. Am J Clin Nutr. 2009 Feb; 89(2): 509-517.

Liese AD, Nichols M, Sun X, D'Agostino RB Jr, Haffner SM. Adherence to the DASH Diet is inversely associated with incidence of type 2 diabetes: The insulin resistance atherosclerosis study. Diabetes Care. 2009 Aug; 32(8): 1,434-1,436.

Martínez-González MA, de la Fuente-Arrillaga C, Nunez-Cordoba JM, Basterra-Gortari FJ, Beunza JJ, Vazquez Z, Benito S, Tortosa A, Bes-Rastrollo M. Adherence to Mediterranean diet and risk of developing diabetes: Prospective cohort study. BMJ. 2008 Jun 14; 336(7,657): 1,348-1,351.  

Rossie M, Turati F, Lagiou P, Trichopoilos D, Augustin LS, La Veechia C, Trichopoilos A. Mediterranean diet and glycaemic load in relation to incidence of type 2 diabetes: Results from the Greek cohort of the population-based European Prospective Investigation into Cancer and Nutrition (EPIC). Diabetologia. 2013 Nov; 56(11): 2,405-2,413.

Rumawas ME, Meigs JB, Dwyer JT, McKeown NM, Jacques PF. Mediterranean-style dietary pattern, reduced risk of metabolic syndrome traits, and incidence in the Framingham Offspring Cohort. Am J Clin Nutr. 2009; 90(6): 1,608-1,614.

von Ruesten A, Illner AK, Buijsse B, Heidemann C, Boeing H. Adherence to recommendations of the German food pyramid and risk of chronic diseases: results from the EPIC-Potsdam study. Eur J Clin Nutr. 2010 Nov; 64(11): 1,251-1,259.

Zamora D, Gordon-Larsen P, He K, Jacobs DR Jr, Shikany JM, Popkin BM. Are the 2005 Dietary Guidelines for Americans associated with reduced risk of type 2 diabetes and cardiometabolic risk factors? Twenty-year findings from the CARDIA study. Diabetes Care. 2011 May; 34(5): 1,183-1,185.