Nutrition, Metabolism and Cardiovascular Diseases
The role of diet in the prevention of type 2 diabetes
Introduction
The increase in the prevalence of type 2 diabetes (henceforth, diabetes) across the world has become an important public health problem given that this disease ranks among the leading causes of blindness, renal failure and lower limb amputation, besides being a significant risk factor for coronary heart disease and stroke [1]. From recent data on the frequency of diabetes in different countries, a worldwide prevalence among adults aged 20–79 years increasing from 285 million in 2010 (6.4%) to 439 million in 2030 (7.7%) has been estimated [2].
There is compelling clinical trial evidence that diabetes can be prevented or its onset can be delayed by lifestyle interventions, thus it is critical to delineate which are the best dietary strategies [3], [4], [5], [6], [7]. The importance of diet in the context of diabetes medical nutrition therapy has been the topic of several reviews, but few have focused on diabetes prevention [8], [9]. Recently, Buyken et al. (2010) and Spence et al. (2010) reviewed the role of diet in the prevention of diabetes, with particular emphasis on carbohydrates, and Risérus et al. (2009) reviewed the role of dietary fats [10], [11], [12]. The present paper intends to be a comprehensive up-to-date review of epidemiologic and clinical trial evidence on nutrients, foods and dietary patterns as they relate to the prevention of diabetes, including discussion of the possible mechanisms of the reported associations.
Data for this review were obtained by searching Medline (PubMed) and the ISI Web of Science with the key words: “diabetes prevention and diet”, “diabetes prevention and nutrition”, “diabetes prevention and dietary patterns” or “diabetes prevention and lifestyle”. The criteria for selecting publications were that they reported the results of: a) prospective cohort studies, randomized clinical trials, or meta-analyses of studies with this design; b) studies published in a scientific journal in the database of the Science Citation Index or Medline between 1995 and 2010, and c) assessment of diabetes risk among study’s outcomes.
Clinical trial evidence from dietary interventions influencing intermediate markers of diabetes is reviewed as well. For this reason we have also selected relevant reports that shed light on the possible mechanisms whereby dietary components or food patterns might have a beneficial impact on the prevention of diabetes.
Expectably, studies provide different degrees of scientific evidence. According to the hierarchy of research designs, the results of randomized controlled trials are considered as providing the highest level of evidence, whereas observational studies are viewed as having less validity because they are reportedly amenable to various biases, including residual confounding. Among observational studies, the highest level of evidence can be obtained from large prospective cohorts with adequate control of confounders. The potential for bias is higher in case-control and cross-sectional studies. For this reason, a particular effort is made to differentiate the studies according to the hierarchy of their research designs.
Section snippets
Weight loss as the driving force to reduce the risk of diabetes
Excess body weight is the most important modifiable risk factor for the development of diabetes. The incidence of diabetes clearly rises as obesity prevalence increases [13]. In general, the relationship between BMI and diabetes is stronger for women than for men [14]. In the observational cohort of the Nurses’ Health Study (NHS), the single most important risk factor for diabetes was overweight and obesity [15]. Risk ratios for incident diabetes were 38.8 for individuals with BMI ≥ 35 kg/m2 and
Lifestyle in diabetes prevention
Several randomized clinical trials involving lifestyle changes with an outcome on incident diabetes that were conducted in individuals at high risk have been published [3], [4], [5], [6], [7]. The first was the Da Qing trial in China. In this study 577 individuals with IGT were randomized to dietary counseling, increased exercise, diet plus exercise, or control (general recommendations) [3]. The cumulative 6-year incidence of diabetes was significantly lower in the diet group (44%), the
The role of carbohydrates
Large observational studies have provided conflicting results, showing both positive and negative associations of total carbohydrate intake with diabetes risk [35], [36], [37], [38]. Instead, the quality of carbohydrates ingested may be of extreme importance in determining the ability to raise glucose levels, which depends to a great extent on its influence on gastrointestinal transit and the velocity of nutrient absorption, and the long-term risk of diabetes [10]. Four important qualitative
Importance of fat quantity
Because fat is the most energy-dense nutrient, the conventional dietary strategy for obesity and related conditions (i.e., diabetes) has been a low-fat diet (<30% of total energy). However, this concept has been contested as there is mounting evidence from observational studies that total dietary fat is not a risk factor for developing diabetes [71], [72], [73], [74].
Recent results of the large observational cohort of the NHS also suggest that a diet low in carbohydrate and high in protein,
Coffee and tea
Unexpectedly, a strong inverse association between coffee consumption and diabetes risk was reported in a large Dutch cohort (n = 117 111) [135]. Subsequently, other large observational studies have found similar and fairly consistent results. Two meta-analyses summarize the available information, which is based entirely on observational prospective studies, with no clinical trial evidence as yet. Using prospective information on 457 922 participants, the pooled estimate was that drinking 3–4
Dietary patterns
More important than isolated foods or nutrients, the study of complete dietary patterns represents the most adequate approach to assess the role of diet on the risk of diabetes. The assessment of whole dietary patterns has become instrumental in nutritional epidemiology. The rationale for this concept is that synergistic or antagonistic effects may exist between the different components of a food pattern [158].
Scores appraising adherence to a particular dietary pattern can integrate most of the
Diet, inflammation and diabetes
Similarly to atherosclerosis and other chronic disease, the diabetic state is associated with chronic, low-grade inflammation, particularly in adipose tissue, and inflammatory signals are known to disrupt insulin action and mediate insulin resistance in obesity [167], [168]. In this regard, epidemiologic data suggest that inflammatory biomarkers may serve as important indicators for the risk of diabetes and are, at the same time, predictors of cardiovascular events in both diabetic and
Conclusions
A healthy lifestyle is critical to prevent diabetes in the population and delay its onset in susceptible individuals. A prudent diet, physical exercise, and maintenance of an ideal body weight are essential lifestyle components, and weight loss in obesity is the main driving force in prevention. In agreement with the ADA’s current recommendations and the guidelines of the Diabetes and Nutrition Study Group of the European Association for the Study of Diabetes for treatment and prevention of
Acknowledgments
Funded in part by the Spanish Ministry of Health (Instituto de Salud Carlos III, Fondo de Investigaciones Sanitarias) projects PI051839, G03/140, RD06/0045, PI1001407. FEDER (Fondo Europeo de Desarrollo Regional). CIBERobn is an initiative of Instituto de Salud Carlos III, Spain.
References (200)
- et al.
Global estimates of the prevalence of diabetes for 2010 and 2030
Diabetes Res Clin Pract
(2010) - et al.
Prevention of type 2 diabetes by lifestyle intervention: a Japanese trial in IGT males
Diabetes Res Clin Pract
(2005) - et al.
Diabetes and nutrition study group (DNSG) of the European association for the study of diabetes (EASD). Evidence-based nutritional approaches to the treatment and prevention of diabetes mellitus
Nutr Metab Cardiovasc Dis
(2004) - et al.
Dietary fats and prevention of type 2 diabetes
Prog Lipid Res
(2009) - et al.
Relationship between obesity and incident diabetes in middle-aged and older Japanese adults: the Ibaraki Prefectural Health Study
Mayo Clin Proc
(2010) - et al.
Finnish diabetes prevention study group. Sustained reduction in the incidence of type 2 diabetes by lifestyle intervention: follow-up of the Finnish diabetes prevention study
Lancet
(2006) - et al.
The long-term effect of lifestyle interventions to prevent diabetes in the China Da Qing Diabetes Prevention Study: a 20-year follow-up study
Lancet
(2008) - et al.
Relation between changes in intakes of dietary fiber and grain products and changes in weight and development of obesity among middle-aged women
Am J Clin Nutr
(2003) - et al.
Plausible mechanisms for the protectiveness of whole grains
Am J Clin Nutr
(1999) - et al.
Carbohydrates, dietary fiber, and incident type 2 diabetes in older women
Am J Clin Nutr
(2000)