The quality of evidence is upgraded by consistent findings and a clear dose-response gradient.
A diet based on vegetables, fruits, and whole grains is recommended for all persons at increased risk of type 2 diabetes.
A diet based on vegetables, fruits, and whole grains is also beneficial for several other health outcomes and rarely has any harms. In a societal perspective, wide use of such a diet reduces carbon emissions of food production.
A meta-analysis 2 assessing prospective observational studies included 9 trials involving a total of 307 099 participants with 23 544 cases of incident type 2 diabetes (T2D). A significant inverse association was observed between higher adherence to a plant-based dietary pattern and risk of type 2 diabetes (RR 0.77, 95% CI 0.71 to 0.84, I² = 44.5%) in comparison with poorer adherence. Similar findings were obtained when using the fixed-effects model (RR 0.80, 95% CI 0.75 to 0.84). Consistent associations were observed across predefined subgroups. This association was strengthened when healthy plant-based foods, such as fruits, vegetables, whole grains, legumes, and nuts, were included in the definition of plant-based patterns (RR 0.70, 95% CI 0.62 to 0.79). Most studies were deemed to have good quality in terms of dietary assessment, disease outcomes, and statistical adjustment for confounding factors.
Another meta-analysis 3 of prospective studies evaluated the relation between intake of 12 major food groups and risk of T2D. Three food-groups decreased the risk of T2D with increasing consumption (whole grains, fruits, and dairy), 3 increased the risk with increasing consumption (red meat, processed meat, and sugar sweetened beverages), while nuts, legumes, and fish were neutral in the linear dose-response meta-analysis (table T1). There was evidence of a non-linear relationship between fruits, vegetables, processed meat, whole grains, and sugar sweetened beverages and T2D risk. Optimal consumption of risk-decreasing foods resulted in a 42% reduction, and consumption of risk-increasing foods was associated with a 3-fold T2D risk, compared to non-consumption. The meta-evidence was graded "low" for legumes and nuts; "moderate" for refined grains, vegetables, fruit, eggs, dairy, and fish; and "high" for processed meat, red meat, whole grains, and sugar sweetened beverages.
| Food group | Risk ratio (95% CI) | |||
|---|---|---|---|---|
| Servings per day | 0 | 1 | 2 | 3 |
| Inverse association | ||||
| Whole grains (1 serving = 30 g/day) | 1.00 | 0.78 (0.76-0.81) | 0.75 (0.71-0.79) | 0.76 (0.70-0.82) |
| Vegetables (1 serving = 80 g/day) | 1.00 | 0.96 (0.94-0.98) | 0.93 (0.90-0.96) | 0.92 (0.89-0.95) |
| Fruits (1 serving = 80 g/day) | 1.00 | 0.95 (0.94-0.96) | 0.92 (0.89-0.94) | 0.90 (0.88-0.93) |
| Dairy (1 serving = 200 g/day) | 1.00 | 0.97 (0.95-0.99) | 0.95 (0.92-0.98) | 0.94 (0.91-0.97) |
| Positive association | ||||
| Refined grains (1 serving = 30 g/day) | 1.00 | 1.01 (0.99-1.02) | 1.01 (0.98-1.05) | 1.02 (0.98-1.06) |
| Eggs (1 serving = 55 g/day) | 1.00 | 1.16 (1.09-1.23) | NA | NA |
| Red meat (1 serving = 85 g/day) | 1.00 | 1.18 (1.14-1.21) | 1.37 (1.30-1.43) | NA |
| Processed meat (1 serving = 35 g/day) | 1.00 | 1.29 (1.25-1.33) | 1.35 (1.28-1.42) | 1.39 (1.27-1.54) |
| Sugar sweetened beverages (1 serving = 250 ml/day) | 1.00 | 1.19 (1.14-1.23) | 1.28 (1.20-1.38) | 1.37 (1.23-1.53) |
| No association | ||||
| Nuts (1 serving = 28 g/day) | 1.00 | 1.01 (0.92-1.12) | NA | NA |
| Legumes (1 serving = 100 g/day) | 1.00 | 1.00 (0.95-1.05) | 0.97 (0.90-1.03) | NA |
| Fish (1 serving = 100 g/day) | 1.00 | 1.03 (0.98-1.09) | 1.03 (0.89-1.20) | NA |
Yet another meta-analysis 4 of prospective studies evaluating different dietary patterns with diabetes incidence included 16 cohorts. Significant risk reductions were associated with Mediterranean diet (RR for comparing extreme quantiles: 0.87, 95% CI 0.82 to 0.93), Dietary Approaches to Stop Hypertension (DASH) (RR 0.81, 95% CI 0.72 to 0.92), and Alternative Healthy Eating Index (AHEI) (RR 0.79, 95% CI 0.69 to 0.90). Principal component analyses characterized by red and processed meat, refined grains, high-fat dairy, eggs, and fried products ("mainly unhealthy") were positively associated with diabetes (RR 1.44, 95% CI 1.27 to 1.62), whereas patterns characterized by vegetables, legumes, fruits, poultry, and fish ("mainly healthy") were inversely associated with diabetes (RR 0.84, 95% CI 0.77 to 0.91).
A study 5 assessed the effect of low-carbohydrate, high-fat diets (LCHF) for type 2 diabetes (T2DM) prevention (2008-2016). In the overall study sample, 194 (6.0%) had diabetes. Mean intake was 48.0%E for carbohydrates, and 34.9%E for total fat. An increase of 5% food energy from carbohydrate was associated with a 12% ‘lower odd' of having diabetes (95% CI 0.78 to 0.99; P = 0.03). Every 5%E decrease in carbohydrate, and every 5%E increase in fat, was associated with 12% (95% CI 0.78 to 0.99; P = 0.03) and 17% (95% CI 1.02 to 1.33; P = 0.02) higher odds of diabetes, respectively. Among the participants without diagnosed diabetes (n = 3130), every 5%E decrease in carbohydrate was associated with higher %HbA1c by + 0.016% (95% CI 0.004 to 0.029; P = 0.012), whereas every 5%E increase in fat was associated with higher %HbA1c by + 0.029% (95% CI 0.015 to 0.043; P < 0.001). Higher adherence to conventional dietary recommendations (basing meals on starchy carbohydrates, lower fat and saturated fat contents, eating more fruits and vegetables) was associated with lower HbA1c concentration.
In a case cohort study 1 for a subcohort of 15 450 participants the diet was modeled with other protein sources instead of red meat. There was a lower hazard for type 2 diabetes for the modeled replacement of red and processed meat (50 g/day) with cheese (HR 0.90, 95% CI 0.83 to 0.97) (30 g/day), yogurt (0.90, 0.86 to 0.95) (70 g/day), nuts (0.90, 0.84 to 0.96) (10 g/day), or cereals (0.92, 0.88 to 0.96) (30 g/day) but not for replacements with poultry, fish, eggs, legumes, or milk.
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