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 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 «Qian F, Liu G, Hu FB et al. Association Between Pl...»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 «Schwingshackl L, Hoffmann G, Lampousi AM et al. Fo...»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 «Relative risks from nonlinear dose–response analysis of food groups and risk of T2D...»1). 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 «Jannasch F, Kröger J, Schulze MB. Dietary Patterns...»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 «Churuangsuk C, Lean MEJ, Combet E. Lower carbohydr...»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 «Ibsen DB, Steur M, Imamura F et al. Replacement of...»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.
A systematic review and meta-analysis of prospective studies «...»6 included 24 cohorts. There was moderate CoE for a lower risk of CVD when substituting processed meat with nuts (HR 0.73, 95% CI 0.59 to 0.91, 8 cohorts), legumes (HR 0.77, 95% CI 0.68 to 0.87, 8 cohorts), and whole grains (HR 0.64, 95% CI 0.54 to 0.75, 7 cohorts), as well as eggs with nuts (HR 0.83, 95% CI 0.78 to 0.89, 8 cohorts). Furthermore, There was a moderate CoE for an inverse association with T2D incidence when substituting red meat with whole grains/cereals (HR 0.90, 95% CI 0.84 to 0.96, 6 cohorts) and red meat or processed meat with nuts (HR 0.92, 95% CI 0.90 to 0.94, 6 cohorts), as well as for replacing poultry with whole grains (HR 0.87, 95% CI 0.83 to 0.90, 2 cohorts) and eggs with nuts or whole grains (HR 0.82, 95% CI 0.79 to 0.86, or HR 0.79, 95% CI 0.76 to 0.83, 2 cohorts). Moreover, replacing red meat for nuts and whole grains, processed meat with nuts and legumes, dairy with nuts, and eggs with nuts and legumes was associated with a reduced risk of all-cause mortality.