Strong and Bitter Vegetables from Traditional Cultivars and Cropping Methods Improve the Health Status of Type 2 Diabetics: A Randomized Control Trial

Abstract

Vegetables rich in bitter-tasting phytochemicals may exert enhanced beneficial effects against key factors associated with type two diabetes (T2D). This study investigates whether selected cultivars of bitter and strong-tasting (BST) Brassica and root vegetables exert greater health benefits on T2D patients compared to equivalent modern mild and sweet tasting (MST) vegetables. A 12-week randomized, controlled, parallel intervention study involved 92 T2D patients, who were allocated three different diets: (1) 500 g daily of bitter and strong-tasting (BST) vegetables; (2) 500 g daily of mild and sweet-tasting (MST) vegetables; (3) 120 g daily MST normal diet (control). Both vegetable diets contained root vegetables and cabbages selected based on sensory differences and content of phytochemicals. Prior to and after the study, all participants underwent an oral glucose tolerance test (OGTT), 24 h blood pressure measurements, DEXA scans, and fasted blood samples. Both diets high in vegetables significantly reduced the participants' BMI, total body fat mass, and HbA1c levels compared to control, but in the BST group, significant differences were also found regarding incremental area under the curve glucose 240 min (OGTT) and fasting glucose levels. A high daily intake of root vegetables and cabbages showed significant health improvements in both vegetable groups. BST vegetables had the greatest impact on insulin sensitivity, body fat mass, and blood pressure compared to control; moreover, they further improved glycemic control compared to MST vegetables.

Keywords: cultivars; glucose tolerance; phytochemicals and sensory analysis; type 2 diabetes mellitus; vegetables.

Figure 1

The study design. The far left shows the three groups in the top (A) the control group (green); (B) mild and sweet tasting (red); and finally (C) bitter and strong tasting (blue). Screening took place approximately 2 weeks prior to project start. At weeks 0 and 12, fasting blood and urine samples were taken, 24 h blood pressure (BP) and oral glucose tolerance test (OGTT) were performed, and DEXA scans were conducted. At weeks 0, 6, and 12, participants filled out thorough questionnaires. Randomization took place at week 0.

Figure 2

Flow chart of the participants in the study with the BST, MST, and control diet. BST; bitter strong tasting. MST; mild sweet tasting.

Figure 3

Change (Δ) in (A) area under the curve (AUC) glucose (240 min) during the OGTT, (B) fasting glucose changes, (C) HbA1c changes, and (D) changes in HOMA-IR; after 12-week intervention. p < 0.05 (*); p < 0.001 (**).

Figure 4

OGTT before and after 12-weeks of intervention. (A) CON, (B) MST, (C) BST. Data are presented as mean (±SEM). Significance testing was performed on between group differences in change in iAUC OGTT glucose (please see Figure 3A).

Figure 5

(A) Change (Δ) in BMI, (B) change in total body fat (†) percentage Data are presented as mean (±SEM). (*) p < 0.05, (**) p < 0.01.