Abstract/Summary

Cardiovascular diseases (CVDs) are leading causes of mortality and morbidity in sub-Saharan Africa. Cowpea leaves, one of the region's important and commonly consumed leafy vegetable, may potentially improve metabolic health. However, data on their composition and role in metabolic health are limited. This thesis explores the metabolic health benefits of leafy vegetables, focusing on cowpea leaves. A systematic review of randomised control trials (RCTs) and cohort studies on the association between leafy vegetable consumption and the incidence of metabolic syndrome and its risk factors was conducted. Only seven RCTs and two cohort studies were included. Beneficial effects on blood glucose and blood pressure regulation were reported. Cowpea leaves, along with underutilised stalks and pods, were analysed for their micronutrient, fibre, nitrate, and (poly)phenolic content. Two cowpea varieties, ken kunde and kunde mboga, were studied. The effect of farm inputs and planting location on these compounds was investigated. . The leaves stalks and pods were freeze-dried prior to analysis and concentrations were recorded on a dry weight basis. Potassium, iron, and folate were the most abundant micronutrients in the leaves, with concentrations ranging from 12.43–31.59 mg/g, 0.24–1.07 mg/ g, and 8.32–19.11 µg/g, respectively. Nitrate and fibre in the leaves ranged from 0.05–0.81 mg/g and 22.44–26.38 g/100g, respectively. Twenty-three (poly)phenolic compounds were detected, with m-coumaric acid being the most abundant, ranging from 26–998 µg/g in leaves. Ken kunde had higher micronutrient and (poly)phenol content, while kunde mboga had higher nitrate and fibre levels. Manure application produced the highest micronutrient content, and fertiliser increased nitrate levels. Field planting yielded higher micronutrient and nitrate content than greenhouse. Planting location and farm inputs influenced each (poly)phenol differently. A pilot RCT was conducted on the effect of cowpea leaves consumption on postprandial blood glucose in individuals of Black ethnicity. The incremental area under the curve (iAUC) and the area under the curve (AUC) for postprandial blood glucose after consuming cowpea leaves were 7.8±2.4 mmol·min/L and 60.3±2.0 mmol·min/L, respectively. These values were lower compared to the control, where the iAUC and AUC were 11.7±1.8 mmol·min/L and 67.2±2.1 mmol·min/L, respectively. No effect on blood pressure or microvascular dilation was observed after consuming cowpea leaves. These results suggest that leafy vegetables, including cowpea leaves, may have the potential to regulate blood glucose. However, farming practices influence the concentration of the compounds responsible for this effect.