Examination of coffee as a functional food towards metabolic syndrome prevention

Abstract

Evidence regarding the association between coffee consumption and metabolic syndrome is inconsistent between epidemiological and acute studies. This could be due to variation in consumption habits that were seldom considered in previous studies, such as the type of coffee consumed, the use of milk and sugar, and the time of coffee consumption around mealtime. This thesis aimed to examine the role played by these factors in the acute effects of coffee consumption on metabolic health biomarkers, as well as the association between coffee consumption and metabolic syndrome incidence.

In the first acute feeding study, apparently healthy, overnight-fasted participants (n = 21) preloaded a serve of either caffeinated (espresso, instant, or boiled coffee) or decaffeinated coffee with low-fat cow’s milk and white sugar 60 minutes before consuming a high glycemic-index (GI) meal. Results showed that preloading the caffeinated coffees caused the postprandial glucose levels to decrease faster from the peak when compared with preloading water. The incremental area-under-curve (iAUC) after preloading decaffeinated coffee was significantly smaller than preloading water, possibly due to a more rapid insulin response. Furthermore, preloading coffees with milk and sugar added led to significantly smaller postprandial glycemic excursions in all coffee types (25% reduction in decaffeinated coffee, 26% reduction in espresso, and 29% reduction in boiled coffee, all p < 0.05) when compared with preloading black coffees (n = 10). Postprandial levels of triglycerides, total cholesterol, active glucagon-like peptide-1, and nitrotyrosine were not significantly different among the test drinks.

In the second acute feeding study, which involved apparently healthy, overnight-fasted participants (n = 10), consuming decaffeinated coffee with low-fat cow’s milk and white sugar immediately after a high GI meal led to a 10% higher glucose AUC than preloading the test drink either 30 or 60 minutes before the meal (both p < 0.05), as well as a 38% higher insulin AUC than preloading 60 minutes before (p < 0.001). Nitrotyrosine levels were not significantly different between treatments.

The association between habitual coffee consumption and metabolic syndrome incidence was analyzed using data from the Blue Mountains Eye Study (BMES), which involved a population of Australian elderly. Results showed that those who consumed coffee once per week to once per day had a significantly lower risk of having low high-density-lipoprotein cholesterol (HR: 0.50, 95% CI: 0.25-0.99) than those who consumed coffee less frequently, yet no significant results were observed for metabolic syndrome, as well as other health outcomes.

The results of these studies showed that coffee consumption with milk and sugar before mealtime could benefit postprandial glucose control without increasing insulin secretion. Nonetheless, a temporal association was not observed between coffee consumption and metabolic syndrome. Findings in this thesis were insufficient to recommend coffee consumption for preventing metabolic syndrome. More acute feeding studies of longer duration will be needed to observe the changes in lipid profiles and oxidative stress, while data on milk and sugar usage with coffee and time of coffee consumption should be collected in dietary assessments of future epidemiological studies.