Gary Williamson

Gary Williamson
Monash University (Australia) · Department of Nutrition and Dietetics

About

526
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Publications

Publications (526)
Article
Full-text available
Background: Postprandial oxidative stress markers in blood are generated transiently from various tissues and cells following high-fat and/or high-carbohydrate (HFHC) meals, and may be suppressed by certain phytonutrients, such as polyphenols and carotenoids. However, the transient presence of phytonutrients in circulation suggests that timing of...
Poster
Objectives High-fat diets are associated with endothelial dysfunction, the first step in the progression to atherosclerosis and cardiovascular disease. We aimed to determine the postprandial endothelial response (flow-mediated dilation (FMD)) to a high-fat meal in various populations and define how the response varies by conducting a systematic rev...
Article
Objectives An individual's ability to adapt to a dynamic environment is termed ‘phenotypic flexibility’ and can be weakened by chronic stress, leading to dysregulation of normal homeostatic processes. A long-term high energy and high fat high carbohydrate (HFHC) diet increases risk of metabolic diseases, however, the acute effect of a single HFHC m...
Article
Full-text available
Background Citrus fruits are commonly consumed worldwide in both fresh and processed forms, especially as juices. While fruit consumption is perceived as beneficial for long-term health, the effects of fruit juices are more controversial, linked to high intrinsic sugar content. On the other hand, citrus juices, like the fruits, are rich in many nut...
Article
Full-text available
The origin of inter-individual variability in the action of bioactive small molecules from the diet is poorly understood and poses a substantial obstacle to harnessing their potential for attenuating disease risk. Epidemiological studies show that coffee lowers the risk of developing type 2 diabetes, independently of caffeine, but since coffee is a...
Article
Full-text available
The aim was to determine inhibition of human α-amylase activity by (poly)phenols using maltoheptaoside as substrate with direct chromatographic product quantification, compared to hydrolysis of amylose and amylopectin estimated using 3,5-dinitrosalicylic acid. Acarbose exhibited similar IC50 values (50% inhibition) with maltoheptaoside, amylopectin...
Article
Background Uric acid, a metabolic product of purine degradation in humans, is a risk factor for developing gout and type 2 diabetes, and supplementation with quercetin lowers plasma uric acid in mildly hyperuricemic men. Here we examined the mechanism of inhibition of enzymes involved in uric acid metabolism by quercetin, conjugates and microbial c...
Article
Full-text available
Insulin resistance (IR) is apparent when tissues responsible for clearing glucose from the blood, such as adipose and muscle, do not respond properly to appropriate signals. IR is estimated based on fasting blood glucose and insulin, but some measures also incorporate an oral glucose challenge. Certain (poly)phenols, as supplements or in foods, can...
Article
Full-text available
There is a lack of focus on the protective health effects of phy-tochemicals in dietary guidelines. Although a number of chemical libraries and databases contain dietary phytochemicals belonging to the plant metabolome, they are not entirely relevant to human health because many constituents are extensively metabolized within the body following ing...
Article
Commonly used drugs for treating many conditions are either natural products or derivatives. In silico modelling has identified several natural products including quercetin as potential highly effective disruptors of the initial infection process involving binding to the interface between the SARS-CoV-2 (Covid-19) Viral Spike Protein and the epithe...
Article
Epidemiological studies show a convincing long-term and dose-dependent protection of coffee and decaffeinated coffee against developing type 2 diabetes. The mechanisms of this effect are still not understood even though several have been proposed, including a potential effect on blood glucose by chlorogenic acids. However, there is minimal effect o...
Article
Single cell-type models are useful for determining mechanisms, but in vivo, cell–cell interactions are important, and neighbouring cells can impact endothelial cell function. Quercetin can attenuate endothelial dysfunction by modulating vascular tone and reducing inflammation. We determined the effect of quercetin on a co-culture between Human Umbi...
Article
Full-text available
Scope Dietary flavonoids and phenolic acids can modulate lipid metabolism, but effects on mature human adipocytes are not well characterised. Materials and methods Human adipocytes were differentiated, and contained accumulated lipids, mimicking white adipocytes. They were then cultured either under conditions of actively synthesizing and accumula...
Article
Acyl‐quinic acids (chlorogenic acids) are produced by many plants, including fruits, vegetables, and herbal remedies, with coffee and maté particularly rich dietary sources. Epidemiological and intervention studies suggest that they can reduce the risk of developing type 2 diabetes and cardiovascular disease. This review addresses their metabolic h...
Chapter
Dietary intake of flavonoids, found in a wide variety of plant-based foods and beverages, varies widely between individuals but is typically several hundred milligrams per day. For many flavonoids, such as flavanols, flavanones, and flavonols, a substantial percentage of the ingested dose is absorbed and rapidly metabolized and excreted within 24 h...
Article
Full-text available
Many terms for plant-derived food components are commonly used in the literature, but there is a notable lack of standardization and definition of nomenclature. The use of terms is often field-specific, leading to misunderstanding and problems with literature searches and systematic reviews, and results in isolated and divided research; this impact...
Article
Reporting of plasma antioxidant activities in human intervention studies in the British Journal of Nutrition - Volume 122 Issue 7 - Gary Williamson
Article
Full-text available
Consumption of dietary bioactives is an avenue to enhancing the effective healthiness of diets by attenuating the glycaemic response. The intestinal brush border enzyme sucrase-isomaltase (SI) is the sole enzyme hydrolysing consumed sucrose, and we previously showed the acute effects of olive leaf extract (OLE) on sucrase activity when given togeth...
Article
Cholesterol uptake and chylomicron synthesis are promoted by increasing glucose concentrations in both healthy and diabetic individuals during the postprandial phase. The goal of this study was to test whether acute inhibition of glucose uptake could impact cholesterol absorption in differentiated human intestinal Caco-2 cells. As expected, high gl...
Article
Full-text available
Purpose: The secoiridoid oleuropein, as found in olives and olive leaves, modulates some biomarkers of diabetes risk in vivo. A possible mechanism may be to attenuate sugar digestion and absorption. Methods: We explored the potential of oleuropein, prepared from olive leaves in a water soluble form (OLE), to inhibit digestive enzymes (α-amylase,...
Article
Endothelial functionality profoundly contributes to cardiovascular health. The effects of flavonoids shown to improve endothelial performance include regulating blood pressure by modulating endothelial nitric oxide synthase and NADPH oxidases, but their impact on glucose uptake and metabolism has not been explored. We treated human umbilical vein e...
Article
Although polyphenols inhibit glucose absorption and transport in vitro , it is uncertain whether this activity is sufficient to attenuate glycaemic response in vivo . We examined this using orange juice, which contains high levels of hesperidin. We first used a combination of in vitro assays to evaluate the potential effect of hesperidin and other...
Article
The gut microbiome supplies essential metabolites such as short-chain fatty acids to skeletal muscle mitochondria, and the composition and activity of the microbiota is in turn affected by muscle fitness. To further our understanding of the complex interactions between the gut microbiome and muscle, we examined the effect of microbiota-derived phen...
Article
Hyperglycemia augments formation of intracellular reactive oxygen species (ROS) with associated mitochondrial damage and increased risk of insulin resistance in type 2 diabetes. We examined whether quercetin could reverse chronic high glucose-induced oxidative stress and mitochondrial dysfunction. Following long-term high glucose treatment, complex...
Article
There is increasing evidence that consumption of polyphenol and phenolic-rich foods and beverages have the potential to reduce the risk of developing diabetes type 2, with coffee a dominant example according to epidemiological evidence. One of the proposed mechanisms of action is the inhibition of carbohydrate-digesting enzymes leading to attenuate...
Article
Full-text available
Transient hyperglycaemia is a risk factor for type 2 diabetes and endothelial dysfunction, especially in subjects with impaired glucose tolerance. Nutritional interventions and strategies for controlling postprandial overshoot of blood sugars are considered key in preventing progress to the disease state. We have identified apigenin-7-O-glucoside,...
Article
Full-text available
After consumption of plant‐derived foods or beverages, dietary polyphenols such as quercetin are absorbed in the small intestine and metabolized by the body, or they are subject to catabolism by the gut microbiota followed by absorption of the resulting products by the colon. The resulting compounds are bioavailable, circulate in the blood as conju...
Article
Only limited data are available on the inhibition of the sugar transporter GLUT5 by flavonoids or other classes of bioactives. Intestinal GLUT7 is poorly characterised and no information exists concerning its inhibition. We aimed to study the expression of GLUT7 in Caco-2/TC7 intestinal cells, and evaluate inhibition of glucose transport by GLUT2 a...
Chapter
Full-text available
Making health claims for botanical and plant food supplements (PFS) requires serious investigation and a collection of scientific evidence. The present chapter summarizes different aspects that should be considered for the evaluation of PFS benefits. Well-designed translational in vitro methods combined with human studies provide the best predictiv...
Article
Full-text available
Fatty acyl-Coenzyme A species (acyl-CoAs) are key biomarkers in studies focusing on cellular energy metabolism. Existing analytical approaches are unable to simultaneously detect the full range of short-, medium-, and long-chain acyl-CoAs, while chromatographic limitations encountered in the analysis of limited amounts of biological samples are an...
Article
Polyphenols are beneficial for health, but are metabolised after consumption. We compared the vasorelaxant capacity of twenty-one physiologically relevant polyphenol metabolites in isolated mouse arteries. Hesperetin, urolithins and ferulic acid-4-O-sulfate...
Article
We optimized the assays used to measure inhibition of rat and human α-glucosidases (sucrase and maltase activities), intestinal enzymes which catalyze the final steps of carbohydrate digestion. Cell-free extracts from fully differentiated intestinal Caco-2/TC7 monolayers were shown to be a suitable source of sucrase-isomaltase, with the same sequen...
Article
Background: Low-glycemic index diets have demonstrated health benefits associated with a reduced risk of developing type 2 diabetes.Objectives: We tested whether pomegranate polyphenols could lower the glycemic response of a high-glycemic index food when consumed together and the mechanism by which this might occur.Design: We compared the acute eff...
Article
Flavonoids and phenolic acids (polyphenols) are naturally-occurring bioactive compounds from plants, often found in high amounts in many foods and beverages. They are also present in many plant based dietary supplements, at levels up to pharmaceutical doses. The pathways of absorption and metabolism of the most common dietary polyphenols are now mo...
Article
Full-text available
Significance: Flavonoids can interact with multiple molecular targets to elicit their cellular effects, leading to changes in signal transduction, gene expression, and/or metabolism, which can, subsequently, affect the entire cell and organism. Immortalized cell lines, derived from tumors, are routinely employed as a surrogate for mechanistic stud...
Article
Scope: High glycaemic sugars result in blood glucose spikes, while high doses of post-prandial fructose inundate the liver, causing an imbalance in energy metabolism, both leading to increased risk of metabolic malfunction and type 2 diabetes. Acarbose, used for diabetes management, reduces post-prandial hyperglycaemia by delaying carbohydrate dig...
Article
Full-text available
Polyphenols are found in plant-based foods and beverages, notably apples, berries, citrus fruit, plums, broccoli, cocoa, tea and coffee, and many others. There is substantial epidemiological evidence that a diet high in polyphenol-rich fruit, vegetables, cocoa and beverages protects against developing cardiovascular disease and type 2 diabetes. The...
Article
The effect of temperature (6, 15 and 30 °C) during ageing on the colour, phytochemical composition and bioactivity of roselle wine was investigated over 12 months. At the end of aging, wines stored at 6 °C had the highest colour density and lowest polymeric anthocyanins. The initial concentration of most of the individual phenolic compounds decreas...
Article
(Poly)phenols are a large group of compounds, found in food, beverages, dietary supplements and herbal medicines. Owing to their biological activities, absorption and metabolism of the most abundant compounds in humans are well understood. Both the chemical structure of the phenolic moiety and any attached chemical groups define whether the polyphe...
Article
Consumption of foods rich in ferulic acid (FA) such as wholegrain cereals, or FA precursors such as chlorogenic acids in coffee, is inversely correlated with risk of cardiovascular disease and type 2 diabetes. As a result of digestion and phase II metabolism in the gut and liver, FA is converted predominantly into ferulic acid-4-O-sulfate (FA-sul),...
Article
Endothelial cells are routinely exposed to elevated glucose concentrations post-prandially in healthy individuals and permanently in patients with metabolic syndrome and diabetes, and so we assessed their sugar transport capabilities in response to high glucose. In human umbilical vein (HUVEC), saphenous vein, microdermal vessels and aorta, GLUT1 (...
Article
Full-text available
Dietary fibre-derived short chain fatty acids (SCFA) and phenolics produced by the gut microbiome have multiple effects on health. We have tested the hypothesis that long term exposure to physiological concentrations of SCFA can affect the transport and metabolism of (poly)phenols by the intestinal epithelium using the Caco-2 cell model. Metabolite...
Article
Three varieties of Hibiscus sabdariffa were analyzed for their phytochemical content and inhibitory potential on carbohydrate-digesting enzymes as a basis for selecting a variety for wine production. The dark red variety was chosen as it was highest in phenolic content and partially inhibited α-glucosidase (maltase), with delphinidin 3-O-sambubiosi...
Article
Polyphenol and fibre-rich foods have the potential to affect postprandial glycaemic responses by reducing glucose absorption, and so decreasing the glycaemic response of foods when consumed together. A randomized, single blind crossover study was conducted on 16 healthy volunteers to test whether polyphenol and fibre-rich foods (PFRF) could attenua...
Conference Paper
Full-text available
Cutaneous photoaging is associated with dermal elastic fiber remodeling; daily photoprotection is therefore essential to prevent ultraviolet (UV)-induced skin damage. Green tea (C sinensis), rich in polyphenol catechins (GTC), have been reported to have significant skin benefits in vitro and in vivo. We have performed a double-blind randomised cont...
Conference Paper
Full-text available
Photoaged skin is clinically characterized by deep wrinkles, rough texture and altered pigmentation. Continual cutaneous exposure to solar ultraviolet radiation impacts upon papillary dermal structure, which can be identified histologically and is characterized partially by loss of fibrillar collagens. Green tea catechins (GTCs) are reportedly prot...
Article
Full-text available
The hypothesis that dietary (poly)phenols promote well-being by improving chronic disease-risk biomarkers, such as endothelial dysfunction, chronic inflammation and plasma uric acid, is the subject of intense current research, involving human interventions studies, animal models and in vitro mechanistic work. The original claim that benefits were d...
Article
Full-text available
Ferulic acid is released by microbial hydrolysis in the colon, where butyric acid, a major by-product of fermentation, constitutes the main energy source for colonic enterocytes. We investigated how varying concentrations of this short chain fatty acid may influence the absorption of the phenolic acid. Chronic treatment of Caco-2 cells with butyric...
Article
Full-text available
Elevated plasma uric acid concentration is a risk factor for gout, insulin resistance and type 2 diabetes. Quercetin, a flavonoid found in high levels in onions, tea and apples, inhibits xanthine oxidoreductase in vitro , the final step in intracellular uric acid production, indicating that quercetin might be able to lower blood uric acid in humans...
Article
Full-text available
Dietary flavonoids may protect against sunburn inflammation in skin. Preliminary reports using less complete analysis suggest that certain catechins and their metabolites are found in skin biopsies and blister fluid after consumption of green tea; however, it is not known if they are affected by solar-simulated ultraviolet radiation (UVR) or whethe...
Article
Full-text available
Single doses of resveratrol have previously been shown to increase cerebral blood flow (CBF) with no clear effect on cognitive function or mood in healthy adults. Chronic resveratrol consumption may increase the poor bioavailability of resveratrol or otherwise potentiate its psychological effects. In this randomised, double-blind, placebo-controlle...
Conference Paper
Full-text available
Green tea is consumed globally and is reported to have anti-inflammatory properties, which may be mediated through impact on cyclooxygenase (COX) and lipoxygenase (LOX) pathways. Recent data suggest green tea catechins (GTC) reduce acute UVR effects, and our pilot study suggested reduced UVR inflammation. Thus our aim was to perform a double-blind...
Article
Full-text available
Safe systemic protection from the health hazards of ultraviolet radiation (UVR) in sunlight is desirable. Green tea is consumed globally and is reported to have anti-inflammatory properties, which may be mediated through the impact on cyclooxygenase and lipoxygenase pathways. Recent data suggest that green tea catechins (GTCs) reduce acute UVR effe...
Article
Establishing and linking the proposed health benefits of dietary polyphenols to their consumption requires measurement of polyphenol intake in appropriate samples and an understanding of factors that influence their intake in the general population. This study examined polyphenol intake estimated from 3- and 7-day food diaries in a sample of 246 UK...
Article
In observational studies, fruit intake is associated with a reduced risk of cardiovascular disease (CVD), though fruit type has been less frequently explored. The aim of the current study was to explore the association between total fruit and fruit subgroup intake according to polyphenol content and CVD mortality in the UK Women’s Cohort Study. Tot...
Article
Dark chocolate contains many biologically active components, such as catechins, procyanidins and theobromine from cocoa, together with added sucrose and lipids. All of these can directly or indirectly affect the cardiovascular system by multiple mechanisms. Intervention studies on healthy and metabolically-dysfunctional volunteers have suggested th...
Article
ScopeHesperetin-7-O-rutinoside (hesperidin) reduces blood pressure in healthy volunteers but its intestinal absorption and metabolism are not fully understood. Therefore, we aimed to determine sites of absorption and metabolism of dietary flavanone glycosides in humans.Methods and resultsUsing a single blind, randomized crossover design, we perfuse...
Conference Paper
Excessive post-prandial glucose concentrations are associated with an increased risk of developing diabetes, thus controlling overshooting plasma glucose has been suggested as an important measure in the prevention and management of diabetes. The aim of this work was to assess the acarbose-like activity of German chamomile extract (GCE) and related...
Conference Paper
Excessive post-prandial glucose concentrations are associated with an increased risk of developing type 2 diabetes. Polyphenols represent a biologically active class of secondary plant compounds which have been tested as supporting or alternative therapies for a number of chronic diseases. The aim of this work was to assess the acarbose-like activi...
Article
Full-text available
MK571 is a multidrug resistance protein-2 (ABCC2, Mrp2) inhibitor and has been widely used to demonstrate the role of Mrp2 in the cellular efflux of drugs, xenobiotics and their conjugates. Numerous reports have described modulation of Caco-2 cellular efflux and transport of flavonoids in the presence of MK571. Since flavonoids are efficiently conj...
Article
Some intervention studies have shown that quercetin supplementation can regulate certain biomarkers, but it is not clear how the doses given relate to dietary quercetin (e.g. from onion). We conducted a two-period, two-sequence crossover study to compare the bioavailability of quercetin when administered in the form of fresh red onion meal (natural...
Article
Insulin-regulated glucose metabolism in cells is critical for proper metabolic functioning, and insulin resistance leads to type 2 diabetes. We performed a human study to assess the availability of structurally related dietary flavonols and tested their ability to affect cellular glucose uptake, metabolism and glucose transporter gene expression in...
Article
ScopeCoffee is rich in quinic acid esters of phenolic acids (chlorogenic acids) but also contains some free phenolic acids. A proportion of phenolic acids appear in the blood rapidly after coffee consumption due to absorption in the small intestine. We investigated in vitro whether this appearance could potentially be derived from free phenolic aci...