A single serving of caffeinated coffee impairs postprandial glucose metabolism in overweight men

Nutrient timing and metabolic regulation symposium review from "Novel dietary approaches to appetite regulation, health and performance (2021)"

Daily (circadian) rhythms coordinate our physiology and behaviour with regular environmental changes. Molecular clocks in peripheral tissues (e.g. liver, skeletal muscle and adipose) give rise to rhythms in macronutrient metabolism, appetite regulation and the components of energy balance such that our bodies can align the periodic delivery of nutrients with ongoing metabolic requirements. The timing of meals both in absolute terms (i.e. relative to clock time) and in relative terms (i.e. relative to other daily events) is therefore relevant to metabolism and health. Experimental manipulation of feeding–fasting cycles can advance understanding of the effect of absolute and relative timing of meals on metabolism and health. Such studies have extended the overnight fast by regular breakfast omission and revealed that morning fasting can alter the metabolic response to subsequent meals later in the day, whilst also eliciting compensatory behavioural responses (i.e. reduced physical activity). Similarly, restricting energy intake via alternate‐day fasting also has the potential to elicit a compensatory reduction in physical activity, and so can undermine weight‐loss efforts (i.e. to preserve body fat stores). Interrupting the usual overnight fast (and therefore also the usual sleep cycle) by nocturnal feeding has also been examined and further research is needed to understand the importance of this period for either nutritional intervention or nutritional withdrawal. In summary, it is important for dietary guidelines for human health to consider nutrient timing (i.e. when we eat) alongside the conventional focus on nutrient quantity and nutrient quality (i.e. how much we eat and what we eat).

Coffee constituents with antiadipogenic and antidiabetic potentials: A narrative review

Coffee consumption has been associated with the reduction of several chronic diseases, including type 2 diabetes mellitus (T2DM) and obesity. The aim of this review was to summarize the research conducted in the last five years (or older, when appropriate) on the relationship between the consumption of coffee bioactive compounds, obesity, and T2DM. A bibliographic search was performed using the Web of Sciences, Scopus, and Google Scholar. Keywords used were "caffeine," "coffee," "coffee consumption," "coffee extraction," "coffee bioactive components," "chlorogenic acid," "obesity," "antidiabetic," and "antiadipogenic." Epidemiological, clinical, animal, and cell culture studies were reviewed. Caffeine, chlorogenic acid, and diterpenes have been identified as potential bioactive compounds in coffee that exhibit antiadipogenic and antidiabetic effects. The concentration of these compounds in coffee depends on the coffee preparation method. The relationship between coffee consumption and obesity risk is inconsistent, as not all results report a positive association. The addition of sugar and cream may be responsible for these mixed results. The consumption of coffee and its constituents is consistently associated with a lower T2DM risk. Caffeine, chlorogenic acids, and diterpenes have antidiabetic properties and are associated with these effects. The available data do not allow us to draw a conclusion on the effect of coffee or its constituents on adipogenesis. Therefore, more tightly controlled human intervention studies are required for a deeper understanding about this relationship.

Correlations between Coffee Consumption and Metabolic Phenotypes, Plasma Folate, and Vitamin B12: NHANES 2003 to 2006

Metabolic syndrome (MetS) is prevalent not only among the overweight and obese but also normal weight individuals, and the phenotype is referred to as a metabolically unhealthy phenotype (MUHP). Besides normal weight individuals, overweight/obese individuals are also protected from MetS, and the phenotype is known as a metabolically healthy phenotype (MHP). Epidemiological studies indicate that coffee and micronutrients such as plasma folate or vitamin B12 (vit. B12) are inversely associated with MetS. However, correlations among coffee consumption metabolic phenotypes, plasma folate, and vit. B12 remain unknown. Our objective was to investigate the correlation between coffee consumption, metabolic phenotypes, plasma folate, and vit. B12 as well as to understand associations between plasma folate, vit. B12, and metabolic phenotypes. Associations among coffee consumption metabolic phenotypes, plasma folate, and vit. B12 were assessed in a cross-sectional study of 2201 participants, 18 years or older, from 2003-2004 and 2005-2006 National Health and Nutrition Examination Surveys (NHANES). MUHP was classified as having > three metabolic abnormalities. Coffee consumption was not associated with metabolic phenotypes, but negatively correlated with several metabolic variables, including BMI (p < 0.001). Plasma folate was positively associated with MUHP (p < 0.004), while vit. B12 was inversely associated with MUHP (p < 0.035). Our results suggest the potential protective impact of coffee on individual components of MetS and indicate a positive correlation between coffee consumption and MUHP among overweight individuals. Identifying possible dietary factors may provide practical and low-cost dietary intervention targets, specifically for early intervention. Larger and randomized intervention studies and prospective longitudinal studies are required to further evaluate these associations.

Coffee and Lower Risk of Type 2 Diabetes: Arguments for a Causal Relationship

Prospective epidemiological studies concur in an association between habitual coffee consumption and a lower risk of type 2 diabetes. Several aspects of these studies support a cause–effect relationship. There is a dependency on daily coffee dose. Study outcomes are similar in different regions of the world, show no differences between sexes, between obese versus lean, young versus old, smokers versus nonsmokers, regardless of the number of confounders adjusted for. Randomized controlled intervention trials did not find a consistent impact of drinking coffee on acute metabolic control, except for effects of caffeine. Therefore, lowering of diabetes risk by coffee consumption does not involve an acute effect on the post-meal course of blood glucose, insulin or insulin resistance. Several studies in animals and humans find that the ingestion of coffee phytochemicals induces an adaptive cellular response characterized by upregulation and de novo synthesis of enzymes involved in cell defense and repair. A key regulator is the nuclear factor erythroid 2-related factor 2 (Nrf2) in association with the aryl hydrocarbon receptor, AMP-activated kinase and sirtuins. One major site of coffee actions appears to be the liver, causing improved fat oxidation and lower risk of steatosis. Another major effect of coffee intake is preservation of functional beta cell mass via enhanced mitochondrial function, lower endoplasmic reticulum stress and prevention or clearance of aggregates of misfolded proinsulin or amylin. Long-term preservation of proper liver and beta cell function may account for the association of habitual coffee drinking with a lower risk of type 2 diabetes, rather than acute improvement of metabolic control.

Glucose control upon waking is unaffected by hourly sleep fragmentation during the night, but is impaired by morning caffeinated coffee

Morning coffee is a common remedy following disrupted sleep, yet each factor can independently impair glucose tolerance and insulin sensitivity in healthy adults. Remarkably, the combined effects of sleep fragmentation and coffee on glucose control upon waking per se have never been investigated. In a randomised crossover design, twenty-nine adults (mean age: 21 (sd 1) years, BMI: 24·4 (sd 3·3) kg/m2) underwent three oral glucose tolerance tests (OGTT). One following a habitual night of sleep (Control; in bed, lights-off trying to sleep approximately 23.00-07.00 hours), the others following a night of sleep fragmentation (as Control but waking hourly for 5 min), with and without morning coffee approximately 1 h after waking (approximately 300 mg caffeine as black coffee 30 min prior to OGTT). Individualised peak plasma glucose and insulin concentrations were unaffected by sleep quality but were higher following coffee consumption (mean (normalised CI) for Control, Fragmented and Fragmented + Coffee, respectively; glucose: 8·20 (normalised CI 7·93, 8·47) mmol/l v. 8·23 (normalised CI 7·96, 8·50) mmol/l v. 8·96 (normalised CI 8·70, 9·22) mmol/l; insulin: 265 (normalised CI 247, 283) pmol/l; and 235 (normalised CI 218, 253) pmol/l; and 310 (normalised CI 284, 337) pmol/l). Likewise, incremental AUC for plasma glucose was higher in the Fragmented + Coffee trial compared with Fragmented. Whilst sleep fragmentation did not alter glycaemic or insulinaemic responses to morning glucose ingestion, if a strong caffeinated coffee is consumed, then a reduction in glucose tolerance can be expected.

Differences in the effects of Kenyan, Tanzanian, and Ethiopian coffee intake on interstitial glucose levels measured by FreeStyle Libre: A pilot case study

Background

Although generally considered part of a healthy diet, coffee consumption has been suspected to be associated with elevated epinephrine levels and increasing insulin resistance.

Objectives

We studied the effects of the intake of 3 different types of coffee (Tanzanian, Ethiopian, and Kenyan) on postprandial interstitial glucose levels.

Method

Interstitial glucose levels were measured every 15 minutes using the FreeStyle Libre glucose monitoring system (Abbott Diabetes Care Ltd, Witney, United Kingdom) in each individual after drinking coffee compared with when not consuming coffee.

Results

Unlike Tanzanian and Ethiopian coffees, Kenyan coffee suppressed the increase of postprandial interstitial glucose levels. Kenyan coffee beans contain less anhydrous caffeine and more chlorogenic acid than Tanzanian and Ethiopian coffee beans. These findings may explain the different effects of these coffee types on postprandial interstitial glucose levels. Furthermore, Kenyan coffee beans inhibited α-glucosidase activity, which may partially explain why Kenyan coffee reduces postprandial interstitial glucose levels.

Conclusions

Coffee is widely consumed as a beverage worldwide, and our findings suggest that patients with diabetes mellitus may benefit from drinking Kenyan coffee because of its ability to reduce postprandial interstitial glucose levels. (Curr Ther Res Clin Exp. 2020; 81:XXX-XXX).

Consuming decaffeinated coffee with milk and sugar added before a high-glycaemic index meal improves postprandial glycaemic and insulinaemic responses in healthy adults

The present study aimed to compare the effects of drinking different types of coffee before a high-glycaemic index (GI) meal on postprandial glucose metabolism and to assess the effects of adding milk and sugar into coffee. In this randomised, crossover, acute feeding study, apparently healthy adults (n 21) consumed the test drink followed by a high-GI meal in each session. Different types of coffee (espresso, instant, boiled and decaffeinated, all with milk and sugar) and plain water were tested in separate sessions, while a subset of the participants (n 10) completed extra sessions using black coffees. Postprandial levels of glucose, insulin, active glucagon-like peptide 1 (GLP-1) and nitrotyrosine between different test drinks were compared using linear mixed models. Results showed that only preloading decaffeinated coffee with milk and sugar led to significantly lower glucose incremental AUC (iAUC; 14 % lower, P = 0·001) than water. Preloading black coffees led to greater postprandial glucose iAUC than preloading coffees with milk and sugar added (12-35 % smaller, P < 0·05 for all coffee types). Active GLP-1 and nitrotyrosine levels were not significantly different between test drinks. To conclude, preloading decaffeinated coffee with milk and sugar led to a blunted postprandial glycaemic response after a subsequent high-GI meal, while adding milk and sugar into coffee could mitigate the impairment effect of black coffee towards postprandial glucose responses. These findings may partly explain the positive effects of coffee consumption on glucose metabolism.

Impact of Foods and Dietary Supplements Containing Hydroxycinnamic Acids on Cardiometabolic Biomarkers: A Systematic Review to Explore Inter-Individual Variability

Plant-based diets rich in bioactive compounds such as polyphenols have been shown to positively modulate the risk of cardiometabolic (CM) diseases. The inter-individual variability in the response to these bioactives may affect the findings. This systematic review aimed to summarize findings from existing randomized clinical trials (RCTs) evaluating the effect of hydroxycinnamic acids (HCAs) on markers of CM health in humans. Literature searches were performed in PubMed and the Web of Science. RCTs on acute and chronic supplementation of HCA-rich foods/extracts on CM biomarkers were included. Forty-four RCTs (21 acute and 23 chronic) met inclusion criteria. Comparisons were made between RCTs, including assessments based on population health status. Of the 44 RCTs, only seven performed analyses on a factor exploring inter-individual response to HCA consumption. Results demonstrated that health status is a potentially important effect modifier as RCTs with higher baseline cholesterol, blood pressure and glycaemia demonstrated greater overall effectiveness, which was also found in studies where specific subgroup analyses were performed. Thus, the effect of HCAs on CM risk factors may be greater in individuals at higher CM risk, although future studies in these populations are needed, including those on other potential determinants of inter-individual variability. PROSPERO, registration number CRD42016050790.

Genetic Polymorphisms in ADORA2A and CYP1A2 Influence Caffeine's Effect on Postprandial Glycaemia

The liver enzyme cytochrome P450 1A2 (CYP1A2) is responsible for 90% of caffeine metabolism, while caffeine exerts many of its effects via antagonist binding to adenosine A2a receptors (ADORA2A). This study aimed to examine whether functional single nucleotide polymorphisms (SNPs) in 1976T > C (ADORA2A; rs5751876) and −163C > A (CYP1A2; rs762551) influence the effect of caffeine on the postprandial glucose (GLU) response to a carbohydrate meal. We report that individuals with the 1976T > C CC, but not CT/TT genotypes display elevated GLU levels after consuming caffeine and carbohydrate (CHO + CAFF) versus carbohydrate only (CHO). The GLU area under the curve (AUC) was also greater during the CHO + CAFF condition compared to the CHO condition in CC, but not the CT/TT genotypes. The −163C > A AC/CC, but not AA, genotypes displayed greater GLU concentrations 60-min post meal during CHO + CAFF versus CHO. Our data suggest that caffeine-induced impairments in postprandial glycaemia are related to 1976T > C and −163C > A SNPs.

Effects of coffee consumption on glucose metabolism: A systematic review of clinical trials

Epidemiological studies indicate an inverse association of coffee consumption with risk of type 2 diabetes mellitus. However, studies to determine the clinical effects of coffee consumption on the glucose metabolism biomarkers remain uncertain. The aim of this systematic review was to evaluate the effects of coffee consumption on glucose metabolism. A search of electronic databases (PubMed and Web of Science) was performed identifying studies published until September 2017. Eight clinical trials (n = 247 subjects) were identified for analyses. Participants and studies characteristics, main findings, and study quality (Jadad Score) were reported. Short-term (1-3 h) and long-term (2-16 weeks) studies were summarized separately. Short-term studies showed that consumption of caffeinated coffee may increase the area under the curve for glucose response, while for long-term studies, caffeinated coffee may improve the glycaemic metabolism by reducing the glucose curve and increasing the insulin response. The findings suggest that consumption of caffeinated coffee may lead to unfavourable acute effects; however, an improvement on glucose metabolism was found on long-term follow-up.

Caffeinated Drinks Intake, Late Chronotype, and Increased Body Mass Index among Medical Students in Chongqing, China: A Multiple Mediation Model

Background: This paper investigates the problems regarding caffeinated drinks intake, late chronotype, and increased body mass index (BMI) among medical students at a Chinese university. Methods: This cross-sectional study was conducted in 2018 with 616 medical students from Chongqing Medical University in Chongqing, China, whose information were collected by a self-reported questionnaire that included four sections: Demographic characteristics; Caffeinated drinks intake and physical state; Morningness-Eveningness Questionnaire; Depression Anxiety Stress Scale 21. Multiple mediation analyses were conducted to test the impact of late chronotype on increased BMI through caffeinated drinks consumption through two models. Results: The significantly mediated effect of caffeinated drinks consumption was revealed (estimate: -0.01, SE = 0.01, 95% CI [-0.02, -0.01]), and which played a positive role in linking late chronotype (B = -0.01, SE = 0.01, p < 0.001) and increased BMI (B = 1.37, SE = 0.21, p < 0.01), but their significant association did not be found in reversed model. In addition, physical activity and inactivity times demonstrated significant indirect effects in the two models. Conclusions: Interventions should focus on reducing caffeinated drinks intake and sedentary behavior time, enhancing physical activity among medical students.

Are coffee's alleged health protective effects real or artifact? The enduring disjunction between relevant experimental and observational evidence

BACKGROUND

There is a large corpus of observational evidence claiming that coffee is health protective and a similarly large corpus of experimental psychopharmacological evidence to suggest that habitual caffeine consumption may be harmful to health.

AIM

The purpose of this study was to examine the disjunction between observational and experimental findings with specific reference to the implications of coffee/caffeine consumption for elevated blood pressure, cardiovascular disease, type 2 diabetes and neurodegenerative disease.

METHOD

Illustrative recent major reviews alleging health protective effects from coffee consumption were examined in light of findings from relevant experimental studies of caffeine.

FINDINGS

Decades-long coffee consumption is but one of countless lifestyle variables that may benefit or harm health. Contradictions concerning the implications of coffee/caffeine consumption for health between observational and experimental research are attributable mostly to poor control over potential confounders in observational studies.

CONCLUSION

When considered in the context of experimental evidence concerning caffeine's known pharmacological actions, there is reason to be sceptical about observational findings alleging health-protective effects from coffee consumption. Long-term randomised trials are needed to end the enduring interpretative disjunction between observational and experimental evidence concerning coffee/caffeine consumption and health.

Postprandial glycaemic and lipaemic responses to chronic coffee consumption may be modulated by CYP1A2 polymorphisms

There is much epidemiological evidence suggesting a reduced risk of development of type 2 diabetes (T2D) in habitual coffee drinkers, however to date there have been few longer-term interventions, directly examining the effects of coffee intake on glucose and lipid metabolism. Previous studies may be confounded by inter-individual variation in caffeine metabolism. Specifically, the rs762551 SNP in the CYP1A2 gene has been demonstrated to influence caffeine metabolism, with carriers of the C allele considered to be of a ‘slow’ metaboliser phenotype. This study investigated the effects of regular coffee intake on markers of glucose and lipid metabolism in coffee-naïve individuals, with novel analysis by rs762551 genotype. Participants were randomised to either a coffee group (n 19) who consumed four cups/d instant coffee for 12 weeks or a control group (n 8) who remained coffee/caffeine free. Venous blood samples were taken pre- and post-intervention. Primary analysis revealed no significant differences between groups. Analysis of the coffee group by genotype revealed several differences. Before coffee intake, the AC genotype (‘slow’ caffeine metabolisers, n 9) displayed higher baseline glucose and NEFA than the AA genotype (‘fast’ caffeine metabolisers, n 10, P<0·05). Post-intervention, reduced postprandial glycaemia and reduced NEFA suppression were observed in the AC genotype, with the opposite result observed in the AA genotype (P<0·05). These observed differences between genotypes warrant further investigation and indicate there may be no one-size-fits-all recommendation with regard to coffee drinking and T2D risk.

Decaffeinated coffee improves insulin sensitivity in healthy men

Epidemiological studies have found coffee consumption is associated with a lower risk for type 2 diabetes mellitus, but the underlying mechanisms remain unclear. Thus, the aim of this randomised, cross-over single-blind study was to investigate the effects of regular coffee, regular coffee with sugar and decaffeinated coffee consumption on glucose metabolism and incretin hormones. Seventeen healthy men participated in five trials each, during which they consumed coffee (decaffeinated, regular (containing caffeine) or regular with sugar) or water (with or without sugar). After 1 h of each intervention, they received an oral glucose tolerance test with one intravenous dose of [1-13C]glucose. The Oral Dose Intravenous Label Experiment was applied and glucose and insulin levels were interpreted using a stable isotope two-compartment minimal model. A mixed-model procedure (PROC MIXED), with subject as random effect and time as repeated measure, was used to compare the effects of the beverages on glucose metabolism and incretin parameters (glucose-dependent insulinotropic peptide (GIP)) and glucagon-like peptide-1 (GLP-1)). Insulin sensitivity was higher with decaffeinated coffee than with water (P<0·05). Regular coffee with sugar did not significantly affect glucose, insulin, C-peptide and incretin hormones, compared with water with sugar. Glucose, insulin, C-peptide, GLP-1 and GIP levels were not statistically different after regular and decaffeinated coffee compared with water. Our findings demonstrated that the consumption of decaffeinated coffee improves insulin sensitivity without changing incretin hormones levels. There was no short-term adverse effect on glucose homoeostasis, after an oral glucose challenge, attributable to the consumption of regular coffee with sugar.

The Potential Effects of Caffeinated Beverages on Insulin Sensitivity

Caffeinated beverages, most commonly tea and coffee, may have important effects on insulin regulation that may give their consumption an important role among nutritional factors in the development of diseases of glucose and insulin metabolism, such as diabetes and atherosclerotic vascular diseases. These beverages include compounds that may have contradictory effects on insulin and glucose: Caffeine impairs insulin sensitivity, but polyphenolic molecules within tea, coffee, and cocoa augment the effects of insulin. In addition, epidemiologic associations exist between greater consumption of such beverages and lower risk of diabetes. The beneficial effects of such beverages might be enhanced by changing the process of their preparation and substitution of other substances commonly added to caffeinated beverages that impair the effect of insulin, such as sugar or milk.

The effect of acute caffeine intake on insulin sensitivity and glycemic control in people with diabetes

The prevalence of diabetes is growing globally, and with no current cure for the disease, management is focused on optimizing blood glucose control to limit complications. The purpose of this review was to examine the effect of caffeine intake on blood glucose levels in people with diabetes. Electronic searches were completed using Pub Med, CINAHL, and Web of Science using the search terms "coffee and insulin," "caffeine and insulin," "caffeine and diabetes," "caffeine and type 1 diabetes," "caffeine and type 2 diabetes," and "caffeine and glycemia." Seven trials were found to meet the search criteria. Five of the 7 studies suggest caffeine intake increases blood glucose levels, and prolongs the period of high blood glucose levels. Future research should focus on larger clinical trials to confirm the relationship and mechanism of action related to caffeine intake and glycemic control in individuals with diabetes.

Environmental/lifestyle factors in the pathogenesis and prevention of type 2 diabetes

BACKGROUND

Environmental and lifestyle changes, in addition to the ageing of populations, are generally believed to account for the rapid global increase in type 2 diabetes prevalence and incidence in recent decades.

DISCUSSION

In this review, we present a comprehensive overview of factors contributing to diabetes risk, including aspects of diet quality and quantity, little physical activity, increased monitor viewing time or sitting in general, exposure to noise or fine dust, short or disturbed sleep, smoking, stress and depression, and a low socioeconomic status. In general, these factors promote an increase in body mass index. Since loss of β-cell function is the ultimate cause of developing overt type 2 diabetes, environmental and lifestyle changes must have resulted in a higher risk of β-cell damage in those at genetic risk. Multiple mechanistic pathways may come into play.

CONCLUSIONS

Strategies of diabetes prevention should aim at promoting a 'diabetes-protective lifestyle' whilst simultaneously enhancing the resistance of the human organism to pro-diabetic environmental and lifestyle factors. More research on diabetes-protective mechanisms seems warranted.

Environmental/lifestyle factors in the pathogenesis and prevention of type 2 diabetes

BACKGROUND

Environmental and lifestyle changes, in addition to the ageing of populations, are generally believed to account for the rapid global increase in type 2 diabetes prevalence and incidence in recent decades.

DISCUSSION

In this review, we present a comprehensive overview of factors contributing to diabetes risk, including aspects of diet quality and quantity, little physical activity, increased monitor viewing time or sitting in general, exposure to noise or fine dust, short or disturbed sleep, smoking, stress and depression, and a low socioeconomic status. In general, these factors promote an increase in body mass index. Since loss of β-cell function is the ultimate cause of developing overt type 2 diabetes, environmental and lifestyle changes must have resulted in a higher risk of β-cell damage in those at genetic risk. Multiple mechanistic pathways may come into play.

CONCLUSIONS

Strategies of diabetes prevention should aim at promoting a 'diabetes-protective lifestyle' whilst simultaneously enhancing the resistance of the human organism to pro-diabetic environmental and lifestyle factors. More research on diabetes-protective mechanisms seems warranted.

Insulin, glucose and beta-hydroxybutyrate responses to a medium-chain triglyceride-based sports supplement: A pilot study

There is a current trend in endurance sports to move athletes towards a low-carbohydrate diet or use periods of low carbohydrate consumption to increase both health and performance. As a result, a market is developing for sports supplements to provide nutritional support during training and racing for athletes who follow a low-carbohydrate lifestyle. PHAT FIBRE (PF) is a powdered sports supplement that includes medium-chain triglycerides suspended in a digestion-resistant carbohydrate and is tailored to the needs of low-carb athletes. Eleven healthy participants were administered 25 g of PF after an overnight fast. After 30 minutes, median blood glucose increased by 6 mg/dl from 94 mg/dl to 100 mg/dl (p = 0.002). At the same time points, median blood beta-hydroxybutyrate (BHB) increased from 0.3 mmol/L to 0.5 mmol/L. The increase in BHB was significant (p = 0.02) after excluding one outlier who had elevated levels of fasting BHB. Insulin levels did not change significantly at any point during the study. In a single participant, a revised formulation of PF (PFv2) produced a 0.6 mmol/L increase in BHB with no effect on blood glucose. These data suggest that PF can provide a source of energy for the low-carb athlete by supporting ketone production without negatively impacting insulin or blood glucose levels.