Showing papers by "Thomas M.S. Wolever published in 2013"

Is glycaemic index (GI) a valid measure of carbohydrate quality

Abstract: Recent criticisms of the glycaemic index (GI) focus on its validity with assertions that GI methodology is not valid, GI values are inaccurate and imprecise, GI does not predict what foods are healthy and that whole grain and fibre are better markers of carbohydrate quality than GI. None of the critics provide sound reasons for rejecting GI because some of their arguments are based on flagrant errors in understanding and interpretation while others are not supported by current data or are inconsistent with other nutritional recommendations. This paper addresses current criticisms of GI and outlines reasons why GI is valid: (1) GI methodology is accurate and precise enough for practical use; (2) GI is a property of foods; and (3) GI is biologically meaningful and relevant to virtually everyone. Current dietary guidelines recommend increased consumption of whole grains and dietary fibre but do not mention GI. However, this is illogical because the evidence that GI affects health outcomes is at least as good or better than that for whole grains and fibre. GI is a novel concept from a regulatory point of view and a number of problems need to be addressed to successfully translate GI knowledge into practice. The problems are not insurmountable but no progress can be made until bias and misunderstanding about GI can be overcome and there is better agreement about what is the actual state of knowledge on GI so that the real issues can be identified and addressed.

Age, Dietary Fiber, Breath Methane, and Fecal Short Chain Fatty Acids Are Interrelated in Archaea-Positive Humans

Abstract: Recent attention has focused on the significance of colonic Archaea in human health and energy metabolism. The main objectives of this study were to determine the associations among the number of fecal Archaea, body mass index (BMI), fecal short chain fatty acid (SCFA) concentrations, and dietary intakes of healthy humans. We collected demographic information, 3-d diet records, and breath and fecal samples from 95 healthy participants who were divided into 2 groups: detectable Archaea (>10(6) copies/g; Arch+ve) and undetectable Archaea. Dietary intakes, BMI, and fecal SCFAs were similar in both groups. The mean number of Archaea 16S rRNA gene copies detected in Arch+ve participants' feces was 8.9 ± 0.2 log/g wet weight. In Arch+ve participants, there were positive correlations between breath methane and age (r = 0.52; P = 0.001), total dietary fiber (TDF) intake (r = 0.57; P = 0.0003), and log number of fecal Archaea 16S rRNA gene copies (r = 0.35; P = 0.03). In the Arch+ve group, negative correlations were observed between TDF/1000 kcal and fecal total SCFA (r = -0.46; P ≤ 0.01) and between breath methane and fecal total SCFA (r = -0.42; P = 0.01). Principal component analysis identified a distinct Archaea factor with positive loadings of age, breath methane, TDF, TDF/1000 kcal, and number of log Archaea 16S rRNA gene copies. The results suggest that colonic Archaea is not associated with obesity in healthy humans. The presence of Archaea in humans may influence colonic fermentation by altering SCFA metabolism and fecal SCFA profile.

Preoperative carbohydrate loading in patients undergoing coronary artery bypass or spinal surgery

Abstract: BACKGROUND:Surgical stress creates a state of insulin resistance which may contribute to the development of hyperglycemia and, subsequently, postoperative complications. Consumption of an oral carbohydrate supplement before surgery may improve insulin sensitivity and reduce hyperglycemia. In this tr

Attenuation of glycemic responses by oat β-glucan solutions and viscoelastic gels is dependent on molecular weight distribution

Abstract: Oat β-glucan attenuates postprandial glycemic responses when solubilized to form viscous solutions. High molecular weight (MW) β-glucan is associated with high solution viscosity, which is in turn associated with lower glycemic responses. However, low MW β-glucan is also able to form viscoelastic gels. The effect of low (145 000 g mol−1) and high (580 000 g mol−1) MW β-glucan presented as liquid drinks and gels on glycemic responses was determined. Healthy subjects (n = 15) consumed 50 g glucose drinks with no β-glucan; 4 g low MW; or 4 g high MW β-glucan; and gels containing 4 g low MW; 2 g low plus 2 g high MW; or 3 g high plus 1 g low MW β-glucan. Overall, β-glucan solutions elicited lower glycemic responses than gels. For gels, peak blood glucose rise (PBGR) decreased with increasing dose of high MW β-glucan (r2 = 0.976, P > 0.05), and PBGR for the gel with 3 g high-MW was lower than for the control (P < 0.05). However, β-glucan gels retained glucose better than solutions under in vitro analysis. Observed effects were found to be related to the rheological properties of the foods. β-Glucan solutions and not gels effectively attenuated in vivo glycemic responses.

Increasing the viscosity of oat β-glucan beverages by reducing solution volume does not reduce glycaemic responses.

Abstract: The soluble fibre (1 → 3)(1 → 4)-β-D-glucan attenuates postprandial glycaemic responses when administered in solution. This attenuating effect is strengthened when solution viscosity is increased by increasing the β-glucan dose or molecular weight (MW). The effect of varying solution viscosity by changing solution volume, without changing the β-glucan dose or MW, on glycaemic responses was determined. A total of fifteen healthy subjects received six 50 g oral glucose beverages prepared with or without 4 g of high-MW (HMW, 580,000 g/mol) or low-MW (LMW, 145,000 g/mol) β-glucan, with a beverage volume of 250 or 600 ml. Postprandial plasma glucose concentration was measured over 2 h, and the peak blood glucose rise (PBGR) and the incremental area under the glycaemic response curve (AUC) were calculated. Subjects served as their own controls. The physico-chemical properties of the beverages were measured to examine their relationship with glycaemic response results. The HMW β-glucan beverage was more viscous and achieved greater reductions in PBGR than the glucose beverage with LMW β-glucan (P 9-fold difference) but not in PBGR (P > 0·05). No differences in AUC were detected among the beverages (P = 0·147). The effects of β-glucan on glycaemic response were altered by changes in beverage viscosity achieved through changes in MW but not in volume. Therefore, β-glucan dose and MW are the most vital characteristics for optimising the bioactivity of β-glucan solutions with respect to glycaemic response.

Altering source or amount of dietary carbohydrate has acute and chronic effects on postprandial glucose and triglycerides in type 2 diabetes: Canadian trial of Carbohydrates in Diabetes (CCD)

Abstract: Background and aims Nutrition recommendations for type 2 diabetes (T2DM) are partly guided by the postprandial responses elicited by diets varying in carbohydrate (CHO). We aimed to explore whether long-term changes in postprandial responses on low-glycemic-index (GI) or low-CHO diets were due to acute or chronic effects in T2DM. Methods and results Subjects with diet-alone-treated T2DM were randomly assigned to high-CHO/high-GI (H), high-CHO/low-GI (L), or low-CHO/high-monounsaturated-fat (M) diets for 12-months. At week-0 (Baseline) postprandial responses after H-meals (55% CHO, GI = 61) were measured from 0800 h to 1600 h. After 12 mo subjects were randomly assigned to H-meals or study diet meals (L, 57% CHO, GI = 50; M, 44% CHO, GI = 61). This yielded 5 groups: H diet with H-meals (HH, n = 34); L diet with H- (LH, n = 17) or L-meals (LL, n = 16); and M diet with H- (MH, n = 18) or M meals (MM, n = 19). Postprandial glucose fluctuations were lower in LL than all other groups ( p p p = 0.028). In LH, triglycerides were consistently (0.18–0.34 mmol/L) higher than Baseline throughout the day, while in LL the difference from Baseline varied across the day from 0.04 to 0.36 mmol/L ( p Conclusion Low-GI and low-CHO diets have both acute and chronic effects on postprandial glucose and triglycerides in T2DM subjects. Thus, the composition of the acute test-meal and the habitual diet should be considered when interpreting the nutritional implications of different postprandial responses. Clinical Trials: ISRCTN Register number ISRCTN81151522. URL: http://www.controlled-trials.com/ISRCTN81151522. Registered: 12 September, 2005.

Glycemic index claims on food labels: review of Health Canada's evaluation

Abstract: Recently Health Canada (HC) published its opinion that including glycemic index (GI) values on food labels would be misleading and not add value to nutrition labeling and dietary guidelines to help consumers make healthier food choices. Important areas of concern were identified by HC, but the discussion of them is scientifically invalid. HC concluded that GI has poor precision for labeling purposes based on incorrect application of the standard deviation. In fact, GI methodology is precise enough to distinguish, with high probability, low-GI (GI ≤ 55) from high-GI (GI ≥ 70) foods and to pass the Canadian Food Inspection Agency Nutrition Compliance Test procedure. HC rightly concluded that GI does not respond to portion size, whereas glycemic response does, but no valid evidence was provided to support the assertion that a lower-GI food could have a higher glycemic response. HC's focus on glycemic response could promote a low-carbohydrate diet inconsistent with nutrition recommendations. HC correctly concluded that GI is unresponsive to the replacement of available- with unavailable-carbohydrate but this is irrelevant to GI labeling. HC is rightly concerned about promoting unhealthy low-GI foods; however, this could be avoided by prohibiting GI labeling on such foods. Therefore, HC has provided neither a helpful nor scientifically valid evaluation of GI for labeling purposes but has contributed to the wealth of misinformation about GI in the literature. Currently, Canadian consumers only have access to unregulated and misleading information about GI; well-crafted guidelines for GI labeling would provide consumers accurate information about GI and help them make healthier food choices.

Comment on: Wolpert et al. Dietary Fat Acutely Increases Glucose Concentrations and Insulin Requirements in Patients With Type 1 Diabetes: Implications for Carbohydrate-Based Bolus Dose Calculation and Intensive Diabetes Management. Diabetes Care 2013;36:810–816

Abstract: I read with great interest the recent article by Wolpert et al. (1) in which they compared postprandial responses elicited by low- and high-fat dinner test meals and concluded that dietary fat increases glucose levels and insulin requirements in people with type 1 diabetes. This is consistent with recent results …

Glycemic and insulinemic response to four different sweeteners in healthy individuals: A double blind, randomized controlled trial.

Abstract: BackgroundThe non-nutritive sweetener, erythritol, does not change postprandial glucose levels, whether this holds true for forms which are modulated to be more intensely sweet is not known. Object...