Early work on dietary fiber showed fiber viscosity to be a determinant of postprandial glycemic and insulinemic responses. The reduced glycemic response was hypothesized to be due to the ability of viscous fiber to reduce the rate of glucose absorption from the small intestine. Evidence for slow absorption came from studies showing prolonged suppression of serum free-fatty acids (FFA). The postprandial glycemic responses elicited by many foods were measured to see if they were related to food fiber content; this lead to the development of the glycemic index (GI). Studies using different sources and amounts of avilable-carbohydrate produced a mathematical model that accurately predicted the glycemic impact of mixed meals relative to that elicited by 50g glucose. The digestibility of foods in-vitro was inversely related to food GI; the amounts of available-carbohydrate malabsorbed accounted for only a small fraction of the reduced glycemic response but provided carbohydrate for colonic fermentation. It was known that carbohydrate fermentation by colonic bacteria produced gases and short-chain fatty acids (SCFA). A method to assess carbohydrate malabsorption from breath hydrogen excretion was validated against direct measurement from subjects with an ileostomy. The effects of rectally infused SCFA on serum SCFA, glucose and FFA were studied. We were able to show that consuming an inulin increased postprandial serum SCFA and suppressed FFA and that long-term fiber intake increased serum GLP-1 in humans. I have been fortunate to be able to conduct such studies and been both astounded and delighted when results support hypotheses.
Dr. Wolever obtained a medical degree from Oxford University in 1980, a PhD in Nutritional Sciences from the University of Toronto in 1986, a Doctorate in Medicine from Oxford in 1993, an Honorary Doctorate in Health Sciences and Medicine from the University of Ottawa in 2018 and the Robert H Herman Memorial Award from the American Society of Nutrition in 2020. He is Professor Emeritus in the Department of Nutritional Sciences, University of Toronto, and Principal Scientist & Medical Director at INQUIS Clinical Research. Dr. Wolever’s research centres on the effects of dietary carbohydrates on human physiology and metabolism. He has written or co-authored over 380 papers in peer-reviewed scientific journals, and written a book entitled: The Glycaemic Index: A Physiological Classification of Dietary Carbohydrate. In 1997, Dr. Wolever founded Glycaemic Index Testing, Inc. to provide confidential GI testing services to industry. To cope with increased demand and provide a wider range of clinical research services, INQUIS (formerly GI Labs) was formed in 2004. Dr. Wolever is married with 3 children and enjoys cycling, orienteering and playing the recorder.