My mother had type 2 diabetes. It contributed to cardiovascular disease, including two bypass operations during her life. Although she tried to watch her diet and manage her blood glucose levels, she was a brittle diabetic. She constantly struggled with hypoglycemic episodes, especially when her activity levels changed – family visits to their home, trips to other households.
A new study from Joslin Hospital may help others with diabetes. For years, scientists have focused on carbohydrate intake. Over 30 years ago, the glycemic index was introduced. The GI evaluates the blood glucose response to a standardized carbohydrate load (usually 100g of available carbohydrate (AC) where AC = total carbohydrate minus dietary fiber content). The interesting feature of the GI is that it favors carbohydrate-rich foods containing fructose over glucose. Thus, a pre-sweetened ready-to-eat-cereal, e.g. Frosted Flakes has a lower GI than the unsweetened cereal, e.g. Corn Flakes. Why? Because the AC of Corn Flakes consists predominantly of glucose from starch whereas Frosted Flakes has sucrose (sugar) which consists of fructose and glucose.
Two excellent reviews of the GI have been written by Dr Julie Jones, Professor Emeritus, College of St Catherine:
- Glycemic Index: The State of the Science, Part 1 – The Measure and its Variability. 2012 Nutrition Today 47:207-213. doi: 10.1097/NT.0b013e31826c4fc4
- Glycemic Index: The State of the Science, Part 2- Roles in Weight, Weight Loss, and Satiety. 2013 Nutrition Today 48:7-16. doi: 10.1097/NT.0b013e31827d8515
However, I digress. The important insight is that the Joslin report shows that individuals with diabetes, and their healthcare professionals, should not solely focus on the amount (or type) of carbohydrate being consumed.
The gut is integral to glucose homeostasis. Digestion and absorption takes time. The 42% increase in insulin levels reported by Dr Howard Wolpert may derive from the stimulatory effect of fat on the release of gut hormones, like glucagon-like peptide 1. Almost 8o years ago, this intestinal impact on glucose homeostasis was coined the ‘incretin’ effect. The fact is that intestinal hormonal responses to luminal fat and glucose stimulate the pancreas to secrete more insulin as blood glucose levels rise. Assuming of course that the pancreas is capable of producing more insulin. Increased insulin secretion will help move glucose from the blood into tissues, primarily muscle and fat, to normalize postprandial blood glucose levels. Assuming that these tissues are responsive to insulin. When muscle and fat are insulin resistant, then elevated insulin AND glucose levels will persist. The composition of one meal can affect metabolic responses to the following meal, i.e. the ‘second meal effect‘.
Our bodies are complex. Our diets are variable. The entire sequence of eating, digesting, absorbing and metabolizing or storing is an exquisitely beautiful sequence. So much to still understand.