Evidence is accumulating that over-eating -- frequently associated with the development of obesity and diabetes -- is intimately associated with the development of memory disorders and more ominous conditions such as Mild Cognitive Impairment and even neurodegenerative disorders such as Alzheimer disease. For these reasons, I was interested to see a recent posting describing new research that investigated the link between dietary composition and appetite.

Researchers measured the levels of insulin and GLP-1 (short for Glucagon-like peptide-1) following two different types of meal. The meals differed in what is called GI (Glycemic Index). GI is a parameter that describes how various types of carbohydrate foods affect the body's blood sugar levels in the hours following their ingestion. High GI carbohydrates (including bread, cakes, cookies and cornflakes) markedly elevate blood glucose levels following a meal. Low GI carbohydrates increase blood glucose levels much less when consumed. They include most vegetables and non-starchy fruits. Low GI carbohydrates are usually broken down and digested more slowly than high GI foods thus releasing sugar into the bloodstream more slowly.

A low GI diet is known to cause reduced appetite, but the precise mechanisms behind this effect were not known. To address this, Dr. Reza Norouzy and colleagues at King's College London looked at the impact of a single low versus high GI meal on gut hormone levels in twelve healthy volunteers. Each subject was given a medium grade GI dinner the night before, fasted and then was randomly provided either a low (46) or high (66) GI meal for breakfast. Blood samples were taken every thirty minutes for 150 minutes and blood levels of the gut hormone GLP-1 and insulin were measured.

Volunteers who consumed the low GI breakfast had GLP-1 levels that were 20% higher than those eating the high GI meal. They also had 38% lower insulin levels over the same time interval. It is known that GLP-1 potently decreases appetite. These studies show for the first time that a low GI meal elevates GLP-1 levels and these are associated with diminished appetite. This observation provides a physiological mechanism to explain how a low GI meal makes you feel fuller than a high GI meal.

This insight might be used to guide food choices that diminish appetite and (hopefully) help us all maintain optimal weight and brain function at any age.