Foreword

By Jennie Brand-Miller

I n some quarters, carbohydrates get an undeserved bad rap. But books like the The Good Carbs Cookbook are ahead of the curve, taking advantage of new knowledge of why carbs belong in a healthy diet. If you are a student of human evolution, you will learn that dietary carbohydrates have played an instrumental role throughout our 3-million-year journey from a small upright walking ape (Lucy, Australopithecus afarensis ) to the tall, smooth-skinned creature with a very large brain who can perform high-level maths as well as prolonged strenuous marathons (Homo sapiens sapiens ). How do we know that carbohydrates were important? Well, it’s written in our genes as well as our physiology.

The academic study of the diet of Paleolithic humans is currently a lively topic of research that integrates information from anthropology, archaeology and nutritional sciences, as well as genetics and physiology. In 2015, a small multidisciplinary group of scientists proposed that our brain, reproductive and other tissues, such as the oxygen-carrying red cells in the blood, could not have evolved the way they did without a rich source of glucose molecules in the diet (Quarterly Review of Biology . 2015; vol. 90, no. 3, pp. 251–68.).

The most telling evidence includes the fact that we have evolved multiple copies of the salivary amylase gene, AMY1, which kicks off the digestion of the starch in cooked foods. AMY1 has no other function. Amylase cannot act on raw starch, only starch that has been broken down by heat and water. And the product of starch digestion by amylase is millions of glucose molecules. To perform the act of cooking, humans must have mastered the use of fire, and some scientists such as Richard Wrangham, professor of anthropology at Harvard, have gone so far as to say ‘cooking made us human’.

Today, we know that humans vary in AMY1 copy number from two to as many as sixteen copies. This raises some interesting questions – why were multiple copies an advantage? Did it mean these people digested more starch per meal? Did it make starch taste better – sweeter perhaps? Did it mean more calories were absorbed?

Or did the additional glucose derived from starch digestion provide a specific advantage such as the ability to outrun prey or the likelihood of successful offspring? Our studies at the University of Sydney indicate that those with a higher copy number show a higher blood glucose response after consuming any starchy food. It raises the intriguing possibility that a higher blood glucose level at early stages of human evolution was a distinct advantage.

Specific tissues prefer glucose as their major fuel source. Glucose fuels our energy-demanding large brain and fetal growth as well as strenuously exercising muscles. Having multiple copies of AMY1 allows us to digest starch faster and release glucose into the blood more rapidly and, in theory, permits greater feats of human endurance. Glucose powers the growth of a healthy human fetus born with substantially more body fat than any other primate. Low maternal glucose levels means a small baby with little body fat who fails to thrive outside the womb.

Humans have adapted to dietary shifts in the past. For example, we know for certain that mutations in genes causing lactase persistence (which means we can digest the sugar in milk – lactose) became widespread over the past 5000 years. But the key point about the increase in AMY1 copy number is that the genetic signature suggests it may have begun as long as 1 million years ago. That’s a long time in the course of human evolution. The advent of cooking of starchy foods meant a concentrated source of pre-formed glucose became available for the first time. In theory, therefore, we are programmed to utilise and enjoy starchy foods.

The challenge is to ensure we consume the high-quality carbs that are digested at a rate our bodies can accommodate, preventing burnout of our insulin-producing machinery. Alan Barclay, Kate McGhie and Philippa Sandall are to be commended for giving us no excuse – easy, practical and most of all nutritious and delicious recipes that give us not just good carbs but a micronutrient and phytonutrient mix that is second to none. So next time you hear that carbohydrates should be limited, think again.

Professor Jennie Brand-Miller (AM, PHD, FAIFST, FNSA, MAICD ) is an internationally recognised authority on carbohydrates and the glycemic index with over 250 scientific publications.
She holds a Personal Chair in Human Nutrition in the Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders in the Charles Perkins Centre at the University of Sydney.