From turtles to tortillas: the evolution of our low GI diet
PACKED INTO four-wheel drive vehicles, ten middle-aged men and women traveled nearly two days on bumpy dirt roads and trails to reach a remote location, deep in the middle of nowhere. For seven weeks they would live off the land as hunter-gatherers, completely cut off from the niceties’ of the modern world they were born into. Before embarking, each was weighed, measured from one end to the next, tests conducted, and blood and other samples collected. At the end of the seven weeks, lots of weight was lost and markers of major metabolic abnormalities attributed to diseases of their modern lifestyle were either greatly improved or completely normalized. They had begun to feel human again.
This wasn’t an episode of Survivor or new twist on Biggest Loser. It took place over 30 years ago and those dirt roads stretched north out of Derby, in the northern Kimberly region of Western Australia, and the ten participants were full-blood diabetic Aborigines. In this relatively short reversal from urban life, the participants transitioned from breadavores and pastavores to true omnivores. They reverted back to the diet that selected the Paleolithic genome that they (we) all carry today. They had gone on a low-GI diet.
From Janet Jackson to Larry the Cable Guy, people everywhere are achieving and maintaining better health by paying attention to dietary strategies based on some basic and inescapable biological realities buried deep in our ancient genome. For 99.9% of the time that the genus Homo has been around (2.5M yrs), our carbohydrate intake was – on average – lower than the 250 to 400g per day consumed in modern diets (that translates into 1,000 to 1,600 calories a day). But more importantly than quantity, is the change in the quality of carbohydrates we are consuming today compared to our ancestors. And the glycemic index (GI) is a handy way to measure that quality.
“The GI is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin levels, and have proven benefits for health. Low GI diets have been shown to improve both glucose and lipid levels in people with diabetes (type 1 and type 2). They have benefits for weight control because they help control appetite and delay hunger. Low GI diets also reduce insulin levels and insulin resistance. Any farmer or rancher who raises chickens, goats, pigs, or cattle, will tell you if you want to fatten an animal before slaughter, just feed them high-GI foods (like corn) or antibiotic-laden feeds. (The Glycemic Foundation)”
For seven weeks, the overweight and diabetic Aborigines subsisted on a diet of turtles, kangaroo, birds, fish, crocodiles, figs, yabbies (look that one up!), yams, various vegetables, bush honey and so forth. In order of energy contribution at a macronutrient level, the diet was dominated by protein, followed by fat, then carbohydrate. Though they were “living off the land” and digging yams and walking around a lot, the researchers accompanying them were actually amazed at the low level of physical activity.
Contrast this diet with the urban setting before setting out on this little walk about. Back home the main dietary components were flour, sugar, rice, carbonated sugary drinks, booze, powdered milk, cheap fatty meats, potatoes, onions, and small amounts of fruits and veggies. Unlike the protein>fat>carb diet in the bush, the urban diet went carb>fat>protein. The latter should sound familiar, as carbohydrate intake in affluent countries average 50%. And thanks to decades of bad science and misinformation on the evils of fat, government recommendations on carbohydrates range as high as 65%.
Since our Aboriginal group was living a hunter-gatherer existence, they did not have access to agricultural goods like wheat, corn, etc. This is exactly how all humans lived for the last 99.9% of human history (no agriculture). This meant that the carbohydrate (plants) we did consume – and that was consumed by our wayward travelers in the outback – was minimally processed. Processing can mean a lot of things that can range from the temperature and cooking methods (grilling, steaming) to the amount of mechanical processing (e.g., grinding, milling).
The minimally processed diet consumed in the outback meant that what carbohydrate that was eaten, was slowly digested and slowly absorbed into the blood stream and elicited a slow and limited insulin response (i.e., good quality carbs). Tests conducted before, during and after the 7 weeks in the outback, revealed marked improvement in how the individuals utilized and cleared glucose from the bloodstream and importantly, improved insulin sensitivity.
The improved insulin sensitivity is perhaps the most interesting result after the 7 weeks in the bush and the least understood evolutionary mechanism involved in how a low-GI works (note that decreased insulin sensitivity is associated with central obesity, abnormal cholesterol levels, high blood pressure – a cascade of problems known as the metabolic syndrome). As glucose is absorbed into the blood stream from consuming carbs, the pancreas excretes appropriate amounts of insulin, which in turn trigger organs and muscle to absorb the glucose. An insulin resistant person will not be able to absorb that glucose and insulin efficiently and thus it keeps circulating, unused, in the blood. And this is when the problems occur.
Though this may come as a shocker, the metabolic reality of our Paleolithic physiology is that we in no way need up to 65% of our energy to come from carbohydrates – as recommended by the USDA – not even close to that amount. Over the last 2.5M years humans have become steadily more carnivorous and what carbohydrate we did consume were unusable due to the large amount of fiber. It was not until very recently – circa 5-12,000 years ago – with the advent of agriculture, did humans consume energy dense and starchy foods with consistency. However, much of these energy dense cereals were coarsely ground or eaten in whole or cracked forms with large intact portions of fiber. These grains were slowly digested and slowly absorbed (i.e., low-GI). Our Paleolithic genome coped well with the high(er) carbohydrate but low-GI diet. But this was about to change.
The industrial revolution in the 17th century marked the era of the high-GI diet with the introduction of steel roller mills that produced finely ground flours with the fiber easily removed. These finely ground flours were easily gelatinized during cooking and thus increased their digestion and absorption. We in affect began mainlining glucose. And the rest is history.
Once our “modern” Aborigines returned their “ancient” genome to the low-carb and low-GI landscape on which it was selected, everything began to normalize. This low-GI reality means humans are innately insulin resistant. That is, a scarcity of usable carbohydrate, rather than food energy, and a high protein diet over the course of human evolution led to a positive selection of insulin resistance as a survival advantage. What glucose that was available in our ancient veins was used thriftily by our muscles and organs and redirected during pregnancy for fetal growth, resulting in greater survival of offspring. Hence why we are here today. So any diet that includes a significant amount of usable carbohydrates (e.g., pasta, white bread, sugary sodas), will only increase resistance of an already insulin resistant body. However, this does not mean that a heavy vegetarian diet reliant on large amounts and diversity of veggies will do the same – as a significant part of that diet would be unusable (high fiber).
Our modern diet has us awash in insulin and its myriad of metabolic problems ranging from weight gain, diabetes, blood pressure, heart disease, and more. Add to this the Angry Bird Era we have entered – at 750 million downloads and counting, it’s estimated that 200,000 inactive years have been collectively wasted by gamers on this game alone – our lifestyle has gave rise to an unprecedented body composition characterized by reduction in healthy years later in our life cycle. Disease comes earlier.
So we would do well to pay a little more attention to the basics of human biology.