indulgence, but conventional advice tells us that the former is a better health choice, a source of fibre and B vitamins, and rich in ‘complex’ carbohydrates.
Ah, but there’s always another layer to the story. Let’s peer inside the contents of this grain and try to understand why – regardless of shape, colour, fibre content, organic or not – it potentially does odd things to humans.
WHEAT: SUPERCARBOHYDRATE
The transformation of the domesticated wild grass of Neolithic times into the modern brownies, cupcakes or Victoria sponge requires some serious sleight of hand. These modern configurations were not possible with the dough of ancient wheat. An attempt to make a modern jam doughnut with einkorn wheat, for example, would yield a crumbly mess that would not hold its filling, and it would taste, feel and look like, well, a crumbly mess. In addition to hybridising wheat for increased yield, plant geneticists have also sought to generate hybrids that have properties best suited to become, for instance, a chocolate cupcake or a seven-tiered wedding cake.
Modern Triticum aestivum wheat flour is, on average, 70 per cent carbohydrate by weight, with protein and indigestible fibre each comprising 10 to 15 per cent. The small remaining weight of Triticum wheat flour is fat, mostly phospholipids and polyunsaturated fatty acids.1 (Interestingly, ancient wheat has higher protein content. Emmer wheat, for instance, contains 28 per cent or more protein.2)
Wheat starches are the complex carbohydrates that are the darlings of dietitians. ‘Complex’ means that the carbohydrates in wheat are composed of polymers (repeating chains) of the simple sugar, glucose, unlike simple carbohydrates such as sucrose, which are one- or two-unit sugar structures. (Sucrose is a two-sugar molecule, glucose + fructose.) Conventional wisdom, such as that from your dietitian or the USDA, says we should all reduce our consumption of simple carbohydrates in the form of sweets and fizzy drinks, and increase our consumption of complex carbohydrates.
Of the complex carbohydrate in wheat, 75 per cent is the chain of branching glucose units, amylopectin, and 25 per cent is the linear chain of glucose units, amylose. In the human gastrointestinal tract, both amylopectin and amylose are digested by the salivary and stomach enzyme amylase. Amylopectin is efficiently digested by amylase to glucose, while amylose is much less efficiently digested, some of it making its way to the colon undigested. Thus, the complex carbohydrate amylopectin is rapidly converted to glucose and absorbed into the bloodstream and, because it is most efficiently digested, is mainly responsible for wheat’s blood-sugar-increasing effect.
Other carbohydrate foods also contain amylopectin, but not the same kind of amylopectin as wheat. The branching structure of amylopectin varies depending on its source.3 Amylopectin from legumes, so-called amylopectin C, is the least digestible – hence the schoolkid’s chant, ‘Beans, beans, they’re good for your heart, the more you eat ’em, the more you. . . .’ Undigested amylopectin makes its way to the colon, whereupon the symbiotic bacteria happily dwelling there feast on the undigested starches and generate gases such as nitrogen and hydrogen, making the sugars unavailable for you to digest.
Amylopectin B is the form found in bananas and potatoes and, while more digestible than bean amylopectin C, still resists digestion to some degree. The most digestible form of amylopectin, amylopectin A, is the form found in wheat. Because it is the most digestible, it is the form that most enthusiastically increases blood sugar. This explains why, gram for gram, wheat increases blood sugar to a greater degree than, say, kidney beans or crisps. The amylopectin A of wheat products, complex or no, might be regarded as a supercarbohydrate, a form of highly digestible carbohydrate that is more efficiently converted to blood sugar than nearly all other carbohydrate foods, simple or complex.
This means that not all complex carbohydrates are created equal, with amylopectin A-containing wheat increasing blood sugar more than other complex carbohydrates. But the uniquely digestible amylopectin A of wheat also means that the complex carbohydrate of wheat products, on a gram-for-gram basis, are no better, and are often worse, than even simple carbohydrates such as sucrose.
People are usually shocked when I tell them that whole-wheat bread increases blood sugar to a higher level than sucrose.4 Aside from some extra fibre, eating two slices of whole-wheat bread is really little different, and often worse, than drinking a can of a sugar-sweetened fizzy drink or eating a sugary chocolate bar.
This information is not new. A 1981 University of Toronto study launched the concept of the glycaemic index, i.e., the comparative blood sugar effects of carbohydrates: the higher the blood sugar after consuming a specific food compared to glucose, the higher the glycaemic index (GI). The original study showed that the GI of white bread was 69, while the GI of whole-grain bread was 72 and Shredded Wheat cereal was 67, while that of sucrose (table sugar) was 59.5 Yes, the GI of whole-grain bread is higher than that of sucrose. Incidentally, the GI of a Mars bar – nougat, chocolate, sugar, caramel and all – is 68. That’s better than whole-grain bread. The GI of a Snickers bar is 41 – far better than whole-grain bread.
In fact, the degree of processing, from a blood sugar standpoint, makes little difference: wheat is wheat, with various forms of processing or lack of processing, simple or complex, high-fibre or low-fibre, all generating similarly high blood sugars. Just as ‘boys will be boys’, amylopectin A will be amylopectin A. In healthy, slender volunteers, two medium-sized slices of whole-wheat bread increase blood sugar by 30 mg/dl (from 93 to 123 mg/dl), no different from white bread.6 In people with diabetes, both white and whole-grain bread increase blood sugar 70 to 120 mg/dl over starting levels.7
One consistent observation, also made in the original University of Toronto study as well as in subsequent efforts, is that pasta has a lower two-hour GI, with whole-wheat spaghetti showing a GI of 42 compared to white-flour spaghetti’s GI of 50. Pasta stands apart from other wheat products, probably due, in part, to the compression of the wheat flour that occurs during the extruding process, slowing digestion by amylase. (Rolled fresh pasta, such as fettuccine, has similar glycaemic properties to extruded pastas.) Pastas are also usually made from Triticum durum rather than aestivum, putting them genetically closer to emmer. But even the favourable GI rating of pasta is misleading, since it is only a two-hour observation and pasta has the curious ability to generate high blood sugars for periods of four to six hours after consumption, sending blood sugars up by 100 mg/dl for sustained periods in people with diabetes.8, 9
These irksome facts have not been lost on agricultural and food scientists, who have been trying, via genetic manipulation, to increase the content of so-called resistant starch (starch that does not get fully digested) and reduce the amount of amylopectin. Amylose is the most common resistant starch, comprising as much as 40 to 70 per cent by weight in some purposefully hybridised varieties of wheat.10
Therefore, wheat products elevate blood sugar levels more than virtually any other carbohydrate, from beans to chocolate bars. This has important implications for body weight, since glucose is unavoidably accompanied by insulin, the hormone that allows entry of glucose into the cells of the body, converting the glucose to fat. The higher the blood glucose after consumption of food, the greater the insulin level, the more fat is deposited. This is why, say, eating a three-egg omelette that triggers no increase in glucose does not add to body fat, while two slices of whole-wheat bread increases blood glucose to high levels, triggering insulin and growth of fat, particularly abdominal or deep visceral fat.
There’s even more to wheat’s curious glucose behaviour. The amylopectin A-induced surge in glucose and insulin following wheat consumption is a 120-minute-long phenomenon that produces the ‘high’ at the glucose peak, followed by the ‘low’ of the inevitable glucose drop. The surge and drop creates a two-hour roller coaster ride of satiety and hunger that repeats itself throughout the day. The glucose ‘low’ is responsible for stomach growling
