Key, here, is acknowledgement of the fact that different foods disrupt blood sugar levels to different degrees. The extent to which a food does this can be measured and is referred to as its ‘glycaemic index’ or ‘GI’. Pure glucose (obviously, very disruptive indeed) is assigned a GI of 100, against which other foods can be compared. The higher a food’s GI, the more it disrupts blood sugar (and insulin).
Earlier on, we touched on the fact that conventional wisdom tells us that starchy carbohydrates such as bread, potato, rice, pasta and breakfast cereals give a slow, sustained release of sugar into the bloodstream. Let’s see if that stacks up.
The following table provides a list of a wide range of carbohydrate-based foods and their GI values.4 Before looking at the table, just bear in mind that sucrose (table sugar) has a glycaemic index of 68.
Looking at the foods in the table and their corresponding GI values, one thing is clear: many starchy carbohydrates we’re encouraged to have our fill of turn out to be very disruptive to blood sugar levels. Several of these staples, notably cornflakes, porridge, wholemeal bread and baked potatoes, have GIs about the same or even higher than table sugar. Some are almost as disruptive as pure glucose. Other potentially problematic foodstuffs in this respect include beverages such as sugary soft drinks and fruit juices, and we’ll be examining these in more depth in the next chapter.
Within the GI list, you will see that some fruits and vegetables, including beetroot, pineapple and watermelon, have highish GIs too. Does that mean that these foods are equivalent to foods with similar GIs such as sugary soft drinks and Mars bars?
Actually, while the GI is an important measure of the appropriateness of a food, another is its offering of nutrients such as vitamins and minerals (see below). Also, though, the relevance of the GI needs to be taken in the context of how much we eat of a food. The more we eat of a disruptive food the worse it is for us. Conversely, if we only eat a little of it, it’s unlikely to matter. Not much harm can come from us eating a single Ferrero Rocher. If we eat a whole box, though, that’s clearly more of a problem.
Let’s see how this concept plays out in the real world. The GI table tells us that basmati rice and kiwi fruits have similar glycaemic indices (in the 50s). But are they likely to be similarly disruptive to blood sugar in real life?
Answer this: Have you ever come home very hungry, needed something quite quick to eat, and then polished off a meal with a big serving of rice – say a chilli or curry? If you have, then this meal will have contained quite a lot of a food that is generally disruptive to blood sugar levels. In nutritional parlance, this would be a meal of significant ‘glycaemic load’.
On the other hand, however hungry you have been, have you ever come home and polished off a big bowl of kiwi fruits? When people are hungry, kiwi fruits are not usually their go-to food. And when people do eat them, they may eat one or two (if they’re really going for it), but the fact remains that there is not much volume here, and the end result is unlikely to be particularly disruptive to blood sugar levels.
Another example is the potato. This is a generally disruptive food, but in its favour is the fact that potatoes usually make only an accompaniment to a meal, rather than the basis for it. So, some new potatoes alongside a piece of fish and French beans, or a few roasties accompanying a nice roast and some veggies, are not really an issue. However, meals that are based on generally disruptive starches that have considerable glycaemic load (such as most breakfast cereals, sandwiches, bowls of pasta and dinners containing mounds of rice) are generally best avoided.
Are Grains the Staff of Life?
Not everyone agrees with these established facts about grains and their impact on the body’s blood sugar and insulin levels, though, and will remind us of their supposed ‘essential’ nature for energy and life itself. Is this actually true?
Here’s an official list of the established essential elements in the human diet:5
Water
Energy
Certain amino acids (termed ‘essential amino acids’)
Certain fats (termed ‘essential fats’)
Vitamins (such as vitamins A, C, D, E, K and B vitamins)
Minerals (such as calcium, magnesium and iron)
Trace minerals (such as zinc, iodine, selenium and chromium)
Electrolytes (sodium, potassium and chloride)
However much we scrutinize this list, we will find no mention here of sugar, starch or carbohydrate. Part of the reason for this is that the mitochondria can burn alternative fuels (such as fat) for energy (more about this later).
It is true, though, that some of the body’s cells are totally dependent on glucose as they can burn no other type of fuel. However, glucose can be made from other things (notably, certain amino acids – the building blocks of protein) in the liver. It’s believed that the body can produce about 200g of glucose a day in this way – considerably more than we actually need. The fact is, technically speaking, the absolute requirement for glucose in the diet (from either sugar or starch) is none at all.
This does not necessarily mean that we should eat no carbohydrate, and it can play a role in the diet. For example, people engaged in certain forms of exercise and sports may benefit from carbohydrate (see Chapter 6 for more about this). However, basic physiology reveals that the idea that starchy carbohydrates are ‘essential’ for energy is simply wrong.
Some will still maintain, nonetheless, that grains are good for us because they provide ‘vital nutrients’. Again, does the evidence support this?
One way to assess the nutritional value of a food is to compare its nutrient content with the calories it contains. The idea here is that the best foods will be those of higher nutrient content but lower in the calorie department. This has led researchers to develop a concept known as the ‘nutrient density score’.6
Let’s compare the nutrient density scores of grains with those of other carbohydrate-based foods: fruits and vegetables. This figure represents the scores for fruits and veg. The healthiest foods are those that are positioned low (low energy density) and to the right (high nutrient levels) on the graph. Looking at the table we can see that fresh fruits and vegetables, with the exception of the potato, rate generally very well indeed.
Now, let’s take a look at the nutrient density scores for grains.
As you can see, generally speaking, grain-based foods are higher in energy density and lower in terms of their nutritional offering. This includes wholegrain foods such as wholemeal bread. The un-nutritious nature of grains is strongly hinted at by the fact that many of them (notably bread and many breakfast cereals) are ‘fortified’ with additional nutrients. If they were inherently nutritious, why fortify them?
In reality, grains provide us with no nutritional value that cannot be acquired more healthily elsewhere. And it’s also worth bearing in mind that some grains, notably unrefined wheat, contain substances called ‘phytates’ that block the absorption of nutrients such as calcium, magnesium and iron. Phytates compromise not only the nutritional value of grain, but also foods we eat with them.
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