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There are two main considerations if we’re looking to optimize blood sugar levels: when we eat, and what we eat.

The timing of eating can be important because irregular eating can lead to us consuming too little at some times and too much at others. Imagine skipping breakfast, having a snatched sandwich at lunch, and then getting so hungry by the evening that you proceed to eat about half your weight in food washed down with some wine or beer. Irrespective of what you eat, this sort of pattern of eating is far from ideal for blood sugar stability.

Some smoothing out of the eating pattern can be important for some people. This does not necessarily mean eating strictly by the clock or perpetually grazing through the day, but it does generally require eating regularly enough to be able to quell any drive for eating big meals. In Chapter 3 we’ll be exploring eating patterns in more depth.

In this chapter, though, we’re going to focus mainly on what to eat, and specifically the sort of diet that stabilizes blood sugar levels.

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.