GI (glycaemic index) is a measure of how much carbohydrate-containing foods increase our blood glucose levels after consumption, as they are broken down into their constituent sugar molecules. Pure glucose is the base measurement at 100. The lower the GI, the lower the rise in blood glucose.

Why does it matter?

In response to a rise in blood glucose, our bodies release the hormone insulin. Insulin works to lower blood glucose by directing the sugar into our cells for use as fuel. But if we have more sugar in our blood than we need for our immediate energy needs, insulin moves the excess into our liver & muscle cells for later use. But this storage space is limited, and any additional amount beyond this level is converted to fat. The presence of insulin also inhibits fat metabolism, to allow the body to preferentially use sugar as its energy source. Aside from triggering fat storage and inhibiting our ability to utilise stored fat, volatility in blood sugar and insulin levels can impact energy, hormone balance, mood, concentration, stress and sleep.

What should we do?

Aim to keep blood sugar levels as stable as possible. By choosing low-GI foods, we ensure a slow and steady release of energy, and typically have lower need for insulin release. But consider not only the GI of individual foods, but also the overall GL (glycaemic load) of your meals. GL is a GI-weighted measure of carbohydrate content which takes into account portion size and food combinations in a meal.

Broadly speaking, when choosing carbohydrate sources, limit processed grains and sugars and opt for wholegrains, fruits and non-starchy vegetables. And combine carbohydrates with proteins and healthy fats to reduce the GL of meals.

  • Wholegrains – their higher fibre content versus processed grains leads to slower digestion and therefore a lower GI, with the added benefit of greater vitamin & mineral content. Opt for wholegrain varieties of bread, pasta and cereals.
  • Processing – not only does processing often remove fibre & nutrients from grains, leading to a higher GI, it can also involve the addition of high-GI refined sugars.
  • Sugars – added sugars will invariably mean a high GI, and even artificial sweeteners may raise blood glucose levels. If you enjoy a sweat treat, opt for natural sugars which supply micronutrients and health benefits, e.g. honey contains various vitamins & minerals, and has anti-bacterial, anti-viral, anti-fungal & anti-inflammatory properties.
  • Combine carbohydrates with proteins and healthy fats – as well as lowering the proportion of carbohydrates in a meal, proteins and fats slow the breakdown of carbohydrates, leading to a lower GL.
  • Healthy snacks – eating snacks between meals can help to keep blood sugar levels stable. But only if you swap the heavily processed and sugar-loaded snack bars for natural foods which contain not only carbohydrates, but protein & healthy fat too.
  • Breakfast – the same applies for breakfast. Watch out for deceptively high-GI cereals, and add protein & healthy fats, to start your day with a flow of steady energy rather than a sugar crash.
  • Look beyond the label – the names of products can often be misleading, so always rely on the ingredient lists. For example, some bread names suggest that they predominantly contain wholegrains, but the ingredient lists tell a different story. And added sugars turn up in more places than you’d imagine. Always check the full ingredients to be sure.

As a word of caution, and with most things nutrition related, GI and GL do not provide a complete picture alone. Not all low GI foods are healthy, and vice versa; there are some occasions when a high GI meal may actually be beneficial, e.g. post intense exercise; individual carbohydrate needs will vary depending on BMR and activity levels.