Is it important to choose low GI foods?
Q: What are your thoughts on glycaemic index (GI) please? How important is it to choose low GI foods? Kindest, Sandra
A: The glycaemic index (GI) is a scale based on how quickly the glucose from the food will hit the bloodstream. Essentially, the faster it gets to the bloodstream, the higher it appears on the index. Low GI is considered to be a score of 55 or less.
However, the GI does not take into account the amount of carbohydrate in a food in comparison to the other macronutrients (protein and fat), micronutrients (vitamins and minerals) or how much you consume in one sitting.
The total amount of carbohydrate that we consume has the greatest impact on our blood-glucose levels, and how much insulin is required. Insulin is a hormone that enables glucose to move from the bloodstream into our cells, so that it can be used for energy and so that our blood-glucose levels are kept within the normal range.
However, it is also a body-fatpromoting hormone.
Another categorisation you might be familiar with is glycaemic load (GL). It is a better indicator of how a carbohydrate food will affect blood glucose levels. GL considers the actual amount of carbohydrate you eat in a sitting. For example, pumpkin is considered a high GI food, but it is high in fibre, water, vitamins, minerals and protective phytonutrients, which alters the way it is digested and promotes excellent health. The GL of a serve of pumpkin is low (a good thing).
I highly doubt that the GI would have become a way of assessing carbohydrates if processed foods didn’t exist. When we apply these scientific measurements to real life, we begin to see how they fail to take into account the way that other things we consume alongside carbohydrates might affect the way our body responds to them, as well as the nutritional value that particular foods offer us.
Both GI and GL are affected by the protein, fat and fibre content of a meal, as they all slow down the release of glucose into the blood and hence the requirement for insulin – so when combined with protein, fat and fibre, a highGI food is unlikely to reach our bloodstream in the same way.
Consider a piece of chocolate cake that you might buy from a bakery – many of them are low GI (due to their poor-quality fat content) and, if we chose ‘‘healthy’’ foods this way, they would be a ‘‘good’’ option. Yet they contain high levels of refined sugars, poor-quality fats, virtually no nutrients and are high GL. In other words, the GI can be highly misleading if that is all you use to guide your carbohydrate choices.
It has also been shown that the way a particular food or meal is metabolised and how it impacts blood glucose levels can vary significantly from person to person. So the GI value of a food may not even be an accurate indication of how it will impact your blood glucose levels.
It’s no wonder people feel confused and overwhelmed at times about dietary information! Fortunately, we stop needing concepts like this when we simply eat whole, real foods. So rather than focusing on the GI, I’d encourage you to embrace the statement ‘‘just eat real food’’.
❚ Dr Libby is a nutritional biochemist, best-selling author and speaker. The advice contained in this column is not intended to be a substitute for direct, personalised advice from a health professional. See Dr Libby live during her What Am I Supposed To Eat? tour which is currently under way in New Zealand. For more information, visit drlibby.com