Episode 73 – Should We Care About Glycaemic Index?

Key Topics Covered

What is the glycaemic index? 

  • The glycaemic index is a measure of how quickly and how much blood glucose levels rise in response to a certain amount of a carbohydrate-rich food 
  • Low GI = <55  
  • High GI = >70 
  • The current validated system has glucose at 100, for everything else to be compared to. 

Why was it designed?

  • It was designed to help identify which foods raise blood glucose levels (BGL’s) more. 
  • This is particularly relevant for people with diabetes – although we will talk about some more thoughts on this topic later. It has also been linked to positive outcomes for those with PCOS, but that faces similar complexities too. 
  • It also has links with improving acne. 

Does it affect body composition? 

  • The short answer is no, it does not really matter. Most people would be better off not thinking about it. 
  • The long answer is that the research links it with weight loss in uncontrolled settings. 
  • Part of this is because on average, people who consume lower GI diets will typically consume a lower-calorie diet. Their diets will likely be more micronutrient-rich too. 
  • People might stay fuller for longer. 
  • But we also have a lot of research indicating that when total calorie intake is matched, the glycaemic index is mostly irrelevant for body composition. 
  • On average, a lower GI diet is going to have some advantages and make fat loss easier for some people. But knowing that it is not actually due to the GI content is important because since it helps us make certain decisions more easily e.g. you don’t need to stress about having a higher GI fruit instead of a low GI option. 

Where it falls apart? 

  • Inter-individual variation – it is based on AVERAGE response. 
    • When you look at individual scores within research on this topic there is a pretty big variation even between people’s responses to foods. E.g. one food might be a higher GI for one person and lower for another, but the opposite for another set of foods. 
  • Intra-individual variation: The same food can have a different effect on you at different times due to different responses related to stress, sickness, insulin resistance, etc 
  • Riper fruit often has a higher GI. 
  • Fat content decreases GI. It slows down the digestion and absorption of carbohydrates. This means BGLs raise slower. This causes issues in people who are viewing “low GI = better” e.g. chocolate is often low GI. 
  • It doesn’t account for TOTAL carbohydrate content, which is a hugely important component. 

What is Glycaemic Load? 

  • Glycaemic load is basically the combination of glycaemic index AND total carbohydrate.
    • Accounts for both  
  • It basically involves multiplying the GI by the total carbs.
    • Then technically, you divide by 100, to give a nicer number that is easier to understand.  But for now, just think of it as GI x Carbs. 
  • This means a high GI food that is high carb will be a high glycaemic load. Vice versa for a low-carb, low-GI food. 

Why is Glycaemic Load a Better Tool? 

  • Where it gets interesting is when you mix the two e.g. if you had 2g of straight-up sugar, that would be high GI, but relatively low carb. Even though it is high GI, it is still a low glycaemic load. 
  • This is super relevant for certain foods. Let’s use watermelon as an example. Watermelon is high GI. But in normal amounts, it is not super high carbs. So the impact on BGLs is not much. 
  • But say you had >100g of carbs coming from a low GI form of rice, that would still raise BGLs heaps over time since all of those carbs eventually need to break down into glucose.  
  • This is even more relevant for conditions. It also gives flexibility e.g. you can still eat high GI foods in small amounts. Whereas without understanding this, it almost creates a good vs bad list. 
  • BOTH carb total AND glycaemic index have their place. 
     

Summary

  • Most people don’t need to think much about GI. Just focus on having an overall nutrient-rich diet that has an appropriate amount of calories, macros and micros.  
  • For situations where GI does, it is better to focus on the glycaemic load instead. 

Key Topics Covered:

Studies Mentioned:

Related Blog Post: