Glycaemic Index and Weight Loss

What is the Glycaemic Index vs the Glycaemic Load?

The Glycaemic Index (GI) is “a classification of the blood glucose-raising potential of carbohydrate foods relative to glucose or white bread”.  (1)  More specifically the GI is “a measure of the ability of the available carbohydrate in carbohydrate-rich foods to increase blood glucose on a gram-for-gram basis”. (2) The glycaemic response is “the effect the food will have on blood glucose after consumption”.  One failing of the GI Index is that it does not take into account the amount of the foods you are eating.  So watermelon might be fairly high on the glycaemic index, but the absolute number of carbohydrates in a general serving size of watermelon is pretty low. Or other foods, like carrots and bread, for example, might be similar in glycaemic index, but you have to eat a lot more carrots to get the same absolute number of carbohydrates than you do bread.

So to ensure people do not avoid foods that are actually beneficial for them, this led to the development of a further concept – the Glycaemic Load (GL).  The GL index “accounts for how much of carbohydrate is in the food and how each gram of carbohydrate in the food raises blood glucose levels”.  This measure is in particular used as a basis for weight loss and diabetes control. (1)

Determining the GI of a Carbohydrate

A useful way to discern the GI of a carbohydrate is to ask yourself is it man-made or nature made.  Man-made carbs always have an element of processing involved – refining the  foods.  Examples of man-made carbs would include foods such as bread, biscuits, refined sugar, genetically modified maize, over glutenised bread, crisps, chips and sweets. Nature made carbs on the other hand would include foods like fruit and root vegetables like carrots and beetroots – both high in fibre and antioxidants.  So nature made carbs not only contain carbohydrate but also important nutrients and phytonutrients.  For example did you know that potatoes contain more Vitamin C than oranges? (3)

The main focus of a Low GI diet is to make the lower GI foods the main focus of your diet, especially to reach weight loss goals and for general health.  See table 1 below for an example of High and Low GI foods.

Table 1: GI of common foods (1)

However you will see from Table 1 that some foods that are high GI actually have health benefits – such as pineapple containing useful digestive enzymes. (4)

Benefits of a Low GI Diet

So what are the benefits of a Low-GI diet?  A 2014 study found that a “low-GI and energy-restricted diet containing moderate amounts of carbohydrates may be more effective than a high-GI diet and low-fat diet at reducing body weight and controlling glucose and insulin metabolism.” (7)  A further study found that a low-GI diet has many favourable metabolic effects due to the reduction in spikes in the blood sugar.  These include “reduced CVD risk through effects on oxidative stress, blood pressure, serum lipids, coagulation factors, inflammatory mediators, endothelial function and thrombolytic function.” (8)

Shortcomings of the Low GI Diet

But there is a lot of conflicting evidence.  Further studies found no significant difference between low-GI and high-GI diets on weight loss. (9)

A second short coming with the Low GI diet is that we are not always eating carbohydrates in isolation.  We often combine carbohydrates with other macronutrients such as fibre, protein and fat (foods groups that do that impact blood sugar balance).  It is possible to lower the GI and GL of a carb-rich food when these foods are consumed with a minimum of two other macronutrients (eg fat, protein, fibre). (2)   One study concluded in doing so this lead to “significantly lower actual GI and GL values than those derived by nutrient-based calculations. Thus, consuming various macronutrient containing meals is beneficial in regulating [glycaemic response]”. (2)

Health Benefits of Potatoes

Further to this point, white potatoes have become quite a vilified food in recent years due to the high GI.  However, research is providing evidence for the beneficial inclusion of potatoes in our diets.  While mashed potatoes have a high GI on their own, when they are combined with chicken, olive oil and salad the GI was only 54 bringing the meal into the Low GI range. (5)  Of course the portion size should be moderated.  Another research paper found that the benefits of eating potatoes outweighed the negatives, with the extra nutrients and fibre that they bring to the diet. (6)  One caution though, white potatoes should not be a substitute for leafy green or colourful vegetables, which should be increased in the diet. (6)

A third shortcoming of the Low GI diet is that it assumes that everyone will respond in the same way to the sugars in foods.  But the common thread running through our philosophy is that we are all different and people respond differently to foods.  If you are fairly active and have normal blood sugar balance you are going to respond differently than a sedentary person with metabolic issues. (9)

Best use of the Low GI Diet?

So with several shortcomings and conflicting research on the Low GI diet – how can we utilise it?  The index still gives us a good idea about the amount of sugar in carb-rich foods.  The GL index addresses at least one of the shortcomings of the Low GI diet, by addressing the portion size of the food, so might be a better overall index to use.  Perhaps a more useful question when we are selecting carbohydrates is whether they are man-made or nature-made. Nature-made having the benefits of many extra nutrients, phytonutrients and fibre – basically a whole food diet. Man-made often containing anti-nutrients like food additives, refined and processed sugars and grains.  And remembering to combine our carb-rich foods with other macronutrients to slow down the release of sugars into the blood.

A balanced diet has room for Soul Food

I would like to say a quick word about “soul food” here.  A term coined by nutrition and health practitioner Ian Craig in his book “Wholesome Nutrition for You”.  Soul food is food which makes us feel good.  And we consume soul food based on a “quality” rather than “quantity” basis.  Soul food might include a bottle of craft beer, a glass of red wine, a piece of dark chocolate.  Food to be enjoyed in moderation with positive psychological benefits.  Remember the 80/20 rule and enjoy soul food once in a while!

References:

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4994556/
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6449539/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3650503/
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4998156/
  5. https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/protein-and-fat-modify-the-glycaemic-and-insulinaemic-responses-to-a-mashed-potatobased-meal/51D3162EA04C1473FD5C59C450CD0E9D
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3650503/
  7. https://www.ncbi.nlm.nih.gov/pubmed/24787494
  8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2654909/
  9. https://chriskresser.com/is-the-glycemic-index-useful/

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