July 23, 2020
Americans eat an average of 27 pounds of bananas per person per year. This humble fruit has recently made headlines after a physician from the UK who specializes in diabetes care, claimed that they are as bad for you as eating six teaspoons of sugar. But other medical experts clearly disagreed with his claims, calling them 'misleading' and 'unscientific.'
So, what's the science behind the squabble? Are bananas really as bad for you as eating pure sugar? And is it scientifically plausible to equate all foods to equivalent spoons of sugar anyway? Here's our take.
When you eat a banana, or pure sugar, or any other food, for that matter, your body breaks down all the carbohydrates into simple sugars that move into your bloodstream, causing your blood sugar levels to rise.
Ultimately, all of the carbohydrates in your food end up in our blood as sugar - a fact that’s central to the claim that eating bananas is equivalent to eating pure sugar.
According to this idea, it should therefore be possible to express the nutritional impact of all foods in terms of their equivalent number of spoonfuls of sugar, from chili peppers to candy bars, potatoes to peppermints.
Your average banana contains around 23g of carbohydrates, including 2.6g of fiber and 12g of simple sugars. If you were to measure out the equivalent amount of granulated sugar (about six teaspoons) with 23g of carbohydrate, it would contain 23 g of pure sugar.
But this sum doesn’t really add up.
It isn't just the total amount of carbohydrate in a food that's important. We also have to consider how quickly the sugar hits your bloodstream - and how your body responds to it - in order to get the full picture.
How quickly the carbohydrate in your food becomes, blood sugar depends on which carbohydrates are in your food and how accessible they are to your body.
The GI system rates food using a number up to 100 to indicate how quickly the carbohydrates in the food will enter your blood as sugar, based on average measurements after people have eaten the food. As an example, a banana has a GI of 51 while table sugar has a GI of 63.
These numbers tell us that the average person will experience a greater increase in blood sugar levels after eating sugar compared with a banana. In this case, the difference between the two comes down to a concept called the 'food matrix'.
Table sugar (sucrose) is made up of the simple sugar molecules, glucose and fructose, joined together in pairs. It has a simple crystalline structure and dissolves easily in water. This means that its sugars are easily accessible, so your body releases them quickly and they get fast-tracked into your bloodstream.
By contrast, a banana has a complex structure made up of water, fat, protein, fiber and myriad other molecules, as well as carbohydrates in the form of simple sugars and starches. This complex structure is called a food matrix.
When you eat a banana, your body has to spend time and energy digesting the banana's complex structure before it can get to the carbohydrates. Then the starchy carbohydrates are broken down into simple sugars before they can enter your bloodstream.
This difference explains the lower GI rating for bananas compared with table sugar.
It's worth remembering that GI ratings are based on average responses to a particular food. But the results from our PREDICT study shows that there’s no such thing as the average human: everyone responds differently to food, depending on their own personal metabolism. And different people can respond differently to the same foods, even if they are identical twins.
So, GI alone doesn't fully explain how you will respond to a food, whether that’s a banana, a bagel or anything else.
To really understand what impact bananas or any other food will have on your blood sugar and your overall health, you need to understand how your body responds to food. In short, you need to know your own ‘personalized GI’ to different foods so you can choose those that don’t trigger large peaks and dips in blood sugar.
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