“Are bananas good for you?” This actually really is a question I am frequently asked. At first I thought it was a pretty silly question because I believed everybody knew that ALL fruits and ALL vegetables were good for you. However, I know why bananas have gotten a bad rap. Although I won’t name names, I am well aware numerous fad diets have been responsible for popularizing the myth that eating foods like carrots, potatoes, bananas and beets are “fattening” and not healthy.
Diet gurus who forbid foods like bananas and potatoes (both of which by the way contain a super special type of fiber called “resistant starch” that helps control blood sugar and reduce fat storage after meals–certainly not a bad thing!) encourage dieters to be conscious of the glycemic index (GI) of the carbohydrate-containing foods they eat.
Low GI foods are considered “good” while high GI foods are considered “bad”. Since carbs like carrots, potatoes, bananas and beets all rate high on the GI index they have all been labeled “bad”, albeit unjustifiably I might add. But to understand this all a bit more you need to understand a smidgen about the GI…
What is the Glycemic Index (GI)?
The glycemic index is a numerical system of measuring how quickly a carbohydrate- containing food turns to glucose (blood sugar). Once glucose from the food you eat is absorbed into your bloodstream blood glucose levels go up and your pancreas starts secreting insulin to help get that sugar out of your bloodstream and into your brain and muscles where it is needed (after all, it is not safe to have high blood sugar levels.)
On the GI index, the slower a carbohydrate containing food is turned to sugar the better and the lower the GI score will be. Here’s a very general scale…
• A GI of 70 or more is considered high
• A GI of 56 to 69 is considered medium
• A GI of 55 or less is considered low
The theory behind the Glycemic Index is simply to minimize insulin-related problems by identifying and avoiding foods that spike blood sugar levels. This sounds simple and reasonable enough. But things aren’t always as simple as they seem.
Research shows a diet that contains unrefined “whole” carbs in their natural form such as bananas, carrots, “whole” potatoes, whole grains and beans does not negatively impact blood sugar or insulin levels—just the opposite! In fact, studies have shown that a diet based on such “whole” carbs can actually reduce fasting insulin levels 30-40% in just three weeks (1). The key is that the diet must be based on unrefined and fiber-rich “whole” carbs.
Carbohydrate-rich refined and empty calorie sugary and floury foods like pretzels, fat free cookies, pizza dough and white bread are not what I am talking about. If you eat refined carbohydrates like these (all of which incidentally happen to have a high GI), you will no doubt negatively impact your blood sugar and secrete more fat-storing insulin than is desirable.
Would You Eat 3 Bananas All at Once?
In addition to unjustifiably classifying some “whole” carbs in the “bad” category, another problem with the GI rating system is that measuring the GI value of food does not take into consideration the normal portion size a person would typically eat. Would you eat 3 bananas at one single sitting? Probably not. But that’s the amount of bananas the GI rating system assumes you would eat in a single serving and that is the serving the GI system is based on.
How is the GI of a Food Determined?
Here’s the deal: the GI value of a food is assessed by giving 10 or more volunteers a serving of a carbohydrate-containing food with 50 grams of digestible (this would not include fiber or the non-digestible portion of the resistant starch) carbohydrate. Scientists then take blood samples every 15 minutes to test how long it takes the 50 grams of carbohydrates to turn into blood sugar. The subject’s response to the carbohydrate being tested is compared with the subject’s sugar response to 50 grams of pure glucose. Since glucose is standard, it is the reference food and the testing of glucose on the subject’s blood sugar levels is done on a separate occasion. The average blood sugar response from 8-10 people will determine the glycemic index (GI) value of that particular carbohydrate containing food. And yes, it is complicated (far too complicated I might add!)
Using the complex GI assessment method, carrots end up ranking high, or “bad”. But, and this is where the GI index is not very useful, the typical 3 ounce serving of carrots contains just 9 grams of carbohydrates and 2 grams of fiber (7 grams of digestible carbs). It’s not at all accurate to say that carrots have a high GI because it’s practically impossible to eat 21 ounces of carrots, the amount needed to obtain the 50 grams of net carbs used to measure the GI of a food. Bananas have a high GI rating too…but you would need to eat nearly 3 whole bananas in order to obtain 50 grams of net carbs. Again, I’m betting you have never eaten 3 whole bananas in a single day, much less all at once! The portion distortion issues with the GI system are just one reason why it is not a reliable method for making healthy food choices.
But Are Bananas Good For You?
Yes!!! Yes!!! Yes!! And so are carrots, potatoes (with their fiber-rich skin), beets and all other “whole” carbohydrates that are eaten in their natural and unrefined form but also happen to have a high / “bad” GI rating. To give you a clearer idea of what I mean by eating these foods in their “natural” and “unrefined” form I mean eating corn, not corn flakes and steel cut oats rather than a granola bar “made with oats.
When you choose to eat “whole” carbs—like bananas!!—you really don’t need to worry about overeating or the GI. “Whole” carbs are difficult to overeat because they take up a lot of bulk and space in your stomach. They work mechanically to fill you up. That’s why you never see anybody gorging on bananas! And I can assure you if you have excess pounds to lose it is most likely NOT because you were eating too many bananas.
An Australian study actually showed that 240 calories of plain boiled potatoes (which are “whole” carbs and rather bulky) satisfied test subjects an astounding 7 x’sas much as a very non-bulky–but low GI— 240 calorie croissant serving. The boiled potato / croissant study clearly demonstrates one reason why food volume / bulk is so important in weight management—the more space a food takes up in your stomach, the more full you feel and the fewer calories you eat. (2)
Additional Major Pitfalls of the Glycemic Index (GI):
The GI doesn’t take the nutritional value of the food into consideration. Just because a food has a low GI does not make it a nutrient-dense food! According to the Glycemic Index the following foods are equally healthy choices simply because they have similar GI ranks:
- Carrots and white pasta
- Bananas and potato chips
- Watermelon and white bread
- Baked Potato and glucose
- The GI goes against common sense. Even with the most rudimentary nutrition education, common sense tells you carrots, bananas, watermelon and baked potatoes are healthier than white pasta, potato chips, white bread and glucose!
- The GI is too complicated!! Doing calculations for everything you eat and memorizing complex GI food charts is NOT practical for real life.
- The GI doesn’t take into consideration that carbohydrates are often eaten in combination with other foods that contain fiber, protein and fat—–fiber, protein and fat all slow the conversion of carbohydrates to blood sugar and reduce the glycemic load of the entire meal.
What About the Glycemic LOAD?
The intrinsic portion distortion problem with the glycemic index ultimately led scientists to come up with the idea of glycemic load, which is better than the GI but still imperfect and too complicated.
The glycemic load (GL) considers the total amount of absorbable carbohydrate (again, not counting fiber or resistant starch) in a 100 gram serving portion of the food being measured that you eat in addition to the GI of that food. Because the glycemic load factors in quantity (and therefore calories) it is a considerably better system than the GI. Using this system low density foods like potatoes, bananas, watermelons and carrots that happen to have a high GI offer a relatively low glycemic load. But regardless, the glycemic index and the glycemic load are a ridiculously complex way to approach eating. Like the misleading Nutrition Facts label, the GI food ranking system is just not the best way to choose your foods.
If You Can’t Rely on the Glycemic Index Then How Can You Tell if a Carbohydrate is “Good” or “Bad”?
The only thing you need to worry about when trying to figure out whether a carbohydrate is “good” or “bad” is whether or not it is a “whole” carbohydrate that is unrefined. That means ALL fruits, ALL vegetables, ALL beans, ALL legumes, ALL whole grains (quinoa, steel cut oats, wheat berries, sprouted flourless whole grain bread, amaranth, barley, etc.), corn and potatoes (with their skins on!!) are all healthy, slimming and good carbohydrate choices. It does not need to be made any more complex than that.
Banana Nutrition 101
But let’s get back to bananas. Are bananas good for you? Here’s just a bit of what you’ll find in a single banana—you decide!
- 100 calories (and I would say a banana sure beats one of those “100 calorie snack packs” for nutrition and convenience!!)
- Fiber (including resistant starch that helps control blood sugar and reduce fat storage after meals)
- Potassium (great for lowering blood pressure)
- Magnesium (important for muscles and bone health)
- Anti-aging antioxidants including vitamin C
- Anti-aging and disease-fighting phytonutrients
- Prebiotics (learn more here) in the form of fructoogliosaccarides (FOS)
- Vitamin B6
Ready to go back to eating bananas? Check out our yummy banana smoothie recipe!
- Barnard RJ, et. al. “Role of diet and exercise in the management of hyperinsulinemia and associated atherosclerotic risk factors.” Am J Cardiol. 1992 Feb 15;69(5):440-4.
- Holt SH, et. al. “A satiety index of common foods.” Eur J Clin Nutr. 1995 Sep;49(9):675-90.