This one drives me bananas. I have done the research, but am not 100% sure where this fallacy came from. Maybe someone saw a monkey with a big belly eating a banana, and made the connection? I once saw an overweight man eating a salad, and have not touched one since.
In all seriousness, there is one theory as to why this fallacy may exist, and understanding it will help you with similar fallacies in other foods.
The Glycemic Index Theory
According to its founders, the glycemic index (GI) "is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Foods with a high GI are those which are rapidly digested and absorbed and result in marked fluctuations in blood sugar levels. Low-GI foods, by virtue of their slow digestion and absorption, produce gradual rises in blood sugar and insulin levels, and have proven benefits for health."
The typical Western diet, for instance, is based on high-GI foods, such as soda, refined bread, high-sugar cereal and doughnuts (not bananas). I do not think our overweight society is known for eating too much fruit! Low-GI foods make us feel more full (i.e. satiated), and promote the use of fat at the expense of carbohydrate use. Subsequently, we know that a Western diet of the more unhealthy high-GI foods is condusive for fat gain, along with other health concerns, such as obesity and diabetes1.
As a standard, pure sugar or glucose has the maximum GI of 100.
Low GI Foods < 55
High GI Foods > 55
What about Bananas?
Bananas rank high among the fruits, and are lower than other high-GI foods (>55). Bananas can actually be low or high on the GI index, based on how ripe they are (more ripe = higher GI).
Here are some examples taken from the GI database, which compare a banana to more common foods in the Western diet.
|High-GI Food||Glycemic Index|
|Banana||42 - 62|
|Coca-Cola||53 - 63|
|White Bread (1 slice)||70 - 75|
|White Potato (baked, without skin)||98|
So, Are Bananas Fatty?
No. GI is specific to blood glucose changes. So, when comparing bananas to 'unhealthy' foods that are linked to fat gain, we need to consider other things, such as nutritional value. Even though high-sugary foods and drinks (with little to no nutritional value) are linked to fat gain, the GI is not able to (or designed to) provide a complete picture of the health of the food or the role it might play on fat gain.
Take the following example:
|1 Original Glaze
Krispy Kreme Doughnut
|1 Coca-Cola (can, 12oz)||140||0g||0g||No||39g||Yes||0g||0%||0%|
Clearly, despite all being moderate- to high-GI foods, there are major differences in the quality of the foods. Not only is the total added sugar content different, we see important differences in fat, use of hydrogenated oils and corn syrup, fiber content, and vitamins/minerals. Plus, bananas are a natural, whole food.
The GI of a food is impacted greatly by these other factors, and proponents of the GI do not typically promote low carbohydrate diets, because they restrict most fruits. Diabetics, according to the American Diabetes Association, are allowed to eat bananas, and the starch from bananas (with fiber) have even been used to help obese type 2 diabetics.2 In addition, we have ample research in both children and adults that fruit and vegetable consumption is associated with weight-control, and not weight or fat gain.
Common sense, our understanding of the glycemic index, and scientific research tell us that eating bananas are not the root of our obesity epidemic, much less the culprit to our societies belly fat problems. Be weary of any diet or thought that make such claims.
1Brand-Miller, J.C., Holt, S., Pawlak, D.B., & McMillan, J. (2002). Glycemic index and obesity. The American Journal of Clinical Nutrition, 76(1), 2815-2855.
2Ble-Castillo, J.L., et al. (2010). Effects of native banana starch supplementation on body weight and insulin sensitivity in obese type 2 diabetics. International Journal of Environmental Research and Public Health, 7, 1953-1962.