Normally, the most I would do would be half a frozen banana, but I ate two bananas yesterday in a smoothie I bought at the gym after a workout.
It depends on who you ask.
In his book, the Longevity Diet, Dr. Valter Longo seems to take the position that certain inflammatory amino acids in animal protein are the thing to limit and that sugar from whole food sources like bananas aren’t as much of a problem. But then you have the Dr. Gundry and Perlmutter camp with books like the Plant Paradox and Grain Brain. These physicians, and you can throw in Peter Attia for good measure, seem to side more on the sugar in all its forms is the enemy side of the fence. So, preliminarily, your attitude on sugar is going to set the table for how you feel about bananas. We tend to settle these debates using genetics and our nutrition plans. Some diet types in our matrix are associated with macro ratios that are more conservative with fruit and carbohydrate intake due to a genetic propensity towards insulin resistance and type 2 diabetes, other diet types can be more liberal glycemic load.
But at the end of the day, no one is going to claim that bananas are “unhealthy” in the same way that say, vegetable oil or refined grains are unhealthy. For some, they are a perfectly healthy option.
Having said that, I have struggled with this question for a bit and want to mind dump my thoughts on the potential health benefits of bananas (as well as the negatives I see) here in this blog post.
The good news on bananas
Fiber and resistant starch
Bananas are high in fiber, and especially before they ripen, resistant starch. This means that they deliver fermentable plant matter to the colon where it can produce healthy short chain fatty acids that protect the wall of the gut. The microbiome works as an ecosystem, which means the name of the game with gut health is to feed the good microbes and keep the bad, like Candida, in check. Foods like bananas can help in this balancing act, as can physical exercise like taking short runs.
When we eat foods high in carbs, but low in fiber, like processed grains, much of the nutrient count gets absorbed in the small intestine early on in the digestive process.1 Over time, this has the result of feeding microbes in the small intestine that aren’t supposed to be there, as well as spiking blood sugar, which is a major cause of inflammation.2 For more on how elevated blood sugar leads to inflammation, check out the post I did on my HbA1c levels.
At least in theory, the high fiber count of green bananas prevents the feeding of bad guys in the small intestine and instead passes nutrients down the line for the short chain fatty acid producing bacteria in the colon. As Dr. Gundry points out in the Plant Paradox, green bananas are a rich source of resistant starch, which is plant matter that is tough to break down and therefore ferments nicely. You can think of resistant starch as a sub-class of fiber.
For more on the “ideal” fiber intake, you may be interested in Aaron’s post breaking down the large fiber study that appeared in the journal Lancet in 2019. Based on that research, 25g a day if fiber seems to the sweet spot.
However, as bananas ripen, the starch count gives away to increased amounts of simple sugars, a topic we will touch on in greater detail in a moment.
Good source of potassium and B6
Bananas are packed with a ton of nutrients and minerals, with potassium being one of the most notable. With a whopping 422mg, one banana contains about 10% of the daily recommendation for potassium intake.3 While I think uric acid is probably more important metric for blood pressure than is mineral balance, getting adequate potassium is definitely part of the puzzle in keeping blood pressure in check. Having said that, foods like sweet potato and avocado both contain more potassium than do bananas.
Bananas also contain significant amounts of vitamin B6 at about 0.5mg per banana. As a nutrition nerd, I think it’s kind of ironic that bananas contain so much B6. Vitamin B6 is a co-factor for the production of diamine oxidase, the enzyme that breaks down histamine in the gut, and yet banana is also a high histamine food, especially as the fruit ripens and browns.
For more on histamine, take a look at my post on histamine intolerance.
In this blog post we did a while back on the effect that different fruits have on liver cancer cells in a test tube, bananas performed well. The chart below illustrates data collected at Cornell about how different fruit compounds inhibited liver cancer in vitro (in a test tube). And that’s the thing that has always gotten me about the sugar in fruit phobias: they also contain antioxidants, so it’s not as open and shut as say eating an ice cream cone is.
Cost effective and convenient
Even in New York City, where a cup of coffee will often run you $5 or more, you can grab a banana from a bodega for about a buck. Stuck in an airport with nothing to eat? A banana and maybe a handful of nuts can be a great option.
But despite the fact that bananas are packed with fiber and essential nutrients, they are not without some negatives, which I will address now.
The bad news on bananas
Bananas are high in histamine
Especially as they ripen, bananas pack a fairly large dose of histamine, so they might not be a great option for people suffering from seasonal allergy or some degree of mast cell mediated dysbiosis of the gut.4
High in amylose – not great for mold sufferers
Amylose is a type of resistant starch, which is a good thing, right? Yes, under normal circumstances. But the best and brightest mold physicians we have out there, like Dr. Richie Shoemaker, put their patients on a low amylose diet to starve the fungal bad guys who feed on these foods. Now, keep in mind, this issue does not need to be on the radar of most people, however, with the increasing prevalence of gut problems, there are a number of people who stand to benefit from some degree of low amylose / low sugar diet while the microbial balance in the gut returns. Long story short, in people with mold, lyme, and other autoimmune type conditions, a low sugar diet may be what the doctor ordered. This means bananas may need to come off the menu for a time.
High in sugar and fructose
This is the big one where the keto crowd has takes swipes at the banana (and fruit in general). They are high in sugar, they contain fructose, they raise blood sugar.
Dr. Robert Lustig is one of the physicians who has sounded the alarm on fructose and its link to non alcoholic fatty liver disease (NAFLD).5 Now, Lustig is adamant that the issue is processed food and added, refined sugars, not whole foods, however, the fact that fructose ages cells at a rate much faster than glucose has many applying the warnings on added sugar to fruits. The thinking is: why not banish all fructose if any is harmful?
But what is the actual glycemic load of a banana?
The glycemic index measures just how fast a given food will spike blood sugar. We want to keep blood sugar level because elevated blood sugar, both over time and in the “post prandial” period after meals gives rise to inflammation. According to the International GI database, ripe banana has a glycemic index of 51, which isn’t bad. Contrast that with the potato which usually measures in the low 90s. Carrots are thought to be around 70, but they have no fructose, so slightly different analysis. The fructose count of an average banana is 7.1 grams, but there is about 14 grams of sugar in a medium banana. One teaspoon of sugar is equal to about 4 grams. So, about 3.5 teaspoons of sugar in a banana, which is a reason some may want to do only a half of a banana or exclude them altogether. At the end of the day, no two people are going to have the same blood sugar response to any food, so if blood sugar is a concern, you may want to buy a blood glucose monitor and start to get a feel for what fruit does to your levels.
I am going to continue adding a half of a frozen banana to my smoothie recipes, but won’t usually do the two banana a day thing either. The glycemic load of bananas isn’t that bad, and the resistant starch is attractive, especially before they fully ripen.
I think the big reasons to avoid bananas center around certain types of chronic illness. If you have an imbalance in the gut, insulin resistance, histamine, mold or lyme issues, bananas may not be a good choice.