Headaches
Eating more bananas than your body is able to tolerate can trigger headaches. This is because bananas contain certain amino acids that are known for causing blood vessels to dilate. This can be especially problematic if you eat bananas that are overripe.
Sleepiness
Bananas contain tryptophan, that amino acid in turkey known for making people sleepy at Thanksgiving. A banana’s carbohydrates block other amino acids from entering the brain, so there is an influx of tryptophan that leads to an increase in the production of serotonin, another sleepiness trigger. Bananas are also high in magnesium, which relaxes the muscles. Bananas contain about 7% of the daily recommended allowance for magnesium, so eating more than a dozen and a half per day will likely trigger an overdose of this mineral. These same properties that trigger sleepiness from just a single banana makes it a great bedtime snack.
Hyperkalemia
Bananas are a great source of potassium, but too much of a good thing can be dangerous. Too many bananas cause an excess of potassium, which can trigger hyperkalemia. This condition causes nausea, a slower pulse, and an irregular heartbeat. It can also trigger cardiac arrest. More than a dozen bananas in a short span of about a day can lead to too much potassium in the system. This might need to be treated with diuretics and kidney dialysis.
Nerve Damage
Believe it or not, too many bananas in a shot period of time can cause nerve damage. This is a risk for those eating a banana-only diet. Bananas contain a great deal of vitamin B6, again, something that is healthy in the right dosage. However, too much can numb the extremities and cause permanent damage in the nervous system. Keep in mind you would need to eat more than 100 bananas per day to overdose on B6, so chances are unless you are entering a banana eating contest, you are in the clear. In the rare event you feel tingling after several days of eating several bananas, you might want to skip a few days or keep your consumption to a single banana per day.
Tooth Decay
Bananas are a sugary fruit, which usually is not a problem for most people. Since it is natural sugar, it does little harm, other than boosting caloric intake. However, if you overdo it, you can experience all the usual disadvantages of eating too much sugar, including tooth decay. The acid from too many bananas can eat away at your tooth enamel, damaging your dental health.
Lack of Fat
Bananas contain no fat, which makes them ideal for some dieters. However, everyone needs a little bit of fat in their diet, so a practice of eating only bananas would prove detrimental to a person’s overall health. Dietary fat is essential to brain development and good health, so avoid eating only a banana for a meal. It makes a great snack or can be paired with other foods, such as peanut butter or almonds, to up the protein and fat content in the meal.
Lack of Protein
In addition to containing no fat, bananas are also low in protein. They contain about one gram, so nowhere near enough to create a healthy meal. Protein helps your body build and repair tissue, and is an essential part of a healthy diet. Since bananas are high in carbohydrates, but low in protein, they are great for a pre-workout snack, but should be skipped for a post-workout refueling.