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There are 95 calories in a banana. That is assuming the banana is medium sized and after peeling weighs 100g.
A ripe banana contains exactly the same number of calories as an unripe one – even though it is a lot sweeter. However, because of the way our bodies digest food, the ripe banana may deliver around 10 extra calories to us. Let me explain…
Fewer of the calories in the unripe banana make it through digestion to be used by the body as fuel because of the (TEF).
Our bodies use energy (calories) in processing and digesting all the food we eat. On average it is about 10% of the food’s calorific value.
Eating, chewing, swallowing, digesting, carrying around the extra weight of the food and so on all uses energy, and most of this energy is used in the digestive process. The energy loss incurred by processing what we eat and drink is known as the thermic effect of food.
However, it gets a little more complicated than the 10% average. Some types of foods take much more energy for our bodies to process, and some much less. Simple sugars and fats are easy work for our tums, and only 3% of their calories are used up in digestion.
Proteins are much harder – around 30%. And complex carbohydrates lose about 20% in digestion – that’s double the 10% average.
Now let’s go back to our 100g banana which has 95 calories – ripe or unripe. A breakdown of its food types reveals:
0.3% fat 2.6% fibre 1.0% protein 22.1% carbohydrates
All fat contains 9 calories per gram, all protein contains 4 calories per gram and all carbohydrates contain 4 calories per gram. Fibre does not contain digestable calories.
We can now break down where the calories in the banana are coming from:
0.3% fat x 100g x 9 calories per gram = 2.7 calories 1% protein x 100g x 4 calories per gram = 4 calories 22.1% carbohydrates x 100g x 4 calories per gram = 88.4 calories
Total 95 calories
As you can see, nearly all the calories in our 100g banana come from carbohydrates.
In an unripe (green) banana most of those carbohydrates will be starch, and in a ripe banana most will have turned to sugar. In fact, in a fully ripe banana 91% of the carbohydrates will have become simple sugars.
As for an unripe banana – we must assume it is still edible, otherwise the comparison is meaningless. So let’s say the banana isn’t fully green, but has ripened so that it is just about palatable to eat. I would estimate around 25% of the carbohydrates will have turned into a simple sugar at this point.
So the two comparables are the unripe banana with 25% of its carbohydrates being simple sugars, and the fully ripe banana with 91% of its carbohydrates turned into simple sugars.
Nutrition of unripe banana
0.3% fat 2.6% fibre 1.0% protein 22.1% carbohydrates (25% sugars) of which: 16.6% complex carbohydrates 5.5% simple carbohydrates (sugar)
Nutrition of ripe banana
0.3% fat 2.6% fibre 1.0% protein 22.1% carbohydrates (91% sugars) of which: 2% complex carbohydrates 20.1% simple carbohydrates (sugars)
Now we can apply the thermic effect of food to both the ripe and unripe banana nutrition breakdown to see how many calories make it through digestion:
Thermic effect of food on an unripe banana
0.3% fat x 100g x 9 calories per gram x 97% TEF (thermic effect of food) = 2.6 calories 1.0% protein x 100g x 4 calories per gram x 70% TEF = 2.8 calories 16.6% complex carbohydrates x 100g x 4 calories per gram x 80% TEF = 53.1 calories 5.5% simple carbohydrates (sugar) x100g x 4 calories per gram x 97% TEF = 21.3 calories
Total 100g unripe banana calories after thermic effect of food = 79.8 calories
Thermic effect of food on a ripe banana
0.3% fat x 100g x 9 calories per gram x 97% TEF (thermic effect of food) = 2.6 calories 1.0% protein x 100g x 4 calories per gram x 70% TEF = 2.8 calories 2% complex carbohydrates x 100g x 4 calories per gram x 80% TEF = 6.4 calories 20.1% simple carbohydrates (sugars) x 100g x 4 calories per gram x 97% TEF = 78 calories
Total 100g ripe banana calories after thermic effect of food = 89.8 calories
Yes, whilst the ripe and the unripe banana contain exactly the same amount of calories, because of the way we process food, our bodies receive more calories from the ripe banana.
In the case of the medium 100g banana in this example 10 extra calories are received by our bodies after digestion from the ripe banana.
This example contains an extreme, and some estimates. The extreme is the fully ripe banana in the example. This would be very mushy and completely brown on the outside (not like my photo). In reality your ripe banana may actually have more like 75% sugars, rather than the fully ripe 91%.
The thermic effect of food is still being studied, so note that the percentages given for different food types are estimates – especially where the complex carbohydrates are concerned.
However, the principle still applies. In everyday living I would estimate that your body receives on average between 5 and 10% more calories from a ripe banana than from an unripe one – even though they both contain the same amount of calories in their pre-eaten state.
By David Hart
(c) Copyright 2012. All rights reserved.
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