Bananas and weight loss: What does the science say?

Bananas have been proposed as a miracle answer to the age-old question, “How do I lose weight?” Although they are a great source of fiber and potassium, claims that they are good for weight loss are not rooted in good quality science. 

Americans eat an average of 27 pounds of bananas each year. This is the equivalent of just over 100 medium bananas.

ZOE’s PREDICT program — which is the largest nutritional study of its kind, with over 10,000 participants — found that your body's response to the foods you eat is unique. 

This means that while some people can enjoy bananas in moderation, others should eat them only occasionally.  

If you want to lose weight, it's important to consider what works best for you and your body. Although bananas are a better choice than cookies, they are probably not the best fruit option.

No single food has a magical power to make you lose weight. Success lies in having a balanced diet and picking foods that avoid big blood sugar spikes, which can make you hungry again soon after eating them.

Keep reading to learn more about why our science shows that bananas are not great for weight loss and what foods to eat instead.

Bananas and weight loss

The reason why many people claim a link between bananas and weight loss is largely due to the fruit’s high fiber content. A medium sized banana contains around 3 grams of fiber, which is 10% of the recommended daily intake. 

Research indicates that a high fiber diet can assist with weight loss because high fiber foods are more filling than their low fiber counterparts.

This makes you feel full for longer and stops you from eating again soon after, thereby contributing to weight loss. 

But many other fruits are also high in fiber, as well as being high in the vitamins and minerals required for your health.

In fact, raspberries have twice the amount of fiber per portion compared with bananas, so this could be a good switch. Other common high fiber fruits are apples, pears, oranges, and strawberries

For weight loss, our science suggests that bananas are not a good option because of the high sugar content in the fruit and how your body responds to it. 

When you eat a banana, all the carbohydrates it contains are broken down into simple sugars, which cause a rise in your blood sugar levels. 

How quickly we see this rise is known as the glycemic index (GI). The GI system rates foods from 0 to 100, with 0 causing the slowest blood sugar rise and 100 causing the fastest. 

A ripe banana has a GI of 51, table sugar has a GI of 65, and pure glucose has a GI of 100. This tells us that glucose will cause the sharpest spike in blood sugar, followed by table sugar, and then a banana. 

By comparison, a single chocolate bar has a similar GI ranking of 49. This gives you an idea of how much a banana can cause your blood sugar to rise when you eat it.

These big blood sugar spikes lead to blood sugar crashes, which make you feel tired and hungry.  You are also more likely to eat again sooner.

Although these GI values are based on an average response, our research shows that there is no average person. We are unique in the way we respond to different foods. 

A change in blood sugar after eating is part of a normal, healthy response. But data from our PREDICT study has shown that many people have strong blood sugar spikes in response to eating bananas, which then lead to blood sugar crashes and feeling hungry again soon after. 

These examples of a moderate and a large blood sugar spike from ZOE's data show that individual responses to bananas vary widely across the population.

Banana nutrition facts

At face value, bananas paint quite a good picture with their high fiber and low calorie content. 

Nutrients in an average banana:

  • Calories: 89

  • Water: 74.9 g

  • Protein: 1.09 g

  • Carbs: 22.8 g

  • Sugar: 12.2 g

  • Fiber: 2.6 g

  • Fat: 0.3 g

But at ZOE, we have found that individual responses to bananas vary widely across the population, which means that these numbers don't actually tell you what happens when you eat a banana.

We found that roughly 41% of people have very large blood sugar spikes after eating bananas. They should therefore only eat bananas in moderation.

ZOE's PREDICT study shows that roughly 41% of participants experience very large blood sugar spikes after eating bananas.

This is worlds away from the generic information provided by nutrition outlets, which say that bananas are good for weight loss and that we should be increasing our intake to lose weight.

When you look at the nutritional information of a food without knowing how your body responds to it, you are only getting half of the story. 

You might respond well to bananas and can eat them regularly, or you might respond badly and should only eat them in moderation. If you know how your body responds to different foods, you can make the best choices for your own health.

You can take ZOE’s personalized quiz to find out how you can discover your own unique blood sugar and blood fat responses to food.

Health benefits of bananas

Our research shows that bananas are not the holy grail answer to losing weight, but that doesn’t mean bananas are unhealthy. 

Bananas are a good source of potassium and magnesium, which is essential for controlling blood pressure and maintaining heart health. Research suggests that a potassium-rich diet can significantly reduce your risk of heart disease.

Bananas can also improve digestive health because they contain two types of fiber: resistant starch and pectin. Resistant starch is a great food source for your gut microbiome, which is made up of the trillions of microbes that live in your gut. 

These microbes break down resistant starch, and your body uses the molecules for important functions. Some early research also suggests that pectin can protect against colon cancer.

If you do endurance sports, bananas are a great choice before, during, and after your workout, according to one study. They may also help with recovery by reducing cramps and soreness following exercise. 

Other than before or after a workout, the best time to eat bananas depends on your body and how it responds to food. For some people, this might be in the morning. For others, it might be at the end of a meal. 

If you’ve had a bad night’s sleep, steer clear of bananas. Our latest unpublished research shows that how much and how well you sleep can affect your blood sugar response to food the next morning. 

This means you are more likely to have a sugar spike followed by a crash if you eat a banana after a bad night of sleep. 

Is unripe or ripe best for nutrition? 

How ripe a banana is can affect your blood sugar response after eating it. Ripe bananas have a GI of 51, but unripe bananas have a much lower GI of 42. This means that ripe bananas will cause a higher blood sugar spike than unripe bananas.

As mentioned above, bananas contain resistant starch, which is a great food source for your gut microbiome. As bananas ripen, they lose their starch. Unripe bananas contain 70-80% starch, whereas ripe bananas can have as little as 1% starch. 

The levels of pectin also decrease as bananas ripen, causing them to become soft. Pectin and resistant starch can benefit your gut microbiome and reduce your blood sugar response after eating. 

Unripe bananas are a better choice, but many people prefer soft and sweet ripe bananas. 

A great way to combat the blood sugar spikes that occur after eating ripe bananas is to combine them with a fat or protein source to slow down absorption in the digestive tract. 

This stops the blood sugar from rising as quickly and is also a great opportunity to incorporate protein and healthy fat in your diet. Some great ingredients to combine with bananas include nut butters, pumpkin seeds, and full fat yogurt. 

To understand the impact bananas or any other food will have on your personal, unique blood sugar levels, you need to understand how your body responds to food. 

The ZOE program analyzes your blood sugar in combination with your blood fat and gut microbiome to show you which food combinations work best for you and your body.


No single food can help you lose weight, and bananas should definitely not be your go-to solution.

It’s important to eat a varied and balanced diet that contains all key nutrients for your health. Although bananas work well for some people’s metabolism, this is not the case for most people. That’s why suggesting a one-size-fits-all diet to aid weight loss doesn’t work.

Our research at ZOE shows that a lot of people have a strong blood sugar response to bananas, meaning this fruit is not a good option for weight loss. 

There are plenty of other fruits that might work better for you. Look for seasonal fruit that is available in your local store. Additionally, frozen fruits are a great alternative to fresh. 

But do remember that bananas are not an unhealthy food. You can still enjoy them a few days per week, and they are definitely a healthier snack option than processed food. 

Regardless of how your body responds to a banana, it is still going to be better than a cookie or a brownie.

Ready to discover the best foods for you? You can take a free quiz to learn more about how ZOE can help you understand your body’s unique responses to food and to identify the best foods for your body and your metabolism.


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