How Bananas Assist In Combating Oxidative Stress

Introduction

Oxidative stress has been linked to many chronic diseases. However, the relatively cheap and widely available banana, containing a multitude of bioactive compounds, might be just the answer to combatting this.

What is oxidative stress?

Oxidative stress is defined as the disturbance in the balance of antioxidants and free radicals within the body. When this imbalance happens, your body experiences oxidative stress, which can play a significant role in the development of chronic diseases such as cardiovascular diseases, diabetes and possibly cancer.¹

Whilst there can be some benefit to oxidative stress, generally this phenomenon has more harmful properties than beneficial ones. As such, managing the balance of antioxidants and free radicals in the body is important to managing your overall health.

What is a free radical?

Free radicals are unstable atoms produced in the body in response to normal biological processes such as breathing and digestion. These atoms have an uneven number of electrons, allowing them to easily react with other molecules in the body.

At low concentrations, free radicals play an essential role in many biological processes. Researchers believe that free radicals may play a role in cell signalling [known as redox signalling], the maintenance of homeostasis and immune function.² However, at higher concentrations, as these free radicals interact with other molecules, they can cause damage to the body.¹

What are the risk factors?

As previously stated, free radicals are naturally occurring within the body in response to natural processes. However, you may also be exposed to exogenous sources of these free radicals within the environment through:

• Cigarette Smoke
• UV Radiation
• Ozone
• Drugs or Toxins
• Pesticides/Insecticides
• Allergens

Similarly, a poor-quality diet with high levels of fat, sugar, alcohol and processed food may also increase your exposure to these free radicals.³

How can free radicals and oxidative stress impact your health?

When the amount of free radicals in the body exceeds the amount of antioxidants, these free radicals begin to do damage, leading to cellular dysfunction and interrupting vital cellular processes.⁴

Indeed, research suggests that free radicals and oxidative stress may play a significant role in the development of conditions such as:

• Cancer
• Stroke
• Myocardial Infarction
• Diabetes
• Atherosclerosis
• High Blood Pressure
• Neurovegetative conditions [i.e., Parkinson’s or Alzheimer’s]

There was also a theory that free radicals and oxidative stress contributed to the ageing process. However, this has since been deemed unlikely.⁵

Managing oxidative stress: the role of antioxidants

Natural antioxidants have received much attention in managing oxidative stress. Antioxidants are molecules stable enough to ‘donate’ an electron to these free radicals, breaking the chain reaction and preventing oxidative stress from occurring.⁶

Whilst it is impossible to completely avoid exposure to free radicals and oxidative stress, increasing the amount of these antioxidants you consume will help decrease the likelihood of any damage occurring.

Where can I find these antioxidants?

Some antioxidants, such as glutathione and ubiquinol, are produced naturally within the body.⁷ However, exogenous sources of antioxidants need to be supplemented through the diet. By increasing your intake of fruits and vegetables, you ensure that you provide your body with what it needs to produce these antioxidants.

The power of these antioxidants is one of the main reasons why a diet rich in fruit and veg is often considered to be linked to a decreased risk of all-cause mortality.⁸

Some of the main antioxidants that you will find in your diet include:

• Vitamin A
• Vitamin C
• Vitamin E
• Phytonutrients
• Polyphenols

However, what is important to note is that whilst fruits and vegetables have high antioxidant content, the body may not absorb it all. This concept is known as bioavailability and is linked to how that food is broken down in the gut, meaning whilst some foods may initially be high in antioxidants [like berries], variety in your diet is key to ensure digesting as much of those antioxidants as possible.

A good tip

The antioxidant colour wheel helps visualise where you might get the most antioxidants when it comes to choosing your fruit and veg, with darker colours being related to higher antioxidant capacity.⁹

Remember: whilst some fruits and vegetables may score lower on the antioxidant scale, they contain plenty of antioxidants as well as other important nutrients, so don’t disregard them. Aim to ‘eat the rainbow’ every time you have a meal.

So, how can bananas help?

The consumption of fruit is known to promote good health and lower the risk of chronic diseases such as heart disease, stroke, gastrointestinal disorders, and certain types of cancer, as well as lower cholesterol and improve immune function.¹⁰

Whilst abundant in carbohydrates to help with energy production, reviews^11,12 have reported bananas to also be rich in carotenoids, flavonoids, phenolics, amines, vitamin C and vitamin E, of which all have profound antioxidant benefits to the human body. A full table of nutrients can be found here.

Vitamin C

Also known as L-ascorbic acid, Vitamin C is a water-soluble vitamin naturally present in bananas as well as other fruits and vegetables. As humans cannot produce Vitamin C, this is considered an essential dietary component.

Vitamin C has been shown to reduce the incidence of free radicals within the body, directly and cooperatively. Directly, Vitamin C has been shown to protect leukocytes from oxidative stress as well as completely protecting lipids from detectable oxidative damage from free radicals and oxidative stress.¹³ Further to this, studies have found that a single banana meal reduces plasma oxidative stress and enhances the resistance of lipids to oxidative stress.¹⁴

Cooperatively, Vitamin C has been shown to enhance other antioxidants within the body, namely Vitamin E.¹⁵ Vitamin E is a fat-soluble vitamin found in vegetable oils, nuts and fish and plays an imperative role in protecting cell membranes and nervous tissues.¹⁶ The interaction between Vitamin C and E has been dubbed as ‘vitamin E recycling’, in which Vitamin C helps replenish the antioxidant capacity of Vitamin E and further helps minimise lipid peroxidation [the breakdown of lipids through oxidative stress].¹⁶

The recommended dietary allowance (RDA) for vitamin C is 75mg for women and 90mg for men, based on both the vitamin’s role as an antioxidant and protection from deficiency.¹⁵ For context eating 1 banana per day will account for around 12% of your RDA for Vitamin C.

Carotenoids

Carotenoids are a pigment found in plants, vegetables and fruit that produce bright yellow, red and orange colouring. These carotenoids are a class of compounds with over 600 variations, of which some of these variations are precursors to Vitamin A, with some others having exceptional capacity for managing the accumulation of free radicals and thus limiting oxidative stress.

The main carotenoids found in bananas are:¹⁷

• A-carotene
• B-carotene
• B-cryptoxanthin
• Lycopene
• Lutein

These carotenoids have been described as the most potent natural antioxidants, with particular reference to b-carotene as being the most effective of these for minimising the oxidation of free radicals.¹⁸

Yellow- and orange-fleshed bananas have been shown to contain the highest levels of b-carotene, with consumption of fruits rich in carotenoids such as b-carotene reported to boost immunity and reduce the risk of various diseases such as cardiovascular issues, type 2 diabetes and some cancers.¹⁹

Phenolics [Polyphenols]

Polyphenols are plant compounds usually found in plant-based foods such as fruits, vegetables, dark chocolate, red wine, herbs and tea.

Most of the benefits associated with polyphenols are linked to their role as a potent antioxidant and their effects on protecting cells from damage and inflammation caused by free radicals and oxidative stress.²⁰

Over 8000 polyphenols have been discovered, with much research to do on how they all affect the human body. However, they are categorised into 4 groups:

• Flavonoids
• Phenolic acids
• Phenolic amides
• Other polyphenols

Whilst bananas are not considered to be the richest source of polyphenols [top 100 list here], they are rich in health-promoting polyphenols and flavonoids.

• Flavonoids

Bananas are also rich in compounds known as flavonoids, which further contribute to overall health due to their antioxidant characteristics.¹²

Due to their anti-inflammatory and antioxidant effects, current research into flavonoids has been studying their potential as an anti-cancer drug. A recent review paper has shown that flavonoids interact with enzymes within the body, which have a protective role against cellular damage by ‘detoxifying’ carcinogens and helping stop cancer cells from multiplying.²¹

Further to this, such flavonoids have been shown to have a significant effect on lowering high blood pressure²² as well as a 2018 meta-analysis indicating that high flavonoid intake through the diet correlates well with a decreased risk of developing type 2 diabetes.²³

Whilst more studies are needed to fully ascertain the health benefits of flavonoids, they are easy compounds to include in your diet, whether that be through bananas or other sources.  

Summary

Bananas are grown and consumed all over the world due to their taste and nutritive value. Bananas contain great diversity and a sufficient amount of beneficial bioactive compounds for energy and health promotion. Many of these components within a banana have been linked to powerful antioxidant capabilities, which may reduce the risk of development of diseases such as cancer, type 2 diabetes, heart disease, and many neurological conditions.

Given that bananas come ready to eat in most countries, fitting them into your diet should be relatively straightforward, but if you are stuck, then here is a quick recipe to get you started: