Why the humble broad bean might secretly be your nemesis.
Unlikely connections in life on Earth.
If you ever lie awake at night, letting your mind wonder, and arrive at pondering if broad beans and blood cells could ever be interconnected (pretty niche, I must admit)… then you’re in luck! Over the next few minutes you can become an expert on a somewhat surprising relationship between these two seemingly distant relatives.
In order to understand how an unassuming broad bean could have a profound impact within your blood, we need to go right back to the beginning. All of the cells in your body are in a constant flux of communication, both within and amongst themselves. At the crux of it all are the gossips of the molecular world: electrons. Electrons are responsible for the chemical reactions happening in your cells. From this, I can see how you might think that electrons are therefore the holy grail of cellular metabolism but as you are about to discover, they don’t always play by the rules. Electrons are somewhat bipolar individuals, happy when paired up but rather reactive as singletons. Every molecule in your cells carries a set of electrons which it uses to perform innumerable chemical reactions to keep you functioning. However, you may be surprised to learn that these very reactions keeping you alive also present a paradoxical problem.
During cellular metabolism reactions, molecules occasionally lose an electron. This leaves an unhappy, unpaired electron and the molecule becomes a highly reactive, unstable ‘free radical’. These turbo charged particles will cause damage to DNA, proteins and any other complexes in their path within your cells if they are not subdued. If a cell becomes too damaged, it bursts. Contradictory, right? Our own reactions plotting against the very cells they take place within… Formation of free radicals is unavoidable, it happens in healthy individuals and contributes heavily to aging. External factors such as smoking, drinking, UV exposure and consuming a poor diet can exacerbate the formation of radicals. This is why daily SPF is quite possibly the elixir of youth for your skin!
So, if we are constantly making such large numbers of these destructive particles from our myriad of metabolic reactions, why are we not feeling the effects quickly?
The human body has engineered its own mechanism to neutralise free radicals: antioxidants. An antioxidant is simply a molecule that is stable enough to donate an electron to rampaging free radicals and thus reduce the capacity for damage. They act as a natural ‘off switch’ for the free radicals. Our bodies make antioxidants such as glutathione or uric acid, but other antioxidants can also be supplied by eating a good diet. If this isn’t a sneaky ad to encourage you to eat your blueberries today, then I don’t know what is!
Now, you might be able to guess after our journey so far that the balance of free radicals and antioxidants in our body is crucial for maintaining a healthy cellular environment. And here we get to the nitty gritty of why broad beans are the unsuspecting enemy of 400 million people worldwide.
Your red blood cells (RBCs) contain an enzyme known as Glucose-6-Phosphate Dehydrogenase or ‘G6PD‘ for short. This enzyme is the catalyst for the first step in a process called the Pentose Phosphate Pathway. We wont delve into the ins and outs of this process (I’ll leave a diagram for those interested) but the important takeaway is that from its reaction, G6PD produces a molecule called NADPH. NADPH is an important reducing agent and cofactor for many enzymes, including glutathione reductase (ring a bell?) which produces the powerful antioxidant glutathione. So, G6PD is an enzyme crucial to maintaining enough antioxidants to fight free radicals in red blood cells.
For those of you still following, some people have an inherited mutation in their gene coding for G6PD which causes the enzyme to not function properly or not be produced in their RBCs. Without G6PD, their red blood cells cannot produce enough antioxidant glutathione. Broad beans contain the compounds Vicine and Covicine, which are metabolised by red blood cells to form free radicals… Is the puzzle coming together? Broad beans are therefore a trigger in people with G6PD deficiency as their RBCs cannot make enough antioxidants to combat the increased level of free radicals. Subsequently, the blood cells burst, this is known as haemolytic anaemia. Most people with G6PD never develop symptoms, and avoiding triggers like broad beans and other legumes helps to circumvent complications.
Some interesting trivia about G6PD deficiency is that it’s most common in sub-Saharan Africa where 1 in 10 people possess the mutation. You may ask why it hasn’t been eradicated by evolution and why the numbers of affected people are so high, but there is a sneaky reason why it is most prevalent and still remains in this region today. The increased oxidative stress in RBCs has been shown to give some protection against Malaria. It makes it more difficult for the parasite to survive due to the high number of damaging radicals and higher turnover rate of RBCs. Areas where malaria is most prevalent correlate with higher numbers of G6PD deficient individuals.
So there you have it. The complex interplay of life on Earth is fascinating, and often unexpected, something that this discussion on the unlikely connection between beans and blood highlights. Feel free to leave your thoughts.
References:
Lieberman M, Peet A. Figure 7.3 NADPH in the red blood cell as a means of reducing glutathione. Adapted under Fair Use from Marks’ Basic Medical Biochemistry. 5th Ed. pp 549. Figure 27.7 Hemolysis caused by reactive oxygen species (ROS). 2017.
