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Biology and diet | How biology, willpower and opportunity shape our diets

Do you eat when you’re hungry? And when you’re hungry, do you choose what you would like to eat or what you should eat or grab what happens to be in the fridge?

Have you ever thought about biology and diet? It might be worth a few moments to ponder the connections. 

How do you decide what to eat? 

It’s a fundamental decision we all make daily, sometimes several times a day. And yet we take for granted the options available to us regarding our diet. 

Each week someone comes up with a new diet proposal that will fix our drift to overweight and obese bodies, and, of course, we’re told what we should eat. The foods that are good for us, foods we should eat or shouldn’t, and foods we can have in moderation—no whole bars of chocolate or tubs of lard in the curry. Keep the carbs low and avoid sugar. 

You are not alone in the eating well challenge. 1.4 billion people need some weight reduction to return to a healthy weight.

People are unhealthy as a result of what they eat. And for the first time in many decades, life expectancy is going down, with diet as a significant contributor.

beer glasses and great pub food a place where biology and diet come together
Photo by Elevate on Unsplash

Making the diet choice

As you settle down to a good Netflix binge after dinner, and you really fancy some chocolate, a fourth beer, or some peanuts to go with the beer, what decision process goes through your head?

I know I shouldn’t, but hey, why not? 

Once or twice, now and again, is acceptable. 

But should that little extra comfort food become a habit, your body will not thank your brain and ask what happened to your willpower. 

Now we won’t go into the details of the consequences of the decision to eat some more because it will take us down all sorts of rabbit holes of gossip, argument, opinion, and a shortage of facts. These matters are extensively explored on sustainably FED in our diet category, the D in FED

Here the question is, how do we make a choice? 

What is it that results in the extra ale being drunk or not? What makes us reach for the pound and a half in every bar, only to put it back in the cupboard unopened? 

There are three main features of the decision to eat.

A primal desire for sugars, fats and salt

The first reason is innate. It is the drive from our basic biology toward foods that were rare in our evolutionary past and yet very helpful to our survival. 

The desire for sugars, fats, and salt is in our genes.

Obtaining sugar and fat was challenging in hunting and gathering systems. Remember that the hunters were not chasing stall-fed pigs or fattened cows; they were pulling down game animals that have spent their lives avoiding being eaten. Game meat is some of the leanest meat that you can find. So fat was in relatively limited supply to most early humans. It is also why what we now call offal were the prime cuts.

Similarly, sugar had a few widely spaced sources. Fruit and honey were prized for their value to well-being. Before agriculture, sugar would have been an occasional, opportunistic addition to the diet. 

Seeking out fatty, salty and sugary tastes were essential for survival.

In the after-dinner decision, the first thing to overcome is the innate desire for food items that used to be unusual in the diet because we knew they were valuable. 

bee on a honeycomb
Photo by Meggyn Pomerleau on Unsplash

The second reason is innate too.


It is willpower born of our psychology. It is how we use the mind to overcome instinct, that innate drive to find delicious sugar and fat that hit the spot every time. 

Strong willpower is needed to avoid eating sugary, fatty and salty food if they are always available at every turn of the supermarket aisle. 

Indeed foods that shouldn’t need a lot of sugar, a tin of baked beans, for example, contains 15g of sugar or three teaspoons each 150g serve. Sugar is almost everywhere in our dietary options, and keeping those items out of your diet is hard. 

When food is in excess, all organisms tend to consume until they are full to bursting. 

The third thing, related to the second, is what food is available. 


Certain isles in the grocery store are regularly visited as a person zigzags through the opportunities to purchase. Some are easy to miss; only pet owners need aisle 10, but the design of these stores is specific. The easy, fresh, and low markup items are harder to find than processed foods. Manufacturers pay good money to the retailers to have their products front and centre.

It is hard to pretty up an onion or a cauliflower where no packaging is needed. Cheese and onion-flavoured chips, on the other hand, have endless options to attract our attention. 
Consumers must work hard to pop in and get all the fresh stuff. You have to go around the edges to find the fruit and vegetables.  

Photo by Stephen Kong on Unsplash

Food choices

Choosing the right foods is possible. 

A diet balanced according to whatever balance might look like in the current description requires an active choice. It takes effort. 

The food production system that supplies modern cities is for profit, making sales and production efficiency stronger reasons than the importance of diet. So the link between what people should be eating and what the producers are growing should be tighter than it is. In other words, the availability of foodstuffs is reflected in what is produced rather than what should be eaten. 

When the market drives food production, it has powerful momentum. Producers and supply chain actors are in business. They can only persist if, at a minimum, they break even. If they are leveraged, a business cost is the loan repayment, a profit to the lender. So even if they are not profitable themselves, someone makes rent.

The desire to persist and strive for profit is a powerful motivator. Playing in the market often means growing and processing the foods people like and are most likely to purchase. And back we go to sugary, fatty and salty products.

We shouldn’t be incredulous when the market doesn’t go in a favourable direction. It is following its own rules. 

We could look to education to raise awareness—such as by following food advice—but sometimes even this is risky. The aware souls still have to say no to the cheezels.

We could change the food choices at the source. Food producers should diversify production for all sorts of reasons. Still, one of the critical reasons is to change the availability of foods to make diet choices easier for more people. 

Only the trend is for consolidation of production and diversity of processing.

For example, there’s been a shift in the last decade or three around what food types are available in Africa. The diversity of plants and animals in the food systems has declined dramatically to be replaced by near-ubiquitous wheat, maize, and rice. 

These primary sources of carbohydrates are the so-called empty foods or nutrient commodities. All that is needed to make them sell is salt, oil and sugar. This loss of diversity of production in the foods available is recognized as a cause of food insecurity in large parts of Africa in particular, but also Asia. 

What sustainably FED suggests about biology and diet

We decide what to eat based on our innate biological desires, willpower and opportunity.  

Few of us are strong enough to consistently resist sugary, salty and fatty foods presented in a dizzying array of colours and attractive packaging in modern supermarkets. 

Next time you sit on the couch with a remote in hand or peer into the fridge to decide what to make for lunch, pause. 

Think about biology and diet. 

Not because you need to lose 10 pounds as summer’s coming, and someone might see you in your board shorts. Just think about your biology, evolutionary history, and what the market has put into your fridge. 

What goes in there is as much product of the food supply system as it is your choice. And when we think of diet in terms of biology, willpower and opportunity, it changes how we think about food. 

Enjoy your lunch.

Hero image from photo by Charles Etoroma on Unsplash


Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

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