How often has a calorie count impacted your food choice?

Example:

You walk into Pret at lunchtime and scan the shelves.

You’re drawn to a satisfying option, but immediately see the calorie count and think, gosh I can’t possibly have that, and pick something within a “safe” range instead.

Seeing or knowing the calories in a particular food item can play quite a significant role in our choices. But more importantly, is this information accurate and do you find it helpful or unhelpful?

Before we begin, it might be helpful to understand what calories even are

Calories or Kcals, are units of energy. Specifically, they are units of heat energy required to raise 1g of water by 1 degree Celsius.

Pretty banal for something that can play such a role in our food choices, no?

How are calorie counts on food determined?

Good question.
Pre-1990s a method called Bomb calorimetry was used to determine the calories in food items. Bomb calorimetry involves placing a food item in a sealed bag within water, and burning it to a crisp. The rise in water temperature recorded determines the number of calories.

The problem with this method is that it doesn’t account for non-digestible components of food such as fibre. In a bomb calorimeter, all the food is burnt to a cider, but in the digestive tract, non-digestible foods such a fibre will be passed in the stool. Therefore, bomb calorimetry may overestimate calories.

Moreover, in 1990, the FDA requested all food manufacturers label calories and nutrients of foods and so methods needed to become a little easier and less expensive. Enter in, the Atwater system. This much easier system is based on looking at the macronutrient composition of food and working out calories per gram. For example, 1g of carbohydrate contains 4 kcals and therefore 20g of potato would roughly be equated to 80 kcals.

But how accurate are these calorie counts?

Well, this is the interesting part. According to research, calorie counts on foods may not be as accurate as we think. The FDA, for example, allows food companies 20% leeway inaccuracy of food labels. To put this into perspective, an 100 kcal item could, therefore, be 80 kcals or 120 kcals.

A study in 1993 aiming to determine the accuracy of calorie counts of diet and health foods specifically, found that calories in packaged foods different from the label by about 25%. A similar study exploring this in restaurant and frozen meals found calories to be out by 200-245%. Most recently, Jumpertz et al looked into accuracy on snack food items and found that inaccuracy of calorie counts may be down to miscalculated serving sizes and carbohydrate content. This begs the question of whether we should be looking to external calorie counts as such a major determinant of our food choices.

Back to the Atwater system

Now, what’s interesting is that while the Atwater system accounts for energy losses passed in our poop e.g. the energy in food that is passed through the system and excreted, it doesn’t account for variations in the type of food and our own individual factors.

It is very important to remember that there’s quite a big difference between the total number of calories locked up within a particular food, and those that we will actually digest and absorb.

Numerous factors may impact this including but not limited to:

Food processing
Cooking methods
Our gut microbiota

Food processing

Food processing and cooking methods can play quite a significant factor in determining the calories we actually obtain from food. In his book Gene Eating, Dr Giles Yeo gives the very good example of the difference between corn tortillas and corn on the cob.

Both food items are carbohydrates, which under the Atwater system would be 4 kcals per gram. Indeed 100g of each would equal 400 kcals.

But, if you’ve ever had a sneak peek of your poop before, you may have seen some evidence of undigested corn. This means that the total calories locked into the corn on the cob aren’t all contributing to our overall energy intake. Corn that’s dried, ground down and made into a tortilla, however, is less likely to be seen again, and thus indicates more of the energy has been absorbed. Yet, both packets will still say the same calorie counts for 100g.

Cooking methods

Cooking helps to break down the cell structure of food which allows us to absorb more of the nutrients and energy. This has played a very powerful role in preventing us from becoming malnourished, and also an onslaught of raw veggies, starch and grains would be hideous to digest. Therefore, cooking plant foods like potatoes or vegetables will mean much more of the energy and nutrients are available to us. Interestingly, the same is true between cooked and raw foods that aren’t from plants and don’t contain cellulose like meat.

Gut microbes

Even our gut microbiota, the trillions of bacteria residing in our gut may play a role in energy available. Some microbes, namely a certain species called firmicutes are more efficient at metabolising energy from food and therefore may influence how many units of energy we harvest from a specific food item. This will, of course vary between individuals.

So, what might be a better way to decide which food options are best for us?

Well, rather than turn to external cues on what to eat, can we turn inwards instead.

I invite you to ask yourself:

What am I hungry for?
What is going to help me feel full (satiated)?
What will satisfy me, i.e. hit the spot which means I probably won’t think about the option from Pret that I really wanted but didn’t pick all afternoon?
What will consider my nutritional needs and my taste buds with mutual importance?
What will make me feel energised, content, etc?

There is absolutely no right or wrong but it’s important to consider our own intensions and bodily signals. Making decisions based on our own internal wisdom, rather than the external (calorie counts / my fitness pal), helps us develop a more trusting relationship with our body and means that the pressure to eat the “right” or “perfect” option fails to exist.