A Calorie is a Calorie?

The other day I heard an interesting interview with Dr Lee Goldman on the radio. In it, he discussed how evolution has done the dirty on us. For thousands of years those who ate all they could and stored the excess as fat were more likely to survive, breed, and have living children. As a result, humans have a tendency to eat more than they need and store fat. Now, with abundant food for many, we are suffering the effects of obesity, diabetes, heart attacks etc. And because the effects occur after most people have already had children, there is no evolutionary pressure to reverse the trend.

Then when asked why some people can eat as much as they like and not put on weight, he said something foolish:

"Calories in and Calories out. Number of Calories you eat, if that exceeds the number of Calories you burn, in terms of your exercise, you'll gain weight."

There are a number of problems with this statement which made me wonder whether his main hypothesis was flawed (must follow up sources at some stage).

What is a "Calorie"?

A "Calorie" (big C) is actually a kilocalorie, that is, 1000 calories (small c). That is, roughly, the amount of energy needed to raise 1 litre of water 1°C. (I still remember measuring this for sugar in 5^th form chemistry and being rapt that my result was within experimental error of the official value.)

It comes from the Age of Steam when the calorific value of various fuels was important to know. But biology is more complicated than chemistry. The first hurdle is, not everything in food with calories is digestible by humans. So about 1990, for food labelling, the simple bomb calorimeter method was replaced by the Atwater system which sums the energy of the nutrients such as protein, carbohydrates, fats etc.

Calories In

Okay, but a person is not a steam engine. It is not the case that you put 500g of potential fuel into a body and get x Calories of energy available.

The Atwater system is an approximation. It does not take into account the interaction between nutrients that will affect the energy available and is out for some diets – such as a low-fat high-fibre one.

Then let's look at "indigestible fibre". Some people have the gut microbes that allow them to digest it to some degree - not as much as a cow but maybe as much as 1.5 calories per gram of fibre. But it varies. People's gut flora are as individual as a fingerprint.

In fact, some people's microbiomes are more efficient all round. For a given amount of food some people get more out of it. If one person with the better harvesting microbiota and another with the inefficient type eat the same amount of food – and they are alike in every other way – then the person with the better microbiota is going to put on more weight.

Which bring me to the next point. People are not made the same. One obvious difference is their sex. Another is their soma type which is a reflection of their genetics. For instance, in theory the best body type for a dancer is an endomorph as they have flexibility and strength – however they also have extremely efficient digestive systems which means they tend to put on more weight than is commercially acceptable in an entertainer.

And added to this are a range of diseases that affect how well food is metabolized – diabetes, Crohn's disease, food poisoning for example. And other factors such as a lack of a gallbladder, hormone levels, and various medications.

Finally, people's ability to absorb food changes with time, environment, stress, age, etc.

So, the Calorie information on the packet may be wrong in terms of how it is metabolized by the human body. It may be wrong because of the type of gut microbes you have, genetic inheritance, epigenetics, your sex, disease, medication, stress – to mention a few factors.

Calories Out

Again people use energy at different rates – even when doing exactly the same thing in the same environment.

Calories are used just to stay alive. They are burnt in sleep as well as work, sitting, lying, or running. Each person has their own mix of activities – and their own efficiency in doing them ("more efficient" means you use less energy so are more likely to put on weight).

And obviously more energy is expended when the body is cold to maintain core temperature. What might surprise you is that in extreme cold this can be 180%. So you can eat almost twice as much as in a normal temperature environment.

Exercise has some effect on the calories burnt but not as much as you might think. Doing nothing the brain uses 20% of the body's energy.

And although cardiovascular exercise uses calories, dance involves "exercising smarter". What is seen as "grace" is the result of training your body to generate movement with the least amount of muscle. If you do the same number of hours practice, as you improve you will "exercise" less. Which is a good reason to up your practice hours, add some folk, or cross train with something more cardio vascular.

Summary

Unfortunately it isn't as simple as "calories in, calories out". How the in‑calories are digested is individual to each person and their current environment and health. And although exercise will have an effect on how many calories you use – it may not be as many as you might think.

But the last word from Dr Goldman was no matter how hard it is to not put on weight, taking it off is much harder as you struggle against millennia of evolution.