Today we’ll look at possibly one of the most confusing aspects of nutrition in general – and “weight-loss diets” in particular- calorie control.
As you’re probably aware, there are dozens if not hundreds of different diets that are promoted as being the ultimate weight-loss plan. Although they may be different in content, the one thing that they will all have in common is that they’ll encourage you to “reduce calories”. In other words, eat less.
Some will give general guidelines while others may be specific enough to require that you have your kitchen scales and calculator nearby in order to weigh and measure your meals.
So what exactly are calories, and how much do we need to focus on them? We can start by understanding that a Calorie – also known as a Kilocalorie- is simply a unit of measurement of energy. It’s actually the amount of energy required to raise the temperature of I kilogram of water by 1 degree Celsius.
Therefore we can measure the food we eat in terms of the amount of calories -or energy – that it will provide. Likewise, physical activity is rated in terms of how much energy or calories we use up while doing it. As mentioned earlier, all successful weight- loss diets rely, to some degree, on creating a calorie deficit, which means that you’ll be using up more calories in daily activity than you’ll take in through your food and drink.
However creating this deficit is not an exact science and your body is not some kind of calorie bank or accounting system where deposits and withdrawals lead to a predictable, “statement” at the end of the week or month.
There are a number of reasons for this:
Calorie labelling is questionable
According to the Precision Nutrition website, a study in Boston found that some frozen food manufacturers underestimated calories in their products by an average of 8%, while the average underestimation at selected restaurants was 18%. The researchers had deliberately chosen items that were labelled “low-Calorie”. Anybody who ate this food regularly because of its supposed low calorie content was bound to be in for a nasty surprise when they stood on their weighing scales!
All Calories are not created equally
Some diet plans say that you can eat “whatever you want” as long as you keep within your calorie target. This assumes that a calorie is a calorie regardless of the source. However this does not account for the Thermic Effect of Feeding (TEF). This is the name given to the amount of energy needed by your body to digest and absorb the food you eat. Protein has the highest TEF at around 20-30%, followed by carbohydrates at around 5-10% and finally fats at 0-3%.
In other words if you ate 100 calories from protein, 20-30 of them would be used up in digesting the meal, leaving you a net intake of 70-80 calories. However if you eat 100 calories of “carbs”, only 5-10 of these calories are used to digest it. That would leave you with 90-95 calories of carbs to be used as energy to move or else to be stored as fat.
And it’s not only the different food groups that create different levels of TEF. A 2010 study showed that a cheese sandwich made from multigrain bread and real cheddar cheese had a significantly higher TEF than a sandwich made from processed bread and cheese.
This was partly due to the higher content of fibre and protein in the “Wholefood” sandwich, but mostly due to the fact that processed food requires your digestive system to do less “processing” and therefore has more calories that can potentially be stored as fat.
Estimation of Calorie requirements are even more complicated (and inaccurate)
If you think the numbers I hit you with today are hard going, you should see some of the equations used to work out your Resting Metabolic Rate! These estimations of your daily calorie requirements are at best only accurate to within 10% either way. So you may require 2000 calories a day to maintain your current weight or it could be 1800 or 2200!
It’s for all of the above reasons that I don’t encourage calorie counting for weight-loss clients. Life is too short to get hung up on such an inexact science.