Why calories count

Calorie counts on labels are inaccurate

To accurately calculate the energy available in foods, requires a laboratory and a bomb calorimeter. This measures the heat given off by a substance when it is burned, to estimate the total energy within it. While this is the most accurate way to calculate the energy in our foods – it's not a very practical solution for day-to-day use.

So today, instead of this, we use the Atwater System to estimate the calorie content of the foods we eat. Created by a scientist called Wilbur Atwater in the late 1880-90's, he and his team calculated the energy and macronutrient content of thousands of everyday foods using bomb calorimetry. They also had volunteers who ate specific foods and then tested their faeces, to help estimate the calories lost from food during digestion. This research led to the discovery that each gram of carbs contains 4 calories, each gram of fat contains 9 calories, and each gram of protein contains 4 calories – as an estimate. These are the figures we use today to estimate the overall energy value of our foods.

With nutritional information there will be a margin for error – so yes, the calories listed on nutrition labels may not exactly match the actual energy provided by that food – which is why food labelling laws allow for a small tolerance. On that basis, some foods may be underestimated, and others overestimated. If you're looking at it from an odds point of view, there's a 50:50 chance of each. So across 100 foods, 50 could have underestimated calorie counts and 50 could have overestimated calorie counts, the net result being any tolerances are offset.

Bottom line...

I agree that the calorie figures we're given on foods may not be 100% accurate. What I don't agree with is that this then makes calorie counts entirely redundant. Even with some margin for error, having a calorie figure as a guide on products or menus can help us to make comparisons and better choices depending on our goals.

Take this example: you're trying to lose a little weight and go out for dinner. You can't decide between the lasagne, which the menu says contains 800 calories or the spaghetti bolognese, with 600 calories. Now even if the lasagne is actually 850 calories and the bolognese 630 calories, from an energy intake point of view you can safely assume the bolognese has fewer calories than the lasagne. It's about providing guidance so informed choices can be made.

The net calories our body receives from food isn't the same as the calories in food before digestion

It's true that it takes energy to extract energy – i.e. our body utilises energy to digest our food. So the net energy received from what we've eaten is always a little lower than the total energy of the food before digestion. The amount of energy needed for the digestive process varies between macronutrients too – fats require the least amount of energy and protein requires the most, with carbs somewhere in between. This can mean that a higher protein diet would result in a higher calorie burn from digesting the foods, than say a high-fat diet. This is called the 'thermic effect of food'.

All-in-all it's estimated that the thermic effect of food (the energy required to digest it) accounts for around 10% of our total daily energy expenditure. Which isn't a huge amount in the grand scheme of things. Effectively, it just means we end up with less energy from the foods we eat than we thought.....which would actually help to counterbalance a potential underestimation of calories going in. Just a thought!

It's all about estimations providing a helpful guide. Yes one area may underestimate and another overestimates, but the net effect is that these inaccuracies balance out.

The nutrient make-up of our diets is more important than calories for weight loss

A big argument from those who are anti-calorie counting, is that all calories are not equal and to focus solely on calories is to overlook the overall nutritional make-up of an individual's diet. I'm in complete agreement that we need to focus on our diet as a whole and not just on calories. While a calorie is a calorie, in terms of the energy it provides the body with, it's true that not all calories are equal – you'll get a lot more nutritional benefit from eating an apple than you would from the same calories of chocolate. Which is why Nutracheck is more than a calorie counter. It also tracks protein, fats, carbohydrates, fibre, sugar and salt. The aim is to give you a more complete picture of your dietary intake and how this measures up to healthy guidelines for all nutrients. However keeping a focus on calories is still important if you are trying to lose weight – it's absolutely possible to overeat with healthy foods, so maintaining an awareness of total energy intake is useful.

There is a view that certain types of diets result in better weight loss results too, which is why some people believe calories are not as important. But it's important to look in detail at the research around this before making a conclusion. One study concluded that a low-carb diet resulted in more weight loss than a low-fat diet, when participants were asked to stick to specific nutrient targets [3]. However, when you look at the stats for this research, you can see that those on a low-carb diet consumed fewer calories than those on a low-fat diet. Plus low-carb diets tend to promote more water-weight loss as carbs are stored with water – so these factors can explain why the participants lost more weight.

Another study however found that those on a low-fat diet lost significantly more weight than those on a low-carb diet, because those on the low-fat diet were eating 550-700 calories per day less than those on the low-carb diet [4].

There's also research linking a diet high in processed foods with more weight gain [5]. But again, this is simply because when people eat more processed foods, they tend to eat more calories – as the research showed that they ate around 500 calories more each day.

These studies highlight that it all comes down to total calories consumed, and while the dietary choices you make can affect how easy you find it to stick to a low-calorie intake, ultimately the overall energy intake of your diet is the defining factor in weight loss.