PERSPECTIVES WITH DR ALAN BARCLAY

NUTS ABOUT CALORIES? 
Despite the excited claims of the latest fad diet, the proportion of carbohydrate, fat and protein in your diet really doesn’t make much difference when it comes to weight loss. Research has repeatedly demonstrated that provided “the diet” provides less energy (Calories/kilojoules) than what you were consuming before, you will lose weight. This is the simple reason why most fad diets work in the short-term. You are eating less.

To help us to keep an eye on our total energy consumption, the energy content of most commonly eaten foods and drinks is now readily available on food packages, restaurant menu boards, in books, apps and government databases.

However, have you ever stopped to think how they calculate (estimate) the Calories/kilojoules in a food or drink?

Over 100 years ago, in the USA, carbohydrates, fats, proteins and alcohol were obtained from a wide range of commonly eaten foods and burnt in what is known as a bomb calorimeter to see how much they heated up a fixed volume of water. A Calorie is the amount of energy that is required to raise 1 gram of water one degree Celsius at normal (one atmosphere) pressure. Because a gram is a relatively small amount, we typically use 1000 grams of water and correspondingly the kilocalorie, or Calorie with a capital C. The average Calorie values for the macronutrients are: 

• Carbohydrates (available) – 4 Calories / 17 kJ per gram
• Fats – 9 Calories / 37 kJ per gram 
• Proteins – 4 Calories / 17 kJ per gram 
• Fibres – 2 Calories / 8 kJ per gram
• Alcohol – 7 Calories / 29 kJ per gram

Commercially, most food companies measure the amount (grams) of water, fat, protein dietary fibre, alcohol and ash in food, and what is left over, they call available carbohydrate. They then multiply the amount (grams) of carbohydrate, fat, protein, fibre and alcohol by their respective energy factors (Calories or kilojoules) and add them all together to estimate the average energy content of a serve (and in Australia and New Zealand 100g) of food.

While the method is considered the best currently available, it may not be so accurate for individual foods however. Almonds are a good example. A recent small study fed 18 healthy adults either 9, 42 or 84 grams of almonds a day for 9 days, and collected all urine and feces from all participants. Based on this, the researchers estimated that the average energy content of almonds was 4.6 Calories (19 kilojoules) per gram. Using the bomb calorimeter method, almonds are estimated to contain 6.05 Calories (25 kilojoules) per gram – a 32% difference.

When you think about how well an average person is able to chew nuts like almonds, this may not come as a big surprise. If you ate a teaspoon of almond paste that had been prepared in a steel-bladed food processor, you would probably obtain the full 6.05 Calories per gram, but masticating a handful of nuts in our mouth is not as efficient – we don’t all have perfect dentition, salivary flow and chew each mouthful 30 times before swallowing!

So while we may need to take the Calorie/kilojoule content of whole almonds with a grain of proverbial salt, we should keep in mind that overall, Calorie counting is sufficiently accurate for the planning of weight reduction diets.

 
Alan Barclay, PhD is a consultant dietitian. He worked for Diabetes Australia (NSW) from 1998–2014 . He is author/co-author of more than 30 scientific publications, and author/co-author of  The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).