WHEN IS A CALORIE NOT A CALORIE?*
The word ‘calorie’ comes from Latin calor meaning heat (one of the 5 classic signs of inflammation).
The calorie was first defined by Nicolas Clément (1799-1842), a French physicist and chemist. Between 1819 and 1842, he referred to calories as a measure or unit of heat in his lectures, and published his data in the journal Le Produsteur in 1824.
The simple definition of calorie, as we were taught in school physics, is ‘the amount of heat required to raise the temperature of one gram of water by one degree Celsius, from 14.5°C to 15.5°C at standard atmospheric pressure’.
The name ‘calorie’ is used for two units of energy:
· The small calorie or gram calorie (symbol cal) is the approximate amount of energy needed to raise the temperature of one gram of water by one degree Celsius.
· The large calorie, kilogram calorie, dietary calorie, or food calorie (symbol Cal) is the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius. Thus it is equivalent to 1000 small calories.
Although these units are part of the metric system, they have been superseded in the International System of Units by the joule (J). One small calorie (cal) is about 4.2 joules, and one large calorie (Cal) is therefore 4.2 kilojoules (kJ).
In spite of its now non-official status, the large calorie (Cal) is still widely used as a unit of food energy in Australia, USA, UK and some other Western countries. In Australia, “joules” have started to replace “calories” as a measure of energy in foods, but calories are so well-known that calorie is used in this newsletter.
The small calorie is often used in chemistry, though the amounts involved are typically expressed in thousands as kcal, an equivalent unit to the large calorie (Cal).
The energy required to increase the temperature of a given mass of water by 1°C depends on the atmospheric pressure and the starting temperature (and is difficult to measure precisely!). As a result there are several further definitions of the calorie that attempt to make the definition more precise.
· Thermochemical calorie - the amount of energy equal to exactly 4.184 joules.
· 4°, 15°, 20° calorie - the amount of energy to warm one gram of air-free water from 3.5° to 4.5°, 14.5° to 15.5° and 19.5° to 20.5° respectively, at standard atmospheric pressure.
· Mean calorie - 1/100th of the amount of energy required to warm one gram of air-free water from 0°C to 100°C at standard atmospheric pressure.
Experimental values of the 15°C calorie ranged from 4.1852 to 4.1858 joules. Since 1950, one calorie (15°C calorie) has been known as equivalent to 4.1855 joules (J). The thermochemical calorie, as indicated above, is 4.184J.
Rule of thumb conversions use the factor 4.2 to express calories (cal) as joules (J).
When is “A Calorie Not a Calorie”?
People in the wealthier, Western countries are getting fatter. In Australia, the USA and the UK, in round figures, about two-thirds of the population are overweight and at least one-fifth are obese. This has been happening despite an enormous increase in weight-loss diets, which have been popularised in an attempt to stem the epidemic of overweight/obesity.
Cutting back calories, or reducing caloric intake, is the standard recommendation to lose weight and maintain a healthy weight. But are all calories equal in the energy equation within our bodies?
The latest research into weight-loss diets has two strains of thought:
· The actual diet doesn't matter so long as you reduce your caloric intake and do more exercise.
A lot of the profusion of diets, recommended and published as books and articles, tend to focus on the constituents of food ... the macronutrients, ie fats, proteins and carbohydrates. Hence there are the high fat diet (Atkins type), low fat (fat is the evil component), different types of carbohydrates (eg The Starch Solution), different combinations like the 80:10:10 diet (80% of calories from carbohydrates, 10% each from fats and proteins) and so on.
However research has shown that the differing proportions of carbohydrate, fat and protein doesn’t really matter in terms of weight loss. All you had to do was to reduce the overall caloric intake in a way that was healthy to your heart (low levels of saturated fats and cholesterol, and high levels of dietary fibre). The individual macronutrient choice does not matter; just reduce the calories with some exercise.
· While reducing caloric intake is an important part of achieving and maintaining a healthy weight, a calorie that you eat may not add up to a calorie available in your body. "A calorie is not a calorie"!
The number of calories assigned to each food is based on a system set up in 1900 by an American, Wilbur Atwater (1844-1907). He obtained his doctorate in agricultural chemistry in 1869. He simple "burnt" each food type - fat, protein and carbohydrate - in a machine that he invented called a respiration calorimeter, and measured how much energy it generated. His method is called the Atwater system. From that, he worked out how much energy was in each foodstuff depending on its relative proportions of fat, protein and carbohydrate. And this is the system that is still used today.
But the real energy which our bodies obtain from foods is much more complicated. The net energy, that which is available after the food is digested and metabolised, is not the same as the energy, hence calories, listed for the food.
· Fats need only two to three percent of their inherent energy to be used as the body digests and metabolises them.
· Carbohydrates need five to ten percent.
· Proteins need up to 25% to unravel the tightly bound amino acids that they are made from.
So, if you eat 100 calories of fat or a 100 calories of protein, your body will have access to 98 calories from the fat, but only 75 calories from the protein.
Moreover, the Atwater method deals with the total potential energy in the food. But what if all the food is not digested and absorbed into the body? For example, in the case of almonds, a significant amount of energy, about one third, does not get extracted but goes straight through the gut into the faeces.
Furthermore, what about the method of food preparation? Depending on the food, more energy will be availed to the body if it is first processed by grinding to increase the surface area. Chewing in part achieves this also, but so often food is swallowed after only minimal chewing. Cooking and fermenting foods also alters the available energy. For example, a study showed that mice lost weight when they only ate raw sweet potato, but gained weight when they ate cooked sweet potato.
Yet another factor that needs to be taken into consideration is that all people are not the same, they differ from one another. The efficiency, or health, of the digestive system varies greatly from individual to individual. The length of the gut varies: the longer the intestines would enable more energy to be extracted from the diet. A healthy bacterial population in the bowel is also linked to efficiency in extracting energy (as well as the micronutrients, ie vitamins, minerals, trace elements, phytochemicals, antioxidants etc) from the diet. Many of us have reduced healthy bacteria in the gut due to antibiotics, both prescribed antibiotics and those contained in certain foods as a result of farming methods.
It requires more energy to process whole foods than processed foods. If the caloric content of the whole foods or processed food are the same, less net energy results from eating whole foods. This is part of the success of the raw food diets (being mainly whole and unprocessed foods) in gaining weight loss.
By its very definition, a calorie is a calorie.
But the net energy (calories) from a food after it is eaten, digested and metabolised is not identical to, or the same as, the caloric (energy) content of the food ... as is listed on packaging, and increasingly in cafés and restaurants.
A successful diet for weight reduction must take into account many of the variables set out above.
The ideal diet is one which is made up of 75-80% alkali-forming foods (vegetables, fruits, lentils, nut, seeds - essentially plant based) and 20-25% acid-forming foods (all animal products, including milk and cheese, and refined foods). A detailed list of acid and alkaline-forming foods can be accessed from my September 2005 newsletter Acid / Alkaline Balance - The Ideal Diet. This is the diet that will lead to health and longevity.
The only way to lose weight is to eat a diet that results in supplying, after digestion etc, less calories than you burn up. Lifestyle affects the amount of energy utilised: a sedentary life with no exercise obviously requires less energy (calorie) intake than an active lifestyle.
*Copyright 2014: The Huntly Centre.
Disclaimer: All material in the huntlycentre.com.au website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.Back to the list Print friendly version