One Calorie is the heat required to raise the temperature of one gram of water by 1°C. In dietetics (food matters) a kilocalorie (kcal) is equal to 1,000 calories.
The kcal therefore, measures the energy value of food in terms of its heat output: 1 oz (28 grams) of protein yields 120 kcals, 1 oz (28g) carbohydrate yields 110 kcal, and 1 oz (28g) fat yields 270 kcal. So, 1g of protein equates to 4.2 kcals, 1g of carbohydrate equates to 3.9 kcals and 1g of fat is 9.6 kcals.
Now for the important bit if you are trying to lose weight whilst eating healthily. Losing, gaining or maintaining weight is a simple matter of adjusting the quantity of fuel you put into your body against the fuel your body uses. If you put in more fuel than you use, you will gain weight and conversely if you take in less fuel than you use, weight loss will result. I’ll state the obvious here just in case it didn’t come to mind, you can burn more kcals by doing some exercise. The traditional swim, run, walk, cycle etc. are excellent forms of exercise but you could also think about other not so obvious forms which aren’t usually labelled as exercise such as housework, dancing, gardening etc. In addition, you should try to get the correct balance of the composition of your diet through carbohydrates, proteins and fats as they are all important elements which the body requires. You should be consuming approximately 60% carbs, 30% protein and 10% fat. However, it is clear from the above information on food calorie contents that if you can reduce the fat content of foods you eat, you will be more easily able to eat fewer calories.
When you see a food item that states its fat content, it is almost certain to be as a percentage of the weight of the product. However, as you can see from the above kcal values for food types, fat has over twice the calorific content of proteins and carbohydrates. In other words, if you are trying to lose weight and therefore reduce your calorific input, you need to work out the percentages in real fuel terms. To do this you simply take the weight (in grammes) of the fat in the item and multiply it by 9.5 (kcals per gram of fat) then divide that by the total kcals of the item. This will give you the fat content as a percentage based on calories and not weight. Try it, it’s a real eye opener! You can do the same for carbs and protein but use a multiplication factor of 4 (4 kcals per 1 g). In additon, another little trick the food manufacturers use is to lower the fat content by increasing the overall calorie content. Why do they do this? Because people buy based on the wrapper marketing. If during development a product has a 5% fat content (by weight) the manufaturers can add sugar to reduce the fat content as a percentage, but of course at the same time they increase the calories in the product. But they know people will buy the product because the wrapper states “only 3 % fat”. Do the calculation next time you see this and you will find it is more likely to be nearer to 50% fat as a percentage of calories. If you also find a similar product not purporting to be a diet product, it might well have less total calories than the low fat product. By doing this calculation you won’t be sucked in to the trap of the marketeers!