Your math is way off, because it's not being applied properly. First, a pound of fat contains 3500 Calories. Most healthy individuals do not eat that in a day unless they are high level athletes who use all of those calories. Never think you are going to lose a pound of fat a day.
So we have 1 pound which is roughly equivalent to 454 grams of body weight. An equal mass of fat will require 3500 Calories to sustain it.
If you want to gain or lose that amount, you have to remove or add that amount to your weekly net energy expenditure. To understand this, you have to know how many calories are required to maintain your current body mass.
We have an active person with a decent build, no six pack, and weighs around 80 kg (176 lbs). After some experimentation they find that it takes 2400 Calories a day to maintain their body mass.
In order to figure out how much they need to adjust their diet to lose 454 g (1 lb) you need to look at things over the week:
- 2400 Calories X 7 days = 16,800 Calories a week
- To lose 454 g (1 lb) you need to take away 3500 Calories for the week
- 16,800 Calories - 3,500 Calories = 13,300 Calories for the week
- To find out what that means each day, we have to divide by 7 again
- 13,300 Calories / 7 days = 1,900 Calories a day
To simplify that, taking 500 Calories out of your daily diet will have you losing 1 lb a week.
Your conversion is flawed
According to this article, one calorie (note the small 'C') contains 4.184 Joules. One kcal, or more commonly written as a Calorie (note the capital 'C') contains 4.184 kJ.
1427 kJ / 4.184 kJ/kcal = 341 kcal
NOTE: from chemistry conversions we learn that units matter and when we divide units they cancel out. To simplify this the progression gets expanded like this:
- a kJ / b kJ/kcal = a kJ X 1/b kcal/kJ
- the kJ units cancel out, leaving
- a X 1/b kcal
This is how unit conversions work. Of course you do need the conversion factors to do this properly.
When talking about food, Calories are always kcal in scientific terms. Not everyone is careful enough to handle the capitalization correctly.
The body is a complex system
When everything is operating normally, the calories in vs calories out model works well enough. It's when you get to extreme cases of trying to lose massive amounts of weight that your body doesn't get enough to survive that we run into problems.
Many things work together, so we need an appropriate amount of protein, fat, and carbohydrates to function well. Completely disregarding one of these macronutrients can cause health problems in the long term. A short term (6-8 weeks) ketogenic diet (no or very little carbs) can work very well if you have enough protein, but any longer than that and weight loss slows to a crawl as other hormones come into play. A long term plan always ensures your necessary nutrition is present.
Don't starve yourself, and don't engorge yourself. Small changes over time add up.
NOTE: you may want to check out this article which provides the number of Calories and kJ in a pound and a kilogram of fat: http://www.caloriesperhour.com/tutorial_pound.php