Saved data getting replaced by new data on app relaunch - ios

Question

I am making a calorie counter which displays the total calorie count of various foods added. I have written code to save data following this tutorial. When I relaunch the app I can see the calorie count is the same as when I quit the app but when I add a new food item, the calorie count is reset and the count begins from the start. Why is the value not being saved??
EDIT:
This is a snippet of my code:
if(alertView.tag == ChickenAlertView) {
NSString *buttonTitle = [alertView buttonTitleAtIndex:buttonIndex];
if([buttonTitle isEqualToString:#"Ok"]){
float chicken= ([ChickenText.text floatValue]);
currentnumber = (chicken/100)*219;
result = result + currentnumber;
calories.text= [[NSString alloc] initWithFormat:#"%.f",result];
}
}
From NSLog, i can see the value of result is going to 0 every time I relaunch the app. How do I prevent it?
This is where I save the code:
- (NSString *) saveFilePath {
NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
return [[path objectAtIndex:0] stringByAppendingPathComponent:#"savefile.plist"];
}
- (void)applicationDidEnterBackground:(UIApplication *)application {
NSArray *values = [[NSArray alloc] initWithObjects: NameLabel.text, AgeLabel.text, HeightLabel.text, WeightLabel.text, BMILabel.text, calories.text, [NSNumber numberWithFloat:result], nil];
[values writeToFile:[self saveFilePath] atomically:YES];
[values release];
}
- (void)viewDidLoad
{
foodData = [[foodData alloc]init];
NSString *myPath = [self saveFilePath];
BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:myPath];
if (fileExists)
{
NSArray *values = [[NSArray alloc] initWithContentsOfFile:myPath];
NameLabel.text = [values objectAtIndex:0];
AgeLabel.text = [values objectAtIndex:1]
HeightLabel.text = [values objectAtIndex:2];
WeightLabel.text = [values objectAtIndex:3];
BMILabel.text = [values objectAtIndex:4];
calories.text = [values objectAtIndex:5];
result = [[values objectAtIndex:6] floatValue];
[values release];
}
UIApplication *myApp = [UIApplication sharedApplication];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(applicationDidEnterBackground:)
name:UIApplicationDidEnterBackgroundNotification
object:myApp];
[super viewDidLoad];
}