Interesting. I thought of a scale too, though honestly I imagined every item sitting on a scale at all times. A single scale would work as well, but then you have all the repeated data entry(what is this item, what is its caloric density, upper consumption limits, etc).
You could probably implement an RFID system for identification and a database of common items. When you buy a new container of icecream you just plop the "icecream" rfid tag on it and you don't have to enter all that data. As you remove it for dispensing you weigh it and then weigh again upon return. The database automatically increments.
Using this system each person in the family could have their own rfid identifying tag as well. The fridge would default to a locked state and if your tag has remaining callories alloted for consumption, the fridge unlocks.
I imagine in my house that we would probably steal eachothers identification tags though, so subdermal implants would most likely be preferred.
@caleb Maybe there's an altenative way to measure the food output, measure the food input by placing a scale in front of the refrigerator. Set the weight to a target range--when you're outside the range the refrigerator door either automatically locks or the refrigeraor automatically dispenses a gallon of ice cream.
This isn't a bad idea but there are several key hurdles to overcome.
1. food isn't packaged in calory servings. So lets say you cooked a meal, you used two tablespoons of butter. The fridge would need a way to calculate how many calories you consumed based on that item.
2. identification. How would the fridge know the food was intended for you? what if you cooked a meal, what portion was yours and should be counted against the daily calorie limit?
We should raise the bar on "tasty cooking" with microcontrollers in the kitchen. For starters, they should be powered by the food (remember the potato powered clock?). Then the circuits could be printed on the food and made of edible materials. Eating the food in different patterns (disabling different portions of the circuit) would produce different results. Colors of the food could be made to change or different patterns could be displayed. Maybe some day, as you eat your steak, the vegetables will light up and say "eat your vegetables".
The Honeywell kitchen computer with the built in cutting board reminds me of the giant 1950s system at the Computer History Museum in Mountain View, CA that had a console with a built-in ash tray. "This computer can be hazardous to your health!"