Me too. But then again I am seriously overweight.
Just for an example, the average male in the United States is 5'7". At 5'7", a healthy weight is considered to be between 121 and 153 pounds. For a hypothetical 5'7" 30 year old who is sedentary (let's be honest here, US folks!) to maintain a healthy weight, he should eat approximately 1660 - 1840 calories. If you're active, obviously that calorie count goes up.
You're supposed to eat three meals per day, which means 554 - 614 calories per meal (and in reality, breakfast should be much larger than lunch which is larger than dinner). So, 400 calories seems about right for a meal. If you drink nothing but water all day, you're a touch short of your calorie goal and should find yourself a snack at that rate, but if you have a glass of milk or orange juice or something with breakfast or a non-diet soda you'll easily make up the difference.
Now, all of that is just about calories. Nobody is arguing that these meals are particularly good for you or that they should be eaten three times per day, seven days per week. A homecooked meal will taste better and if done right, be healthier overall. But you definitely won't "starve."
TL;DR
If you're a healthy weight and trying to stay that way, these meals have a fine calorie count and should be plenty.