I can guarantee you that the last thing you want is a calorie-dense paste diet. The largest problem with obese people is the amount of food they eat and the calorie density. A calorie dense paste is basically a perfect description of cake frosting. You want high density or weight and low calories.

Tasty food makes people happy.

This is taking away from other's happiness, as many people enjoy eating food, and will also cause many people to lose their jobs. This would also cause a food shortage, as a lot of food is unhealthy.

Your poop would smell really bad from all the vitamins.

In doing so, you will destroy millions of jobs. This move will eliminate virtually all jobs in farming and food service. Millions of distribution jobs would be affected as well.