There is a difference

There is a big difference between Intermittent Fasting (Time-restricted Eating) and a diet (Calorie Restriction).

In the Flipping the Metabolic Switch: Understanding and Applying Health Benefits of Fasting (Obesity, 2018 Feb., 26(2): 254-268) paper by Mark P. Matson et al. they are defined as follows,

• Intermittent Fasting (IF) – This eating pattern involves fasting for varying periods of time, typically for 12 hours or longer.
• Calorie Restriction (CR) – This eating pattern involves a continuous reduction in caloric intake without malnutrition.

Your typical diet

During regular diet when caloric intake is restricted a few things happen to your body.

1. The body tunes down your metabolism. As a consequence you can have a feeling of cold, mood change and feeling of tiredness.
2. Due to lower Leptin hormone, which signals to the brain that you have not enough stored energy, you start feeling continuous hunger.
3. While at first you lose some weight (mostly muscle), in the end after struggling with the diet you gain your weight back, but more. After all 99.5 % of diets fail.

As for Intermittent Fasting

While you fast for at least 16 hours, which allows your body to deplete glycogen stored in muscles and liver, your body will switch from using glucose as a main source of energy to using ketones produced by liver from fatty acids (fat).

1. When this transition happens your body is perfectly happy, there is no feeling of hunger.
2. Metabolism is actually elevated and you feel good.
3. There is almost no loss of muscle mass, but a connective tissue. Instead what is lost is the fat that was stored by your body. And if you do resistive training or walking while fasting there will be actually muscle mass gain!

Conclusion

So diet and fasting are complete opposites of one another.

One thing to mention is that it takes time (a number of weeks) for body to get used to fasting.
And even then you still could feel hunger in evenings due to naturally elevated level of the Ghrelin hormone. So it’s not simple, but doable and has such health benefits, not mentioning fat loss, which makes it beneficial in the long run.