If you deprive yourself of food by restricting calories, your body may go into a low-metabolic starvation mode, thereby hampering weight loss. It is important, in fact, that you maintain a reasonably-high intake of fat calories. Do not avoid fats on this diet. You may trim excess fat from red meat, but it is important to make use of desirable fats, such as olive oil, flax seed oil, canola oil, and butter when cooking. Again, it varies with the individual.
Some people feel nothing special the first week.
Others have bouts of constipation or diarrhea. Still others complain of a slight headache for a day or two. Many people say they feel more energetic, even euphoric after a few days on the diet. Most likely, you won't notice much in the way you feel the first week. After the first two weeks, most people definitely feel like they have more energy.