The best thing you can do is to let nature and your body's innate wisdom do the work of regulating the metabolism. Just as the body will automatically slow during a fast, it will gradually speed up when eating is resumed.

The most important thing you can do is not to go back to your old eating habits. After fasting you will need to very gradually increase your caloric intake and your exercise. You may need to eat only about 500 calories a day for the first week. You can do this by eating a lot of raw fruits and veggies. Later introduce cooked greens to your diet. These are nutrient dense for very few calories. They are mineral rich and will help rebuild your system. Steamed broccoli is an excellent choice for body building protein. Leafy greens are rich in iron, magnesium and calcium for blood, bone and joint health. The fiber rich greens will stimulate your entire digestive system, continue to cleanse your body. Coconut oil is supposed to help regulate thyroid production and safely stimulate the metabolism. After a week or two you might want to drizzle a teaspoon of virgin coconut oil on your veggies. Some people also use kelp since its natural Iodine can stimulate the thyroid. This needs to be used carefully and in moderation to prevent over stimulation.

Exercise is also important, but you need to be into the rebuilding phase of your fast before beginning strenuous exercise programs. During the fast itself only walking at a moderate pace or gentle stretches should be done. Too much exercise can actually contribute to muscle wasting in some fasting bodies. Yoga books often recommend deep breathing and neck stretches and rolls to keep up the metabolic rate.

For good health and longevity, the metabolic rate should not be too high. You do not want the body to be burning itself up. Rather than concentrating on reving up the metabolism so you can eat whatever you want, concentrate on eating right for your body's unique needs. This is ever changing and will require a lifetime commitment. I suggest you read "Eat To Live" by Joel Fuhrman MD to give you the basics of healthy eating. You can modify his diet to meet your specific needs, for example I need some animal protein and more healthy fats than he recommends to feel my best. Also, "The Miracle Of Fasting" by Paul Bragg will show you how to incorporate regular short fasts into an overall healthy lifestyle. Short fasts will cleanse the body and help cut total caloric intake without compromising the metabolism.