There have been a number of studies that indicate that fasting for one or more days at a time is a life extension.  This diet is close to that.

From the Amazon site for the Alternate Day Diet (one of the authors is an MD):

http://www.amazon.com/The-Alternate-Day-Diet-Skinny-HealthierLife/dp/03995349...

Diet only half the time with this revolutionary, easy-to-follow, safe, and science-based program.

The Alternate-Day Diet is based on scientific and clinical studies that show how restricting calories only every other day activates a gene called SIRT1?the ?skinny? gene?which results in reduced inflammation, improved insulin resistance, better cellular energy production, and releasing fat cells from around the organs to promote weight loss.

This easy-to-follow two step plan will enable readers to enjoy these remarkable and measurable benefits:

- Lose fat easily and quickly without deprivation, discomfort, or stress
- Improve fat metabolism and avoid regaining lost fat
- Slow the aging process
- Find relief from symptoms of asthma, heart disease, Type 2 diabetes, autoimmune and inflammatory diseases, and menopause-related hot flashes

The authors -

About the Author

And one significant review of the diet of a person who started with a BMI of 33.2 (obese) -

A Year on the Alternate-Day Diet (an ongoing review)

This is an ongoing review which I updated frequently for over a year, monitoring my progress, starting on Jan 18, 2010. The blog-like updates follow this summary.

The Alternate-Day Diet (ADD for short) is the best plan I've found for quick weight loss (I lost 43 lbs on it in six months). It truly changed my life, and I'm forever grateful for that. I'm in better health, in better shape, better-looking, more confident, more social, and more physically active than I've been in decades. My four-star rating is a tribute to how it's helped me achieve those changes. This diet is effective and relatively easy considering how drastically it restricts calories.

But it is drastic, and cuts your average caloric intake in half. It can be difficult or impossible for active people to sustain for the long term, and it seemed to slow down my metabolism like most other quick weight-loss diets. After six months, it quickly became a study in frustration, with no lasting additional weight loss. However, it's entirely possible that less active people will find it easier than I did.

So do I recommend it? It's not that simple. You'll have to make your own decision. These are some pro and cons.

Pros:
1. It works! You can definitely expect to experience dramatic weight loss, and to sustain it for several months.
2. No foods are forbidden. After a two-week introductory period, only calories are restricted, and only every other day. You can literally have your cake and eat it, too.
3. Results come quickly, so you get positive reinforcement quickly and often.
4. No changes are required in your shopping, but you'll save money by eating less.
5. Your body will not have to adjust to a major shift in food types.
6. It's easy to recover from a slip-up, at least in the first few months. Just make the next day a "down" (low-calorie) day. In case of an extended departure, just restart from the beginning.
7. There's no carb-/fat-/protein-juggling nonsense. No macro-nutrients are demonized or deified.
8. Light exercise is part of the program (although it's not emphasized enough).
9. As a more palatable form of caloric restriction, this diet may have longevity and health benefits beyond mere weight loss.

Cons:
1. It takes discipline and planning. Read the book carefully and give yourself a week or so to prepare yourself and build a support network before starting. It will be a *major* shift in an important part of your lifestyle.
2. Social occasions, especially unexpected ones, will pose challenges.
3. Hunger happens. After the first few days it's not bad, and it becomes easier as you progress, but on down days, especially in the evening, you will need to be prepared.
4. The healthiness of the diet is up to the you. Many people will find themselves desiring and eating healthier foods, but it is possible to remain on the SAD (Standard American Diet), and not improve your actual nutrition.
5. Heavy exercisers may find it very difficult if their caloric needs require day-to-day satisfaction.
6. You do have to count calories on the down days.
7. Diet fatigue may become a serious or even insurmountable problem after several months, although some people have kept with it for years.
8. Leaving it may lead to quick weight regain. There is no "exit strategy"; the maintenance plan is to stay on a less-extreme version of it for the rest of your life.
9. I believe it slowed my metabolism.* (Dr. Johnson points to a study that indicates ADD doesn't slow metabolism, but that study was for 3 weeks only.

Here's my experience:
**********
Start
January 18, 2010 --- 225 lbs, 102 kg
BMI 33.2 - Body Fat 35%
waist 46in, 117 cm - WHtR 67%

I was very intrigued by this plan when I saw it, since I have been aware of the benefits of calorie restriction; on the other hand, calorie restriction always seemed way too--well, restrictive to me. This seems doable, and I'm encouraged by the testimonials of the reviewers who say they've been on the plan for two years or more.

I desperately need to lose weight, so I'm giving it a shot. One thing to be aware of as I start this is that I'm training for a half-marathon in March. So far, I haven't lost any weight since I began training (actually, I've gained a few pounds), so I'm really looking to the diet to help me with weight loss.

**********
February 2, 2010 --- 218.5 lbs, 99 kg
BMI 32.2 - Body Fat 35%
waist 45in, 114cm - WHtR 65%

It's been two weeks, and I'm glad to be able to move out of the "shakes only" phase. I did bend the rules there a bit, eating protein bars more than shakes, and sometimes a bit a dried fruit as well, although I was careful not to go over my 500-calorie limit. Hunger wasn't too bad a problem, except late at night a couple of times. I didn't notice any problem with sleeplessness as some reviewers did. My main complaint has been "Atkins burps" on my low days... (if you've done the Atkins diet, you know what I mean). I'm thinking that that will pass as I begin eating real food on the low days. As far running goes, I've been sidelined with an Achilles injury, so that hasn't had anything to do with my weight loss.

Looking forward to continuing with it!

**********
March 2, 2010 --- 212 lbs, 96 kg
BMI 31.3 - Body Fat 34%
waist 44in, 112cm - WHtR 64%

My lowest weight in about five years. Early last month, I wrecked several short days in a row due to unexpected food--birthdays at work, a Superbowl party, etc. so I've really been doing this for 5 wks. now instead of 6. Now if I fall off the wagon on a low day, I just start alternating again the next day. Haven't used the recipes much... on low days I tend to do a protein bar, a bag of microwave popcorn and a piece or two of fruit. Not too hungry if I don't stay up too late. My face is showing the weight loss most, and I'm seeing a younger man in my mirror. This month I should get below 203 lbs--out of obese territory. I'm excited about this. Also, I dropped out of this month's half-marathon, I'll start training soon for a later one.

**********
April 4, 2010 --- 204.5 lbs, 93 kg
BMI 30.3 - Body Fat 31%
waist 42in, 107cm - WHtR 61%

My lowest weight in seven years. And 75% of what I've lost has been fat! My pants are getting baggy, though I'm reluctant to buy new ones this far from my goal. I'm running again, and occasionally working with light weights. This is part of the plan, though I had actually forgotten it (see pp. 92-100). My difficulty is unexpected social occasions, which I encountered even more of this month. That part isn't easy, but this plan is worth it. This is the good "ADD"!

***** Special update, April 17, 2010 ***** Yesterday I weighed in 202.5 lbs (92 kg), a BMI of 29.9. I am no longer obese! The pounds lost were exactly 10% of my starting weight; it seems 10% is a common "plateau" zone. This may be why it took longer to reach than I expected. I've also added Waist-to-Height Ratio (WHtR) to my updates, and my main goal for now is to lower my WHtR to 49% (34in waist). Four inches down, Eight more to go!

**********
May 3, 2010 --- 199 lbs, 90 kg
BMI 29.4 - Body Fat 27%
waist 40.5 in, 103 cm --- WHtR 59%

Finally crossed the 200-pound mark! I've been looking forward to this moment for years! Other good news: I'm burning fat faster, I ran in a 5K race, and overall, the diet is much easier--didn't blow any down days this month, although I have felt a bit of hunger. Weight loss has been a bit slower, probably due to stress and my body's adaptation to the new activity and calorie levels. My plan is to keep with it, watch the short days, drink more water, and get more sleep.

**********
June 7, 2010 --- 197 lbs - 89 kg
BMI 29.1 - Body Fat 25%
waist 40 in, 101 cm - WHtR 58%

Not bad, considering I had stalled in early May, had a knee injury that sidelined me for a while, fell off the diet for 2 1/2 weeks and *gained* weight, just got back on a week ago, and still lost overall!

The hunger was becoming way too much on down days, so a week ago, I decided to *increase* my down-days to 800 cal, and I was able to return to running as well. Since then, the diet is easy again! My new DD calorie level is still 25-30% of my up day intake; both have increased because my activity level is much higher now. (running 10-17 mi/wk)

Since the basis of the diet is to keep the body guessing, I wonder if a short departure from it every few months might actually be helpful. This week my progress has been like when I first began it. In the past, a slip like this would have discouraged me, but now I'm more determined than ever

**********
July 6, 2010 -- 189 lbs - 86 kg
BMI 28 -- Body Fat 24%
waist 38.5 in, 98 cm - WHtR 56%

36 pounds down, and less than 5 inches to go! I had to bite the bullet and buy some new pants, even though I know I'll be doing that again in a few months. Social events caused some trouble with down days this month, but overall they're much easier now. I'm feeling very good physically. I ran in an 8K, and I'm still training for the half-marathon.

**********
August 3, 2010 -- 182 lbs, 83 kg
BMI 26.9 -- Body Fat 22%
waist 37.5 in, 95 cm - WHtR 54%

I've now lost 43 lbs, and I'm within 13 lbs of BMI 25 -- end of the overweight zone. For two weeks I was on vacation in Spain, and I continued to lose weight there, although I certainly wasn't trying to follow the diet. (I believe the reasons were almost constant walking, and that I only ate when I was hungry. I completely fell out of the meal structure of the workaday world.) At any rate, I'm back at work, back in the States

What is Intermittent Fasting?

There are many variations on the intermittent fasting (IF) theme. Some recommend fasting two days per week, say Monday and Thursday. Others suggest fasting for 16-20 hours per day, four to six days per week. The plan I have been following is a feeding period of 4-6 hours per day and fasting for 18-20 hours each day. I am allowing one "cheat-day" every week or two, for both social and metabolic benefits.


Some variations on the Intermittent Fasting theme:

* The Warrior Diet (20/4 hrs fast/feed.)

* The Fast-5 Diet (19/5 hrs fast/feed.)

* LeanGains (16/8 hrs fast/feed.)

* Eat. Stop. Eat. (24 hour fast, twice per week.)

My Experience and Results, so far...

I prefer the steady-state of the 20/4 Warrior Diet, and I am losing 1-2 lbs of fat per week. I eat a healthy snack at 4PM, and a normal family dinner at 7PM, after a gradual transition in week 1. After a few weeks, I never feel any hunger. Now in week 12. Feeling great. Lots of energy, good mood, good mental clarity and focus. Lost 15 lbs fat, gained 2 lbs lean mass.

The Essence of the Warrior Diet: "...skip big breakfast and lunch, eat your main meal at night, and you'll notice how you're leaning down and strengthening without even changing your calorie intake." - http://www.warriordiet.com/