timed eating
First, If you have a medical illness or are taking prescription medications you need to discuss your plans with a medical professional before you make serious changes in your diet or there can be unintended consequences, including fatal ones. Lots of doctors are fasting and low carb friendly these days. Here's a nice link to low carb friendly health care providers around the country.

You have read articles in the lay press saying that fasting and ketogenic diets are dangerous. Well that is true if the person going on them has a serious illness, especially if they are taking diabetes medications that can lower blood sugars or a medicine to lower blood pressure because on these diets high blood sugars (a bad thing) are going to go down (a good thing) but if you are taking a medication that lowers blood sugar it could go too low (a bad thing). Likewise your blood pressure is going to go down on a ketogenic diet with fasting (a good thing) but if you are on medicines to lower your blood pressure then your blood pressure could go too low (again, a bad thing).

There is nothing inherently dangerous about these diets. If you consider all the humans who have ever lived then 1000 humans have lived on a ketogenic diet with intermittent fasting for every human who has lived on a high carb diet with 2-3 meals a day since humans have only engaged in widespread farming for 10,000 of our almost 200,000 years on the planet.

I don't have time to explain the detail of how to do intermittent fasting. For information on how to do it and for references to the scientific studies supporting it's safety and efficacy I would refer you to Dr. Jason Fung's wonderful book "The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day and Extended Fasting".

How much fasting do I think people need to do? I think a young healthy person who has not developed any insulin resistance doesn't need to fast much at all. I still think these healthy folks should avoid eating, especially any stimulant containing foods like coffee, caffeinated sodas or tea for the 4 hours before bedtime as good restful sleep is one of the major if not the most important key to great health. I also recommend that metabolically healthy people use minimal refined sugar, avoid excessive alcohol intake and avoid refined seed oils.

Unfortunately 60-70% of Americans have metabolic damage from a combination of overconsumption of sugar, refined seed oils and alcohol, chronic sleep deprivation and chronic stress. I wrote about that in this post: "There's a Raging Epidemic - What Can You Do to Protect Yourself and Your Loved Ones?." This post: Am I Insulin Resistant? will tell you how to determine if you are insulin resistant and have to earliest indication you are on the road to diabetes and major health problems called: "The Metabolic Syndrome".

If you are insulin resistant, the keys to avoiding the pitfalls listed in the article on the epidemic of the metabolic syndrome are intermittent fasting and a low carb, high fat diet. I feel that the more insulin resistant you are the narrower the eating window will need to be. Again there are no controlled studies to go by but from experience over the last 3-4 years talking to people about this it seems to me that insulin resistant people, even if it is mild insulin resistance need to keep the daily eating window no wider than 8 hours. For moderate to severe insulin resistance a 6 hour eating window with 2 all you want meals of food that is 70-80% fat calories is the way to go. I personally have found that a 12 hour eating window every other day works out best with my schedule and I have followed this regimen for the last 290 days (I was formerly on the 6 hours per day plan).

How do you know if it's working? First you should slowly and steadily lose weight until you are at or near your ideal weight then level out. I've been there for 3 years. Well there are 5 lab tests that I as a doctor think are important. First is the Triglycerides/HDL Cholesterol ratio. If this number is <1.5 (If your report is in the European values of mmol/l [millimoles per liter] you must then multiply the value by 2.3 to get the correct ratio) then you have the healthy, fluffy, large LDL Cholesterol and your risk of heart disease is very low. Also it indicates that any insulin resistance you had is "in remission" though it could easily come back if you went back to a high carb, round the clock diet.

To make sure you blood sugars are controlled you need to follow a Hemoglobin A1c test. The A1c tells you the average level of sugar in your blood for the last 3 months. It should be <5.5% as this is the level where the complications of diabetes begin to be seen. I also recommend following your Albumin level. This comes on the standard chemistry profile that doctors routinely do on patients. Albumin is a large protein in your blood made by the liver. These large fluffy protein molecules act like "large sponges" in our veins that keep water from running out of our veins which are quite porous to water. It is almost identical to chicken albumen which comprises most of chicken egg white. If you're not getting enough protein or are are sick it can begin to drop.

Checking a complete blood count once a year to look for Iron deficiency or Vitamin B related anemias is also reassuring that a persons nutritional status is excellent.

And finally the metabolic syndrome is caused by inflammation which is an "overreaction" of our own immune system to the fat in the liver and pancreas that consuming too much refined sugar or alcohol leads to. Some people for whatever reason respond with a stronger inflammatory response than others, hence 30-40% of people seem to be genetically protected from the metabolic syndrome. So the best way to test the overall rate of inflammation in the body is the C-reactive Protein test. It should be less than 1.5 mg/L if it is higher then either the fat percentage in the diet needs to be increased or the eating window needs to be closed a bit.

Finally I would like to recommend another book by Dr. Fung called "The Obesity Code". The rationale about what I am going to explain along with citations to the scientific studies supporting this dietary approach are spelled out in detail in this wonderful books. Counting calories or it's equivalent, stopping eating before you are full because you want to make sure you're going to lose weight is a recipe for total disaster. You should always eat until your feel full and content. If you start "cutting back on how much you eat" your body will respond by lowering your basal metabolic rate making you feel tired and listless and breaking down lean body mass and converting it to sugar which leads to insulin release which traps fat in your cells totally torpedoing your weight loss while making you feel miserable.

The true magic behind both intermittent fasting and a ketogenic diet is lowering insulin levels.
Both carbs and protein lead to insulin release (fat doesn't cause insulin release). So if you are not losing the weight you want that means your insulin levels are still too high and you either need to decrease your protein and carb consumption and/or narrow your eating window. Since your body does not needs a single carbohydrate to be healthy but does need 0.8-1.2 grams per kilogram of protein per day to be healthy, one of the beauties of the zero carb diet is that it minimizes carbohydrate intake and allows for a very healthy protein intake without initiating too much insulin release.

I wrote this post on exactly how I follow a low carb, moderate protein, high fat diet without counting anything by learning what foods are 70-80% fat calories and only eating those in this post: The 3 Great Pitfalls to Losing Weight on Zero Carb.