The first step I recommend in starting your KetoFast journey is to stop eating three hours before bedtime. Eating before you go to sleep tasks your body with digesting at a time when it is geared to perform functions of repair and regeneration instead. It also provides calories at a time when your energy needs are lowest, so the energy derived from that food tends to be stored as fat. But perhaps more important, the fuel backs up in your system and burns very inefficiently, resulting in an excess of potentially harmful free radicals. These free radicals then damage the DNA, cell membranes, and proteins in your cells and mitochondria, the organelles within your cells where energy is manufactured. When you give yourself a few hours to digest your food well before you go to sleep, you support your body’s natural housekeeping processes. You also give your body more of a chance to deplete its glycogen stores overnight, which encourages the switch to burning fat.
Once you are used to avoiding food for at least three hours before going to sleep, your next step is to begin implementing Peak Fasting, and gradually reduce your window of eating down to six to eight hours a day. Peak Fasting will further encourage your body to manufacture and burn ketones, and enhance your rest and repair functions.
While you are going through the process of gradually expanding your Peak Fasting, you should also be eating a ketogenic diet—that is, a low-net-carb, high-fat, moderate-protein diet (as described in my book Fat for Fuel) that gets you into a state known as ketosis where you are burning fatty acids, known as ketones, for fuel.
Once you know you are in ketosis—because you are monitoring your ketones with either a blood or urine monitor—you can begin cycling in one or two higher-net-carb and protein days each week while also honoring a restricted six-to-eight-hour eating window. Ideally on these days you’ll be doing exercise that includes some form of strength training.
This cycle of eating a ketogenic diet for five or six days a week and eating more carbs one or two days a week is known as cyclical ketosis. The ketogenic aspect of the diet is designed to improve many vital markers of your health, such as your fasting glucose and insulin levels, while adding in regular “feast” days, when you consume more carbs, helps you maintain these benefits over the long term. (The cookbook Pete Evans and I collaborated on in 2017, Fat for Fuel Ketogenic Cookbook, contains nearly 100 recipes that support the guidelines of a cyclical ketogenic diet and taste delicious.)
Once you are adapted to a cyclical ketogenic diet, you can begin replacing one day a week of ketogenic eating with a KetoFast day, when you consume only 300 to 600 calories of carefully chosen foods (such as those outlined in the recipes in this book), which will keep your body in a fasted state and stimulate your body’s natural healing response.
You can gradually work up to two KetoFast days per week.
Step one: Stop eating three hours before bedtime.
Step two: Begin shortening your eating window—typically this is most easily done by continuing to not eat for three hours before bedtime and then delaying breakfast.
Step three: As you gradually reduce your eating window to between six and eight hours a day, begin following a ketogenic diet.
Step four: After you are regularly producing ketones, add in one “feast” day a week when you eat more net carbs and protein in what’s known as a cyclical ketogenic diet.
Step five: Add in one day of KetoFasting a week for one month (a total of four weeks).
Step six: If you are doing well and feel comfortable, progress to two days a week of KetoFasting. The other days you should still be following a cyclical ketogenic diet—four days of a strictly ketogenic diet, one day when you consume a higher level of carbs (say 50 to 100 grams) and two days of KetoFasting a week. You can continue with this strategy until you reach your health goals.
It is important that you don’t overeat on your KetoFast days, as you want your body to have a typical physiological response to a lack of food. If you eat too much, your body won’t go into a fasted state. So you want to be precise about the number of calories you consume.
The way you determine how much you should be eating on your KetoFast days is to subtract your body fat percentage from 100—that number is your percentage of lean body tissue. (To determine your body fat percentage, I recommend buying an electronic scale that calculates it. There are many models available online that cost about $25, although you can also use calipers or a dual-energy X-ray absorptiometry [DEXA] scan to measure it.) Then multiply your total body weight by your percentage of lean body tissue; the result is your lean body mass. Finally, multiply your lean body mass by 3.5 to arrive at the approximate number of calories you should have on your KetoFast day—it should be somewhere between 300 and 600 calories. In general, a small woman requires about 300 calories and a larger man needs closer to 600 calories.
It’s best to have all your calories as one meal rather than breaking it up throughout the day. An early lunch may be ideal, as it gives you three to four hours after rising and before you go to bed to be burning fat; it also generally coincides with the time when your energy needs are highest for the rest of the day, unless you have a highly physical job, such as landscaping or carpentry, that requires you to expend a lot of physical energy early in the morning.
On your partial fasting days, it’s important to consider what types of calories you consume—not just how many. There are three main types of foods, known as macronutrients: protein, fat, and carbohydrates. You want to keep the ratio of these macronutrients in proper proportion so that you maintain ketosis and keep your fat-burning high. That means you will want to keep both your carbohydrate and protein intake below 15 to 20 grams each. If the calories from these two categories of foods don’t add up to your targeted intake, add the remaining calories as fat, typically in the form of coconut oil or MCT/C8 oil. To help you keep track of your macronutrient intake, I suggest you use Cronometer—a food tracking tool that I discuss—to input the food you plan to eat on your KetoFast day before you have eaten it, so you can see how much additional fat you’ll need to take to meet your caloric total.