Preparing for a Fast

After reading all about the excellent benefits that fasting provides, you’re finally ready to try it out yourself. You could gobble down all the junk food you anticipate you won’t be eating for your fasting window, but it’s better to prepare your body for optimum success even before you begin fasting.

The magic of fasting happens when your body enters ketosis, a state where your liver glycogen has been depleted, and instead of using glucose as its primary fuel, it begins metabolizing and burning a different kind of fuel known as ketone bodies. This window is different for every person but on average begins after about 16–18 hours of fasting, or 2–4 days on a fasting mimicking diet, such as the keto diet.

If you’ve spent the week leading up to your fast eating lots of carbohydrates and processed foods, your liver may have a harder time burning up its excess glycogen. Give it a head start instead by eating the following foods:


Since the popularity of the keto diet, some people believe that all forms of fasting mean you should eat little to no carbohydrates. But many forms of fasting just ask you to restrict the number of calories or the window in which you eat them. So definitely don’t forget to eat your veggies; the carbs you get from many vegetables are not at all the same as the carbs you get from chocolate or bread. Lean toward veggies that provide you with extra doses of insoluble fiber. Hint: the green leafies, such as kale, spinach, swiss chard, bok choy. Also broccoli, cauliflower, and cabbage are high in insoluble fiber.

Insoluble fiber is the kind that isn’t broken down by your gut bacteria, and thus it passes through you, helping keep you regular, among many other benefits. According to Dr. Stephanie Estima, eating this kind of fiber also has a negligible effect on blood sugar levels and insulin, so eat up!


If your sugar cravings go into high gear anticipating a reduction in sugar during your fast, try to feed it in the form of whole fruit, which also comes with fiber and nutrients, versus donuts, chocolate, or any other sweet treat. Not all fruit is ideal, either. You want to choose fruit that’s lower on the glycemic index (lower in carbohydrates), as well as lower in sugar/fructose and higher in fiber. Fruits like berries are among the best options to choose, as well as grapefruit and pears. Remember that fruit juices, while natural and often organic, lack the balancing effects of the fiber, vitamins, and other nutrients in a piece of whole fruit and can spike your insulin levels. So, avoid all juice prior to your fast.


Since we’re talking about high fiber, don’t forget your legumes (unless you are on the keto diet, in which case, you’ll want to limit them), which include beans, lentils, and peas. Legumes are also high in protein, which can make a nice substitute for meat if you want to take a break before and after your fast. Some legumes, such as white beans and lentils, are also high in resistant starch — carbohydrates that don’t break down easily in the gut and thus don’t interfere with keto diets because they have negligible impact on blood glucose and insulin levels. These can be added to salads, lean protein, or consumed on their own. Most legumes can be made even more digestible by soaking them (especially if they’re dry to begin with), typically overnight.

Healthy fats

Fat has long been vilified, but research shows that not all fat is created equal. You need healthy fats for a number of important bodily functions including your hormone production, and the healthy development of your brain, immune system, nervous system, and blood vessels. Healthy fats contribute to feeling full and satisfied after eating and can set you up to be less hungry during your fasting periods. Avoid trans fats and minimize animal fats such as bacon, butter, and dairy, but embrace your essential fats such as avocados, olives, and coconut oil. Also, in moderation, enjoy fats from nuts such as almonds, Brazil nuts, and cashews (particularly if they are raw to begin with and have no added sugars or salt). Also tasty and healthy in moderation are seeds such as sunflower, pine nuts, and pumpkin seeds, as well as chia and flax seeds — though the latter two may need to be blended or chopped into other food for optimum taste.


You could ideally get all the protein you need from the veggie and legume options mentioned above, which would be a nice way to kick-start a fast. But if you still enjoy other forms of protein, make sure you’re choosing lean, organic options. Perhaps eat a little less meat in the week leading up to your fast, or transition from red meat to chicken or pork. Consider replacing meat with only eggs or eating a soy-based protein such as tofu or tempeh. You can also get a lot of protein from dairy, but balance your intake so you’re not suddenly upping your dairy intake, which can be higher in fat and calories.

Macros and meal timing

Other key areas to consider before a fast are: macronutrient distribution (i.e., the percentage of kcal that falls into the carbohydrate, protein, and fat categories), the quality of your nutrient intake, and meal timing. Being purposeful in your approach to these can make the transition into a ketogenic state, and thus your fast, much easier, especially if a prolonged fast is your goal. This will help keep your hunger low and energy level up so you can obtain the benefits of fasting sooner.

Consider cleaning up your diet and altering your macronutrient distribution about two days to one week prior to your fast (depending on the type of fast you are completing and the duration). This means cutting out the sugar and processed carbs, and beginning to decrease the total amount of carbs you are consuming, specifically those from the previously mentioned categories, as well as some from the fruits and grains/starches categories. Keep protein about the same and you can increase your fat consumption slightly if needed. For example, instead of having a macronutrient distribution that is 50% carbohydrates, 20% protein and 30% fat, consider shifting that closer to a 20% carbohydrates, 20% protein and 60% fat during the days leading up to your fast.

Gradually shortening your feeding window about one week prior to your fast can also help train your body on how to function without food and get you into a more fat-adapted state. For example, if you don’t do time-restricted feeding already, you can start with a 14/10 feeding/fasting time frame and slowly decrease that feeding window closer to a 16/8 or even 18/6 the day before your fast. If you are already an avid time-restricted feeder, consider going to one meal a day (OMAD) or decreasing total portion sizes a few days before the fast.


A final note about coffee/caffeine. If you plan to do a fast without caffeine and are a big coffee/tea drinker, plan to start tapering your intake down one week prior to your fast to avoid caffeine withdrawals. Even those who drink one cup per day could benefit from a reduction in caffeine a few days prior to their fast.

Perhaps the best way to approach fasting in general is to treat it as the beginning of a shift in how you treat your overall health. Before you get your first fast underway, begin to eat as healthy as you can.

Posted in Health & Science


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