The newest craze in the nutrition and dieting world is a type of diet known as intermittent fasting (IF). IF involves eating your daily calorie allotment during a specified “eating window,” and fasting (not eating) during the remaining portion of the day. There are three basic variations of intermittent fasting to consider that involve different elements and benefits.
Types of Fasts
24-Hour Fast – This is completed 1-2 times per week and involves fasting for an entire 24-hour period. For example, you might stop eating at 8 pm on Saturday, and not eat again until 8 pm on Sunday.
8:16 Fast – This is a more common type of fast, usually followed every day, where you eat during an eight-hour window and fast the remaining 16 hours (including sleep). The most common arrangement is to eat between 1-9pm every day. You basically skip breakfast every morning and wait until lunch to have your first meal. This can also be done periodically throughout the week and doesn’t have to be every day.
5:2 Fast – Also referred to as a “modified fast,” this style of fasting involves dropping calories to 500-600 total calories two days each week and eating normally for the remainder. This style of fasting can be a good introduction to those who can’t fathom extended periods of time without eating anything. The total calories are usually split into two equally-sized meals during the day.
12:12 Fast – This is most closely resembles a normal eating routine where you eat during a 12-hour window (i.e. 9am-9pm) and fast the remaining 12-hours (including sleep).
IF Supports Fat loss
For fat loss, the main benefit of IF is in how it creates a caloric deficit. There is nothing magical about this type of diet. However, one could see how it would be less likely to overeat calories when you restrict yourself to a limited eating window every day. Additionally, a intermittent fasting type of diet would allow you to eat larger meals than eating regularly throughout the day. If you have a preference for larger, more infrequent meals, then IF could be a suitable alternative.
Increased Insulin Sensitivity
I could write a whole article on insulin, but for our purpose imagine insulin as the key that opens the door to put the nutrients you eat into the cells of your body to be used for energy (or stored). Insulin is released as a result of eating carbohydrates and plays an important role in muscle building and energy production. However, if too much insulin is released over an extended period of time you can become desensitized, meaning your body changes the locks and your keys no longer work. When insulin function becomes dramatically impacted, this develops into Type 2 diabetes. IF has been shown, in some studies, to improve insulin sensitivity.1
IF May Decrease Your Appetite and Fight Disease
The benefit of decreased appetite2 depends on where you place your eating window. When you eat your hunger hormones (ghrelin and leptin) are stimulated to produce. These hormones are responsible for making you feel hungry. When you eat first thing in the morning, these hormones are rearing to go all day long, which can make you hungrier throughout the day. By waiting further into the day to eat, you postpone the production of these hormones which can decrease your appetite throughout the day. This can further lead to reduced calorie consumption. Some studies have shown that those who consume a healthy breakfast tend to weigh less than their breakfast-skipping counterparts. Physiologically, eating breakfast bears no advantage for fat loss. However, many people find themselves famished by the afternoon and often give themselves permission to overindulge in whatever piques their appetite—because they can afford the extra calories from a missed breakfast. If you find you fall into this category of afternoon binging, starting an IF diet could prove problematic (at least initially).
Studies have also shown that IF can increase cellular repair, increase cell resistance to oxidation, and help prevent chronic diseases such as Type 2 diabetes, heart disease, and Alzheimer’s.3, 4
Who Should Consider IF?
If you are often in a rush in the morning or generally busy with work IF can be great for your productivity. It’s easier to plow through your workload when you don’t have to worry about stopping to prepare or eat food. In fact, I practice the 16/8 fast 2 times per week and those are my most productive days.
If you find you aren’t too hungry in the mornings but get cravings late at night that leads to snacking, IF can be one potential way to mitigate over-consumption. Again, IF allows you to eat larger meals later in the day, so you will likely feel less of a need to snack into the late hours.
While you get used to fasting for extended periods of time, now and again you do experience hunger hours before you are planning to eat anything. Most people overeat because they can’t stand this feeling, and unfortunately, we often feel hungry for reasons other than actual hunger (stress, habit, entertainment, boredom, etc). Learning to “sit” with this hunger, and recognizing that it’s not that bad, and it goes away after some time, allows you to have better self-control with your eating behaviors.
Who Should Avoid IF?
If you already struggle to meet your caloric goals, then IF might make this even harder to achieve. Again, your appetite will be suppressed (even more than it is now), and you will have less time to consume your calories.
If you work out in the morning or late at night it isn’t necessarily a deal breaker, but still something to consider when looking at the pros and cons of IF. You will want to fit your workout in sometime within your eating window. If you plan to stop eating by 9 pm, for example, but don’t workout until 10 pm, then you won’t be able to eat anything afterwards—a problem for strength and muscle gain. Likewise, if you workout in the morning having fasted, you will notice you can’t perform as well. In other words, you will want to have at least one meal pre-workout and one post-workout. Remember, you can shift your eating window to the morning hours, but this will likely make it harder to stop eating throughout the evening given those pesky hunger hormones.
Original research into intermittent fasting involved performing a strength training routine toward the end of a morning fast (working out around lunchtime), then consuming the first meal of the day immediately afterward. If your schedule allows it, and you don’t notice a decrease in performance, then this is another potential option. In so doing you should consume 5-10g of branched-chain amino acids during your workout to prevent muscle loss.
If you’re prone to binge-eating IF may not be a good option for you because there is a period at the beginning where your body is still getting accustomed to the new schedule, so you’ll likely be famished by the time your first meal rolls around—thus putting you in a position to binge eat. If you are prone to binge-eating—uncontrollable eating of anything and everything in sight (usually not healthy stuff)—then IF could exacerbate that desire to binge.
If you have pre-existing medical conditions that contraindicate infrequent food consumption, IF may not be appropriate for you due to your health history. If you have diabetes, for example, and it is imperative to monitor and strictly control blood sugar levels throughout the day, the infrequency of eating due to IF could potentially lead to low blood sugar during the fasted state.
Additional Considerations for IF
Since you are fasting for extended periods of time, you run a greater risk for muscle atrophy (shrinkage—getting weaker). For this reason, it becomes imperative to consume enough protein during your eating window. Vegetarians and vegans will find it harder to meet this requirement. Additionally, the use of a branched-chain amino acid (BCAA) supplement during your fast can help prevent muscle loss.
Weight training should be within your eating window, but because cardio is about relative effort you can still do this without food. Do note that your performance might be lower than you’re used to. Also note: if you are prone to low-blood sugar spells during exercise, this may not be a good option.
Make caffeine your friend and use non-caloric caffeine sources (black coffee, tea, etc.) in the morning during your fast. These drinks can help keep energy levels up and further help control your appetite until the eating window begins.
You need to make sure to drink lots of water during your fast. This will not only keep you hydrated (you likely won’t have room in your stomach for much liquid during your eating window), but can also help keep you comfortable during your fast.
Consider Your Options Carefully
As you’ve seen, there are a lot of considerations to make when contemplating an intermittent fasting diet. Of course, I recommend consulting with your doctor before beginning any new diet or exercise program. However, intermittent fasting does appear to be a beneficial option for those individuals that can make it work with their lifestyle. Remember, the best diet is the one you can stick to without feeling (or being) deprived of any foods or nutrients. The only way to truly know if IF is a good option for you is to experiment and give it a try.
1. Harvie, Michelle N., Mary Pegington, Mark P. Mattson, Jan Frystyk, Bernice Dillon, Gareth Evans, Jack Cuzick et al. “The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women”. International journal of obesity 35, no. 5 (2011): 714.
2. Natalucci, Giancarlo, S. Riedl, A. Gleiss, T. Zidek, and H. Frisch. “Spontaneous 24-h ghrelin secretion pattern in fasting subjects: maintenance of a meal-related pattern”. European Journal of Endocrinology 152, no. 6 (2005): 845-850.
3. Tinsley, Grant M., and Paul M. La Bounty. “Effects of intermittent fasting on body composition and clinical health markers in humans”. Nutrition reviews 73, no. 10 (2015): 661-674.
4. Mattson, Mark P., Valter D. Longo, and Michelle Harvie. “Impact of intermittent fasting on health and disease processes”. Ageing research reviews 39 (2017): 46-58.