Intermittent fasting is not a diet, but a diet schedule that is purported to accelerate fat loss and muscle growth compared to traditional eating schedules. It is promoted primarily in the scientific community, however, there are currently zero scientific studies that have supported intermittent fasting for gaining muscle while losing fat.
Fasting is a period of time when one goes without eating. With intermittent fasting, you break up your fasting periods with eating periods.
With caloric restriction, intermittent fasting can lead to weight loss. In a recent review and one recent randomized clinical trial, authors concluded that intermittent fasting and daily caloric restriction are equally effective at promoting weight loss in overweight and obese individuals. However, no studies to date have been performed with athletes who require maintenance of muscle size, strength, and function. In fact, there are conflicting views on whether intermittent caloric restriction vs. daily caloric restriction best preserve lean muscle mass.
There have been several proposed protocols for intermittent fasting, from skipping one meal per day to eating only every other day. Despite the marketing of intermittent fasting, there are few well-controlled, scientific studies investigating the effects of intermittent fasting on the body composition and performance in athletes.
There are many approaches to intermittent fasting. The most popular and most studied is the alternate-day fasts and extended morning fasts, in other words, skipping breakfast.
One of the key advantages of this extreme form of caloric control is that it allows people to re-conceptualize hunger. Instead of linking “hunger” with “panic” or even “desire”, “hunger” can theoretically be newly associated with “success” or “pride”, or simply ignored.
With any method, there is a critical transition period of about 3-6 weeks during which the body and brain adapt to the new eating schedule. This period can be very uncomfortable, as restricted eating has been anecdotally associated with extreme hunger, irritability, loss of strength, loss of libido, and other negative side effects. Once the body is accustomed, however, the hunger levels may decrease and mood could become positive compared to before the fasting program started.
All of the approaches emphasize the importance of the nutritional quality of the meals that are consumed. Nutrients such as protein, fat, fiber, vitamins, and minerals are essential for good health and, since nutrients are not consumed while fasting, they are especially important when breaking the fast. In addition, drinking a lot of water is encouraged to stay hydrated and to alleviate hunger.
The following are some of the fasting techniques:
The Periodic Fast is a fast for 24 hours once or twice per week, eating sensibly (consuming higher amounts of protein, minimizing processed foods, etc.) the rest of the week. The fast can be started at any time, fasting from breakfast to breakfast, or dinner to dinner, for example.
The LeanGains method is a daily fast where fasting occurs for 16 hours (ex. dinner to lunch the following day or 10pm –2pm), then food consumption occurs in about 3 meals in an 8-hour window everyday. If you plan to exercise, you do so just before lunch, before the first meal, to ensure a large, high-protein post-workout meal. It is recommended taking in 10 grams of BCAAs (branched-chain amino acids) just before training to halt muscle protein breakdown during your workout. On exercise days, meals should include protein, vegetables, and carbohydrates; on non-exercise days, meals should include protein, vegetables and fat.
The Warrior Diet is another diet schedule variation of the daily fast and is one step more extreme than the LeanGains diet. It promotes a single, healthy meal per day (typically dinner). It claims that this pattern of eating is in sync with humans’ circadian rhythm and will promote general health while “removing harmful toxins from the body”. However, there is no scientific evidence supporting these claims.
Alternate day fasting is when food consumption is for 24 hours, then restricted for 24 hours (water is available at all times) for every 2-day cycle. These fasters are encouraged to make healthy eating choices, but they’re allowed to eat what they want on non-fasting days.
When you dramatically reduce your calorie intake, you will lose weight. However, it can also cause all kinds of health problems, including muscle loss. Further, when you start fasting, your body goes into conservation mode, burning calories more slowly.
Keep in mind that the initial weight loss on a fast is primarily fluid not fat. When you go back to eating, any lost weight usually gets a return ticket back. Not only do most people regain weight lost on a fast, they tend to add a few extra pounds because a slower metabolism makes it easier to gain weight. Worse, the weight that is regained is likely to be all fat since lost muscle has to be added back at the gym.
Side effects of fasting include dizziness, headaches, low blood sugar, muscle aches, weakness, and fatigue. Prolonged fasting can lead to anemia, a weakened immune system, liver and kidney problems, and irregular heartbeat. Fasting can also result in vitamin and mineral deficiencies, muscle breakdown, and diarrhea. When you drink laxative concoctions during a fast, there is an increased risk of fluid imbalance and dehydration. The risks get more complicated and severe the longer you stay on a fast, or if you repeatedly go on fasts.
Research is far from conclusive, and more studies are needed. No one knows for sure if intermittent fasting is truly any more beneficial than a traditional type of diet. Results may vary between men and women. Intermittent fasting is not recommended for the very young, elderly, pregnant women, women who are breastfeeding, people with diabetes, underweight people or other people who need to closely regulate their blood sugar. These populations could be at higher risk for experiencing negative consequences of fasting. The best approach still comes down to building consistently healthy habits, eating nourishing foods, and finding what works for you.
Resource: IDEA Fitness Journal, EAS Academy, Nutrition Action