If you're trying to build up your muscle and get rid of fat, intermittent fasting may help. Depending on how you do it, you shouldn't be losing muscle. You're probably already fasting without realizing it — you fast when you're sleeping or when you skip a meal.
Missing a meal doesn't mean you'll start losing muscle. If you've decided to try intermittent fasting as a way to lose weight, you shouldn't lose muscle as long as you are timing your fasting periods right and taking in enough protein.
Losing Muscle While Fasting?
If you decide to try intermittent fasting as a way to lose weight, but you're worried about losing muscle, just make sure you're smart about how you approach your fast. A small study conducted on 34 men and published in the October 2016 issue of the Journal of Translational Medicine has found that intermittent fasting along with resistance training can decrease fat mass and maintain muscle mass. Because of the small study size, further research is needed.
The study participants, all males who previously did weight training, ate their meals within an eight-hour period. In this study, they ate at 1 p.m., 4 p.m. and 8 p.m., while the control group had daily meals at 8 a.m., 1 p.m. and 8 p.m. The group that ate on a compressed schedule lost fat, while neither group lost muscle.
A small study of 12 female athletes yielded similar results. The study, which appeared in the June 2018 issue of the International Journal of Exercise Science, found that weightlifting activities after fasting relied on fat as the main fuel source. Researchers also speculated that increasingly relying on fat for fuel over a period of hours or even days could lead to lower body fat percentages without breaking down muscle.
Another small study focused on 16 male bodybuilders who were observed during Ramadan, which lasts a month. This is when Muslim adults fast from before dawn to sunset. That's about 11 to 16 hours, depending on the time of year.
Researchers concluded that fasting didn't affect men's body mass or body composition. Their findings were published in the April 2013 edition of the Journal of the International Society of Sports Nutrition.
What Is Intermittent Fasting?
Intermittent fasting (IF) has generated a lot of buzz as a weight loss approach. Dr. Monique Tello, writing for Harvard Health Publishing, outlined her thoughts in a June 2018 article "Intermittent Fasting: Surprising Update."
She says that certain enzymes in the human gut break down food into molecules. Carbohydrates, especially white flour and white rice, break down into sugar, which your cells use for energy. If those molecules aren't used for energy, however, they're stored in fat cells as fat.
Sugar needs insulin to penetrate the cells. Insulin helps bring sugar into fat cells and keep it there. Between meals, as long as you're not eating, insulin levels drop and fat cells release stored sugar as energy for you to use. The whole premise of IF is to allow your insulin levels to drop far enough and long enough that you burn fat, says Dr. Tello.
Whether IF works is in how you approach it. A small study conducted on 12 men and featured in the June 2018 issue of Cell Metabolism found that by fasting in sync with human circadian rhythms, men with pre-diabetes could improve their metabolic health. These men ate their meals within an eight-hour period, taking in their last meal of the day by 3 p.m.
The February 2017 edition of Science Translational Medicine published a study of 100 participants on a fasting-mimicking diet. The participants followed a diet low in calories, sugars and protein but high in unsaturated fats for five days each month for three months.
Researchers found that the 71 people who completed the study experienced improvements in body mass index, blood pressure, glucose levels, triglycerides, LDL and total cholesterol levels.
Intermittent Fasting and Health
Tello states that a "circadian rhythm fasting approach" combined with a healthy diet and lifestyle can be a good way to approach weight loss, especially if you're at risk for diabetes. Still, it's always a good idea to check with your doctor before undertaking any sort of diet, especially one that includes fasting.
She suggests that you combine fasting with a healthy lifestyle. You can use this advice to maximize the benefits of your weight lifting or bodybuilding routine while losing fat with IF. Here are her suggestions:
- Avoid sugars and refined grains. Eat a plant-based Mediterranean diet based on fruits, vegetables, beans, whole grains, lean protein and healthy fats.
- Let your body burn fat between meals by not snacking, by being active throughout the day and by incorporating resistance training. This is not the time for taking a week off from lifting.
- Limit the hours of the day when you eat, say, to 7 a.m. to 3 p.m., or 10 a.m. to 6 p.m.
- Don't eat at night.
Another Fasting Approach
There are also some studies on fasting for an entire day. A small study published in the September 2016 issue of the journal Obesity evaluated obese adults and alternate day fasting (ADF). Those who fasted for a day, eating zero calories, and then ate normally for a day, did lose fat and retain lean muscle mass.
An earlier study of 74 participants in the April 2015 edition of Obesity also found that ADF is effective for weight loss, although the subjects ate a small meal of about 25 percent of the previous day's calories. Dieters lost fat and saw their blood pressure drop. They ate their small meal at lunch or dinner on the fast day. Researchers noted that participants did better if the timing of the fast-day meal was flexible.
However, a July 2017 study in JAMA Internal Medicine looked at the effects of alternate day fasting on 100 participants. Scientists have found that those who fasted for a day (consumed about 500 calories) and feasted for a day lost no more weight after a year than those who ate a calorie-restricted diet.
Both groups lost more weight than the control group, which didn't diet at all. The ADF group had similar glucose and insulin numbers, but after one year, the ADF participants had higher LDL cholesterol levels. That's the number that can indicate if you're at risk for clogged arteries, according to U.S. National Library of Medicine.
Additionally, participants in the ADF group were more likely to drop out from dissatisfaction with the diet than those in the calorie-restricted group.
Building Muscle Mass
Use it or lose it is how the Mayo Clinic describes muscle mass. As you get older, lean muscle mass declines naturally. Strength training helps you preserve that muscle mass instead of losing it as you age. It also keeps your metabolism working even when you're at rest, so you're burning more calories throughout the day.
It's a good idea to work with a fitness professional if you're new to weight training. This will ensure that you are using the right technique and form. By stressing your muscles regularly, they'll adapt and get stronger, the same way aerobic exercise helps strengthen your heart.
- Journal of International Society of Sports Nutrition: "Effect of Fed- Versus Fasted State Resistance Training During Ramadan on Body Composition and Selected Metabolic Parameters in Bodybuilders"
- Cell Metabolism: "Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even Without Weight Loss in Men With Prediabetes"
- Obesity: "A Randomized Pilot Study Comparing Zero-Calorie Alternate-Day Fasting to Daily Caloric Restriction in Adults With Obesity"
- Obesity: "Meal Timing During Alternate Day Fasting: Impact on Body Weight and Cardiovascular Disease Risk in Obese Adults"
- Harvard Health Publishing: "Intermittent Fasting: Surprising Update"
- Mayo Clinic: "Improve Your Muscular Fitness"
- Mayo Clinic: "Strength Training: Get Stronger, Leaner, Healthier"
- International Journal of Exercise Science: "Effects of Prior Fasting on Fat Oxidation During Resistance Exercise"
- Islamic Networks Group: "Ramadan Information Sheet"
- JAMA Internal Medicine: "Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial"
- Science Translational Medicine: "Fasting-Mimicking Diet and Markers/Risk Factors for Aging, Diabetes, Cancer, and Cardiovascular Disease"
- MedlinePlus: "LDL: The 'Bad' Cholesterol"