The studies seem to suggest that intermittent fasting can result in similar weight loss and fat loss to continuous dieting. Muscle is preserved with Intermittent fasting, especially with high-protein. Intermittent fasting may not be optimal for increasing lean muscle mass.
HOW TO INTERMITTENT FAST WITHOUT LOSING MUSCLE OVERVIEW
- How to intermittent fast without muscle loss is a frequently asked question.
- An intermittent fasting protein shake can help preserve muscle while intermittent fasting. Most researchers recommend resistance exercise and a protein intake of .8 grams or higher per pound.
- Intermittent fasting muscle loss does not have to occur if your protein intake is high.
- Intermittent fasting may not be optimal for increasing lean muscle mass.
RESEARCH UPDATE: INTERMITTENT FASTING TO LOSE FAT: MECHANISMS OF TIME-RESTRICTED EATING WEIGHT LOSS UNCOVERED
Previously written, intermittent fasting discussed that time-restricted eating and calorie-controlled diets have similar weight loss when calories are similar. There are many different fasting protocols, such as intermittent fasting, skip breakfast or dinner, and 16/8 intermittent fasting morning workout (Fast for 16 hours and feed for 8). Check out the intermittent fasting calculator to help you structure your efforts.
STUDY
A new study has unraveled a new twist: time-restricted eating can contribute to weight loss. Most studies on time-restricted feeding have used apps and other food-tracking devices, which need to be more accurate. Researchers took subjects and placed them in a metabolic chamber for 3 days. When you are in a metabolic chamber, everything gets accurately measured.
Calories, exercise, sleep cycle, and metabolism are tightly monitored. The subjects switched from a regular diet to a time-restricted feeding diet to reduce inaccuracies. The regular diet consisted of an 11-hour eating window, and the time-restricted feeding group had a 5.5-hour feeding window. The time-restricted feeding group ate between 8 am and 1:30 pm.
Both groups ate the same calories: ~1800 kcals, 261 g carbohydrate, 57g fat, and 60 g protein. There were no differences between groups in 24-hour energy expenditure, basal metabolic rate, or sleeping metabolic rate. There were also no differences in non-exercise activity thermogenesis or exercise activity thermogenesis.
Results
Ready for the shocker? The time-restricted feeding group had a 22.7% increase in fecal energy loss and a trend of increasing 14.5% in urine energy compared to the normal diet group.
The authors explain why the time-restricted feeding group was losing more calories thru waste such as feces and urine; it could be because of the larger amount of calories being consumed in a short time compared to having meals throughout the day. ”
The authors found that in one day, fecal and urine output changes by ~40 kcal, which, if held constant, would result in a roughly 280 kcal deficit per week by simply altering the timing of food intake. The author suggests that time-restricted feeding could induce negative energy balance by increasing fecal and urine energy excretion.
This seemingly negligible energy excretion elevation can explain up to 64.3% – 72.2% of weight loss in previous studies. More studies need to be conducted to unravel this mechanism, but this was the first to show increased fecal and urine energy loss with time-restricted feeding.(14)
HOW TO PREVENT MUSCLE LOSS DURING INTERMITTENT FASTING
Intermittent fasting has been advocated to be superior to conventional diets for boosting lean muscle mass and superior fat loss because of higher increases in GH and other metabolic benefits. The pros and cons of intermittent fasting are increased parameters of immune function and weight loss; downfalls include such as reduced anabolic hormones (i.e., decreased testosterone and IGF-1).(1) There are several forms of fasting: Alternate Day Fasting (i.e., eating every other day), Whole Day Fasting (i.e., fasting for 24 hours), and Time-Restricted Feeding (i.e., fasting for several hours at a time).
The most popular method of intermittent fasting to positively change weight and fat loss is 16 hours. Ramadan is the most widely accepted religious reason for fasting for Muslims, in which one does not eat from sunrise to sunset. During Ramadan, Muslims fast for 12-18 hours a day and do this for 30 days. During Ramadan, food and liquid are only eaten at night.
A recent meta-analysis of Ramadan and non-Ramadan intermittent fasting found that fasting can result in small decreases in fat and body weight. Still, the effect of these changes was mediated by the % body fat of the person starting the diet. Those with more body fat lost more weight and body fat during Ramadan than those with less body fat.
DOES FASTING CAUSE MUSCLE LOSS?
The other interesting finding from the study was that Ramadan was not associated with the loss of lean muscle.(2) Research suggests a positive calorie intake is needed for muscle growth. Since fasting consists of long periods without protein, it was suggested that long-term fasting muscle loss occurs. Intermittent fasting and muscle loss were a no-brainer!
However, the study found that this was another fasting muscle loss myth. Other common myths are related to hunger control. In a meta-analysis of intermittent fasting, some of the most common myths regarding fasting were debunked. The results were:
a.) One would suspect that fasting for 16 hours would result in low adherence and high dropout rates; however, intermittent fasting has similar dropout rates to traditional low-calorie dieting.
b.) Intermittent fasting is safe and improves glycemia, although there is a potential for hypoglycemia that has been documented.
c.) Hunger levels remain stable or generally decrease.(3)
Several large-scale literature reviews have found that intermittent fasting is similar to calorie restriction; both equally reduced body weight, body fat, and changes in lean mass.(4-6) There is no “metabolic advantage” to intermittent fasting, as you commonly hear referred to by social media fitness influencers. Intermittent fasting is thus an alternative to calorie-restricted diets, but the outcomes are very similar for body composition (i.e., fat loss, weight loss, lean mass).
The benefit of intermittent fasting is that it eliminates calorie counting throughout the day. Studies have shown that intermittent fasting with food restriction lasting 12-24 hours lose weight without counting calories.(7) Thus, intermittent may be an easy way to create a caloric deficit compared to a continuous diet in which calories must be meticulously calculated for the day.
CAN YOU BUILD MUSCLE WHILE FASTING?
Intermittent fasting has been suggested to be great for losing fat but not for building lean muscle mass. a common thread by many bodybuilders is, “Do you lose muscle while fasting?” Check out the intermittent fasting muscle loss Reddit thread.
A 2019 study by Tinsley et al. had the intermittent fasting community saying, “See, I told you so…you can gain muscle while fasting,” when he found that intermittent fasting produced similar increases in lean mass as a conventional diet. This study found that prolonged fasting and muscle loss do not have to occur if you follow the right diet.
HOW TO GAIN MUSCLE WHILE INTERMITTENT FASTING
The study compared body composition changes from resistance training in three different conditions: a.) non-fasting (13.5-hour feeding window), Fasting (7.5-hour feeding window), and Fasting + HMB supplementation (7.5-hour feeding window).
HMB supplementation has anti-catabolic properties, so the researchers wanted to see if it would preserve lean mass during intermittent fasting. After eight weeks, all groups built a similar amount of muscle with no differences between the groups.
If you deeply dive into the methods sections, the intermittent fasting group consumed 4 meals per day. They consumed a protein shake before and immediately after exercise (i.e., intermittent fasting protein shake) and then consumed two additional meals later in the day. The normal diet group ate five meals a day. To preserve muscle, intermittent fasting and exercise should be performed for optimal results.
HOW TO FAST WITHOUT LOSING MUSCLE
All groups consumed the same protein, calories, etc. This suggests that if you want to maintain muscle mass, having a protein shake pre and post-exercise and having your normal meals several hours later is a viable way to use intermittent fasting and maintain muscle mass.(8)
ANOTHER INTERMITTENT FASTING MUSCLE LOSS STUDY FINDS NO MUSCLE LOSS
Another study examined the 5:2 effects of an intermittent fasting diet in which you eat a normal diet Monday thru Friday and then on Saturday and Sunday (i.e., a 48-hour fasting period). Researchers had one group follow a continuous caloric deficit of 20% and another follow a 5:2 intermittent fasting schedule. The subjects in the 5:2 group didn’t fast completely for 48 hours. They dropped their calories to approximately 30% of their normal eating pattern (<600 calories).
The subjects drank whey protein shakes, high protein stews, and raw vegetables between noon and six pm on the fasting days. This study used a high protein diet in both groups, with protein intake at 1.4 g/kg/bw or .6 grams per pound of body weight. The subjects performed resistance exercises three times a week.
At the end of the study, both groups gained lean mass and lost body fat, with no differences between the groups.(9) The ultrasound measurements for hypertrophy were intriguing; they found that the continuous dieting group had a small (non-significant) increase in leg growth compared to the 5:2 group. This study was conducted on untrained lifters.
We don’t know if advanced lifters will respond the same way. The good news is that if you want to cut back on your calories for just two days, you can lose body fat while preserving muscle. These studies suggest that if you want to know how to prevent muscle loss when fasting, maintain adequate protein above .7 grams per pound of body weight or greater.
ONE MEAL A DAY (OMAD) FASTING AND BUILDING MUSCLE
In the news, several athletes and Hollywood actors have said they eat one meal a day for longevity and health purposes. A common question among fasting enthusiasts is, “how long can you fast without losing muscle?” More specifically, “will I lose muscle if I fast for 3 days” and “will I lose muscle if I fast for 7 days” No studies exist on this topic, but the answer depends on how much body fat you have.
Studies with intense calorie restriction have found that those with greater body fat lose less muscle. A recent study examined one meal a day (i.e., at dinner between 5 and 7) versus three meals a day and its effect on body composition and performance in healthy adults. The calories were self-reported, which they calculated with a phone diet app.
THE STUDY
The subjects were allowed unlimited water, coffee, and tea (i.e., without sugar). There were no differences in the calories between the two groups at the end of the study. The researchers did several tests to measure aerobic capacity and strength tests. At the end of the two weeks, there were no differences in aerobic or strength capacity performance, but again, these were not lifters, just healthy living adults.
RESULTS
One meal a day had a greater increase in fat oxidation after exercise and lower blood glucose concentrations in the second half of the day. The one-meal-a-day group lost more weight and fat mass than the three-meals-a-day group, with no changes in lean mass (i.e., not statistically significant between the two groups). If you examine the lean mass, the one meal-a-day group lost -0.7 kg of muscle while the three meals-a-day group lost -0.3 kg of muscle.(10)
This was only a 2-week study, but the one-meal-a-day group was starting to move forward toward losing more muscle mass. Longer-term studies are currently bring conducted before saying that one meal daily does not result in muscle loss. Intermittent fasting and building muscle will depend heavily on how much muscle you have; if you are already lean, it will be extremely difficult to gain muscle compared to someone with more body fat. One meal a day lost more body fat, but there was a trend towards greater lean muscle mass in the one meal a day group.
One meal a day lost more body fat but there was a trend towards greater lean muscle mass in the one meal a day group.
““From our current understanding of muscle protein metabolism and taking a “muscle-centric” view for diet; we highlight that current acute evidence suggests intermittent fasting may represent a counterproductive strategy to optimize muscle mass and, as far as protein turnover can remodel old/damaged proteins, muscle quality.”
There are many studies conducted on intermittent fasting having the capacity to preserve lean muscle, but very few studies have shown intermittent fasting can increase lean muscle. A 2020 meta-analysis of the literature shows that intermittent fasting with resistance exercise can preserve lean mass. Yet, of all the studies analyzed, there was insufficient evidence that intermittent fasting and resistance exercise can increase lean muscle mass.(11)
Things to Consider when Intermittent Fasting
This suggests that intermittent fasting is not optimal for increasing lean muscle mass, given that most studies involve resistance exercise increases lean muscle mass. Some suggest that intermittent fasting, infrequent meals, and prolonged fasts lead to suboptimal increases in protein synthesis, resulting in a net overall protein balance compared to more frequent meals in a caloric restriction.
There are many studies on intermittent fasting having showed the capacity to preserve lean muscle, but very few studies have shown intermittent fasting can increase lean muscle. A 2020 meta-analysis of the literature shows that intermittent fasting with resistance exercise can preserve lean mass. Yet, of all the studies analyzed, there was insufficient evidence that intermittent fasting and resistance exercise can increase lean muscle mass.(11) Thus, it’s a myth that intermittent fasting causes muscle loss, but few studies show it’s conducive to gaining muscle.
This suggests that intermittent fasting is not optimal for increasing lean muscle mass, given that most studies involving resistance exercise increases lean muscle mass. Some suggest that intermittent fasting (i.e., 14/10 intermittent fasting, 18/6 intermittent fasting, 14/10 intermittent fasting), infrequent meals, and prolonged fasts lead to suboptimal increases in protein synthesis, resulting in a net overall protein balance compared to more frequent meals in a caloric restriction.
How to Intermittent Fast Without Muscle Loss
In a review on intermittent fasting and resistance exercise, the author Williamson Moore stated, “From our current understanding of muscle protein metabolism and taking a “muscle-centric” view for diet, we highlight that current acute evidence suggests intermittent fasting may represent a counterproductive strategy to optimize muscle mass and, as far as protein turnover can remodel old/damaged proteins, muscle quality.”(12)
Alternate-day fasting is worse for sparing lean mass compared to intermittent fasting. One study compared a 25% continuous caloric restriction alternate-day fasting for three weeks in lean, healthy individuals.
The daily calorie restriction group lost less muscle and more fat compared to alternate-day fasting. The researchers suspected that the drop in physical activity from fasting could have resulted in fewer calories burned. The researchers concluded that alternate-day fasting was less effective at reducing body fat than daily caloric restriction.(13)
KEY POINTS
- The studies suggest intermittent fasting can result in similar weight loss and fat loss to continuous dieting.
- Intermittent fasting may not be optimal for increasing lean muscle mass.
REFERENCES
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