Intermittent Fasting is Not a Fat Loss Recipe for Everyone
Although intermittent fasting has dramatically impacted the traditional dietary rules, more practitioners have begun to try this diet to realize the dream of high-efficiency fat loss. It literally means that it is an “intermittent non-eating” diet, usually divided into the following two categories:
- Eat at a specific time each day, but the food remains the same, and the daily eating time should have a limit like 6-8 hours, such as “not eating after lunch”;
- “5:2 intermittent fasting” means that calorie intake has a limit of two days a week, and the remaining five days remain the same.
However, the effects of intermittent fasting on metabolism and health are inconclusive in science. It can affect the body’s metabolic mechanism, but a calorie gap is vital for losing weight, like continuous calorie restriction. Therefore, its only advantage may be to change the way of “eating,” i.e., limiting the time of eating makes it easier for people to reduce calorie intake.
In addition, we also interviewed many office professionals, fitness enthusiasts, and fitness coaches. Intermittent fasting does not have a special aura of fat loss. More importantly, intermittent fasting also has taboos and risks, and it does not apply to everyone.
Intermittent fasting and limited time eating
Many people understand intermittent fasting from social media and video websites at home and abroad. For example, searching for “Intermittent Fasting” on Youtube, the top ten videos have more than 5 million views. In addition, there are TED talks by nutritionists, popular science by doctors, and fitness bloggers.
The most recommended intermittent fasting is 16:8, i.e., the eating time has a limit of 8 hours a day; another popular intermittent fasting method, 5+2, is based on the weekly unit, 5 per week. Eat normally every day and limit calories for the other two days. Most bloggers do not distinguish between the types of intermittent fasting but use “intermittent fasting” to refer to all discontinuous fasting methods, including 16:8 and 5+2.
However, in scientific research, 16:8 and 5+2 aren’t intermittent fasting. Although the two more accurate terms are intermittent energy restriction (Intermittent Energy Restriction, IER), they represent two types: limited time feeding (The term time-restricted feeding, TRF) and intermittent fasting (Intermittent fasting regimens, IMF).
IMF and TRF
The term time-restricted feeding (TRF) characterized by 16:8 limits food intake to a time window of 8 hours or less per day. For example, (E) means eating in the early part of the day (such as 9:00-17:00), and (F) means eating in the middle of the day (such as 13:00-19:00). In addition to 16:8, time-limited eating includes 4:20 (fighter diet, eating within 4 hours).
Intermittent fasting (IMF), represented by 5+2, refers to an individual with little or no energy intake for an extended period (such as 16-48 hours) and eats typically at other times.
Common intermittent fasts include: (A) fasting every other day (zero calorie intake on fasting days), (B) modified fasting every other day (energy limit on fasting days> 60%), (C) fasting two days a week Eating or modified fasting (2DW), (D) Regular fasting for 2 to 21 days or more.
The main difference between the two types of fasting methods is that intermittent fasting (IMF) has a longer fasting time, usually in units of more than days. At the same time, limited-time feeding (TRF) is generally repeated every day, in hours, the time of fasting Shorter.
There is no specific distinction between different types of intermittent fasting for the general public. Most people understand that as long as there is a “restricted eating time” or “fasting for a period of time,” it means intermittent fasting.
Intermittent fasting can lose weight, but the key is still a calorie gap
Low Calorie Intake
For many people who have heard of intermittent fasting, the most curious question is: Can it lose weight? Is it safe to lose weight? Of course, and many practitioners of intermittent fasting, the original intention is to lose weight or reduce fat.
Internet practitioner Fei Xiong has been a fitness enthusiast for many years. His exercise time squeeze during his entrepreneurial period, so he tried intermittent fasting and carried out weight management from the diet side. He had practiced 5+2 and 16:8 for a period of time. Asked if there is a fat-reducing effect, he affirmed.
ZE SPEED trainer Andy started to try 16:8 intermittent fasting three years ago. After the fat loss is effective, it has continued to this day.
They all believe that the main reason that intermittent fasting can help to lose weight is that the eating time has a limit and the calorie intake is low.
This has also been confirmed in many scientific studies: In the case of a calorie gap, intermittent fasting can indeed lose weight.
A meta-analysis published in Nutrients in 2019 summarized 11 studies of intermittent fasting, all of which lasted longer than eight weeks, with energy restriction on the intervention day. Studies have found that intermittent fasting produces a weight loss effect equivalent to that of continuous sexual energy restriction, indicating that intermittent fasting effectively replaces continuous sexual energy restriction to lose weight.
Some bloggers who introduced and praised intermittent fasting also mentioned the mechanism of intermittent fasting to lose weight. Dr. EricBerg DC, a blogger with 5.46 million followers on Youtube, is dedicated to researching intermittent fasting and ketogenic diets. He explained intermittent fasting through multiple videos. The most played video explains the effects of insulin and growth hormone on fat loss and how intermittent fasting affects these two hormones to help us burn fat.
In fact, from the perspective of metabolic mechanisms, intermittent fasting does trigger a series of biochemical reactions in the body. During fasting, blood sugar levels are low, liver glycogen reserves are consumed, and gluconeogenesis is activated. Fat cells begin to decompose and release fatty acids, which are oxidized to ketone bodies—the body switches from using glucose as a fuel source to fatty acids and ketones.
In this process, insulin plays an important role. When we eat something, Insulin secretion (the only hypoglycemic hormone) is stimulated and promotes anabolism (including fat synthesis). During fasting, insulin secretion is less, and anabolism is weakened.
In general, the body’s response to intermittent fasting is to minimize anabolic processes (synthesis, growth, and reproduction). There is also scientific literature that shows that intermittent fasting can cause autophagy, increase stress resistance, and reduce the incidence of diseases such as cancer and obesity.
Calorie Gap is Always Needed
However, when the calorie gap is the same, compared with continuous sexual energy limitation, the fat-reducing effect of intermittent fasting is not superior. Multiple analyses have shown no significant difference between the two in reducing body weight and body fat. In addition, although intermittent fasting has a more substantial benefit on insulin levels, there are no differences in metabolic variables such as glucose or cholesterol levels, so it is not better than continuous sexual energy limitation.
The physiological mechanism of intermittent fasting to lose weight is likely to decrease total calorie intake and a decrease in insulin levels. The fact that breaks the aura of intermittent fasting to lose weight is: if there is no calorie gap, intermittent fasting will not lose weight.
Alternate-day Fasting vs Continuous Calorie Restriction
On June 16, 2021, the Center for Exercise and Metabolism of the University of Bath in the United Kingdom published a study in the Science sub-Journal comparing the weight loss effects of alternate-day fasting and continuous calorie restriction. The research team recruited 36 people with a BMI of 20-25 to participate in the experiment. The participants were randomly assigned to three groups:
- The first group: Fasting every other day (IMF), the food intake of the day after fasting is 50% more than usual.
- The second group: three meals a day have reduced calories by 25%, the same calorie reduction as the first group.
- The third group: the same as the first group, but the day after fasting is 100% more than usual, i.e., there is no reduction in total calories.
The study results showed that the third group did not lose weight despite taking intermittent fasting because there was no calorie gap. The first group and the second group had the same calorie gap. There was no significant difference in weight loss between the two groups. The fasting group even lost more muscle.
In the final analysis, reducing fat ultimately depends on whether there is a calorie gap. The secret of intermittent fasting to reduce fat does not lie in activating the fat metabolism mechanism. Even if the body uses more fat for energy during fasting, fat will still be synthesized if excess calories are consumed during eating. The root cause of intermittent fasting to reduce fat is no different from traditional long-term calorie restriction-limiting calorie intake and creating a calorie gap.
For practitioners of intermittent fasting, the advantage of intermittent fasting to reduce fat is not how superior the method itself is, but that it is easier to adhere to than continuous sexual energy limitation.
Intermittent fasting at 16:8 is not challenging for people who are not used to breakfast or dinner. Andy has been on a 16:8 diet for more than three years. His eating time window is 12:00-20:00, and his exercise time is before dinner. Now this time, the arrangement has become a habit for him.
The flying bear who has tried 5+2 and 16:8 said that it is easier for 5+2 to put two days of fasting on weekends; for him who has not overeaten for dinner, he eats at 16:8 for 8 hours is placed early in the day, and it is not difficult to stick to it.
Rather than saying that intermittent fasting can reduce fat, it should be more accurate to say: intermittent fasting makes it easier for practitioners to persist in creating a calorie gap.
Intermittent fasting is not a recipe for fat loss for everyone
Although there is evidence that intermittent scientific fasting has certain health benefits, it can also help create a calorie gap and lose weight. But intermittent fasting is not for everyone.
Intermittent fasting is for certain groups of people. These groups include;
- People who are weak or sick, such as colds, diarrhea, etc.
- People who have or have had an eating disorder/eating disorder (bulimia, dieting, bulimia)
- Pregnant or breastfeeding women
- People with nutritional diseases, such as anemia, hypoglycemia
People with digestive system diseases, including liver, gallbladder, and kidney dysfunction, such as gallstones
Difficult and Risky
You need to be aware that intermittent fasting is not as easy as some bloggers claim. Practicing intermittent fasting is difficult and risky.
First, it is difficult to change eating habits. Many people take three meals a day and change their practices to give the body and the psychological adjustment interval. However, many people want to lose fat overnight. Suddenly switching to a new diet will bring stress to the body, and there is a higher risk of rebound. If you eat multiple meals and switch to intermittent fasting without transition, your body’s metabolism will not adapt. Which will affect your mental and psychological state?
Second, intermittent fasting may cause eating disorders. Studies have shown that intermittent fasting or prolonged non-eating is a risk factor for pathological eating patterns. Eating restrictions may lead to overeating. Many people experience binge-eating after dieting to lose weight. Although intermittent fasting does not impose specific limits on the type of food, it limits eating time. It still produces a sense of restriction. Psychological and physical restrictions can quickly induce eating disorders (bulimia, bulimia, etc.). For example, if you start binge eating at the eating window, the gain is not worth the loss.
Third, intermittent fasting may result in insufficient calorie and nutrient intake. Under the banner of intermittent fasting, many bloggers claim that they lose six lb in three days. The central body loss is water and lean body mass. The so-called intermittent fasting method they adopt is actually related to dieting. There is no essential difference. Intermittent fasting does not limit calories to extremes. On the contrary, scientific and healthy intermittent fasting should take in sufficient calories and nutrients instead of a disguised diet.
Weight loss is an eternal topic for many people, and diet is lasting for people who lose weight. Therefore, various dietary methods aiming at weight loss emerge one after another, and intermittent fasting is only one of them.
A balanced diet and a more reasonable lifestyle are the long-term ways to maintain health and manage weight.
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Will intermittent fasting lose muscle?
Among fitness groups whose priority is to gain muscle, intermittent fasting does not seem to be that popular. Scientific muscle gain requires not only a certain training intensity and training capacity but also a certain calorie surplus. People who seek to maximize the effect of muscle gain will also pay attention to spreading protein intake. It improves the efficiency of the body’s use of protein intake for muscle synthesis. For people who gain muscle, the multi-meal system is more familiar, recognized, and favored by them.
Although intermittent fasting is a weight-loss method, it does not affect muscle mass when energy intake is sufficient. In a 2016 study published in the Journal of Translational Medicine, 34 men with resistance training experience. They were recruited and randomly assigned to limited-time feeding (TRF) and normal diet (ND) groups. The limited-time feeding group took a 16:8 diet but consumed 100% energy demand food within the 8-hour every day. During this period, they performed 85-90% 1RM resistance training (muscle strength training). The results showed that limited time eating combined with resistance training improves some health-related biomarkers and maintains muscle mass.
Similar studies show that adequate energy intake with resistance training, intermittent fasting does not cause muscle loss. Besides resistance training plays an important role.
But it is worth noting that intermittent fasting may indeed affect the training state. The exercise involves the deployment and recruitment of the nervous system, psychological factors, and hormone influences. Intermittent fasting does not affect exercise energy, such as muscle glycogen reserves. It may cause a sense of deprivation and lack at the psychological level and affect training motivation and status.