Does intermittent fasting help weight loss? An article to understand the physiological mechanism and risk of side effects of intermittent fasting
What is intermittent fasting? “Calorie restriction” is different from “time-restricted eating”
Can controlling daily eating periods and total eating time really help lose weight or even improve metabolic syndrome? Metabolic syndrome is considered a major risk factor for the increased prevalence of type 2 diabetes and cardiovascular disease. A paper in the latest issue of “Journal of Internal Medicine” points out that dietary control is an important step in preventing metabolic syndrome. “Intermittent fasting”, which has emerged in recent years, is considered to have benefits such as helping weight loss and preventing hyperglycemia and cardiovascular diseases because of its simple implementation method. , becoming a new choice for many people.
The concept that “fasting” is beneficial to physical health is not unique to contemporary society. Since ancient Greek times, there have been records of using fasting to treat diseases and improve brain cognition. Generally speaking, intermittent fasting refers to limiting eating to a specific period of time, which can be roughly divided into four methods:
Periodic fasting, which involves consuming less than 25% of the required calories for several days within a week, repeated every other week;
Alternate day fasting, one day without consuming calories at all, and the other day eating normally;
Time-restricted eating, with a complete fasting time of more than or equal to 12 hours a day, such as the common 16/8 fast, which means complete fasting for 16 hours a day;
Religion Fasting, the prohibition of food and fluid intake during certain religious fasts or fasting periods.
However, when discussing “intermittent fasting”, it is important to understand that “calorie restriction” and “time-restricted eating” are not exactly the same. Caloric restriction refers to reducing total caloric intake without reaching the level of malnutrition, and caloric restriction has been shown to have the benefits of weight loss and longevity in various species. As for time-restricted eating in intermittent fasting, it usually refers to continuous fasting for a specific period of time and is used as an alternative to caloric restriction.
What is the physiological mechanism of intermittent fasting? Avoid rising blood sugar and fat metabolism?
The main motivations for modern people to adopt intermittent fasting are mostly for weight loss and health. The reason why the “time-restricted eating” diet control strategy may be effective is believed to be related to the biological clock, intestinal microflora, changes in lifestyle habits, and carbohydrates. It is related to the influence of lipid metabolism.
The center of the human body’s biological clock is located in the superior chiasmatic nucleus of the “hypothalamus” of the brain. The hypothalamus is also known as the “satiety center” and controls the urge to eat and the feeling of satiety. The operation of the hypothalamus exhibits a certain rhythm due to the degree of light exposure, and eating is an important factor in stimulating the rhythm. A small study found that as long as the daily routine deviates from the circadian rhythm for 12 hours, the leptin concentration in the body decreases significantly, while the glucose and insulin concentrations after meals increase, leading to an increase in insulin resistance. In addition, blood sugar and insulin rise significantly when eating at night, which indicates that eating less after dinner is more in line with the biological clock and reduces the risk of blood sugar rising.
It has been found in mammals that when fasting, the body’s cellular energy is converted from glucose into fatty acids and “ketone bodies”. Ketone bodies have the function of regulating proteins and have a great impact on the body’s metabolism. Animal experiments have found that intermittent fasting can increase AMP and ADP, promote AMPK activation, inhibit various anabolic metabolism and stimulate the autophagy reaction of cells, thereby eliminating damaged proteins. Fasting for a long time can help improve fat metabolism, reduce abdominal fat and reduce inflammation.
Is intermittent fasting effective for weight loss? Total caloric intake is the key factor
The answer to whether intermittent fasting has a better chance of successful weight loss is not entirely clear. A 2020 systematic review found that by fasting for 12-20 hours, obese people can lose weight and fat mass without affecting lean tissue. However, healthy people only have the effect of reducing fat, and have a negative impact on body weight and lean mass. There were no significant differences in organization.
It is worth noting that in 2022, a longer and more rigorous randomized assignment trial was conducted in China to compare the implementation of calorie control and calorie control “plus” food restriction among obese people (8 a.m. to 4 p.m. Click to proceed), the results showed that there was no significant difference in the weight loss effect between the two groups, which indirectly proved that the weight loss effect of time-restricted eating method or intermittent fasting is most likely due to the reduction in total caloric intake caused by shortened eating time, that is, “calorie deficit” benefits.
A 2023 prospective study on sexual intergenerational studies in the United States analyzed the subjects’ records of eating small amounts (less than 500 kcal), medium amounts (500-1000 kcal), and large amounts (more than 1000 kcal) at each meal and found that the number of meals eaten every day was The length of time from one meal to the last meal has “nothing to do” with body weight. On the contrary, there is a clear correlation between moderate and large amounts of food and body weight. According to current research, the main reason why intermittent fasting can reduce weight may be that limiting eating time indirectly reduces total caloric intake, thereby achieving weight loss benefits.
What are the side effects of intermittent fasting? Consult an expert before making dietary changes
Although intermittent fasting may not directly achieve effective weight loss, other disease-related studies have found that intermittent fasting can help reduce the use of blood sugar drugs and help diabetic people lose weight. A study that randomly assigned HER2-negative 2-3 breast cancer patients also showed that the fasting group had better treatment effects.
In addition, animal experiments have found that fasting can help enhance neurogenesis and activation of brain-derived neurotrophic factor (BDNF) in neural stem cells, prompting the brain to enter a neuroprotective state, and may have a preventive effect on Parkinson’s disease and Alzheimer’s disease. Come to the benefits.
In general, for modern people, especially urban lifestyles, intermittent fasting has the advantage of adaptability to day and night patterns, and is easier to implement than other dietary strategies such as ketogenic diet, pure plant-based diet, and low-calorie diet. . Some studies have also pointed out that intermittent fasting can not only reduce the risk of lifestyle-related diseases (such as metabolic diseases), but also improve the quality of life. However, we should be reminded that the most common side effects of intermittent fasting include hypoglycemia, dizziness, weakness, etc., and excessive blood sugar fluctuations in the elderly can easily increase the risk of falls and fractures. You should still consult a specialist physician and nutritionist before undertaking any dietary modification strategy to ensure it is consistent with your personal health and is safe.
Source:
Physiological Metabolism and Clinical Effects of Intermittent Fasting
Further reading:
JAMA study: Intermittent fasting from 7 a.m. to 3 p.m. can help you lose 2.3 kilograms more
