By Anna Tarabrina ND
Fasting is a voluntary abstinence from food or any calorie-containing drinks for a specific period. In plain terms, fasting is the act of not eating, as simple as that, but let’s not be misguided by the simplicity of fasting, because health benefits that you’ll get from simply restraining from food are numerous and amazing.
Fasting has been practiced in different forms all over the world for thousands of years. All major religions incorporate different forms of fasting in their required practices. We all practice it without even realizing it: We all fast during the night while we sleep, and sometimes if we skip a meal, we can also prolong our fast during the day. These short fasts are part of our normal physiology. 
The beauty of fasting is that there’s not only one “right” way to do it; there are many forms of fasting:
- Extended fasting can be done with restraining from food and drinking just water for periods longer than three days. Extended fasts can last for months, but those longer fasts need to be done under the supervision of a physician.
- Another form of fasting is intermittent fasting, which has become popularized by Michael Mosley’s documentary “Eat, Fast and Live Longer”.  There are many variations of IF: time-restricted feeding, 5:2 diet, alternate-day fasting, etc.
- Many forms of religious fasts are practiced all over the globe. One that most everyone is familiar with is the fast during the holy month of Ramadan, during which devoted Muslims do not eat or drink from sunrise to sunset.
The overall objective of this article is to discuss some benefits and physiological changes during fasting.
FASTING IS GREAT FOR WEIGHT LOSS
The most obvious benefit of fasting is weight loss. Therefore, fasting is contraindicated for people with BMI lower than 19.
Plenty of animal and human studies show weight loss on the regimen of intermittent fasting. People who practice fasting regularly can lose extra weight and stay at a healthy weight.  The weight- lowering effect of fasting is very easily explained physiologically: Fasting decreases the amount of
calories entering the body, and as a result, the body is forced to use available sources of energy like lipids, which are normally stored in fat cells. Studies also show that intermittent fasting increases basic metabolic rate, which means that people who fast burn more calories and as a result burn more fat, while preserving muscle. 
FASTING CAN PREVENT AND HELP IN THE TREATMENT OF TYPE 2 DIABETES
Fasting has been shown to increase insulin sensitivity.  Excessive consumption of simple carbohydrates—like bread, pasta, soft drinks, and any food high in sugar—leads to the development of insulin resistance. Let me explain how. Simple carbohydrates are broken down to glucose after.
Glucose is absorbed into the bloodstream in the small intestine and carried to the cells of the body to be used for energy production. But there is another important player in the process of glucose getting into your cells: insulin. Insulin is a hormone which is secreted by the pancreas after your body senses glucose in the bloodstream. Insulin helps glucose enter the cells by attaching to insulin receptors on the cell membrane. Insulin acts like the key, which opens the pores to glucose so it can get into the cell. When too much glucose is eaten and absorbed, more insulin needs to be secreted by the
pancreas to help all this glucose to get into the cells. After many years of too much glucose in the bloodstream and too much insulin, cells become less responsive to the insulin; they become insulin- resistant. As a result, less glucose can enter the cells and more glucose stays in the bloodstream,
which leads to symptoms of diabetes. During fasting, no glucose enters the bloodstream from food, so the body produces a little bit of glucose to keep feeding some cells in the body, like brain cells, which rely mostly on glucose for their energy needs; during fasting, blood glucose and insulin levels
stay low, which gives the rest of the cells time to repair their insulin receptors. 
FASTING CAN LOWER BAD CHOLESTEROL AND TRIGLYCERIDES
Fasting has been shown to decrease bad cholesterol while maintaining your good cholesterol. High cholesterol and triglycerides have been linked to an increased risk of cardiovascular disease. Cholesterol is believed to be the culprit in plaque buildup in the blood vessels, which can lead to heart attacks and strokes. There are different forms of cholesterol. LDL is the bad guy; if there is too much of it, then there are more chances for plaque buildup in your blood vessels, while having more good cholesterol like HDL is protective against cardiovascular disease. Cholesterol is either ingested
with food or made by the body. Cholesterol is a very important molecule for the production of hormones and the maintenance of healthy cell membranes, so cholesterol in itself is not bad for you, but too much bad cholesterol is bad. Fasting allows the body to get rid of bad cholesterol, while keeping good cholesterol; as a result, you decrease your cardiovascular disease risk. It has also been shown that obese adults on alternate-day fast observe a decrease in blood pressure, which is also protective against cardiovascular disease. 
FASTING NORMALIZES GHRELIN LEVELS
Ghrelin is a hormone secreted to signal the brain that the body needs to eat and makes us feel hungry; it’s the hunger hormone. One would think that ghrelin levels would increase during fasting, which would make it unbearable not to eat, but it’s not the case. Calorie-restricted diets increase ghrelin production, which explains why people on those diets are so miserable and most of those diets do not work in the long term. Fasting, on the other hand, increases ghrelin production at first, but as you practice it, ghrelin levels are normalized and even go down.  Ghrelin secretion also comes in waves,
which are connected to circadian rhythms. This just means that no matter if you eat or don’t eat, the amount of ghrelin secreted is about the same. Another great thing about the wave-like ghrelin secretion pattern is that the feels the same and dissipates whether you eat or don’t eat. During prolonged fasts, ghrelin levels go down, so the person on the longer fast feels less hungry after a few days.  A decrease in ghrelin levels is also helpful after the fast, as people feel full after lesser amounts of food eaten, which further extends the benefits of fasting.
AND FINALLY, FASTING CAN MAKE YOU LIVE LONGER
Studies in animals show that fasting will slow down the aging process. This is some claim to make,but some animal research shows just that. During fasting, the body must rely on other sources of energy like lipids, but the body also starts eating its own cells that are dysfunctional and old. During prolonged fasts, the body also activates stem cells, which allows the body to renew itself. Another benefit of fasting that contributes to health and longevity is the detoxification effects of fasting. Each cell of the body has a certain amount of toxins as a result of creating energy and a absorption of toxic loads from the environment. For the cell to clean itself, its needs energy and time; if this workload is disrupted by the necessity to process and store extra calories, the toxins can accumulate. Fasting allows the cells to get rid of toxic loads. Latest research from the Newcastle University shows another possible mechanism of how fasting makes us healthier. Their research concentrated on mitochondria, tiny energy-producing organelles, present in most of our cells; they studied mitochondrial states in tiny worms. Restricting diets in these worms made their mitochondria healthy and prolonged their lifespan. This study also shows the increase in peroxisome interaction with
mitochondria; peroxisomes are other organelles responsible for fat metabolism. Activation of peroxisome increases fat burning by mitochondria.  Although no human studies show that fasting increases longevity, some human studies show that limiting food intake (fasting) reduces the risks of diseases common in old age and lengthens the period of life spent in good health.
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