The Benefits of Fasting
How fasting can help reset the immune system
The increasing abundance of our food supply over the last several centuries has contributed to excesses of eating. We have shifted away from eating at mealtimes and moved toward eating throughout the day—and for some, through the night. We see more obesity, and with that obesity there are increased risks for cardiovascular disease, cancer, and other chronic illnesses.
These days people typically eat three meals a day, along with periods of snacking and grazing in between. With that, our calorie consumption has become very high. When we eat, our food breaks down to glucose for our bodies to use as energy. The glucose our bodies don’t utilize for energy is converted into fat. The common solution to being overweight is to consider how to reduce body fat: to either increase the expenditure of calories through exercise or to reduce calorie intake. Time-restricted fasting is an option to reduce the amount of time when calories are consumed even when there may not be a large reduction in the number of calories consumed.1
Fasting is an age-old concept that is defined as abstaining from certain foods or drinks for a period of time. Historically, fasting was used in religious observances and has been mentioned in sacred texts such as the Bible, Torah, and Quran. People have also used fasting as a form of nonviolent protest, such as when Mahatma Gandhi fought for India’s independence.
In nature, animals commonly fast. Rodents, for instance, eat their food over several hours, then fast for about 20 hours per day.2 Predatory animals will gorge after a large kill, then go for several days without eating again. Animals may also fast during times of illness or injury, only taking in nourishment when their healing crisis is over.
When we eat, food breaks down into glucose (sugars) and our body uses this as energy. This is considered a low ketone state. Glucose that is not used is turned to fat as triglycerides. On the other hand, during fasting, there is no glucose that the body can use for essential tasks, so the body uses triglycerides and breaks them down into free fatty acids and glycerol. The body uses these free fatty acids as energy. This is considered a high ketone state. Ketones can affect growth factors and molecules that are known to affect aging. For example, they can stimulate a growth factor that appears to have a role in long-term memory, Alzheimer’s, psychiatric illness, and potentially with aging.2
There are several different types of fasting. Intermittent fasting is an umbrella term referring to periods lasting 12 to 48 hours with no caloric intake alternating with periods of regular eating. Intermittent fasting is different from periodic fasting, where there is no caloric intake for 2 to 21 days. Common examples of intermittent fasting are caloric intake reduced to 500 to 600 calories two days per week and normal intake for five days. Alternatively, it can be zero caloric intake for two 24-hour cycles over a seven-day period and normal eating on the other days. Time-restricted feeding involves eating for short periods of time every day. For example, you might only eat during a 6- to 12-hour period during the daytime and fast the other 12 to 18 hours.
We are big fans of intermittent fasting and time-restricted feeding. Dr. R often does intermittent fasting, and Dr. A practices time-restricted feeding; both of us recommend these methods to our patients. Even if overall caloric intake doesn’t decrease with time-restricted feeding, studies show there is still improvement in glucose regulation (blood sugar levels), blood pressure, heart rates, endurance, and loss of abdominal fat. This benefit appears to come from the change in metabolism that occurs when someone goes from a period of eating to a period of fasting.3
Multiple studies have looked at how fasting improves the health of rodents, larger animals, and even humans (although there are only a few studies on humans to date). They’ve shown reductions in body weight,4,5 total cholesterol,6,7 triglycerides,7,8 and glucose,6,9 with time-restricted feeding. In rats, reductions in inflammatory markers were also seen.10
What is even more interesting is that during fasting there appears to be repair of DNA and the removal of damaged or unwanted particles (autophagy), as well as an increased level of antioxidant protection and a reduction of inflammation. Both the process of autophagy and the action of antioxidants are key for fighting free radicals, oxidants, and cancer cells!11 In rats, fasting cycles increased the diversity of their gut bacteria, which are thought to be protective against obesity and other metabolic diseases.12
Fasting also has a role in increasing endurance. In some small animals, fasting was also shown to improve balance and coordination. In a trial of men, one group did resistance training and no fasting, one group did just time-restricted feeding for eight hours, and one group did both. The study showed that after thirty days, the men who did both lost both fat mass and weight. Interestingly, the resistance training only and the fasting group only showed no differences.13 In a study of older adults with mild cognitive impairment, a fasting regimen helped improve verbal memory over time!14
In addition, working out while fasting also improves the amount of fat burning during periods of exercise and appears to reduce appetite following workouts. In essence, fasting can increase the weight loss benefits of exercise.15,16
Summary and Benefits
1.Improved insulin sensitivity (reduced risk of diabetes)
2.Weight loss, reduction of fat, and reduction of abdominal circumference
3.Improved blood pressure
4.Improved cholesterol levels
5.Reduction of oxidative stress and inflammation
6.Increased removal of cellular debris (autophagy)
7.Improved endurance
8.Improved memory
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