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When referring to intermittent fasting and time restricted eating the focus shifts on what we eat to when we eat and it turns out this can have a profound effect on metabolism and how our body functions.
The timing of our meals is so ingrained in our culture and in our psyche. It is just a matter of fact that we eat shortly after awakening, followed sometimes by a snack later morning, a lunch at around noon time, maybe a snack mid-afternoon and then a dinner toward early evening. Intermittent Fasting and Time Restricted Eating questions the wisdom of 3 square meals interspersed throughout the day starting with breakfast right after we get up for the day.
This concept of fasting is not new to human history. Humans evolved in an environment where food was sometimes scarce. Based on this theory, we as a species developed adaptations that allows our bodies to still function even when food was scarce. For the fortunate among us, especially in first world countries like the United States, there is never a lack of food. In fact, we have an abundance of available food that often is very high in caloric density. It has been suggested that the current plentiful food environment of modern life is mismatched with our genetics. In addition, fasting has been part of most cultures in recorded history such as Ramadan in the Muslim tradition, Lent in Christianity and Yom Kippur in Judaism. I have found in my own life, sometimes the practice of fasting makes others not as familiar with the normalness of it uncomfortable, but it is an entrenched part of our human history. Since 5th century BC and the time of Hippocrates, the father of modern medicine, fasting has been used as a therapeutic intervention for a variety of health conditions.
In the literature and popular culture, there are different ways to practice Intermittent Fasting and Time Restricted Eating. I will review the terminology and different methods people use to include fasting in their lifestyle. I am not advocating one way or another. There are pros and cons for each and depends on your current lifestyle and your health goals.
The practice of intermittent fasting involves going for extended periods of time without eating. Typically, people using this method go for 16-48 hours without eating.
This is a popular way to practice fasting. Time restricted feeding refers to limiting the intake of food to 8 hours in the day, commonly between 12 pm and 8 pm. No food is consumed outside this eating window.
Another researched pattern is 5 day / 2 day fasting method. This refers to decreasing the intake of food to 60 % of caloric intake two days per week. This is commonly 500 calories or less for those 2 days. The other five days involves a typical eating pattern.
Alternate day fasting involves eating every other day alternating with fasting.
Periodic fasting is when a person will go 5-7 days without consuming food. A twist on this method is fasting mimicking which limits caloric intake to mostly fats which biologically “mimicks” a fasting state even though food is consumed.
There has been a lot of hype and talk about the benefits of Intermittent Fasting and Time Restricted Eating. To understand why, we have to discuss what is happening at a biological level when we fast. One of the biggest changes that happens with fasting involves our metabolism. When there is dysregulation of metabolism such as in the case of Diabetes, Pre-Diabetes and Insulin Resistance, intermittent fasting can reset and reboot the cells sensitivity to insulin. When these problems are present, you must of course discuss this with your physician prior to changing your dietary pattern, however in my experience, often this will stabilize blood sugars and help the body respond in a more normal way to insulin and glucose.
When we practice Intermittent Fasting, our glycogen stores become depleted. Glycogen is the storage form of glucose or sugar in the body. When our glycogen stores are depleted, our body then must mobilize fat for energy. This is advantageous particularly when we are trying to lose weight. When our body burns fat for energy, ketones are produced. You may have heard a lot about ketogenic diet and intermittent fasting can be used to reap the benefits of ketosis (refers to the biological state when our body is producing ketones by burning fat).
The interesting thing about ketosis is that when our body is in this state, our hunger hormones go down (ghrelin). This means that we experience less hunger as we move into a fasting state.
When we chronically restrict calories the effects on metabolism are different than when we fast intermittently. It is known that when we chronically reduce caloric intake in a way our body gets used to it and metabolism slows down. If weight loss is the goal, chronic caloric restriction is often not sustainable and if you look at long term research it is not a solution for long lasting weight reduction. Intermittent fasting tends to even out blood sugar numbers which in a segment of the population with insulin resistance is very advantageous for the metabolism.
One of the main reasons intermittent fasting is sometimes utilized therapeutically is the effect on the brain. Intermittent fasting can increase neuroplasticity and cognition and reduce neural inflammation. For this reason, intermittent fasting is a strategy is utilized to help slow down early cognitive decline and could potentially decrease the impact of aging and neural inflammation in the brain.
Aside from the impact metabolically which is good for your heart health, intermittent fasting has been shown to improve (reduce) resting heart rate, and blood pressure as well as something called heart rate variability. Heart rate variability time between each heart beat varies slightly and is a sign of vitality and health.
Fasting improves autophagy which is our body’s way of clearing out damaged cells. Our immune system responds to damaged cells. If our body is efficiently cleaning up, then it takes stress off the immune system. I think of this for any condition involving the immune system which of course is all conditions where inflammation is a factor. I think of intermittent fasting as improving the resilience of our immune system.
In the research, I do not feel that one method is better than the others but I do think that some of the methods described above are easier to implement when you are just starting out. The easiest way to start is to try out the timed eating method by extending the overnight fast.
I do think that the quality of the food you eat in the “eating window” matters quite a bit, and even more so when you are eating less volume. You still want to choose fresh whole nutrient dense food in a combination of healthy protein, fats and carbs. In this way, you are supporting your health and using intermittent fasting and timed eating safely to achieve your goals.
