Most of us will do anything that will help us lose weight and feel better. Intermittent fasting has become so popular, it now seems as if everyone is doing it! Intermittent fasting is touted as helping with weight loss, extending your lifespan, fighting cancer, and preventing heart disease. Let’s take an in-depth look at this practice.
What is Intermittent Fasting?
Intermittent fasting is a modern timing method of fasting. Fasting is defined as simply going without food and drink for a period of time. Intermittent fasting has been extrapolated from fasting rituals in ancient times for cleansing the body and enhancing the spirit. Fasting to extend our lifespan is a more modern idea. Intermittent fasting is touted as a way to extend life, cure cancer, lower blood pressure, lose weight, and decrease inflammation.
There are many versions or patterns of fasting to consider. The most popular pattern of intermittent fasting is the 16-hour overnight fast, followed by eight hours of eating during the day. If you cannot tolerate the idea of not eating and the hunger pains that come with it, then this is the easiest way to start because you will sleep through the discomfort!
Another common pattern of intermittent fasting is the 5/2 fast, where you fast two days out of the week. I had a patient who did the reverse and ate only two days a week and fasted for 5 days! The best outcomes for health have been demonstrated by fasting for a full 24 hours, one to two days a week.
The Origins of Intermittent Fasting
Fasting has a deep and long standing history.
- 800 BC: The ancient Greek thinkers Plato and his student Aristotle were devoted to fasting. The ancient Greeks believed that by watching nature; medical treatments could be discovered. Humans, like most animals, do not eat when they become sick. This fasting ‘instinct’ that makes dogs, cats and humans anorexic when sick was referred to as the ‘physician within’.
- 500 AD: Hippocrates wrote, “To eat when you are sick, is to feed your illness”.
- 571 AD: The prophet Muhammad also encouraged fasting on Mondays and Thursdays.
- 1400’s: Julian of Norwich, an English anchoress and mystic, used fasting as a means of communicating with Christ.
- 1500’s: Paracelsus, the founder of toxicology and one of three fathers of modern Western medicine wrote, “Fasting is the greatest remedy – the physician within”.
- 1700’s: Benjamin Franklin once wrote of fasting, “The best of all medicines is resting and fasting”.
- Late 1800s: Studies began and the medical fasting in sanitariums started in the early 1900s.
- 1900s: Medical doctors began overseeing water fasting with the Natural Hygiene Movement. In 1902 naturopathic doctors came to the US and taught cleansing and healing techniques using these fasting methods.
Fasting Practices in Religion
Many religions have fasting practices for spiritual reasons which typically occur in the shoulder seasons. Jewish people have 25 fasting events or holidays a year. In Islam the month of Ramadan is the most practiced fasting period. Pueblo Indians fasted at puberty, during the seasons, and for spiritual connections. Buddhists only eat in the morning. Greek Orthodox Christians observe about 180-200 fasting days a year. Women traditionally gravitate to fasting, especially religious fasting known as anorexia mirabilis (miraculous lack of appetite). Going long periods without nourishment has been regarded as a sign of chastity and holiness in many cultures and religions.
The traditional and historical purpose of fasting is to repent or access spiritual connection, build strength, purge toxins, and accompany life transitions. Often, fasting was limited to the healthy and was forbidden in children, pregnant women, and those that were frail. This is so different from what intermittent fasting is today, where it is hailed as a panacea for the sick, the old, and the strong.
What is The Body Doing When You Fast?
Once you start intermittent fasting, it takes ten days for our body physiology to adapt. First, the body makes sugar out of amino acids that come from your muscles (this is why many people think that fasting causes one to lose muscle). As fasting continues, the body becomes really good at making energy out of fat, called ketosis. These energy molecules (ketones) are acids that burn as energy and can replace glucose for energy in the central nervous system (brain). Now, muscle is spared as a source for glucose. Over time, those that fast have been shown to lose weight and maintain muscle.
When you fast, many hormones change! Insulin drops and so does T3 (hyperthyroid patients may consider intermittent fasting). There is an increase in glucagon (the hormone that tells the liver to make more glucose) and in reverse T3. It is very important for your doctor to know that you are intermittent fasting because lab parameters can change.
Intermittent Fasting Benefits
There are plenty of studies both new and old that show the health benefits of intermittent fasting or fasting in general. However, not many of these were done on humans outside of those practicing Ramadan. Studies have shown that fasting:
- Increases lifespan
- Decreases visits to doctors because people are healthier
- Improves blood sugar regulation
- Decreases cholesterol
- Prevents memory loss
- Cools down women who are menopausal
- Decreases inflammation
- Aids in weight loss/fat loss
- And more!
If you want to geek out on some good studies here are a few on the topic:
In 1946, a study was done on rats which showed the optimal fasting pattern for prolonged lifespan was fasting one day out of every three. They did report that the underlying health of the rat was important in clinical outcomes.
Journal of Nutrition: Apparent Prolongation of the Life Span of Rats by Intermittent Fasting: One Figure
In 1957, there was a Spanish medical study conducted in a retirement home of healthy subjects over 65 years old. The subjects were eating or fasting every other day and it was shown that the fasting group had less overall mortality over three years as well as significantly less visits to the doctor in that same time.
In 2018, a study on mice induced with menopause and Alzheimer’s disease found that intermittent fasting was preventive of memory loss, decreased skin temperature, improved glucose metabolism, and improved lipids. However there was an increased loss in bone density as well as insulin resistance.
National Library of Medicine: Intermittent fasting protects against the deterioration of cognitive function, energy metabolism and dyslipidemia in Alzheimer’s disease-induced estrogen deficient rats
The list goes on, with the peak of studies published on fasting and its effects on health occurring between 2013-2019.
Intermittent Fasting for Athletes
As of 2020, there have been many studies looking at whether or not intermittent fasting can improve athletic performance. Again, most of these studies were done by athletes that observe Ramadan, whereby Muslims fast for one month and consume no solids or liquids during daylight hours. There have been many studies on athletic performance ranging from strength to cardiovascular assessments. So far, no studies conducted have shown improved performance with intermittent fasting.
As a matter of fact, the studies done on explosive sports such as sprinting actually show a decrease in performance for athletes who fasted (2017). Studies in cyclists showed a decrease in performance under a couple of different fasting cycles (1988/2018). Regarding performance for endurance athletes, there are mixed results, so the jury is still out on that one. Additionally, on the subject of muscle vs fat mass in athletes who fasted and who did not, the findings were that the intermittent fasting groups lost more weight, but they maintained muscle mass.
In March 2019 a summary review of all human studies on Ramadan fasting in athletes was conducted. It showed that out of the 12 total studies ever completed, they included a total of 12 women and 171 men, and there was no change in lean mass or total body weight after one month of fasting but there was less fat mass.
A 2010 study showed that in men, fat adaptation in muscle improved when athletes fasted. Training is more potent than fed training to facilitate adaptations in muscle and to improve whole-body glucose tolerance and insulin sensitivity during a hyper-caloric fat-rich diet.
National Library of Medicine: Training in the fasted state improves glucose tolerance during fat-rich diet
What’s the take home message for my athlete patients? If you want to perform well it is essential to nourish the body. The timing of nourishment in athletics is key for performing optimally. I do not support the use of competitive athletic females using intermittent fasting unless they are in the off-season and needing to burn fat. There is a time and place for intermittent fasting for non competitive active females. When women are first getting into exercise and wanting to lose weight and burn fat, or those who have an exercise routine that is less than ten hours a week, intermittent fasting has many benefits, in particular the 16/8 pattern of intermittent fasting.
Intermittent Fasting for Weight Loss
Many women find that while doing intermittent fasting they don’t lose weight or they plateau. The body will find a steady state with consistent dietary practices, so a plateau is normal. Following are several reasons you may not be losing weight with intermittent fasting:
- Eating high glycemic foods
- Eating too late at night
- Eating too much food
- Eating foods that you are intolerant to
Think of it this way, when you fast, cells become more sensitive to insulin thus insulin resistance improves. Great! Then when you eat, if you choose high glycemic foods, the blood glucose goes way up and insulin is secreted and there is a huge response of glucose into cells and drastic clearing of the blood from glucose. That’s when women crash. So, be sure to eat a high fiber, low glycemic meal as the first meal after intermittent fasting.
Fasting the Wrong Way
There is a dark side of fasting. Early on the practice of fasting had been exploited by those taking advantage of desperate and gullible people. In 1912, there was a Dr. Hazzard in the USA who had caused the death of over 40 patients whom she put on strict fasts. She was convicted of manslaughter and years later she died from her own fasting regime. There were also the Victorian fasting girls who claimed to be able to survive indefinitely without food. One of them starved to death at age 12 in the hospital where doctors were testing their claims. I feel concerned that intermittent fasting can also perpetuate disordered eating patterns or an ideation of repression in many of my female patients who stay on it long term. It is important to balance the health benefits with disordered thinking around food. There are also medical complications seen in fasting including gout and uric acid stones (kidney stones), dizziness when you change positions (postural hypotension) and irregular heartbeat.
Smart Intermittent Fasting
Each of us is unique in physiology, lifestyle, genetics and mental health. There are pros and cons to all dietary practices. Intermittent fasting can be challenging for those who have a history of disordered eating. It can also be difficult for someone who is very active or an athlete who is performing at a high level. Intermittent fasting is contraindicated for some people who are on medications that require food to complement their medications.
Today there are concerns about everyone doing intermittent fasting let alone for long periods of time. Generally, however, the data on fasting is very healthful. There are cases where doing intermittent fasting would be contraindicated such as childhood, pregnancy, certain health conditions, and with certain medications. But, if it is done correctly and one takes good care to eat high quality foods and a variety of foods during their eating hours, intermittent fasting has a tremendous potential to help many people lose weight, feel great, and achieve optimal health.
Have questions about intermittent fasting or your health in general? Schedule an appointment with Dr. Kelly Parcell: 303-884-7557.