The Health Benefits of Multi-Day and Intermittent Fasting Part 2

the Benefits Intermittent fasting is a concept with 16:8 hour clock timer for skipping meal and eating keto low carb, high fat food meal healthy nutritional dish with gym exercise for body weight loss

What are the benefits of fasting? This article is the second of a two-part article that focuses on the benefits of fasting. You can read part 1 here.

Type 2 diabetes occurs as a result of high blood sugar. When blood sugar levels are too high for too long, the body produces excess insulin, which causes insulin resistance. Insulin resistance means that the body stops responding to insulin as a result of prolonged exposure to excess insulin.

It’s clear why type 2 diabetes is the fastest-growing chronic disease in the world—because we eat too much and too often, keeping our blood sugar and insulin levels high. For people with type 2 diabetes, dietary changes are the most successful treatment.

Fasting lowers insulin levels naturally and very quickly reverses type 2 diabetes. If you have type 2 diabetes or pre-diabetes, I recommend reading Dr. Fung’s book, The Complete Guide to Fasting. He is an expert on using fasting to treat these conditions. If you have type 2 diabetes, fasting should be done under the supervision of a medical professional.

Benefits of Fasting for Cancer

The benefits of fasting include some positive research with cancer patients.

People with cancer can benefit from fasting in several ways. First, autophagy helps to prevent cancer by naturally removing potentially cancerous cells from the body. 

Second, fasting can limit the growth of glucose-dependent tumors. Some leading scientists, such as Dr. Thomas Seyfried and Dr. Valter Longo, recommend that everyone should fast on a regular basis as a cancer prevention strategy.

Third, fasting has been shown to prevent the toxic effects of cancer treatment. Both fasting and “fasting mimicking diets” increase resistance to chemotherapy in normal cells but not in cancer cells. After fasting, normal healthy cells are stronger and less affected by the toxic cancer treatment, while at the same time, the cancer cells—which do not have the ability to adapt to fasting—have become weaker and are more likely to be destroyed by the chemotherapy.

Fasting and Alzheimer’s Disease

It’s been shown that autophagy is impaired in Alzheimer’s disease. Normally, the process of autophagy would remove the amyloid beta proteins that accumulate in the brain and cause Alzheimer’s. When autophagy is impaired, these proteins eventually destroy neural connections in the parts of the brain responsible for memory and cognition. Research shows that intermittent fasting protects against Alzheimer’s disease in animal models.

Fasting can also help protect against Alzheimer’s disease by lowering insulin levels. Alzheimer’s is now referred to by some doctors and scientists as type 3 diabetes because it involves insulin resistance that occurs in the brain. Research shows that having type 2 diabetes is one of the top risk factors for developing Alzheimer’s. 

Benefits of Fasting for Autoimmune Diseases

Since fasting strengthens the immune system, it seems logical that it could help prevent and resolve autoimmune conditions. Research on this topic is still in its infancy, and there are over 100 autoimmune conditions that will need to be explored. Fasting has been shown to have multiple positive effects on the gut microbiome, an essential part of our immune system that is often affected in autoimmune diseases. So far, fasting has been shown to have potentially positive outcomes for multiple sclerosis and rheumatoid arthritis. Some people use fasting to treat autoimmune conditions such as Hashimoto’s thyroiditis, Crohn’s disease, ulcerative colitis, and others. Still, little to no research has been done on the effects of fasting on these conditions.

Benefits of Fasting for Athletic Training

Image depicts athlete training for a run and how fasting benefits athletes in training.

Athletes may wonder if they can benefit from fasting or if it is even safe. In fact, fasting periodically trains the body to become more efficient at burning fat, which is a huge advantage for athletes. When athletes feel as though they’ve “hit the wall,” it means that they’ve used up all of their stored glycogen as energy, and their body isn’t capable of using their stored fat quickly enough.

“Exercising in the fasted state trains your muscles to burn fat. Instead of relying on limited glycogen stores, you can use almost unlimited energy from your fat stores. Muscles adapt to use whatever energy source is available. When we deplete our glycogen through fasting, our muscles learn to become much more efficient at burning fat. The number of specialized fat-burning proteins is increased, and the breakdown of fat for energy is enhanced. After training in the fasted state, muscle fibers show increased available fat. All these are signs that the muscles are training to burn fat, not sugar.”

-Dr. Jason Fung, The Complete Guide to Fasting, Page 244

Adapting to Fasting for Athletes

Upon starting a fasting regimen, athletes might notice a decrease in athletic performance while their body adapts to burning fat. This is referred to as fat adaptation. Dr. Fung suggests that this period of decreased performance lasts about two weeks, though it varies from person to person depending on their current diet, what type of fasting regimen they adopt, and what type of workouts they do.

In addition to burning stored fat, there are two other significant advantages of fasting for athletes. First, fasting increases adrenaline, so people who train in a fasted state find that they can train harder. Second, fasting stimulates human growth hormone (HGH), which leads to quicker recovery and increased muscle building. For example, one study found that fasting for just two days increased HGH production by five times. Another study found that growth hormone levels were elevated 2000% above baseline after just 24 hours of fasting.

The Pros and Cons of Fasting for Women of Childbearing Age

Young pregnant woman, reading a book at home to her two boys, eating fruits, hugging and laughing

Virtually all of the clinical studies on intermittent fasting have been carried out with test subjects who are men or post-menopausal women. Studies generally do not include pre-menopausal women due to concerns that fasting of any kind may negatively affect hormonal balance and the monthly cycle.

Some pre-menopausal women use intermittent fasting for weight loss, and with great success—you can search the internet to see countless before and after pictures. But there are an equal number of women out there who report that intermittent fasting had significant negative effects on their hormonal balance and monthly cycle. Since controlled studies with pre-menopausal women haven’t been done, we can only guess at the factors that could affect why some women can safely fast while others can’t. They likely include overall health, how much excess weight they have to lose, how long they fast each day, and how much they restrict their overall caloric intake.

My guess is that overall caloric intake is a big factor. Intermittent fasting and caloric reduction are, in fact, two different things. You can intermittently fast every day while still eating your normal amount of calories during your feeding window. This allows you to get some benefits of intermittent fasting, like insulin reduction and training your body to burn fat without dramatic weight loss. When we restrict our caloric intake for too long, our body can go into “starvation mode,” which can potentially upset hormonal balance and monthly cycle.

Fasting and Fertility

On the flip side, there are some potential benefits of fasting for pre-menopausal women when it comes to fertility. First, intermittent fasting is becoming popular among women with polycystic ovary syndrome (PCOS) as a way to lower their insulin levels, lose weight, reduce inflammation, reduce stress, and alleviate depression and anxiety—all symptoms of PCOS. Some of these positive effects have now been proven in studies.

Second, intermittent fasting can lead to weight loss. Being overweight or obese negatively impacts fertility in a number of ways: by raising insulin and blood sugar levels, by increasing the risk of PCOS, by decreasing the sex hormones necessary for conception, and by increasing the risk of anovulation (when no egg is released by the ovaries).

Third, fasting may improve fertility in older women. A 2008 study carried out at Harvard Medical School found that caloric restriction significantly extended fertility in adult female mice. When the calorie-restricted mice reached 12 months of age—advanced age when it comes to mouse fertility—their eggs had far fewer abnormal chromosomes than the eggs of mice whose eating had been unrestricted. The calorie-restricted mice also produced more eggs than normal mice when their ovaries were artificially stimulated, their eggs were more likely to develop into embryos upon fertilization, and their offspring survival rates were dramatically higher than the control mice.

Building Your Egg Supply

Another study showed that when worms are starved, they put reproduction on hold—not surprising. But in worms, their bodies destroy existing eggs during starvation and regenerate a new crop of healthy eggs from stem cells once they begin eating again. In the study, starvation allowed the worms to reproduce when they were 15 times older than normal reproductive age. The starved worms also lived three times longer than worms that were not starved.

This brings us to a topic that is now hotly debated: Do ovarian stem cells exist in humans?

Since 1951, we’ve believed that women are born with all the eggs they’ll ever have. However, a growing body of research suggests that mammals, including humans, do possess ovarian stem cells that are capable of generating new eggs as we age. If this is true, it could explain why women who have been through radiation treatment or bone marrow transplantation, which damages or destroys mature and immature eggs, can regain their fertility.

In the same way that fasting renews the immune system, it may renew women’s egg supply. Fasting induces autophagy, potentially triggering the body to recycle old, damaged eggs. Subsequent refeeding may then stimulate ovarian stem cells to regenerate new, healthy eggs. That’s what happened in the worm study—could a similar process happen in humans? It remains to be seen.

Experts recommend, and common sense dictates, that if you want to use fasting to improve your fertility, you should do it before trying to conceive. Fasting while trying to conceive is counterproductive because the body is much less likely to support a pregnancy when calories are scarce.

Proven Health Benefits of Fasting

Intermittent fasting benefits. Personal diet plan concept. Help your body burn fat. Specific time eating. World s most popular health trend.

In summary, the proven health benefits of fasting include:

  • Induces body fat loss
  • Lowers blood sugar levels
  • Resolves type 2 diabetes and insulin resistance
  • Lowers blood cholesterol
  • Decreases inflammation
  • Triggers autophagy
  • Prevents neurodegenerative disease
  • Slows and prevents tumor growth
  • Lessens the toxic effects of chemotherapy
  • Slows the aging process
  • Increases energy, mental clarity, and concentration
  • Reduces food cravings
  • Improves digestive function by balancing the microbiome and stimulating the regeneration of intestinal stem cells to heal the gut

How to Incorporate Fasting into Your Life

If you’re interested in fasting, there are many ways to do it, and they all have health benefits. You can experiment and find a fasting strategy that works for you. I recommend reading Dr. Fung’s book before starting.

And, be aware that certain people should not fast:

  • Women who are pregnant or breastfeeding
  • Children under the age of 18
  • Anyone who is malnourished or underweight (BMI under 18.5)
  • Anyone who has a history of disordered eating

Dr. Fung recommends fasting under the supervision of a healthcare provider if you have type 1 or type 2 diabetes, gout, gastroesophageal reflux disease, or are taking any medications.

If you’re a woman of childbearing age and you’re interested in intermittent fasting, experts recommend starting slowly and not fasting every day. Pay attention to your hormonal balance and monthly cycle, and back off from fasting if it isn’t working for you.

7 Ways to Fast

  1. Intermittent fasting: Fasting for anywhere between 12 and 20 hours per day and consuming all of your calories during your “feeding window.”
  2. 24-hour fasting: Also known as OMAD (one meal a day), this is just as it sounds—eating just one meal per day and consuming all of your calories for the day during that meal. Some experts advocate doing a 24-hour fast twice per week.
  3. Alternate-day fasting: This approach involves fasting every other day, but you can eat 500 to 600 calories per day on fasting days.
  4. The 5:2 Diet: This approach involves eating normally five days per week and eating just 500 to 600 calories on the two fasting days.
  5. Note: 500 to 600 calories are allowed on fasting days for these two types of fasting simply to increase compliance of people who are doing these fasts for weight loss.
  6. 36-hour fast: Dr. Fung uses this type of fast with his type 2 diabetes patients. He recommends doing a 36-hour fast three times per week until desired results are achieved and then adopting a fasting strategy that works for each individual person in order to maintain results. A 36-hour fast can easily be stretched into a 42-hour fast by skipping breakfast on the final day.
  7. Extended fasting describes fasts lasting at least two full days or 48 hours. If you’re interested in extended fasting, Dr. Fung generally does not recommend doing just a 48-hour fast because the first 48 hours are the hardest for hunger. After the first two days, hunger dissipates, and many people feel euphoric.

Another reason not to bother with a 48-hour fast is that it can take up to two days for your body to burn through its glycogen stores. Once glycogen is used up, you enter ketosis, and autophagy reaches peak levels. This is why a three-day fast is recommended to reset the immune system.

While this may be hard to believe, Dr. Fung reports that fasting for seven to 14 days is only marginally more difficult than fasting for two days because the first two days are the hardest. He often uses seven- to 14-day fasts with patients who have severe type 2 diabetes in order to rapidly improve their blood glucose levels and prevent further damage to their organs.

My Personal Experience with the Benefits of Fasting

Waist-up photo of slightly hesitant young woman with two plates in hands choosing between dessert and fresh fruit and one of the benefits of fasting is cultivating better eating habits.

I’ve been intermittent fasting for six months, and I can’t imagine returning to how I used to eat. Like many people, I used to fast for only nine or so hours per night. I’d have a small snack around 8:30 or 9:00 p.m., then put a big spoonful of honey in my Rasa at 6:00 a.m. Simply skipping that evening snack and leaving the sweetener out of my morning drink extended my fast to 12 hours. After a few months of experimentation, I settled into fasting for 14 to 16 hours per day, which feels right for me.

The benefits of intermittent fasting that I’ve experienced are a dramatic reduction in food cravings, a general reduction of hunger, improved digestion, and loss of several pounds of fat. The reduction in food cravings is the biggest change for me. For the first time in my life, I’m not picking certain foods because of emotions, the feeling of low blood sugar, or an imaginary feeling that I need to eat. I can make completely rational decisions about what to eat, and it’s the healthiest relationship I’ve ever had with food.

Starting a Fasting Regimen: Be Patient

When you start fasting, it’s important to give yourself time to adapt, pay attention to what your body needs, and be prepared for the ups and downs. And if you feel like you really need to eat, then eat!

It’s also important to know that if you want to maximize the benefits of intermittent fasting, you can’t just eat whatever you want during your feeding window—you do need to eat a healthy diet. You should reduce your intake of added sugar as much as possible, eat whole, unprocessed foods, and incorporate healthy fats (like avocados, nuts, seeds, coconut, and extra-virgin olive oil) into your diet.

If you’re looking for an easy way to keep track of your fasting schedule, I use the LIFE app and find it very helpful and easy to use.

How to Do a 3-Day Fast

And did I ever do the three-day fast? Yes! After four months of intermittent fasting, I felt ready and re-motivated to do the extended fast. The first 36 hours were easy, but Days 2 and 3 were tough. I am extremely glad I did it, and I felt so good afterward that I’m actually looking forward to doing it again!

If you want to do an extended fast, I strongly recommend that you:

  • Get very comfortable with intermittent fasting first.
  • Consume high-quality electrolytes and sea salt during the fast.
  • Do your research: Read Dr. Fung’s book or a similar book before starting.
  • Consult with your doctor if you have any diagnosed medical conditions or any health concerns.
  • Don’t put too much pressure on yourself—if you need to eat, then eat!
Reprinted with permission from
sarah warren

Sarah Warren is a Certified Clinical Somatic Educator and the author of the book The Pain Relief Secret. She was trained and certified at Somatic Systems Institute in Northampton, MA. Sarah has helped people with chronic muscle and joint pain, sciatica, scoliosis, and other musculoskeletal conditions become pain-free by practicing Thomas Hanna’s groundbreaking method of Clinical Somatic Education. Sarah is passionate about empowering people to relieve their pain, improve their posture and movement, and prevent recurring injuries and physical degeneration.

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