A Beginner’s Guide to Intermittent Fasting

by Marixie Ann Obsioma, MT, undergrad MD on June 5, 2019
Last updated on May 23, 2021

Why cut back every day if you can be conscious about what you eat only a couple of days a week? This is the logic behind intermittent fasting (IF), which is one of the world’s most famous health and fitness trends today.

a smoothie bowl

There are many people talking about the health benefits of IF. The results you’ll yield by doing a search online can be overwhelming, especially if you are a newbie and fasting is not within your comfort zone.

Studies show that IF can have powerful effects that can help you live longer (1, 2). People are using IF to lose weight, improve health, and simplify lifestyles.

If you are interested in this weight loss strategy, read on to know its health benefits and the studies behind them. This is a beginner’s guide to intermittent fasting.

What is Intermittent Fasting?

IF is a diet regimen that cycles between periods of fasting, with either no food or very low-calorie intake and unrestricted eating. It does not specify which type of food you must eat but rather the time when you should consume them. It is best described as an eating pattern.

Usual IF techniques would involve a 16-hour daily fasting or 24-hour fasting, two times a week. IF is promoted to change body composition by losing weight and fat mass, and to improve markers of health that are related to cholesterol and blood pressure (3).

IF provides physiological benefits over continuous diets for weight loss. It reduces body weight and appetite but not other adaptive responses (4).

Fasting is also often done for spiritual benefits as described in the early texts by Plato, Socrates, and other religious groups (5).

How Does IF Work?

You can do IF in several ways – all of which involve alternating eating and fasting periods within the day or week.

The most popular techniques are the following (6):

  • Eat-Stop-Eat: This involves fasting for 24 hours, at least once or two times weekly.
  • 16/8 Method: Also known as the Leangains protocol, this technique involves not eating breakfast and limiting your eating period to 8 hours. Then you fast for 16 hours in between.
  • 5:2 Diet: This technique advocates no food restriction for 5 days in a week, cycled with a 500-600 calorie diet on the remaining 2 days of the week.

By limiting your calorie intake, all of these techniques should cause weight loss as long as you do not compensate by eating much more after the fasting periods.

A lot of people find the 16/8 technique to be the simplest and most sustainable.

How Can You Benefit from IF?

Several studies show that IF can have powerful benefits for your body and brain.

1. IF Changes Cell Functions, Genes, and Hormones

During fasting, your body initiates cellular repair processes and modifies hormone levels to access stored body fat easily.

  • Blood insulin levels decrease significantly to facilitate fat burning (7).
  • Blood levels of growth hormone increase up to 5-fold to facilitate fat burning, muscle gain, and several other benefits (8, 9, 10, 11).
  • The body induces cellular repair processes like the removal of waste products from cells (12).
  • There are also beneficial changes in genes and molecules related to longevity and protection against diseases (13, 14).

2. IF Can Help Lower Insulin Resistance and Risk of Type 2 Diabetes

Type 2 DM has become incredibly common in the past few years. Its main feature is high blood glucose levels in the context of insulin resistance. Anything that decreases insulin resistance should help lower blood glucose levels and protect against type 2 DM.

IF revealed major benefits for insulin resistance, which led to an impressive reduction in blood glucose levels. Human studies on IF showed that fasting blood glucose has been reduced by 3-6% while fasting insulin has been decreased by as much as 20-31% (15).

A study in rats with diabetes also showed that IF is protective against kidney damage, a serious complication of DM (16).

3. IF Reduces Oxidative Stress and Inflammation

Oxidative stress, an imbalance between the production of reactive oxygen species or free radicals and antioxidant defenses, may cause aging and several chronic diseases (17).

It involves free radicals, which damages important molecules like DNA and protein (18).

Many studies show that IF can enhance the body’s resistance to oxidative stress and help fight inflammation (19, 20, 21, 22).

4. IF Is Good for the Heart

Heart diseases are currently one of the world’s biggest killers (23). Many risk factors are associated with either an increased or decreased risk of heart disease.

Animal studies on IF have shown to improve many risk factors like blood pressure, cholesterol levels, blood triglycerides, blood glucose levels, and inflammatory markers (15, 24, 25, 26).

5. IF May Help Prevent Cancer

Fasting initiates cellular “waste removal” known as autophagy (27). Cells break down and metabolize broken and dysfunctional proteins that accumulate inside the cells.

Increased autophagy may offer protection against cancer (28).

Fasting also has beneficial effects on metabolism. Animal studies indicate that IF can help prevent cancer (29, 30, 31, 32).

Fasting has also helped reduce the side effects of chemotherapy on human cancer patients (33).

6. IF May Help Prevent Alzheimer’s Disease

Alzheimer’s is a common neurodegenerative disease. There is no cure available for this disease, so prevention is very critical.

One study in rats shows that IF can help delay the onset of Alzheimer’s or reduce its severity (34).

In a series of case reports, daily short-term fasts were very helpful in improving Alzheimer’s symptoms in 9 out of 10 patients (35).

Animal studies suggest that fasting may also offer protection against other neurodegenerative diseases like Parkinson’s disease and Huntington’s disease (36, 37).

7. IF For Healthier Brain

IF is known to improve several metabolic features, which are important for brain health. This includes less oxidative stress, less inflammation, and low blood glucose levels and insulin resistance.

Many studies in rats have proven that IF can help increase the growth of new nerve cells for better brain function (38, 39).

IF also increases the levels of a hormone known as the brain-derived neurotrophic factor (BDNF) (39, 40, 41). A deficiency of this hormone has been implicated in several other brain problems and depression (42).

Animal studies also proved that IF protects the brain from damages caused by strokes (43).

8. IF Can Help You Live Longer

One of the most exciting benefits of IF is its ability to extend lifespan.

Rat studies have shown that IF can extend lifespan in the same way as continuous calorie restriction (44, 45). In some of these studies, the effects were dramatic. Rats that fasted every other day lived 83% longer as compared to those who did not fast (46).

Although this is far from being proven in humans, IF has become very popular among the anti-aging crowd.

IF As A Powerful Weight Loss Tool

A lot of people who try IF are doing it to lose weight (47).

IF will make you eat fewer meals so you will end up consuming fewer calories. Also, IF enhances hormone functions to facilitate weight loss.

Decreased levels of insulin along with higher levels of growth hormone and norepinephrine will increase the breakdown of fat for energy. For this reason, short-term fasting will help increase your metabolic rate by 3.6-14%, helping you burn more calories (48, 49).

A 2014 review of literature mentioned that IF can cause weight loss of 3-8% over 3-24 weeks (15). People also lost 4-7% of their waist circumference or belly fat.

Another review study also pointed out that IF caused less muscle loss as compared to continuous calorie restriction (16).

IF helps you eat fewer calories overall. However, if you eat more than usual after fasting, you may not lose any weight at all.

IF Is Not for Everyone

If you are underweight or have a history of eating disorders, IF is not recommended without consulting a doctor first.

There is some evidence that IF may not be as beneficial for women as it is for men. One study showed that IF improved insulin sensitivity in men, but not in women (50).

Though human studies are not yet available, studies in rats also found that IF can make females emaciated, masculinized, and infertile and cause them to miss menstrual cycles (51, 52). There are several anecdotal reports saying that the menstrual period went back to normal when they resumed their original eating pattern.

If you are having issues conceiving, forget about IF. This eating pattern is also not recommended for pregnant and breastfeeding women.

For these reasons, women must be careful with IF.

Should You Try IF?

IF is not something that everybody needs to do. It is just one of the many lifestyle techniques that can help improve your health. Eating real good food, engaging in physical activities, and getting enough sleep and rest are still the most important factors to concentrate on.

There is no one-size-fits-all solution when it comes to weight loss and nutrition. The best diet for you is the one that you can sustain for a long period of time.

IF is good for some people, not others. The only way to know which group you belong to is to try it out with your doctor’s supervision.

If intermittent fasting makes you feel great and you find it easy to maintain, it can be a powerful tool to lose weight and improve your overall health.


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