Intermittent Fasting


(uploaded 15Apr2016)
Intermittent fasting is growing quickly in popularity, “trending” with high profile endorsements from celebrities like Jimmy Kimmel, Benedict Cumberbatch and Hugh Jackman. It is believed to be more a pattern of eating than a diet; easier than a “diet” and like a diet it is supposed to help you lose weight but also provide many health benefits. Does this sound too good to be true? That’s what we aim to find out.

The purported health benefits associated with intermittent fasting include: weight loss, preventing type 2 diabetes and cancer, and improving heart health, brain health and longevity.

A “Fast” History of Fasting

Fasting in one form or another has been around for as long as humans, sometimes as a consequence of having limited access to food, and sometimes due to religious or spiritual beliefs. It is easy to see that we evolved to be able to function without food for extended periods of time, and it is not hard to argue that fasting may in fact be more “natural” than eating three meals a day “on a schedule”.

Until very recently in human history, sporadic or seasonal access to food was the norm. This fits in nicely with the fact that our livers and muscles store carbohydrates in the form of glycogen for quick access, and we can also sustain ourselves for weeks at a time by drawing from our long term reserves – fat.

Humans as Hybrids

Our energy systems work somewhat like a hybrid car, in that we have more than one fuel system and are capable of switching between them. In order to understand how this process works we have to go into some detail, and it all starts with what happens after we eat a meal.

Digestion typically lasts for three to five hours, during which time your body digests and absorbs the food you ate; this is referred to as the “absorptive state”. During this time the glucose produced from the meal is released into your blood and is your body’s primary source of fuel. Excess glucose is converted into glycogen and stored in your muscles and liver. Once these stores are full, any remaining glycogen is converted into fat. According to Dan Benardot, the author of Advanced Sports Nutrition, humans can store approximately 350 grams (1,400 kilocalories) in the form of muscle glycogen, an additional 90 grams (360 kilocalories) in the liver, and a small amount of circulating glucose in the blood (~5 grams, or about 20 kilocalories).

Once digestion is complete, approximately four hours after eating, with glucose no longer being produced, you experience a drop in energy and a hunger response. Most people will eat their next meal at this time but if they do not, the hunger will generally pass. In the evening, most people, if they do not go to bed within four hours after eating, will get hungry and end up having a late evening snack.

If you do not eat when your body runs out of glucose, your body will enter a “postabsorptive state” and start drawing on its reserves stored in the liver to maintain its blood glucose levels. Depending on your activity level, this lasts anywhere from four to eight hours. When these stores in the liver are depleted you once again start to experience hunger, and most people then have their next meal. This typically occurs during the night or if you skip lunch.

When the glycogen stores in the liver are depleted, the body could break down muscle for energy. But fortunately, in most situations ketosis (an adaptation that spares muscle during times of food shortage) kicks in, breaking down fat reserves and manufacturing ketones for fuel.

Interestingly, our body produces ghrelin and other metabolic hormones which determine blood sugar levels, and do so based on our eating patterns. In other words, if you regularly skip breakfast or dinner, your body will stop telling you that you are hungry. This explains why people can easily adapt to regular periods of fasting.(1)

Intermittent Fasting Methods

If you want to give intermittent fasting a shot, three of the most common variations are:

  • Leangains model (2) also known as the 16:8 diet (among other names)
  • 5:2 diet
  • Alternate day fasting

The 16:8 version of intermittent fasting involves extending the night-time fasting period by either skipping breakfast or dinner so that you fast for 16 hours and eat during an eight hour time-frame. It does not require you to change what you eat. Skipping a meal will, in most cases, result in less food being consumed. The theory goes that we are already fasting on a daily basis and in the morning we “break-fast.”

The 5:2 version of intermittent fasting involves fasting for two days per week and eating normally for the other five days.

Alternative day fasting involves eating normally one day, then a very restricted diet the next day (fewer than 600 calories for men and 500 for women).

If these variations do not suit your lifestyle there are other variations. For the most part, these three variations appear to have similar health benefits.

Is Breakfast the Most Important Meal of the Day?

imgres-8Eat Breakfast Like a King, Lunch Like a Prince, and Dinner Like a imgres-1Pauper. This is a widely held belief, but does science back it up?

Breakfast is generally thought of as healthy, and perhaps even more important than other meals. This idea is shared by most official nutrition guides. Indeed, several studies have shown that those who eat breakfast regularly tend to be healthier, less likely to be overweight and are at lower risk of chronic diseases.(3)(4) Interestingly, these studies are observational and do not demonstrate causation. Even though they demonstrate that those who eat breakfast are more likely to be healthy, they cannot prove that eating breakfast caused it.

On the other hand, many studies, including numerous clinical studies, show that intermittent fasting, often involving skipping breakfast, provides numerous health benefits.

One likely reason for this inconsistency could be that those who eat breakfast also tend towards healthy lifestyle choices such as healthier diets, as demonstrated in a 2005 survey covering 47 studies dealing with breakfast habits.(5) A very large observational study of 26,902 American men over 16 years found that breakfast skippers have a 27% higher risk of heart disease. But the study also found that they are also more likely to be smokers, unmarried, less physically active and drink more alcohol.(6) It would appear that breakfast eaters, as a general rule, maintain better dietary and lifestyle habits.

Ramadan Fasting Studies

Ramadan is a religious month for Islam, during which Muslims do not eat and drink during daylight hours. This makes Ramadan a model of prolonged intermittent fasting.

There are numerous studies conducted on Ramadan fasting and the results consistently show consistent weight loss, a generally positive effect on body fat percentage and other health benefits.(7)

The Benefits of Intermittent Fasting


1. Weight Loss

The main motivation for many to try intermittent fasting is to lose weight. And one reason that it works is because it involves eating fewer meals, and unless you compensate by eating much more during the other meals, you will consume fewer calories.

Intermittent fasting is easier than standard calorie restriction diets for most people.(8) Most diets fail because people do not follow the diet over the long term. Several studies have found that intermittent fasting is easier to follow than calorie restriction diets. As a result, more people are willing to stick with it and adapt more easily to an intermittent fasting routine.(9) A 2012 observational study of 16 obese individuals found a high degree of compliance and significant weight loss.(10)

Studies have shown that intermittent fasting enhances hormone function, which helps with weight loss. For example, a 2013 randomized study of 112 overweight women showed that intermittent fasting substantially improved insulin sensitivity and weight loss.(11) Another study showed that two days of fasting can quintuple human growth hormone levels.(12) This process is important in the breakdown of body fat and facilitates the use of fat for energy. As a result, intermittent fasting increases your metabolic rate by up to 3.6% which helps you burn more calories.(13)

Because intermittent fasting causes an increase in human growth hormone it plays an important part in the maintenance of lean body mass and the decrease of body fat.
(14) Raising human growth hormone levels while improving insulin sensitivity results in healthy weight loss. A 2011 review study concluded that intermittent fasting helps with weight loss but, just as importantly, results in less muscle loss than a standard calorie restriction diet.(15)

A 2012 study of 50 healthy Ramadan observers found significant improvement in body fat percentage. Another important finding was that even though the participants had regained the weight lost during the Ramadan fast, six weeks later they had not gained any additional weight as often happens with many types of calorie-restrictive diets.(16)

Part of the reason that many people stick with an intermittent fasting regime has to do with the fact that it works, and they experience weight loss, and nothing breeds compliance like success.

Intermittent fasting works both by boosting your metabolic rate – calories out – and by generally reducing the amount of food you eat – calories in.

2.Type 2 Diabetes

Type 2 diabetes develops when the body does not use insulin properly, or becomes insulin resistant. Your pancreas makes extra insulin to make up for it, but over time it is not able to keep up and cannot make enough insulin to keep your blood glucose at normal levels.

Type 2 diabetes has become a very common disease due to worsening diets and sedentary lifestyles. Unlike type 1 diabetes, it appears to be reversible with lifestyle changes, such as exercise and diet.

Intermittent fasting has been shown to reduce insulin resistance, which leads to a significant reduction in blood sugar levels.(17) A 2015 Ramadan study of 20 healthy males found that they not only lost significant weight, but that fasting is in itself sufficient to improve insulin sensitivity in healthy individuals.(18)

A 2014 Ramadan study of individuals with chronic liver disease found that they lost weight and showed significantly improved symptoms with regard to the liver disease.(19) This is significant because liver disease is a leading cause of death in type 2 diabetes.(20)

These results imply that by reducing insulin resistance and lowering blood sugar levels, intermittent fasting may be very helpful for people who are at risk of developing type 2 diabetes.

3. Cancer

Cancer is characterized by uncontrolled cell growth, and intermittent fasting has been shown to have beneficial effects on metabolism, possibly leading to reduced risk of cancer. Several promising animal studies have shown that intermittent fasting helps prevent cancer in animals.(21)(22) Several human studies have also shown promise. A 2007 study involved ten obese asthma sufferers who were subjected to alternate day calorie restriction for eight weeks. The researchers found significant improvement with their asthma due to improved oxidative stress and reduced inflammation.(23) Both reducing inflammation and improving oxidative stress are also important for reducing the risk of cancer.

A 2012 observational study of 50 healthy Ramadan observers confirmed the results of animal studies, showing weight loss, a marked decrease in inflammation and cancer markers.(16)

A 2009 study of ten cancer patients undergoing chemotherapy found that intermittent fasting can reduce the side effects of chemotherapy.(24) A 2012 animal study found that fasting could replace or augment the effects of chemotherapy.(25)

Another promising result comes from a 2012 review study which found that intermittent fasting reduces production of the hormone IGF-1, which results in slower tumour growth and thereby reduces the risk of cancer. It also found that intermittent fasting improved insulin resistance, which reduces the risk of diabetes. (26)

A 2014 peer reviewed paper entitled A reason for intermittent fasting to suppress the awakening of dormant breast tumours concluded that intermittent fasting will reduce incidence of tumour relapse.(27)

4. Heart Health

Studies have shown that intermittent fasting can improve risk factors for heart disease such as blood pressure, cholesterol levels, triglycerides, inflammatory markers and blood sugar levels. However, most of this is based on animal studies.(28)

There are some promising human studies. A 2007 observational study compared the results of 40 healthy adults (20 men and 20 women) who observed Ramadan, with 28 healthy adults (14 men and 14 women) who did not observe Ramadan. The Ramadan group showed reduced inflammation and improved risk factors for heart disease. The other group did not.(29) These results were confirmed in a 2012 Ramadan study of 50 healthy adults.(16)

A 2012 human randomized study of 50 obese women found that intermittent fasting combined with calorie restriction and liquid meals was an effective way to help lose weight and lower the risk of heart disease.(30)

A 2013 peer review analysis of the literature on intermittent fasting concluded that despite the limited number of human studies, the results are positive for human health; including a decrease in inflammatory responses, lower oxidative stress and cardiovascular diseases, and that it may be a viable intervention for most individuals.(8)

5. Brain Health

In a fascinating Ted Talk in 2014,( Mark Mattson, chief of the Laboratory of Neurosciences at the National Institute on Aging and a neuroscience professor at Johns Hopkins University, spoke about the health benefits of fasting. As a leading authority on neurodegenerative disorders, such as Alzheimer’s, Parkinson’s and ALS, Mattson and his team have published several papers on the benefits of intermittent fasting on these diseases.

Mattson believes that the neurons in your brain benefit from being mildly stressed, similar to what happens when you exercise your muscles, and that this can be accomplished with intermittent fasting. Mattson and others have studied animals and small groups of humans and have found that neurons in the brain become more active while hungry and searching for food.

Mattson postulates that intermittent fasting, unlike dieting, shocks the brain into creating new cells, which makes the brain more resistant to the effects of protein plaques that lead to brain disease such as Alzheimer’s and Parkinson’s.

In a 2014 peer reviewed paper, Professor Mattson wrote that the human brain shares certain attributes with animal brains with regard to what promotes optimal performance, and that two common aspects are how we react to exercise and food deprivation/fasting. Due to the fact that the brain evolved in part for success in seeking and acquiring food, the brain functions best when the individual is hungry and physically active, as typified by the hungry lion stalking and chasing its prey. Indeed, studies of animal models and human subjects demonstrate robust beneficial effects of regular exercise and intermittent energy restriction/fasting on cognitive function and mood, particularly in the contexts of aging and associated neurodegenerative disorders. Unfortunately, the agricultural revolution and the invention of effort-sparing technologies have resulted in a dramatic reduction or elimination of vigorous exercise and fasting, leaving only intellectual challenges to bolster brain function. In addition to disengaging beneficial adaptive responses in the brain, sedentary overindulgent lifestyles promote obesity, diabetes and cardiovascular disease, all of which may increase the risk of cognitive impairment and Alzheimer’s disease.(31)

6. Longevity

Scientists have long since established that restricting calories makes you live longer. There is only one problem, long term calorie restriction is not something that appeals to very many people. Fortunately, intermittent fasting triggers most of the same mechanisms for extending life as calorie restriction and is much easier for most people.


Even though the idea of fasting is daunting for most people, there is substantial evidence that many who try it adapt to it well. Given that it provides a wide range of health benefits without requiring a major lifestyle change, there is a good reason to give it a try.

Intermittent fasting is a relatively simple strategy to lose weight and maintain muscle mass because it requires very little behavioral change. This means intermittent fasting is simple enough that you will actually do it, and effective enough that it will make a difference.

If you have any medical conditions, special dietary requirements, chronic diseases or are pregnant, consult a medical professional before trying intermittent fasting.