Fasting for weight loss seems like a logical step. When you completely cut out food, shouldn’t you lose weight? That is what this article will attempt to clarify. So many people are turning to fasting for weight loss. That is why I saw it necessary to look through the available scientific literature to assess the merit of doing so. You may be reading this article to assess if fasting for weight loss actually works. You will be able to make a sound decision at the end. As I have mentioned before, an investigative article such as this can be quite lengthy and it would be worthwhile for you to bookmark it for future reference.
Table of Contents for Article
- 1 What is fasting
- 2 Fasting for weight loss – What happens during the fast
- 3 Fasting for weight loss – Prolonged fasting
- 4 Fasting for weight loss – When is it recommended
- 5 Fasting for weight loss – Is it for you
What is fasting
Fasting is the act of completely abstaining from solid food, drinks or both for a certain period of time. Most of the time it refers to the abstinence of solid food. Fasts can range from a few hours to many days. Alternate day modified fasting is where one fasts on every alternate day. One consumes 20- 25% of their baseline energy needs on the fasting day. Food consumption on the feeding day is according to baseline energy needs.
Fasting for weight loss – What happens during the fast
The body uses glucose as the primary source of energy in the body. The body obtains glucose primarily from carbohydrate food sources. The body is able to store glucose as glycogen for emergency use in the event that there is not enough glucose available. Glycogen is stored mainly in the liver and muscles. The body breaks down glycogen through a process called glycogenolysis to obtain glucose. While the body can store lots of calories in the form of fat, it can store very little calories in the form of glycogen.
After 4 to 8 hours of starting a fast, the body senses the decline in available glucose. It then turns to the liver to breakdown its glycogen stores into glucose. The body is also likely to break down some amount of muscle protein for fuel. The glycogen fuel source in the liver could be depleted within 8 to 12 hours. The body then turns to the glycogen stored in the muscles which could give another day or two of energy supply.
Only once the glycogen stores are depleted will the body turn to its fat stores for energy.
Fasting for weight loss – Studies
An article was published in the American Journal of Clinical Nutrition in 2009. The objective of the study was to assess the effects of alternate day modified fasting on bodyweight and coronary artery disease risk indicators. The researchers found that dietary adherence was above 86%. Average bodyweight of the 16 obese participants decreased by about 5.5 kg after being on the modified fast for 8 weeks. The average weight of the participant was 97 kg. Average bodyfat reduced from 45% to 42%. This was equivalent to an approximate loss of 2.9kg (i.e. from 43.65kg body fat to 40.74kg body fat). While there was spectacular weight loss of 5.5 kg, the actual fat loss was almost half of this. The rest of the weight loss could be attributed to muscle or water loss.
A study was published in the American Journal of Clinical Nutrition in 2005. Researchers wanted to assess if alternate day fasting was a feasible dietary regimen for non-obese people. They also wanted to assess if it could improve known biomarkers of longevity. The 16 non-obese participants fasted for full 24 hour periods on every alternate day. This was a modified fast but with no meals consumed on the fasting day. On the feeding day, the participants were asked to eat double their usual amount, in order to keep their weight consistent.
The average male participant weighed around 80kg while the average female participant weighed 60kg. After 22 days, researchers found that the participants lost about 2.5% of their bodyweight. That was an average of 2kg for men and about 1.5 kg for women. The researchers found that most of the weight loss was attributed to fat loss with very minimal muscle loss. The rate of weight loss depended on how much the participants overate on the feeding day. Interestingly, the researchers also found that the metabolic rate had a very small decline. Fasting insulin levels decreased by an amazing 57%.
The researchers concluded that alternate day fasting for weight loss was feasible for the non-obese. They also noticed an increase in the body’s fat burning rate. The downside mentioned was that the level of hunger on fasting days did not reduce. This made it unlikely that someone could continue with this type of a diet for an extended period of time. They further suggested that adding one small meal on the fasting day may increase the adherence to the fast.
An article was published in the Journal of Free Radical Biology and Medicine in 2007. Researchers placed the participants on alternate day modified fasting. The researchers wanted to assess if the asthma symptoms in the overweight participants would improve with weight loss. The 10 participants remained on the dietary regimen for 8 weeks. 9 of the participants that adhered to the dietary guidelines lost an average of 8% of their bodyweight over the 8 week period. The researchers also reported that the asthma related symptoms improved significantly.
An article was presented in the Obesity proceedings in 2010. The researchers placed 16 obese participants on the alternate day modified fasting. After 8 weeks, there was an average 5.7kg reduction in weight with 5.4 kg coming from fat loss. Average waist circumference reduction was 4 cm. Lean body mass did not change. These findings again showed the effectiveness of alternate day modified fasting for weight loss.
A study was published in the International Journal of Obesity and Related Metabolic Disorders in 2002. Researchers postulated that the human body defends itself vigorously against an energy deficit. In order to verify this, researchers placed 24 healthy men and women on a 36 hour fast. They wanted to assess how this fast affected the level of calorie intake on the preceding day once the fast was broken. The researchers found that while there was a significant calorie deficit created by the 36 hour fast, the participants did not have a powerful urge to compensate by eating more on the subsequent days. This showed that alternate day modified fasting could effectively create a calorie deficit in people trying to lose weight.
An article was published in the Nutrition Journal in 2010. The objective of the study was to determine how the body adapts to dietary and physical activity when on alternate day modified fasting. The researchers concluded that the 16 obese participants adapted quickly to alternate day modified fasting. The researchers also stated that changes in calorie intake, level of hunger and physical activity influenced the rate of weight loss. You will get lesser weight loss if you overeat on your feeding day. Alternatively, you will get more weight loss if you incorporate physical activity into your lifestyle. So while fasting for weight loss may be effective, it can only be a small component of a larger holistic approach to weight loss. A holistic approach to weight loss is what we call correct weight loss.
Fasting for weight loss – Prolonged fasting
There are very few studies available on the effects of prolonged fasting. Prolonged fasting is also a form of starvation. The best study that depicts the effects of prolonged calorie restriction was published in the Lancet in 1969. The researchers reduced the calorie intake of healthy participants from a baseline of 3500 to 450 cal.
In the first chart, you will notice that the actual weight loss experienced by the participants was far higher than the expected weight loss based on the calorie reduction. This effect is explained by the second chart. The second chart shows the level oxygen consumption and this is an indicator of the level of fat oxidation experienced by the participants. The oxygen consumption reduced by almost 45% and continuing to drop. This resulted in the rate of weight loss reducing with time. The participants did continue to lose weight and fat but at a slower rate. This slow down was due to the body adapting its metabolism to the level of energy available.
Check out the video below of a woman who did 3 regimens of 40 day fasts. The video below is taken on day 1 of the first 40 day fast session.
Here is her video on the last day of her third 40 day fast.
She looks very emaciated. This is extreme and prolonged fasting which is certainly not recommended for weight loss. There are a lot of fasting therapies that have shown tremendous promise for health enhancement. One such therapy is the 42 day Breuss fast to treat cancer. Dr Rudolf Breuss stated that more than 45,000 people were cured from various types of cancers after going on this 42 day fast. However, people should not mix up fasting for therapy or treatment as a substitute for weight loss.
Fasting for weight loss – Summing up what the studies say
It is obvious that prolonged fasting will yield dramatic weight loss. The Lancet study has shown, the body quickly adapts to a situation that it perceives as detrimental to its survival. It lowers the metabolism thus effectively putting the body in starvation mode. The rate of weight loss will become progressively slower. Even though the rate of weight loss slows down, the body continues to shed weight so long as there is no supply of food.
The alternative day modified fasting seems like a good alternative to prolonged fasting. This modified fast may also be easier to adhere to than a prolonged period of hunger. Most scientific studies have shown successful weight loss from this intermittent mode of fasting. Best of all, most of the weight loss came from fat loss.
Do note however that most of these studies were carried out for a duration of 4 to 8 weeks. Studies for durations longer than these are not available. What is also not available are studies on prolonged periods of intermittent fasting. An example of this is being on an intermittent fast for 8 weeks. This is followed by being on a normal diet for say 4 to 8 weeks. This is followed by another 4 to 8 weeks of intermittent fasting. A lot of people would extrapolate the results of the successful studies to get on a prolonged period of intermittent fasting. I personally believe that the body will sense the pattern and eventually slow down the rate of weight loss.
Fasting for weight loss – When is it recommended
Fasting may be effective when you need a psychological victory. The alternative day modified fasting is easier to adhere to. Studies have shown that people can get up to 4 kgs of weight loss within 8 weeks. With this psychological boost, they can then look at committing to exercise and a healthy lifestyle.
There was only one study that showed the 57% reduction in fasting insulin levels. This may be another area where fasting may come in handy. Insulin is a potent fat storage hormone. Most people have trouble losing weight because of elevated levels of circulating insulin hormone in the blood stream. If fasting could help to bring insulin levels down, it may be a fantastic way to kick-start your weight loss efforts. Further studies need to be carried out to validate the findings of this study.
Fasting for weight loss – Is it for you
Some dieters may be sick and tired of the same old advise. All they hear is exercise and nutrition. Some people need a new regimen. They need to attempt something that they have not done before. Alternate day modified fasting for weight loss may be the answer. As I have mentioned before this, alternate day modified fasting for weight loss may be worth considering if you need a psychological boost. This type of fasting does nothing more than bring down your calorie consumption. You could also achieve the same results by reducing your overall calorie intake.
Also do note that the effects of fasting for weight loss over the long term has not been properly studies. Until more conclusive studies are available, you should only consider using alternate day modified fasting for a period no longer than 4 to 8 weeks. Do cardio and body weight exercises on your feeding days. This should help you get very decent amounts of weight loss. What ever you do, do not go overboard with fasting for weight loss. The best regimen is still one of a healthy diet and plenty of exercise.