Obesity is gripping the world. People are moving from one diet to another with desperate hope that one of them will work.
Enter intermittent fasting.
Yet another way to lose weight. Some have knocked it before they tried it; some have given it a half-hearted go.
But many have found trying intermittent fasting for weight loss to be a success.
So I thought I would give you a brief overview of this type of diet, and hopefully clarify your doubts on how it should be done and what to expect.
Terms To Know
Here are some terms I will be using in this article. Feel free to refer back to them as and when you read the article.
Intermittent Fasting (IMF)
What is intermittent fasting?
It is a form of intermittent energy restriction. It includes a >60% restriction in total energy consumed on 2 to 3 days a week.
An example is having a normal diet 4 days a week, and restricting the quantity of food and total calorie intake the remaining 3 days of the week.
Time-Restricted Feeding (TRF)
This is a variant of intermittent fasting. The period of food intake is limited to 8 hours a day, following which the calories are restricted.
An example is eating breakfast at 7 am and lunch at 3 pm, and nothing after that till the day after.
There are 3 patterns that people follow – 16/8, 18/6 and 20/4. 20/4 indicates a 20 hour fast along with 4 hours when food is consumed.
Some consider intermittent fasting and time restricted feeding to be the same thing. For the purposes of this article, we shall do so too.
Continuous Energy Restriction (CER)
This is where the total calories consumed are reduced by 500 to 750 kcal per day or a 30% reduction of what the individual needs at the baseline.
It is a hard diet to adhere to, and many falter and give up within 4 months of starting CER, making them gain back all the weight they lost!
Alternate Day Fasting (ADF)
In this variant, the person eats 75% of their normal intake on one day, and to their heart’s content on the next day, thus alternating between the two.
Does Intermittent Fasting Work As A Diet?
Given how people have been trying continuous energy restriction for years on end, it is natural that most clinical studies would look at whether intermittent fasting is better or comparable to this.
Human studies are hard to conduct as people tend to give up during the study period. On an average, burn out ranges between 0 to 60%. Hence, most of the information comes from animal studies and a few human trials.
Intermittent Fasting For Weight Loss
I start with this subsection, as most people who take up fasting of any sorts are doing it for one reason – to lose body weight.
When I talk about body weight, what I am primarily referring to in this article is body fat content. It is the excessive body fat that is responsible for heart disease and diabetes, so reducing that becomes of prime importance.
Generally, when you lose body fat, you lose body weight as well.
When we eat our food, it is broken down by digestive enzymes into glucose and other components that are needed for normal cells and vital organ functioning.
Glucose is absorbed into the bloodstream and thereon goes to provide energy to all vital structures of the body. The excess glucose generated is stored in the liver in the form of glycogen.
Anything over and above what the body needs is stored as body fat.
In other words, if you eat too much, a large part of what you eat will get converted to body fat, thus raising your body weight.
When you perform intermittent fasting, you make drastic changes to your body’s metabolism.
Let us take an example where you might be following the 8/16 protocol. When you consume food during the 8 hour period, your body glucose level remains high during that time and for a few hours after that. For about 16 hours or so after, during the fasting period, the glucose levels begin to drop.
Adaptive mechanisms kick in to keep the vital organs going, and glycogen from the liver begins to get utilised. Once this is emptied out, the body begins a process called gluconeogenesis, or ‘new glucose’ release. This is generated from the breakdown of fat cells.
As more and more of these fat cells breakdown to provide energy, the total body fat content begins to reduce. This leads to weight loss due to body fat loss.
Mouse studies have shown that the weight loss experienced could range between 13 to 18% on an alternate day fasting regime.
Human studies are limited, and while they too have shown modest weight loss in subjects performing time restricted feeding, there does not seem to be much difference to continuous energy restriction. However, the time restricted feeding group had more overall body fat loss.
In other words, available studies state there is no difference between the weight loss you would experience by performing intermittent fasting compared to just reducing the calories you consume every day.
But if you were never dieting and have now taken up intermittent fasting, then you would expect to lose around 6.5 – 7% of your body weight over an 8 to 12 week period, according to some studies.
This is actually pretty good!
So, if you are planning to take up intermittent fasting for weight loss, then you can be assured to lower your body fat, provided you stick with the regime for a few months at least.
I thought I would touch upon some other important aspects of intermittent fasting as well here.
Intermittent Fasting And Blood Pressure
Intermittent fasting has a positive effect on blood pressure control, and this too has been proven in clinical and animal studies.
A study conducted at the Buchinger Wilhelmi clinic in Germany looked at 1422 individuals subjected to fasting periods over 4 to 21 days. They were restricted to 250 calories per meal as well.
Over a period of one year, these individuals had a lower systolic and diastolic blood pressure control. The lowering of blood pressure is understood to be due to hormonal changes and neurological control mechanism alterations that are brought about by fasting.
However, once the fasting was stopped, the blood pressure returned to normal. This makes it important, once again, to stick to the diet.
Multiple human studies have also confirmed the same.
Interestingly, the heart rate of patients included in the study also reduced. This is beneficial as high resting heart rates have a detrimental effect on heart health.
In short, intermittent fasting has long term benefits on lowering blood pressure and heart rate, provided it is observed for a prolonged period of time.
Intermittent Fasting And Cholesterol
I mentioned earlier about how intermittent fasting can alter the way glucose is handled by the body.
During the fasting phase, all the glucose in the body is exhausted to provide the vital organs with energy. In the process of doing so, new energy has to be generated.
A process called ‘lipolysis’, or fat breakdown begins. The fat cells begin to release fatty acids, which are then transported to the liver. In the liver, these fatty acids undergo a process of oxidation, making them ‘energy-giving’ compounds.
In some time, this leads to changes in the levels of lipids in the body. Blood cholesterol levels are reduced, and animal models have found that the levels of ‘bad’ cholesterol, or LDL, reduce.
Multiple human studies conducted since have shown the same thing, with some even showing elevated levels of good (HDL) cholesterol.
Intermittent Fasting And Diabetes
This is an important one to note, as we currently have nearly 100 million people in our country with diabetes.
Obesity and leading a sedentary lifestyle are closely related to the development of diabetes. So it stands to reason that lowering body weight, along with regular exercise would prevent diabetes.
In patients with type 2 diabetes, intermittent fasting has been found to have numerous benefits, as per a clinical study called the DiRECT trial. In this clinical trial, individuals with type 2 diabetes were given an 850 kcal diet to eat every day for 12 weeks. Each participant lost a significant amount of weight, and this was accompanied with lower fasting blood sugars, lower HbA1c values and improved sensitivity to insulin.
Basically, intermittent fasting makes all the cells of the body respond better to insulin naturally secreted by the pancreas. This means the glucose generated from digestion of food is taken up more effectively by all cells and vital organs.
Intermittent Fasting And Inflammation
I thought I would make a brief mention on the role of intermittent fasting on inflammation.
The reason I wish to is because inflammation is the root cause for heart attacks and strokes. It is the reason fat deposits in the arteries of the heart, leading to atherosclerosis and subsequent heart attacks.
Intermittent fasting has been found to increase the levels of a protein called adiponectin. High levels of adiponectin have a protective effect against the development of heart disease.
In people who are obese, those with diabetes and cardiac disease, the levels of adiponectin are significantly lowered, which increases the risk of atherosclerosis and heart artery ‘blockages’.
Similarly, intermittent fasting lowers the levels of leptin, resistin and similar compounds, all of which are pro-inflammatory and promote atherosclerosis.
In essence, intermittent fasting can lower your risk of heart disease by lowering inflammation within the body.
In A Nutshell
So it is clear that intermittent fasting has many advantages. It can lower weight, lower LDL cholesterol, lower blood pressure and lower the risk of heart attacks and strokes.
Are There Any Disadvantages of Intermittent Fasting?
Well, with everything good, there is always a little bad.
Firstly, intermittent fasting may not be for everyone. Those with diabetes who attempt this must do it under the supervision of a doctor, as medications normally taken can precipitate low blood sugars.
Some studies have reported mood changes, anger, frustration and argumentative behaviors in those who are starting out.
The results for intermittent fasting that have been published with respect to weight loss are all short term studies. There are no long term studies that have evaluated how effective it is over years. While we know there are multiple advantages, we are still limited in our understanding of how it can help lower health problems over years.
Women who undertake intermittent fasting may find that their monthly menstrual cycles become irregular.
Pregnant women must avoid intermittent fasting as it could affect the health of the growing fetus. The same holds for athletes as it could negatively affect their performance.
On a lighter note, eating out in the evening with friends and family comes down, sadly. But your bank balance may improve over time!!!
Intermittent fasting is an effective way to lose weight and stay healthy. However, it may not be better than just reducing your overall calorie intake everyday.
Unfortunately, long term data regarding its true efficacy is limited, but that should not stop you from taking it up. Do remember that for the most effective weight loss, combine your diet with exercise.
Dr Vivek Baliga is a medical practitioner and the director of a diagnostic center – Baliga Diagnostics – in Bangalore. He specializes in diabetes and heart disease, and is a visiting consultant in Internal Medicine at corporate hospitals. He is married and has one son.