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  • Writer's pictureDr. Karuturi Subrahmanyam

Intermittent Fasting


Intermittent fasting is a way of eating that involves having periods of eating and not eating. It can help you with weight loss, blood sugar control, and lower your chances of getting some diseases. But it can also make you feel hungry, tired, and lose muscle. In this article, we will tell you what intermittent fasting is, how it works, and what are its good and bad points.


What is intermittent fasting?

Intermittent fasting is not a diet, but a way of eating. It does not tell you what to eat, but when to eat. There are different ways of doing intermittent fasting, but they all involve splitting the day or week into times when you can eat and times when you can’t. During the times when you can eat, you can eat normally, without counting calories or avoiding certain foods. During the times when you can’t eat, you either eat nothing or very little (usually less than 500 calories).


Some of the most common ways of doing intermittent fasting are:

  • Alternate-day fasting: You don’t eat every other day, either by eating nothing or by eating only one small meal (less than 500 calories).

  • 5:2 fasting: You don’t eat for two days per week, either by eating nothing or by eating only one small meal (less than 500 calories). You eat normally for the other five days.

  • Daily time-restricted fasting: You don’t eat for a certain number of hours each day, usually 16 to 20 hours. You eat all your meals within a shorter time period, usually 4 to 8 hours.

  • The 16:8 diet: You don’t eat for 16 hours each day and eat within an 8-hour period. For example, you skip breakfast and eat from noon to 8 p.m.

  • The Leangains method: You don’t eat for 16 hours each day and eat within an 8-hour period. You also follow some other rules, such as eating more protein and lifting weights.


How does intermittent fasting work?

Intermittent fasting works by changing how your body uses energy. When you eat, your body breaks down food into sugar, which is then used for fuel or stored as glycogen in your liver and muscles. When you don’t eat, your body uses up its glycogen stores and starts burning fat for energy. This process is called ketosis.


Intermittent fasting also affects your hormones and genes in ways that may benefit your health. For example, intermittent fasting can:

  • Lower insulin levels: Insulin is a hormone that regulates blood sugar levels. When you don’t eat, your insulin levels go down, which allows your body to access stored fat more easily.

  • Increase human growth hormone (HGH) levels: HGH is a hormone that promotes muscle growth and fat burning. When you don’t eat, your HGH levels go up, which can help you keep muscle mass and lose weight.

  • Activate autophagy: Autophagy is a process that cleans up damaged cells and recycles them into new ones. When you don’t eat, your body increases autophagy, which can help prevent diseases and slow down aging.

  • Modulate gene expression: Gene expression is the process of turning genes on or off. When you don’t eat, your body changes the expression of genes related to inflammation, stress resistance, and longevity.


What are the benefits of intermittent fasting?

Intermittent fasting can have various benefits for your health, depending on how long and how often you don’t eat. Some of the possible benefits are:

  • Weight loss: Intermittent fasting can help you lose weight by creating a calorie deficit and boosting your metabolism. Studies have shown that intermittent fasting can be as effective as calorie restriction for weight loss.

  • Improved blood sugar control: Intermittent fasting can lower blood sugar levels and improve insulin sensitivity. This can reduce the risk of type 2 diabetes and metabolic syndrome.

  • Reduced inflammation: Intermittent fasting can lower the levels of inflammatory markers in the blood. This can help prevent or treat chronic diseases such as arthritis, asthma, Alzheimer’s disease, and cancer.

  • Improved heart health: Intermittent fasting can improve several risk factors for heart disease . These include blood pressure, cholesterol levels, triglycerides levels, and oxidative stress.

  • Enhanced brain function: Intermittent fasting can protect the brain from damage and degeneration . It can also improve memory, learning, cognition, and mood.

  • Increased lifespan: Intermittent fasting can mimic the effects of calorie restriction on longevity . Animal studies have shown that intermittent fasting can extend lifespan by up to 40%.


What are the risks of intermittent fasting?

Intermittent fasting is not suitable for everyone and may have some negative effects on some people. Some of the possible risks are:

  • Hunger: Intermittent fasting can cause hunger pangs, cravings, and irritability, especially in the beginning. This can make it hard to stick to the plan and may affect your mood and productivity.

  • Fatigue: Intermittent fasting can lower your energy levels and make you feel tired, weak, and dizzy. This can affect your physical and mental performance and increase the risk of accidents and injuries.

  • Muscle loss: Intermittent fasting can cause muscle loss, especially if you don’t eat for too long or too often. This can reduce your strength, metabolism, and bone density.

  • Headaches: Intermittent fasting can trigger headaches, especially if you are prone to migraines or have low blood sugar levels. This can affect your concentration and quality of life.

  • Nutrient deficiencies: Intermittent fasting can make it harder to get enough vitamins, minerals, and other nutrients. This can lead to deficiencies and health problems, such as anemia, osteoporosis, and hair loss.


Who should not try intermittent fasting?

Intermittent fasting is not recommended for people who have certain medical conditions or special needs. These include:

  • Pregnant or breastfeeding women: Intermittent fasting can affect the amount and quality of breast milk and may harm the growth and development of the baby.

  • Children and adolescents: Intermittent fasting can interfere with the growth and development of children and teenagers and may cause eating disorders.

  • People with diabetes: Intermittent fasting can cause low or high blood sugar in people with diabetes. This can be dangerous and require medical attention.

  • People with eating disorders: Intermittent fasting can trigger or worsen eating disorders, such as anorexia, bulimia, or binge eating. This can have serious consequences for physical and mental health.

  • People with kidney stones: Intermittent fasting can increase the risk of kidney stones by increasing the concentration of urine and reducing the intake of fluids.

  • People with gout: Intermittent fasting can increase the levels of uric acid in the blood, which can cause gout attacks or worsen existing gout.

  • People with medication: Intermittent fasting can affect the absorption and effectiveness of some medications, such as blood thinners, anti-diabetic drugs, or anti-seizure drugs. This can cause adverse reactions or complications.


How to start intermittent fasting?

If you want to try intermittent fasting, you should talk to your doctor first to make sure it is safe and suitable for you. You should also follow some tips to make it easier and more effective:

  • Choose a way that fits your lifestyle and preferences. You can start with a shorter or less frequent not eating period and gradually increase it as you get used to it.

  • Drink plenty of water during your not eating period to stay hydrated and prevent dehydration. You can also drink other drinks that have no calories, such as black coffee, green tea, or herbal tea.

  • Eat balanced and nutritious meals during your eating period to get enough calories, protein, fiber, healthy fats, vitamins, minerals, and antioxidants. Avoid processed foods, added sugars, refined grains, trans fats, and alcohol.

  • Exercise regularly to boost your metabolism, burn fat, build muscle, and improve your health. However, avoid exercising too hard or too long during your not eating period as this may cause fatigue or muscle loss.

  • Listen to your body and adjust accordingly. If you feel unwell or experience any negative symptoms during intermittent fasting, stop or change your plan. You may need to shorten your not eating period, increase your calorie intake, or take a break from not eating.


Intermittent fasting is a way of eating that can have various benefits for your health. However, it also has some potential risks and is not suitable for everyone. If you want to try intermittent fasting, you should talk to your doctor first and follow some tips to make it easier and more effective. Remember that intermittent fasting is not a magic solution for weight loss or health improvement. It is only one tool that you can use along with a healthy diet and lifestyle.


Dr. Karuturi Subrahmanyam, MD, FRCP (London), FACP (USA)

Internal Medicine Specialist


Kify Hospital

Danavaipeta

Rajahmundry

Phone : 85000 23456

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