Adopting an intermittent fasting (IF) diet has been gaining traction in recent years. Historically, fasting has also been employed as a healing technique for various ailments. Hippocrates, often regarded as the father of modern medicine, once stated, “To eat when you are sick, is to feed your illness.” The ancient Greeks believed that fasting could enhance cognitive abilities. Philip Paracelsus, known as the founder of toxicology, proclaimed, “Fasting is the greatest remedy—the physician within.” Benjamin Franklin, one of the founding fathers of the United States, also praised fasting, saying, “The best of all medicines is resting and fasting.”
Traditional Caloric restriction vs Intermittent fasting
Obesity is a global, multifaceted condition characterized by an abnormal or excessive buildup of fat that poses health risks. The primary driver of obesity is an energy imbalance, where calorie intake exceeds calorie expenditure. To create the negative energy balance necessary for weight loss, many weight management programs implement a continuous daily calorie restriction of 20% to 40%. Recently, however, there has been growing interest in adjusting the timing of eating, particularly through intermittent calorie restriction or intermittent fasting (IF), as an alternative approach. IF involves refraining from consuming food and caloric beverages for a set period, followed by regular eating periods.
Intermittent fasting (IF) differs from caloric restriction (CR) in that CR involves a continuous reduction in calorie intake, leading to weight loss and health benefits, though it’s hard to maintain long-term. Intermittent fasting, on the other hand, focuses on fasting during specific time periods with little or no calorie intake, making it a popular and potentially effective alternative to CR for weight loss and improving cardio-metabolic health.
Physiological effects of Intermittent fasting
The core principle of fasting is to stimulate changes in metabolic pathways, cellular functions, and hormone secretion. Key physiological effects of fasting on health markers include improved insulin sensitivity, and reductions in blood pressure, body fat, glucose levels, atherogenic lipids, and inflammation. In animal studies, fasting has been shown to improve disease outcomes, such as cancer, type 2 diabetes, and cardiovascular disease (CVD).
In humans, fasting for 12 to 24 hours generally leads to a notable 20% reduction in serum glucose and depletes liver glycogen. During this phase, the body transitions to a ketogenic metabolic state, relying on non-liver glucose, fat-derived ketone bodies, and free fatty acids for energy. These metabolic shifts can also be triggered by carbohydrate restriction. As for the impact of intermittent fasting (IF) on weight loss, studies have shown that individuals with overweight or obesity typically experience an average weight reduction of 4% to 10% over a period of 4 to 24 weeks.
Six intermittent fasting method
- Fast for 12 hours a day: This diet involves choosing a 12-hour fasting window each day, with much of the fasting done during sleep. Fasting for 10 to 16 hours may trigger fat burning and promote weight loss. It’s a beginner-friendly plan that allows for normal daily calorie intake, making it easier to follow. For example, fasting from 7 p.m. to 7 a.m. includes the sleep period, simplifying the process.
- Fast for 16 hours a day: The 16:8 method, also known as the Leangains diet, involves fasting for 16 hours daily, with an 8-hour eating window. Men typically fast for 16 hours, while women fast for 14 hours. This approach may benefit those who didn’t see results with the 12-hour fast. Typically, people finish dinner by 8 p.m., skip breakfast, and begin eating again at noon the next day.
- Fasting for 2 days a week: The 5:2 diet, or Fast diet, involves eating normally for five days and significantly reducing calorie intake on two non-consecutive days. On fasting days, men consume about 600 calories, and women 500 calories. Fasting days are typically spread out, such as fasting on Monday and Thursday, with at least one non-fasting day in between. Research on this diet is still limited.
- Alternate day fasting: Alternate day fasting involves fasting every other day, with variations in how it’s practiced. Some people avoid solid foods entirely on fasting days, while others allow up to 500 calories. On non-fasting days, individuals typically eat freely. This method is considered an extreme form of intermittent fasting and may not be ideal for beginners or those with certain health conditions. Additionally, it can be challenging to sustain long-term.
- A weekly 24-hour fast: The Eat-Stop-Eat diet involves fasting for 24 hours once or twice a week, typically from breakfast to breakfast or lunch to lunch. During the fasting period, only water, tea, and other calorie-free drinks are allowed. On non-fasting days, people return to their normal eating habits without specific food restrictions. This approach helps reduce overall calorie intake while allowing flexibility in food choices.
- The warrior diet: The Warrior Diet is an extreme form of intermittent fasting that involves a 20-hour fasting period where only small amounts of raw fruits and vegetables are consumed. This is followed by a 4-hour eating window, typically in the evening, where one large meal is eaten. During this meal, it’s important to include vegetables, proteins, healthy fats, and some carbohydrates. While small snacks are allowed during fasting, this method can be difficult to maintain due to its strict timing and the challenge of consuming a large meal late in the day. It’s often recommended for those experienced with other intermittent fasting methods.
Is intermittent fasting safe?
Intermittent fasting is safe for many people but it’s not for everyone. Some people should steer of trying intermittent fasting:
- Children and teens under age 18
- Women who are pregnant or breastfeeding
- People with type 1 diabetes who take insulin
- Those with a history of eating disorders
What are the benefits of intermittent fasting?
Intermittent fasting offers more than just weight loss benefits; it allows your digestive system to rest while enhancing metabolism and promoting overall health.
Here are some benefits of intermittent fasting
- Losing weight
- Lower risk of diabetes
- Boost immunity
- Good for heart health
- Improve inflammation
- Enhance memory
- Prolong life
What can I eat while intermittent fasting?
During fasting, you can consume calorie-free items like water, lemon water, unsweetened tea, and black coffee. During the eating window, a regular diet is acceptable, though it’s best to avoid junk food. Instead, focus on eating wholesome, nutrient-rich foods such as whole grains, lean proteins, fruits, vegetables, and dairy products.
References:
Patterson, R. E., & Sears, D. D. (2017). Metabolic effects of intermittent fasting. Annual review of nutrition, 37(1), 371-393.
Vasim, I., Majeed, C. N., & DeBoer, M. D. (2022). Intermittent fasting and metabolic health. Nutrients, 14(3), 631.
Varady, K. A., Cienfuegos, S., Ezpeleta, M., & Gabel, K. (2022). Clinical application of intermittent fasting for weight loss: progress and future directions. Nature Reviews Endocrinology, 18(5), 309-321.
Aqsa Farooq
Ph.D Scholar, University of Agriculture Faisalabad
Visiting Lecturer, GCWUF
