- Understanding the science behind intermittent fasting
In recent years, intermittent fasting has emerged as a popular health and nutrition trend, particularly among people seeking to lose weight and manage diabetes. In Sri Lanka, where obesity, type 2 diabetes, hypertension and cardiovascular diseases are growing public health concerns, interest in this eating pattern has increased.
According to the World Health Organization (WHO), non-communicable diseases (NCDs) account for approximately 83% of all deaths in Sri Lanka. Unhealthy diets, physical inactivity and rising obesity rates highlight the need for practical and sustainable lifestyle interventions.
Unlike conventional diets that focus on what people eat, intermittent fasting regulates when they eat. Supporters claim it can promote weight loss, improve blood sugar control and enhance metabolic health. However, its effectiveness, safety and suitability vary among individuals. Understanding the science behind fasting can help determine whether it is a useful approach to better health.
What is intermittent fasting?
Intermittent fasting (IF) alternates between periods of eating and fasting without necessarily restricting particular food groups. Common approaches include the 16:8 method, in which food is consumed within an eight-hour window followed by 16 hours of fasting, and the 5:2 method, which involves eating normally for five days and significantly reducing calorie intake on two non-consecutive days.
Alternate-day fasting involves alternating between normal eating and fasting or very low-calorie days, while time-restricted eating limits food consumption to a specific daily period, such as 10 or 12 hours.
Although often considered a modern trend, fasting has long been practised for religious, cultural and spiritual reasons, including in Buddhism, Hinduism, Islam and Christianity.
What happens inside the body during fasting?
After a meal, carbohydrates are broken down into glucose, the body's primary energy source. Insulin, produced by the pancreas, helps transport glucose into cells for immediate use or storage.
During fasting, the body gradually uses its stored energy. After approximately 10–12 hours without food, glycogen stores, particularly those in the liver, begin to decline. As glucose availability decreases, the body increasingly breaks down stored fat into fatty acids for energy. During longer fasting periods, the liver converts fatty acids into ketones, which can supply energy to the brain and other organs.
This ability to switch between glucose and fat as energy sources is known as metabolic flexibility. It is one of the mechanisms researchers are investigating in relation to the potential health benefits of intermittent fasting.
Potential health benefits
Weight management: Intermittent fasting may help reduce body weight and body fat by limiting opportunities to eat and lowering overall calorie intake. Some studies have reported reductions in waist circumference and improvements in body composition. A weight reduction of even 5–10% can help improve blood pressure, cholesterol levels and blood sugar control, reducing the risk of several chronic diseases.
Blood sugar control: Research suggests that intermittent fasting may improve insulin sensitivity, reduce insulin resistance and support better blood glucose regulation. These effects may benefit people with prediabetes or metabolic syndrome, although individual responses vary.
Cardiovascular health: Some studies have associated intermittent fasting with improvements in blood pressure, LDL (bad) cholesterol, triglycerides and inflammation. Such changes may contribute to better cardiovascular health, but fasting should not replace prescribed treatment or other established preventive measures.
Cellular repair: Another area of research is autophagy, a natural process through which cells break down and recycle damaged proteins and cellular components. Scientists are investigating whether fasting-related changes in autophagy could support cellular health and healthy ageing. However, much of the evidence comes from animal studies, and the implications for humans remain under investigation.
Brain health: Emerging research is examining whether intermittent fasting may influence memory, cognitive function and inflammation in the brain. Its potential role in reducing the risk of neurodegenerative conditions, including Alzheimer's disease, requires further investigation.
Why is it relevant to Sri Lanka?
The International Diabetes Federation's Diabetes Atlas (2025) estimates that approximately one in every 10 adults in Sri Lanka is living with diabetes, while many others have prediabetes and may remain undiagnosed.
Rice is a staple food in the country. However, excessive portions of polished white rice, frequent snacking and high consumption of refined carbohydrates can contribute to unhealthy eating patterns. Combined with sedentary lifestyles and limited physical activity, these habits can increase the risk of obesity and metabolic diseases.
Intermittent fasting may help some individuals manage their calorie intake and improve blood glucose regulation. It also requires no specialised foods or expensive supplements, potentially making it an affordable option. Nevertheless, fasting alone cannot compensate for an unbalanced diet or an inactive lifestyle.
Food quality remains important
A common misconception is that people can eat anything they want during their eating window. In reality, food quality remains essential. Consuming excessive amounts of fried foods, sugary drinks, fast food and processed snacks can undermine the potential benefits of fasting.
A balanced diet should include nutritious carbohydrate sources such as red or brown rice and whole grains, alongside vegetables, fruits and adequate protein from fish, chicken, eggs, legumes and lentils. Nuts, seeds and healthy fats can also form part of a balanced diet, with coconut consumed in moderation.
Combining intermittent fasting with nutrient-rich meals is more likely to support overall health than focusing exclusively on meal timing.
Risks and practical considerations
Intermittent fasting is not suitable for everyone. People with diabetes who use insulin or blood glucose-lowering medication should seek medical advice before attempting it because fasting may cause dangerously low blood sugar. Pregnant and breastfeeding women, children and adolescents, underweight individuals, frail older adults and people with eating disorders should avoid fasting or seek appropriate professional guidance.
Initial side effects may include hunger, headaches, dizziness, fatigue, irritability and difficulty concentrating. These symptoms may diminish as the body adjusts, but persistent or severe symptoms should not be ignored.
In Sri Lanka, maintaining a fasting schedule may also be difficult because of late-night dinners, work commitments, family meal times and social events. Rather than adopting an extreme schedule, some people may find it more practical to avoid late-night snacking, reduce unnecessary snacks between meals, maintain consistent meal times and gradually extend the overnight fasting period to 12–14 hours.
Staying hydrated and consuming adequate nutrients are essential. Anyone with an underlying health condition should consult a healthcare professional before making significant changes to their eating pattern.
Is intermittent fasting worth trying?
Scientific evidence suggests that intermittent fasting can help some people manage body weight and improve aspects of metabolic health when practised appropriately. However, it is not a miracle cure, and its benefits may not be greater than those achieved through other sustainable approaches to healthy eating and calorie control.
Long-term health depends on several factors, including a balanced diet, regular physical activity, adequate sleep, stress management and avoiding smoking and excessive alcohol consumption.
For people considering intermittent fasting, a gradual approach, attention to food quality and awareness of individual health needs are essential. In Sri Lanka, combining appropriate meal timing with healthier eating habits and regular physical activity may offer a practical and affordable way to support long-term health. Ultimately, sustainable lifestyle changes remain central to preventing obesity, diabetes and cardiovascular disease.
The writer is reading for an MSc in Human Nutrition, Wayamba University
--------------------
The views and opinions expressed in this column are those of the writer, and do not necessarily reflect those of this publication