Intermittent fasting is a dietary pattern which has grown in popularity due its numerous reported health benefits. Fasting means abstaining from food and or liquids for a period of time. There are many different ways in which intermittent fasting is undertaken, but they are all focussed on choosing a regular pattern of eating and fasting. Read on to find out more about the benefits of intermittent fasting, the various regimes and tips to get started.
Intermittent fasting is a regime which focuses on when you eat as opposed to what you eat. There are several ways to carry out intermittent fasting but the basic principle, of cycling between periods of fasting and eating, remains the same. It can involve a daily or weekly regimen and can be tailored to your lifestyle or goals.
It should be emphasised that during eating periods, a healthy, varied diet should be maintained. During fasting periods, it is important to drink water and stay hydrated, often zero calorie drinks such as black coffee and tea are permitted. Before undertaking a fasting regime be sure to consult your doctor to ensure it is safe for you.
Examples of common intermittent fasting regimes include:
16/8 method: This involves eating during an eight-hour time window and fasting for the remaining 16.
5:2 method: This is a well-known approach which involves eating normally on five days of the week week and restricting calories to 500-600 (a quarter of your daily requirement) on the remaining two non-consecutive days.
Alternate day fasting: As the name suggests, this regime involves fasting on alternate days. This can be done for a full 24 hours or, more commonly, with a modified approach which allows 500-600 calorie intake on alternate days.
Eat-stop-eat: This approach is characterised by one or two non-consecutive fasting days per week. In this regime the fasting period is for a full 24 hours.
Over recent years there has been an increase in research carried out on intermittent fasting. It’s been shown to have an array of health benefits. While more research is required to assess long-term outcomes, initial findings are promising. Read on to find out more.
Intermittent fasting along with calorie restriction has shown to be an effective method for weight loss. A systematic review and meta-analysis of randomized controlled trials looking at the effectiveness of intermittent fasting for weight loss in those with obesity, found similar results to traditional calorie restriction.
Intermittent fasting has also been shown to improve body composition, reducing visceral fat and total body fat. One study found that intermittent fasting with protein pacing resulted in reduced visceral fat, which reduces the risk of metabolic syndrome and chronic disease.
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Metabolic health refers to how the body processes substances such as fat and sugar. When food such as carbohydrates are broken down, excess glucose is stored as glycogen in the liver. Intermittent fasting results in reduced glycogen depletion and a metabolic switch. This refers to a shift of using fatty acids and ketones for energy as opposed to glucose. This improves metabolic health and promotes weight loss.
Intermittent fasting has also been shown to improve insulin sensitivity. Insulin insensitivity and resistance are important mechanisms leading to type 2 diabetes. Insulin resistance also promotes atherosclerosis and subsequently vascular disease.
A systematic review and meta-analysis concluded that intermittent fasting has therapeutic effects on glucose and lipid metabolism and significantly improves insulin resistance in those with metabolic syndrome. Additionally, intermittent fasting can improve glycaemic control and promote weight loss in those with type 2 diabetes.
A systematic review and meta-analysis found that intermittent fasting also improves other cardiometabolic risk factors such as circulating total cholesterol, low density lipoprotein (LDL- bad cholesterol) and triglycerides. Dyslipidemia, along with obesity, are significant risk factors for coronary heart disease, a leading cause of mortality in the US.
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On a molecular level, intermittent fasting optimizes cellular metabolism and leads to increased stress resistance. Oxidative free radicals are produced as by-products of oxidative metabolism. Free radicals have the potential to cause genomic mutations and disease. During fasting periods metabolism and protein synthesis is reduced and thereby the production of free radicals.
Fasting also puts cells under stress. This stress response enhances antioxidant mechanisms, autophagy, down regulation of inflammation and DNA repair. When eating and glucose supply is resumed, the cells regain homeostasis and become more stress resistant. Through these mechanisms it is thought that intermittent fasting can slow ageing and disease processes.
A review published in the New England Journal of Medicine summarizes evidence on the effect of caloric restriction and intermittent fasting on ageing, concluding that reduced food intake robustly increases lifespan. However, further clinical trials to assess long-term outcomes on humans are required.
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The importance of diet for brain health and cognitive function is increasingly recognized. The physiological adaptions associated with intermittent fasting such as a reduction in oxidative stress, inflammation and improved vascular health, have implications on the pathological mechanisms of neurodegenerative diseases such as Alzheimer’s and help ameliorate brain ageing.
Animal studies have shown that brain cells maintained on intermittent fasting show improved function and adaptive response to traumatic, metabolic and oxidative stress. There is also pre-clinical evidence which shows that alternate day fasting can delay the onset and progression of Alzheimer’s and Parkinsons disease in animal models. However, data from long-term controlled trials is lacking and further research is required.
Animal studies have also shown that intermittent fasting enhances cognition in multiple domains. A three-year progressive study looking at the effects of intermittent fasting on cognitive function in older adults with mild cognitive impairment, found that those who practised intermittent fasting regularly had improved cognitive scores and better cognitive function at 36 months follow up.
When selecting a fasting regime, it is important to choose a method which fits in with your lifestyle and schedule. Consider your working hours and habits. It’s also important to identify and define a clear personal goal. By having a clear goal and choosing a regime that fits in with your life you will be more likely to stick to it.
Tips For Beginners:
It is important that during eating windows a nutritious and balanced diet is maintained. Eat a variety of fruit and vegetables as well as high-quality protein and wholegrains. These foods will make you feel fuller for longer.
It is important to stay hydrated, especially during fasting periods, because dehydration can lead to fatigue and headaches. Drink to thirst and listen to your body. Zero calorie drinks such as black coffee and tea are allowed.
When you start fasting, you may experience hunger pains and cravings. Avoiding eating sugary food before a fast and ensuring your diet is high in protein and fibre can help with this. Find distractions and make sure you drink plenty of water. Some find that chewing sugar free gum is helpful. Hunger pains and cravings should reduce as your body becomes accustomed to fasting.
Another difficulty with fasting is the feeling of fatigue or low energy levels. Take regular walks and stay hydrated. This should also only be a short-term issue, research has shown that fasting can improve fatigue in healthy subjects.
Intermittent fasting is not for everyone and those with health conditions and older adults should consult their doctor prior to commencing any fasting regime. This is particularly true for those with type 1 diabetes or those with a history of disordered eating. Fasting is also not recommended for those who are pregnant or breastfeeding.
Fasting can increase your risk of not getting enough nutrients. This is why it is important to maintain a varied, healthy diet during eating periods and consult your doctor or a nutritionist prior to starting.
It can also lead to altered mood, sleep disturbance and irritability. It is important to listen to your body and tailor an approach which works for you.
Research in both pre-clinical and clinical settings have shown that intermittent fasting has a range of health benefits in the context of obesity, diabetes mellitus, cardiovascular disease and neurological disorders.
Clinical studies are mainly limited by short term outcomes and further research is required to assess the long-term benefits. An important factor to consider is whether humans can maintain intermittent fasting over years and sustain the same benefits seen in animal models. Nevertheless, initial findings are promising.
It is important to make empowered and positive choices regarding your lifestyle to promote health and wellbeing. This includes intermittent fasting if it is the right choice for you. Be sure to consult a healthcare professional prior to undertaking a regime to ensure it is safe to do so and take note of our tips to get started.
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