Intermittent fasting is the seemingly miraculous new weight loss method, popularised by the 5:2 diet followed by Benedict Cumberbatch, George Osborne, and Philip Schofield. Adherents to the 5:2 diet practise calorie restriction for two days a week (600 kcal for men and 500 kcal for women), and eat normally for five days a week. Intermittent fasting is an umbrella term that, along with the 5:2 formula, also includes diets that involve fasting for between one and three days a week and various calorie limits (from complete abstinence from food to eating 75% of normal calorie intake on fast days). Aside from the dramatic weight loss that dieters experience, researchers have found that intermittent fasting has a range of other effects that can improve health.
Type 2 diabetes is an increasingly common disease due to worsening diets and sedentary lifestyles. In the US, 35% of adults have prediabetes (when some but not all of the symptoms of diabetes are present). 15-30% of prediabetics go on to develop diabetes within five years if no lifestyle changes are made. Intermittent fasting has been found prevent the development of diabetes, as losing around 5-7% of body weight decreases fasting glucose and insulin levels, and reduces insulin resistance. One study showed that alternate day intermittent fasting led to a 3-8% decrease in weight after eight weeks, with subjects drinking a 320-380 kcal shake on fast days. After 8-12 weeks of intermittent fasting, fasting glucose levels in prediabetic individuals dropped by 3-6%, and fasting insulin levels dropped by 20-31%. Reduction in body weight is thought to reduce insulin resistance, and thus delay or prevent type 2 diabetes; the greater the weight loss, the greater the decrease in insulin resistance. This effect was seen in both prediabetic and healthy subjects.
Intermittent fasting also benefits non-prediabetic people. It has been known since the 1930s that calorie restriction increases the lifespan of rats, and more recent studies have shown that intermittent fasting produces several effects that could also increase the lifespan of humans. There are the diabetes-reducing effects described above, as well as a reduction in oxidative damage to proteins, lipids, and DNA. The theory as to why this happens is that because energy intake is reduced, mitochondria produce fewer oxidative stress-causing free radicals, therefore there is less lifespan-reducing tissue damage.
Cardiovascular benefits of intermittent fasting include faster recovery of heart rate and blood pressure after exercise, and improved left ventricular function in overweight people. In rats, resting blood pressure is decreased; this reduces the risk of stroke and coronary artery disease, as hypertension is major risk factor for both. Rats on intermittent fasting diets have better outcomes following induced myocardial infarction too, although there is limited research in this area. The rats were found to have less oxidative damage and inflammation in the heart following the infarction.
Neuroprotective effects of intermittent fasting have been seen in rats, as fasting causes mild stress to brain cells, which causes the cells to adapt to resist more severe stress. Levels of BDNF, a protein which supports survival and growth of neurons, are higher in rats on an intermittent fasting diet, as are levels of stress resistance proteins. BDNF is linked to resistance to stroke, and rats on fasting diets who had been subjected to induced strokes showed less ischaemic brain damage than rats on normal diets.
While the cardiovascular and cerebral benefits of intermittent fasting have mainly been recorded in rats, it is likely that similar effects occur in humans. Intermittent fasting certainly decreases the risk of diabetes in humans, and minor benefits to cardiovascular health have also been seen in humans. As the popularity of intermittent fasting diets increases, more research into the effects of fasting on health is likely to be performed. For now, intermittent fasting is an effective way of losing weight. Hopefully it’s also an effective way of protecting yourself from disease.
Mattson MP, & Wan R (2005). Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems. The Journal of nutritional biochemistry, 16 (3), 129-37 PMID: 15741046
Barnosky AR, Hoddy KK, Unterman TG, & Varady KA (2014). Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational research : the journal of laboratory and clinical medicine, 164 (4), 302-11 PMID: 24993615