Intermittent fasting – also known as “time-restricted feeding” or “food timing” – is an umbrella term for a dietary regime that involves restricting eating to set times. The best known of these feasting-and-fasting programs are the 5:2 diet, also known as “The Fast Diet” (you eat normally for five days a week and fast on the other two days) and the 16:8 diet (you fast for 16 hours a day and eat within an eight-hour window). There’s also the Alternate Day Fasting Diet (you eat 500 calories every second day, and as you normally would on the other days), and numerous other variations on the “you are when you eat” theme.
The basic idea is that by fasting for periods of time you give your body a break and forces it to dip into its stored fat reserves. While there is good evidence that the intermittent fasting diets help people lose weight, it’s wise to keep things in perspective. You might have heard, for instance, that intermittent fasting has been shown to extend lifespan and to improve age-related diseases – it has, in rodents not people.
In fact, there’s little evidence to show that a fasting diet is any better than a conventional calorie-restriction diet. The largest study to compare the two was published this year in the American Journal of Clinical Nutrition. The researchers recruited 150 overweight and obese participants, with one third following a conventional calorie-restriction diet that reduced daily calorie intake by 20 percent; a third following the 5:2 dietary plan reduced calorie intake by 20 percent over the whole week; and a control group, which followed no specific diet plan but was advised, like all other participants, to eat a well-balanced diet.
Both groups following the dietary regimes showed health improvements; they lost weight and reduced unhealthy body fat. Every kilo counted; those who reduced their body weight by only five percent lost about 20 percent of dangerous visceral fat and more than a third of fat in the liver – and it didn’t matter which diet they were on. The researchers didn’t find any difference between the two methods, or their effect on the metabolic values, biomarkers and gene activities associated with disease that were being investigated.
There’s little evidence to show that a fasting diet is any better than a conventional calorie-restriction diet.
Numerous studies have shown that intermittent fasting will reduce your risk of type 2 diabetes – but so will any diet that results in weight loss. Losing a substantial amount of weight can even reverse the disease, as shown by Roy Taylor and his team at the University of Newcastle and their landmark trial published in the Lancet in 2017. The study included 298 adults aged 20-65 years who’d been diagnosed with type 2 diabetes in the previous six years. After being put on a very low-calorie diet (less than 850 calories a day) for three to five months, nearly half of the participants that followed the weight management program could stop taking medication after a year, compared to only 4 percent in the control group.