Fast-track to fitness: do fasting diets really work?

    18 February 2016

    Coldplay singer Chris Martin says fasting for one day a week makes him more creative. Chancellor George Osborne skinnied down by scrapping meals twice a week on the 5:2 diet. And in Germany last summer author Jeanette Winterson felt a ‘profound sense of wellbeing and peace of mind’ when she went the whole hog with an 11-day fast. But while feeling positive about your general health and weight is one thing, the wider interest among medics is whether fasting and ultra-low-calorie diets can be used to reverse type 2 diabetes and other expensive-to-treat Western diseases. Here’s the current evidence…


    If you don’t eat you will lose weight, obviously. But as all crash-dieters discover, constant hunger leaves you feeling weak and a strict 24/7 regime cannot be maintained for long. One alternative is intermittent fasting (IF), of which the best-known method is the 5:2 Diet, devised by BBC science presenter Dr Michael Mosley in 2012. This involves ‘fasting’ on just 500–600 calories for two days each week while eating normally during the remaining five. It’s a simple system that works well for some people, and is supported by specialist doctors. According to a 2014 report in the International Journal of Obesity: ‘Intermittent fasting or alternate day fasting may be an option for achieving weight loss and maintenance.’

    One of the most common myths about IF is that it slows down the body’s metabolism. But Dr Mosley, who co-authored The Fast Diet (Short Books) with journalist Mimi Spencer, says: ‘The initial response of your body to a reduction in calories is to increase your metabolic rate. This is because in our hunter-gatherer past, survival in times of food shortage would have depended on our becoming more active, going out to hunt and look for food.’


    US scientists have established a connection between fasting and fertility in older women. In two 2009 studies, teams from Harvard Medical School and the Fred Hutchinson Cancer Research Centre in Seattle found that a restricted diet could offset the effect of ageing on egg quality and quantity. However, both studies were carried out on mice, and so far there has been little in the way of research on humans. In a 2014 review published in the journal Maturitas, scientists from the University of Colorado warned that no firm conclusions should be drawn.

    In cases of anorexia, extreme calorie reduction can lead to infertility. But while a cohort study of Dutch women who lived on 500 calories a day under Nazi occupation during the second world war showed they were more likely to have irregular menstrual cycles, this did not result in reduced fertility or, ultimately, the size of their families.


    Can fasting boost your health so much that you live longer? Professor Valter Longo of the University of Southern California Longevity Institute, believes so. In 2014 his team reported that fasting for as little as three days can regenerate the entire immune system, even in the elderly. They suggest that starving forces the body to make more new white blood cells, which fight off infection. The professor adds: ‘Strict fasting is hard for people to stick to and it can also be dangerous, so we developed a complex diet that triggers the same effects in the body.’

    On day one you eat 10 per cent protein, 56 per cent fat and 34 per cent carbohydrate (1,090 calories total). On days two to five you eat in nine per cent protein, 44 per cent fat and 47 per cent carbohydrate (725 calories).

    Professor Longo thinks most people would need to do this only two or three times a year to get results. I tried out an early prototype last year and lost five pounds that stayed off till Christmas. After a second five-day fast in January, I lost seven pounds and an inch off my waist. Classed as a Fasting Mimicking and Enhancing Diet, this will be sold over the counter as ProLon this year and will cost about £150. More information at


    Could fasting give you fewer wrinkles? A 2007 review in the American Journal of Clinical Nutrition said it could to reduce ‘oxidative damage’ to lipids, protein and DNA. Perhaps the key is to fast safely, which means following a plan which has the right micronutrients. Madal Bal Natural Tree Syrup is one of the key ingredients of the Lemon Detox, a five- or seven-day plan in which meals are replaced with between seven and ten glasses of water, mixed with the syrup, lemon juice and cayenne pepper. GP Dr Sarah Brewer says: ‘It can cleanse your body from the inside out.’ More information:


    In Bodensee, south-west Germany, is a clinic that specializes in therapeutic fasting. It was set up by Dr Otto Buchinger, whose own rheumatic fever was cured by fasting in the 1920s. Today, residential programmes at the Buchinger Wilhelmi clinic treat all forms of arthritis and soft-tissue rheumatism.

    But scientific evidence of the benefits is not quite there. According to a review in journal Bandolier: ‘There is preliminary evidence (no more than that) that fasting and a vegetarian diet may improve biochemistry and symptoms.’


    The British Medical Journal says one in three UK adults have pre–diabetes (blood sugar levels abnormally high but not in the diabetic range). And by 2025, five million of us will have diabetes. But there is clear evidence that fasting helps. Last October a clinical trial funded by Diabetes UK found that living on 600 calories a day for two months could reverse established diabetes. The study leader, Professor Roy Taylor of Newcastle University and Newcastle upon Tyne Hospitals NHS Foundation Trust, says: ‘It has long been believed that someone with type 2 will always have the disease, and that it will steadily get worse. We have shown that we can reverse the condition.’

    Dr Michael Mosley, who was pre-diabetic before devising the 5:2 diet, has a new book, The 8-Week Blood Sugar Diet: Lose Weight Fast and Reprogramme Your Body (Short Books). It restricts you to 800 calories a day for two months.


    Preliminary human studies of the impact of fasting on chemotherapy has led Professor Longo’s team at the USC Longevity Institute to develop Chemolieve, a four-day Fasting Mimicking and Enhancing Diet that has been effective in reducing side-effects. Followed for three days before and one day after a chemotherapy session, it protects normal cells while sensitising cancerous tissues ready for the treatment.