Doctor's Review: Medicine on the Move

November 21, 2017

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A new book promoting intermittent fasting shot to the top of the bestseller lists in January 2013

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Playing fast with the facts?

It’s often called the 5:2, or Intermittent Fasting (IF) diet. Basically, you eat next to no calories for one or two days a week and normally the rest of the time. It owes its currently popularity to Michael J. Mosley, whose February 2013 international bestseller The Fast Diet re-ignited interest.

As with so many other diets, it seems to be a rehash of some old ideas. Other books, such as 2004’s French Women Don’t Get Fat, and even some dieticians I know, have promoted similar ideas. Mosley’s use of sources and bold claims have raised a few eyebrows. So is there any supporting evidence, or is this approach simply one that’s starved of hard science?

Weight loss

One review article published in 2011 looked at studies that compared a diet in which daily caloric intake was cut back between 15 and 60 percent, with a second diet that alternated eating freely one day and a complete or partial fast the next. Both groups lost similar amounts of body fat, but those who fasted intermittently lost less muscle mass. 1

Heart disease

A 2012 Nutrition Journal study compared two groups of 27 obese women following an IF diet over a 10-week period; the only difference was that one group consumed only liquids. The results showed the liquid diet group lost the most weight, while both groups lost about the same amount of fat mass. Visceral fat, total cholesterol and LDL cholesterol was lower in both groups. Only the liquid group though saw their LDL particle size increased, and heart rate, glucose, insulin and homocysteine decreased.2

Glucose intolerance

Here the results are much less clear. On the one hand, a May 2011 study compared intermittent fasting with a more constant calorie-reduced diet. Both groups lost weight, but the fasting group had greater reductions in fasting insulin resistance and insulin resistance than the CER group.3

In contrast, another group of researchers found that intermittent feeding did not decrease abdominal fat and in the long term promoted glucose intolerance and oxidative insulin receptor inactivation.4

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