Last week, I examined two hot trends in the world of nutrition with Dr Stuart Phillips of McMaster University. He is the director of the Centre of Nutrition, Exercise and Health Research as well as the Physical Activity Centre of Excellence at the university and provided insight along with his expert opinion about the carnivore diet and the new diet for the planet. This week, I've asked him about intermittent fasting (IF), which has gone from being an “alternative” diet to something that has made it into pop culture and the mainstream media in a big way.
Fasting (abstaining from eating or drinking for certain periods of time), historically, has been part of many religions around the world. Hindus, Muslims, Jews, Buddhists and Christians all fast at different times to express devotion, sacrifice and discipline. Intermittent fasting, on the other hand, is an umbrella term for eating plans associated with food restriction aimed, primarily at weight loss. While IF has been around for centuries, it has become a “hot” trend in the last 10 years, driven by bestselling books and documentaries citing current research around caloric restriction and longevity in animals.
More recently, interest in IF has been great enough to spur an industry of diet coaching and supplements for “fasters”. There are two main types of intermittent fasting; whole day and time-restricted.
Whole day fasting involves not eating for an entire day or 2 to 4 days per week. A version of this is called 5:2 where one would eat normally five days per week and abstain from food for two days. A variation of this would be to alternate between days of “eating” and days where no food is consumed. The most popular version of IF involves the idea of eating only during specific hours (For example, eating only between 1 pm and 8 p.m). This allows participants to eat anything they want, as long as it falls between those hours.
For those reluctant to give up specific foods, it means that they can indulge without restriction as long as the indulgence happens during prescribed “eating” hours.
When I asked Phillips about this, he conceded that eating in this way will likely reduce total calories consumed over any given week and result in weight loss. Being able to eat “whatever you want” during feeding times, however, might be problematic as dieters develop a false sense of comfort eating less-than-healthy foods without thinking about nutritional value. Phillips explained that much of the interest in IF has come about as a result of lab experiments that showed that animals, deprived of calories and fed only during specified eating windows, lived longer lives and had a delayed onset of age-related disorders.
While this research goes back decades, there is not enough evidence at this time to suggest the same results would be achieved in humans. According to the National Institute on Aging, it isn't clear exactly why the practice of restricting calories and fasting brings about the results that it does, making it difficult to recommend as an approach for people in general. Although Phillips is a renowned scientist, cited in research papers the world over, he is also a realist. Although he believes there can be benefit to fasting for some people resulting in weight loss and improved body chemistry, it is probably best seen as an “intervention” and not a lifestyle. The overwhelming majority of people will simply be unable to follow a plan where they must continually override the drive to eat, increasing their risk of developing an eating disorder.
It is more important to develop an eating style that can be sustained, and modified over a lifetime. Having said that, I'm sure we'll hear from lots of people who regularly practice IF and have no issues with compliance. The same can be said, in Phillips' view, of every/any diet.