Our circadian rhythm is essentially the body’s internal clock that lets us know when it’s time to sleep and wake (other animals, plants and even bacteria employ a similar process). Evolution has synced our metabolism with our biological clock to encourage us to eat during daylight hours and sleep during night—partly why nighttime snacking leads to an increased risk of obesity and diabetes.
Circadian rhythm fasting simply involves adhering to a strict eating regime whereby food is consumed during a waking-hours-window, say 8am-4pm, with absolutely nothing eaten after the cut-off time. As well as weight loss, studies have shown such prolonged nightly fasts to reduce cancer risk, boost metabolism, and lower blood pressure. While 16-hour cleansing periods may sound a little too stressful for most people’s stomachs, Amy Shapiro, founder of Real Nutrition NYC, says that it’s simply a case of getting used to it until it becomes as routine as cleaning your teeth, and that after a couple of weeks you realise “a lot of what your body wants is simply out of habit”.
Enzymes in our gut are responsible for breaking down consumed food that is then absorbed into the bloodstream. Carbohydrates are fast converted into sugar which serves as energy, but any of this fuel that isn’t used is stored in our fat cells. Insulin is vital in ensuring the sugar reaches cells, and so between meals—so long as there’s no snacking—insulin levels drop, allowing fat cells to release that excess sugar as energy. This leads to weight loss.
When embarking on circadian rhythm fasting, there will be hunger pangs, but those initial bursts will feel like “healthy hunger” says Satchin Panda, circadian rhythm expert and author of The Circadian Code, who recommends you allow yourself a week to adjust to such a new routine. “It’s like having a house full of stuff,” he tells Vogue. “Unless you get rid of it, you shouldn’t go shopping.” By the time you wake up, your body will be literally burning fat, which is then converted to ketone, fuel for our brains and hearts. Panda says it’s not about depriving ourselves of meals or cutting calories, but just picking your hunger-busting battles more wisely to close “the window so you’re not eating during the time when you don’t actually need fuel”.
Circadian rhythm fasting is a form of ‘intermittent fasting’, a catch-all expression for any method that severely limits—or cuts—calorie intake over set time frames. The most well-known is probably the ‘5:2 diet’ that sees participants eat normally for five days of the week, and for the other two reduce their calorie intake to around 500. Rick Hay, nutritionist and author of The Anti Ageing Food & Fitness Plan especially recommends the 5:2 for those in their 40s who have exhausted other diets and can’t be fussed with counting calories. He also points to its benefits in helping to reduce insulin levels while improving both cardiovascular and cholesterol health.
“IF makes intuitive sense,” writes Monique Tello, MD, MPH, in the Harvard Health Blog. “The entire idea of IF is to allow the insulin levels to go down far enough for long enough that we burn off our fat.”
Everyone can perform magic, everyone can reach his goals, if he is able to think, if he is able to wait, if he is able to fast.”
Hermann Hesse, Siddhartha
Just last August medical journal Cell Metabolism published the results of the largest ever study of the effects of various types of fasting such as continuous calorie restriction, alternate-day fasting (ADF) and intermittent fasting—and they were very promising. Those taking part in fasts were found to have, among others, lower cholesterol; lower levels of sICAM-1, a marker linked to age-associated disease and inflammation; continuous up-regulation of ketone bodies—even on non-fasting days—which promotes “health in various contexts’; and less lipotoxic android trunk fat mass, commonly knows as dreaded ‘belly fat’.
Researcher Thomas Pieber, head of endocrinology at the Medical University of Graz, admits that they’re not quite sure why fasting appears more efficient than old-fashioned dieting, but his colleague, Professor Fran Madeo, says it might be down to evolutionary biology: “Our physiology is familiar with periods of starvation followed by food excesses. It might also be that continuous low-calorie intake hinders the induction of the age-protective autophagy program, which is switched on during fasting breaks.”
It is that all-pervasive fear of hunger that forces the failure of so many diets, says Amy Shapiro, which is why we need to fast smart, because if “you eat the right foods, you don’t feel that type of uncomfortable, angry hangry kind of hunger”.
It is recommended to seek medical advice before embarking on any kind of fasting lifestyle—especially for those with pre-existing medical conditions.
