These days you'd be hard pressed to meet someone who's hasn't tried out some form of restricted eating, from vegan or gluten-free diets to paleo or ketogenic ones — whether they're trying to avoid processed foods, gain more muscle, or otherwise get their body to a place where it feels and functions better from the inside out. Lately, one way of eating is particularly on-the-rise and celebrities like Beyoncé and J.Lo among its rumored fans. But are the supposed intermittent fasting benefits actually legitimate? And is it sustainable for your lifestyle? Medical experts and nutritionists can help you answer both questions.
First things first: What exactly is intermittent fasting? As the name implies, the cornerstone of this eating method involved extended periods of caloric restriction, which makes it totally different than something like keto. And as Los Angeles-based holistic nutrition coach Chelsea Gross explains, it can be done a few ways. "The most common type of intermittent fasting is time-restricted eating, usually ranging from 12 to 16 hours (although some people go 24-36 hours, too) when you are not consuming calories," she says. "For example, if you finish eating at 8 p.m. at night, and you are fasting for 12 hours (which includes sleep time) you wouldn’t eat again the next morning until 8 a.m. Or if you finish eating at 8 p.m. at night, and you are fasting for 16 hours, you wouldn’t eat again until 12 p.m., the following day."
Additionally, some people who practice IF divide their fasting periods a bit differently. "There is another method called 5:2 where you eat normally for five days of the week, and have a reduced-calorie intake for the other two days," shares Gross. Often, those trying this method eat between 500 and 600 calories on the restricted days.
Sound a bit extreme? Well, it can be, but according to Dr. Yelena Deshko, a naturopathic doctor and founder of Toronto's Timeless Health Clinic, this major fitness and wellness trend has actually been in practice for years — and there's absolutely a reason for that. "Intermittent fasting benefits were first noted as early as 1945, when a scientific trial showed that it helped mice live longer," she explains. "[IF] has been shown to benefit a wide range of age-related disorders including diabetes, cardiovascular disease, cancers, and neurological disorders such as Alzheimer's disease, Parkinson's disease, and stroke. [It] has also been shown to improve mood and increase alertness and mental acuity."
And Gross adds that some people practice IF as a way to improve their digestive system. "Giving your body a break from constant digestion can help with bloating, discomfort, eliminations, and [other gut-affected] functions [...] like sleep, energy, and mood," she explains. Additionally, many fitness enthusiasts use IF to amp up their workouts, which the nutrition expert chalks up to the fact that it can potentially promote the secretion of human growth hormone, which she says can help with muscle mass and metabolism.
But both professionals agree that IF isn't for everyone. Firstly, it's absolutely something to consult your doctor about, particularly if you have health issues or taking medication. "Intermittent fasting can dramatically affect blood sugar levels, therefore those that suffer from hypoglycemia or diabetes best not to attempt this eating plan without medical supervision," explains Dr. Deshko. "This eating plan is also not suitable if you are pregnant or breastfeeding due to the caloric restriction."
Additionally, since intermittent fasting limits your window of eating, it's important to keep up a healthy caloric intake, and to make sure you're still getting all the beneficial vitamins, minerals, and nutrients with what you're consuming. And speaking of restriction, another important thing to note about IF (or any type of restricted eating plan) is that it can be especially triggering and slippery for anyone with a tendency toward disordered eating.
Gross, who specializes in helping women develop a better body image by encouraging healthy relationships with food, notes that it can be dangerous to look at intermittent fasting as primarily a means for weight loss. "It can be a way to control food that isn’t so obviously disordered, which can therefore fuel disordered eating," she says. "When practicing IF we have to be flexible enough to stray from the 'rules' if we’re hungry outside our feeding window. This gives us the room and space to have a healthy and balanced relationship with food, instead of being too closely regimented and structured that you go against your body’s needs and cravings."
That said, Gross believes the best candidate for IF is someone who has a healthy relationship with food and their body, and who — instead of looking at it as a weight loss method — is looking to improve their overall internal health. "Since food is so abundant to us, and many people are snacking multiple times a day, giving your body and digestion a longer break in between meals can be a really good thing," she explains. "That’s why I would suggest IF to a client who struggles with digestive issues like bloating, diarrhea, or constipation to see if this helps. Or someone who has issues with energy and fatigue, mood, or concentration, and focus." The nutrition expert also adds that those struggling with hormonal imbalances might also be a good candidate for IF, as it may trigger the body's natural ability to correct these imbalances.
All that said, the bottom line is to be mindful and safe when trying out intermittent fasting — both by checking in with your primary doctor, as well as being in tune with your body's needs, including when it's telling you to slow down or stop. As Gross says, "Be sure to still listen to your body and not get overwhelmed or obsessed with the rules."