Intermittent Fasting: What You Need to Know
So often we’re seeking out what’s innovative, what’s cutting edge – especially when it comes to wellness. Yet much of what we know to be effective is rooted in ancient practices that have been around for thousands of years and are now being validated by science.
Intermittent fasting is one of these practices that has received renewed attention for its potential benefit for our bodies and our brains.
It’s something that I’ve personally found beneficial, landing on a modified version of intermittent fasting that works for me. Like many things in the wellness sphere, it’s also remarkably divisive, attracting its share of vocal critics as well as advocates.
Intermittent fasting is such a complex topic, far more than what can fit into this column. I’ll touch on the key elements here, and if you’re looking for more of the scientific background, I have a full podcast dedicated to intermittent fasting that just went live this month. We go deeper into the research and peer-reviewed studies, also how to create your own intermittent fasting approach that works for you, and more resources for getting started.
What is Intermittent Fasting?
Unlike traditional ‘dieting’ or calorie control, which typically focuses solely on the number of calories per day, intermittent fasting is centered on the specific timeframes of eating or fasting throughout the day. It’s all about the window of time that we eat, not how much we eat.
(Side note: When discussing intermittent fasting, the window of time that we eat is typically called the eating window, or even the ‘feeding’ window – but I much prefer to refer to it as the ‘fueling’ window).
Intermittent fasting is incredibly individualized; there are countless approaches that can be effective. Here’s a summary of two of the most common, outside of those for religious or spiritual purposes:
Time-restricted fasting (my preference): With this approach, our fueling window is limited each to a specific duration of time each day. This can be as strict or as loose as we choose, from 12:12 (12 hours fasting with a 12-hour fueling window), 14:10, 18:6, or even 20:4, where 20 hours are spent fasting, with a fueling window of 4 hours (I personally find this extremely regimented, and not something I recommend).
Alternate-day fasting: Fasting days alternate with those of unrestricted or otherwise ‘normal’ eating in various patterns. The 5:2 approach is one of the more common, with two non-consecutive days of fasting or a very low-calorie intake (typically under 500 calories), and ‘normal’ eating for the other five days in the week.
I prefer an intermittent fasting approach that is based on the window of time each day, versus fasting and non-fasting days. In my experience with clients, this may lead to a binge-eating mentality; it can also be difficult to navigate around family and social events.
Benefits of Intermittent Fasting
Much of the conversation around the benefits of intermittent fasting are centered on physiological and metabolic health, with peer-reviewed studies and meta-analyses of randomized controlled trials showing improvement in weight, waist circumference and body composition, including body fat and muscle mass, along with blood pressure, glucose levels, insulin sensitivity and cholesterol profile. Current research supports that intermittent fasting improves these markers significantly compared to typical ‘non-intervention’ diets. What’s not clear yet is whether intermittent fasting is more effective than standard calorie-reduction diets over the long term.
There are also benefits of intermittent fasting that tend to be less quantifiable, like energy levels and mental clarity, along with gut health and brain health.
Following an intermittent fasting approach appears to have a positive impact on the balance and composition of our gut microbiome, which in turn supports our whole-body wellness including immune system, metabolism, mood, energy and more.
It’s the potential for the cognitive benefit of fasting, though – specifically the reduction in risk of dementias, including Alzheimer’s disease – that first caught my attention about 10 years ago. Intermittent fasting is linked to a reduction in the accumulation of B-amyloid, one of the primary markers for Alzheimer’s. And recent evidence shows that the metabolic changes that occur with intermittent fasting (e.g. a 12-hour overnight fast) may enhance brain function in terms of better cognitive performance and improved neuroplasticity, our brain’s ability to change and adapt based on our experiences.
Where to Begin
Start out by determining your timeframe for intermittent fasting – how long do you want to fast, and how long is your fueling window? Your fasting window will start after our last meal of the day until your first meal of the following day.
Aim for at least a 12-hour overnight fast, leaving at least 3 hours between your last meal or snack of the evening, and bedtime.
The actual timing of when this takes place is up to you.
Some people find that a 12-hour fast feels manageable for them, e.g. fasting from 6:00 PM to 6:00 AM, or 8:00 PM to 8:00 AM.
Others may choose to push their fasting window a little later and/or longer, doing a 14-hour fast from 7 PM to 9 AM, for example, or a 16-hour fast from 7 PM to 11 AM.
The time of the day is less relevant – what matters more is the duration of your fasting and fueling window, and making sure the timing works for your lifestyle.
What to Eat and Drink
Throughout the FUELING window: This is pretty much what you might consider part of an otherwise healthy, wholesome diet, just concentrated into this shorter window of time. Ideally this fueling window is centered on real, whole foods including lean proteins, plant-based fats, vegetables, fresh fruits, whole grains and legumes, with extras like bone broth and plain Greek yogurt.
Throughout the FASTING window: Water, sparkling water, unsweetened tea, coffee and chicken broth or vegetable broth are staples.
Fats are also an option during the fasting window, especially for I mentioned the modified approach that I take with intermittent fasting, which includes the addition of fats during my fasting window. It’s not technically fasting, of course, but fats like coconut oil, olive oil or MCT oil (or a splash of real cream in my coffee) don’t raise our insulin levels. Compared to protein or carbohydrates, consuming fats during the fasting window means less disruption to the metabolic benefits of fasting, including cellular repair and regeneration.
Steer clear of: The usual suspects, those foods and ingredients that don’t add quality nutrients into our diets, and also can leave us feeling bottomed out. These include artificial sweeteners, added sugars (e.g. table sugar, honey, agave, coconut sugar) and processed carbohydrates (e.g. white breads, potatoes, pasta, rice). Intermittent fasting is also a great opportunity to start dial back on alcohol, which, not surprisingly, is not recommended during intermittent fasting.
It's Not for Everyone
Intermittent fasting isn’t recommended for people with eating disorders or history of eating disorders, people younger than 18, and pregnant or breastfeeding women. It is also not recommended for those with diabetes who are taking insulin. Talk with your healthcare provider before beginning any fasting protocol, especially if you are on any medications that are to be taken with food.
The Bottom Line
More long-term research is needed to tease out any additional benefits that intermittent fasting may provide above and beyond straightforward calorie restriction. Regardless, compared to a standard diet, intermittent fasting appears to have strong potential to support our physical and mental wellbeing.
What’s most important is to find what works for you. What feels sustainable to fit within the parameters of your family life and social life. What leaves you feeling your best, supporting your energy, mood and mental clarity to thrive in your work and play. And be mindful that what works for us may not be a fit for everyone – and there’s no judgment either way. We’re all in this together, looking to take the best care possible of our body, mind and spirit.
Molly Kimball, RD, CSSD is a registered dietitian + nutrition journalist in New Orleans, and founder of Ochsner Eat Fit nonprofit restaurant initiative. Tune in to her podcast, FUELED | Wellness + Nutrition and follow her on Facebook, Instagram and Twitter at @MollyKimballRD. See more of Molly’s articles + TV segments at www.mollykimball.com, and sign up for the Eat Fit Wellness Bites weekly newsletter here.