Intermittent fasting, or IMF, is an umbrella term used to describe a pattern of cycling between fasting and non-fasting. Intermittent fasting is by all means not a new diet phenomenon; however, its popularity as a health-promoting strategy has been increasing dramatically over the past decade. Particularly more recently, people within the Keto community have started to take note of the particular benefits of intermittent fasting for a Keto Diet.
Although there are several variations of Intermittent Fasting, there are two major subcategories:
- Time Restricted Eating (TRE): Involves daily fasting for a 12 to 20-hour interval (including sleep time!) and limiting food consumption to a 4 to 8-hour “eating window” of your choosing. A popular regimen for this method of IMF is delaying breakfast until mid or late morning and eating dinner no later than 7 pm. This time-restricted eating method allows more flexibility and offers the simplest and most sustainable approach to IMF.
- Alternate-Day Fasting (ADF): Involves fasting one day, whether by not eating at all or eating 500 calories or less (600 calories or less for men), and then eating normally the next day. The cycle then repeats itself for any number of additional days during the week. A popular version of ADF is the 5:2 method, comprised of 5 days of regular eating alternating with 2 days of non-consecutive fasting per week. Since ADF typically involves a longer duration of fasting than the Time Restricted Eating method, ADF may be more challenging to maintain long term.
Regardless of which method you choose, there are a number of benefits associated with IMF. Here are five benefits of intermittent fasting that are especially relevant for anyone on a Keto Diet:
- Weight Loss & Weight Management: One of the most common “perks” of IMF is that it provides an alternative to a continuous calorie-restricted diet, resulting in similar, if not superior, weight loss. In fact, a statistically significant weight reduction has been observed in the vast majority of short-term IMF trials. Weight-loss associated with IMF has also resulted in reductions in both visceral fat (surrounding our organs) and abdominal fat, while still preserving muscle mass. Fortunately, for those on the Keto Diet, IMF and Keto can work synergistically for promoting even more efficient weight and fat loss. Both methods lead to decreased insulin levels and glycogen stores, driving the body to start burning fat for fuel (i.e. ketosis).
- Preservation of Muscle Mass & Metabolic Health: A top priority for anyone trying to lose weight should be the preservation of muscle mass while doing so. This is because your body’s metabolic rate is closely tied to your body’s muscle mass. Research on IMF demonstrates that a lower percentage of lean body mass, or muscle, is lost when losing weight with IMF than with traditional low-calorie dieting. This greater preservation of lean body mass translates into less of a slowdown in your body’s metabolic, or calorie burning, rate. Similar to a ketogenic diet, IMF can also induce a trigger point, referred to as the “metabolic switch”, that shifts our body’s metabolism from storing fat and burning glucose for fuel to mobilizing our fat stores and using fatty acid-derived ketones for energy.
- Diabetes & Blood Sugar Management: IMF has been shown to positively impact blood sugar management by boosting insulin sensitivity throughout the body. Much like the ketogenic diet, IMF is known to lower insulin levels and is another efficient method of reducing insulin resistance, the hallmark of Type 2 diabetes and Metabolic Syndrome. In addition to improving blood sugar control, IMF can improve blood levels of cholesterol and triglycerides (blood fats) in adults with Type 2 diabetes. Research has also demonstrated the ability of IMF to boost the levels of adiponectin, a “hunger management” hormone that plays a crucial role in decreasing insulin resistance.
- Improved Gut Health: IMF has a direct influence over the many microorganisms that reside in our gastrointestinal (GI) tract, known as the gut microbiota. Together, IMF and our “good gut bacteria” have the potential to exert powerful health benefits through a symbiotic-like relationship. In other words, fasting has a beneficial impact on our healthy gut bacteria, and, in turn, these same bacteria can help protect our body during fasting. Our immune system is the main link between our gut bacteria and their influence on our health. Helping to put this into perspective is the fact that 70% of our immune system is housed in our GI tract. Researchers have recently demonstrated that fasting triggers a genetic “switch” that activates an anti-inflammatory response in our gut, protecting both our body and our healthy gut bacteria, as well as strengthening our gut barrier to protect us from harmful microbes, toxins, and other adverse elements.
- Brain Health: IMF has been shown to improve memory, preserve brain function and mental performance, as well as reduce the oxidative stress which can harm the cells of our brain and nervous system. IMF has also demonstrated the ability to boost levels of our body’s antioxidant and anti-inflammatory defenses, promoting both nerve-growth and protection and helping to restore damaged nerve cell circuits. In addition, IMF can lead to both a lower production of unstable molecules known to cause mitochondrial DNA damage, and a dramatic increase in a biological process known as nerve cell autophagy, or cellular cleansing. This process recycles cellular waste and eliminates potentially toxic damaged cell components and harmful protein by-products known as aggregates, which have been linked to a wide range of neurological diseases. Other studies have shown that IMF promotes an increase in a protein produced inside nerve cells known as brain-derived neurotrophic factor, or BDNF. BDNF plays an important role in nerve cell survival and in the regulation of signaling between nerve cells critical for memory and mental performance. Both fasting and the ketogenic diet are associated with increased levels of the ketone bodies β‐hydroxybutyrate and acetoacetate which are known to increase levels of BDNF. Together, they can potentially provide an even greater physiological stimuli for boosting the production of BDNF, helping to reap more of its optimal health and protective effects.
Intermittent Fasting can offer a viable-and safe-approach for losing additional weight and improving metabolic, digestive, and neurological health for those following the ketogenic diet. IMF has shown to be equally, if not more, effective as continuous calorie restriction for improving weight loss, insulin sensitivity and other positive indicators of overall health. Ultimately, any long-term health advantages resulting from implementing both these strategies can only materialize if the diet and eating style are sustainable. Your choice of either version of IMF is based on personal preference, but if you’re a “fasting newbie”, the Time-Restricted-Eating (TRE) form of IMF is a more simple and sustainable “beginner” strategy to jumpstart or boost weight loss on your Keto Diet.
An important caveat: If you are being treated for a chronic medical condition, such as diabetes or heart disease, you should first get the green light from your medical practitioner before embarking on this type of diet or eating strategy. Pregnant or breastfeeding women should avoid IMF.
Written by Mary Paley
Mary Paley is a Registered Dietitian with a Master’s Degree in Nutrition and Dietetics at the MGH Institute of Health Professions. Her current focus is on the benefits of ketogenic diets for both obesity and diabetes management. Having worked in a number of institutional settings for 30+ years, she has interacted with tens of thousands of people with various health disorders, the vast majority within the triad of obesity, diabetes and heart disease. Although she was obliged to give her patients recommendations from the Standard American Diet, she intuitively knew that many of the diet tips were invalid or obsolete. She prefaced her advice with views based on her own observations and valuable feedback from her patients and clients. Recent research has finally helped to vindicate her unconventional viewpoints on nutrition that supported more low-carb foods with healthy fats. Mary currently shares her knowledge and inspirational views on Fearless Keto.