Intermittent Fasting: What Science Says about Eating Less Often
Welcome to our Embrace Wellness blog series, where each month we’ll explore a new theme. We started this month with a webinar about fad diets, or popular diets that promise weight loss and/or health benefits. During our webinar, we touched on one diet that’s become popular recently: intermittent fasting.
What is intermittent fasting?
An ancient practice grounded in global cultures and religions, intermittent fasting restricts the timeframe of eating and drinking. This practice can take many different forms. For example, fasting may restrict eating on certain days of the week or hours of the day. Fasting can also restrict the percentage of calories eaten on fasting days, usually by 20-25% of an individual’s needs.
What is the hypothesis for intermittent fasting?
The broad hypothesis for intermittent fasting suggests that restricting the timeframe of eating and drinking impacts circadian rhythms, the gut microbiome, and lifestyle behaviors. Through these effects, intermittent fasting is proposed to support weight management, metabolism, metabolic biomarkers (cholesterol, triglycerides), gastrointestinal function, and sleep quality (1).
Is intermittent fasting backed by research?
Most of the research on fasting has been conducted in animals; in these studies, intermittent fasting has demonstrated beneficial effects on levels of hunger hormones such as leptin and ghrelin, reduced inflammation, increased insulin sensitivity, and the increased use of fat for energy (2). However, evidence is more limited in humans.
What are the potential benefits of intermittent fasting?
Weight loss. In some studies, overweight and obese participants experienced modest weight loss. However, intermittent fasting was shown to be equivalent, not superior, to daily calorie restriction (1, 2, 3).
Glucose metabolism and insulin sensitivity. Insulin sensitivity describes how sensitive our cells are to insulin, the hormone that allows glucose (sugar) to enter our cells and be utilized for energy. In animal studies on fasting, rats experience improved insulin sensitivity, which helps control blood sugar. In human studies, results demonstrating these effects vary (2).
Hunger and mood. Study participants of normal weight reported more feelings of hunger, irritability, tiredness, and difficulty concentrating during non-restricted eating days (1, 3). In contrast, study participants with overweight and obesity experienced reductions in anger, fatigue, and mood disturbances (3).
How should we interpret the research?
While intermittent fasting may be a promising approach for weight management and improved metabolic biomarkers, more randomized controlled trials on humans are needed. Long-term safety and efficacy of fasting is unknown (3). Potential pitfalls such as overeating on non-restricted eating days and a preoccupation with food also need to be considered. Additionally, it is important to further understand the effects of various types of intermittent fasting on individuals of different weights, backgrounds, and with different medical conditions (2, 3). In sum, no one size fits all when it comes to diet, and we should seek advice from a credentialed health professional before attempting a fast.
Instead of committing to a fast, here are 5 tips for the New Year:
Add fiber. Choose foods rich in fiber to help keep you full throughout the day. These foods include: whole grains (oats, brown rice), seeds (chia, flax), legumes (beans, lentils), fruits, and vegetables.
Time protein intake. Space protein out over the course of the day. Most adults should aim for 0.8 grams of protein per kilograms of bodyweight daily.
Increase water consumption. Aim to drink half your bodyweight in ounces of water, unsweetened seltzer, and tea daily. Keep it interesting by adding a squeeze of citrus, some sliced cucumber, or mint leaves.
Sleep more. Commit to getting the proper amount of sleep, approximately 7 to 8 hours for adults. Go to bed 15 minutes earlier each week until you reach your target.
Pack snacks. Bring snacks for stretches of time when healthy food is not accessible. Healthy snacks include: yogurt, hard boiled eggs, roasted chickpeas, edamame, hummus and vegetables, and fruit and nut butter.
References
(1) Patterson RE et al. Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition 2017;37:371-93.
(2) Cioffi I et al. Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. J Transl Med 2018;16:371.
(3) Harvie M and Howell A. Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight, and Normal Weight Subjects – A Narrative Review of Human and Animal Evidence. Behavioral Sciences 2017;7(4):1-22.
