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How much do you know about this increasingly popular diet form? Take our 8-question quiz to find out.
Intermittent fasting (IF) has become a popular form of dieting in recent years as an alternative to continuous calorie restriction. IF requires consuming little to no calories for various periods of time, typically ranging from 12 hours to several days. Despite its growing popularity, is IF a safe and viable dietary option? Find out how much you really know about IF with our 8-question quiz below.
Answer: D. After 12 hours of fasting. The metabolic switch refers to the point at which the body enters a state of negative energy balance when liver glycogen stores are depleted. The body then begins to mobilize fatty acids and switches from glucose metabolism to the production of ketones derived from fatty acid metabolism.
Answer: B. Calorie restriction. Calorie restriction is commonly used in many weight loss regimens and refers to continuous calorie restriction without malnutrition. Forms of IF include time-restricted feeding (restricting food intake to specific time periods, usually 8-12 hours/day); alternate-day fasting (total fasting for certain days, alternating with a day of unrestricted food intake); alternate-day modified fasting (eating <25% of energy needs on fasting days, alternating with a day of unrestricted food intake); and periodic fasting (fasting 1-2 days/week, with unrestricted food intake on the other days).
Answer: C. Ketones. A growing body of evidence supports the view that ketones are the preferred fuel for the brain and body during fasting. Glycogen is stored in the liver and provides a source of glucose. Triacylglycerol is a form of lipid stored in adipocytes and can be metabolized to free fatty acids during fasting.
Answer: D. May produce similar amounts of weight loss as a calorie-restricted diet. IF is associated with weight loss similar to continued calorie restriction, as well as retention of lean mass. Calorie restriction is common in many weight loss regimens, with one-fourth to one-third of weight loss estimated to be from loss of lean tissue. IF has also been linked to decreased visceral fat mass, improved lipid profiles, and benefits to cardiometabolic health.
Answer: D. All of the above. Fasting as medical therapy has been proposed since at least the time of the ancient Greeks. Early in the twentieth century, it was studied for the treatment of type 1 and type 2 diabetes. Potential risks reported in therapeutic fasts of several weeks or more include nausea and vomiting, edema, abnormal liver function tests, decreased bone mineral density, and thiamine deficiency, to name a few. Several deaths have been linked to therapeutic fasting caused by lactic acidosis, small bowel obstruction, renal failure, and cardiac arrhythmias.
Answer: B. Increased inflammation. Research suggests that IF may have the following effects on cardiometabolic health: increased insulin sensitivity, decreased lipid accumulation, decreased blood pressure, decreased resting heart rate, and increased parasympathetic tone. IF is also linked to decreased inflammation in a number of tissues, which may have benefits for cardiometabolic health.
Answer: B. False. While studies are limited, evidence so far suggests few or no adverse cognitive effects related to extended fasts. Some studies have also suggested that certain cognitive domains, such as executive functioning, learning, and memory may improve with fasting. However, further study is needed.
Answer: A. Increased insulin sensitivity. Both fasting and intense exercise can trigger the metabolic switch. Studies suggest that exercise training while fasting may effect muscle as follows: increased insulin sensitivity, enhanced endurance, decreased inflammation, and increased muscle growth.
Anton SD, Moehl K, Donahoo WT, et al. Flipping the metabolic switch: understanding and applying the health benefits of fasting. Obesity (Silver Spring). 2018;26:254-268.