Intermittent Fasting

Intermittent fasting gains popularity

Can it improve your health?

Intermittent fasting includes several versions of time restricted eating, that is, confining food intake to part of a day (say, from 10 am to 6 pm) or to one or two days each week. Intermittent fasting appears to promote favorable responses of certain organ systems, especially for persons with overweight or obesity. Positive outcomes can include reduced body weight, body fat, blood pressure, risk of type 2 diabetes and other cardiovascular factors. The underlying mechanism seems to be a shift from (the usual) glucose-based metabolism to ketones derived from fat. This shift occurs after about 12 hours of no food intake. Intermittent fasting might be a way for people with overweight or obesity to reduce their body weight and body fat and improve their overall metabolic health.

Losing weight can lead to improved metabolic health but long-term weight loss is difficult to achieve for most people. One possible way to make weight loss easier is to confine eating to a portion of each day. Studies show loss of 3-4 percent of body weight over 3-4 months of time restricted eating. Researchers in Chicago recruited adult volunteers with obesity for a 12-week trial in which members of the experimental group confined their daily eating from 10 am to 6 pm with no food intake limitation during this period. The control group included persons matched to persons in the experimental group and instructed to maintain their usual eating and exercise activities. Members of the experimental group significantly reduced their caloric intake, body weight, body-mass index, and systolic blood pressure compared to the control group. Thus, time-restricted eating might be a way for persons with obesity to lose weight without having to count calories.

Non-alcoholic fatty liver disease (NAFLD) is the most common form of liver disease and is increasing globally. No effective therapy for NAFLD exists, although medical guidelines recommend a low-calorie diet to achieve 7 percent loss of body weight. Alas, low-calorie diets suffer from low compliance. Researchers in Malaysia tested whether an 8-week, modified alternate-day caloric restriction would improve liver health. Members of the experimental group alternated their normal diet with only 30 percent of their normal caloric intake on adjacent days. The members of the control group continued their usual eating patterns. After 8 weeks, members of the experimental group showed significant reductions in body weight, body-mass index, liver steatosis and fibrosis, and a liver enzyme (alanine aminotransferase) compared to the control group. Adherence to the experimental program stayed between 75 – 83 percent during the study. Thus, modified alternate-day caloric restriction might be an effective way for NAFLD patients to slow its progression compared to daily caloric restriction.

Several versions Intermittent fasting exist including zero-calorie alternate-day fasting, reduced-calorie alternate day fasting, the 5:2 diet (with two fasting days during the week along with 5 regular eating days), and time restricted eating (such as not eating between 6 pm and 10 am the next morning). A team of researchers conducted an umbrella review of 11 meta-analyses that included 130 randomized clinical trials to determine effect sizes of intermittent fasting studies on obesity-related outcomes and to evaluate the quality of the evidence. Of a total of 104 unique associations, 28 were statistically significant for reduced body-mass index. Ominously, intermittent fasting predicted lower fat-free (muscle) mass. Six associations were of moderate quality, while all but one of the other associations were of low or very low quality. Only six of the significant associations came from studies lasting more than six months. This umbrella review found some evidence to support the ability of intermittent fasting to improve obesity-related health outcomes, but the studies were usually short-term and the evidence generally weak. While intermittent fasting may work in the short-run, there’s little evidence that it will work in the long-run for most people. Rather like dieting to lose weight in that regard.

Caloric restriction creates a cascade of metabolic changes including shifting an organism’s primary energy source from glucose to ketones. Abundant research shows that caloric restriction slows aging and extends lifespan in animals. In humans, caloric restriction can lead to weight loss, with effects larger than those predicted simply by eating fewer calories. In addition, humans show improvement in cardiovascular health markers, including increased insulin sensitivity and reduced obesity, lipoproteins, hypertension, and inflammation. These positive effects can occur within 2-4 weeks after the onset of intermittent fasting. Intermittent fasting and its positive effects are not easy to achieve for cultural and practical reasons. Convincing people to cut back from three meals a day plus snacks to two meals a day is a tall order. Furthermore, fasters can experience a month of bodily adjustment of hunger, irritability, and difficulty concentrating. Physicians usually lack training to prescribe intermittent fasting. It’s not clear that most people can tolerate intermittent fasting for any length of time, even given the impressive benefits that fasting might provide.


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