Carrying excess body fat (particularly belly fat) increases risk for metabolic syndrome (see page 4) and diseases that include cardiovascular disease, type 2 diabetes, and cancer. Intermittent fasting is currently a popular weight loss method. Evidence suggests it can be as effective as traditional calorie cutting, although it is not appropriate for everyone. Could this eating style be for you?
Think “Fast.” Intermittent fasting involves eating only during specific times of the day ordays of the week. There are several plans that fit this definition: With daily time-restricted eating, all eating is done within a set window of time during the day (usually six to 10 hours). Alternate day fasting is a plan in which you alternate eating on a typical schedule with complete fasting or having only one small meal (around 500 calories). A “5:2 fast” involves eating on a typical schedule five days a week and fasting any two days of your choosing (consecutive or spread out). During fasting periods, drinking calorie-free beverages such as water and black coffee and tea is encouraged to prevent dehydration.
Health Benefits. Reducing the number of calories we take in leads to weight loss, which has clear health benefits in individuals who have excess body fat. Fast periods have the potential to automatically restrict the number of calories we take in. Whether fasting regimens are superior to the more traditional continuous calorie restriction (cutting calories) remains unclear.
Most studies have looked only at the short-term benefits of intermittent fasting (less than 12 weeks). There is little information on potential long-term benefits (or harms).
“One study looking at intermittent fasting versus caloric restriction over a one year period found intermittent fasting was more beneficial than continuous caloric restriction on markers of metabolic health in the short term,” says Sai Krupa Das, a senior scientist on the Energy Metabolism Team and a professor at the Friedman School, “but the two diets led to the same weigh and health improvements over the long term.”
It has been suggested that intermittent fasting helps control hunger and desire to eat, but a recent systematic review and meta-analysis concluded this is not the case.
“Work is underway to rigorously look at long-term health and aging benefits of intermittent fasting in humans,” says Das, “but it will be about 10 years before we have really strong information.”
Health Concerns. “Fasting may not be for everyone,” says Das. “For example, if you are on medications that need to be taken at a particular time and with meals to be effective, the fasting routine may compromise those requirements and the effectiveness of the medications. We need to look at the safety of intermittent fasting throughout the lifecycle and at different weights, especially for people on various medications.” For those who feel unwell when they miss meals, fasting is not a good choice.
What to Do. If you are interested in trying an intermittent fasting regimen, check with your healthcare provider first, especially with regard to medications. It’s important to meet your nutrient needs on whatever calorie-cutting plan you choose, so making healthy dietary choices during eating periods is essential. For people who struggle to cut calories across-the-board, only needing to do so intermittently might be a more feasible option. “The important thing is to find what works for you. Both intermittent fasting and continuous calorie restriction can lead to weight loss and benefit health if done correctly,” says Das.