But while these diets have gained popularity, there have been only a few longitudinal studies on whether they actually lead to sustained weight loss. (U.S. News & World Report has a breakdown of past research into fasting diets.) Now there’s a new credible study to add to the mix: This 50-week study of 150 obese and overweight adults published in The American Journal Of Clinical Nutrition found that the 5:2 fasting diet was “equivalent but not superior to” conventional dieting in terms of weight loss and the prevention of metabolic diseases.


Save high-intensity interval training and heavy weight training for feed days/during your feed window, if you can, when you have the calories for fuel and nutrients for recovery. But if your training schedule calls for a grueling workout on a fast day that can’t be moved, add the calories burned to your count for the day so you don’t burn through muscle. At 200 or 300 calories, you don’t need to compensate, but if you burn 500 or more on a fast day, instead of just 500 maintenance calories with 50g of protein, eat 1,000 calories with 80g or more of protein, Varady advises.
In a physiological context, fasting may refer to the metabolic status of a person who has not eaten overnight, or to the metabolic state achieved after complete digestion and absorption of a meal. Several metabolic adjustments occur during fasting. Some diagnostic tests are used to determine a fasting state. For example, a person is assumed to be fasting once 8–12 hours have elapsed since the last meal. Metabolic changes of the fasting state begin after absorption of a meal (typically 3–5 hours after eating).
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