Expert reviews:

  • “While there are health benefits to intermittent fasting, like with the 5-2 diet, the one concern I have with this 5:2 diet is they have no rules or regulations for the five higher-calorie days. They even say, “no food is off limits, as long as the total calories are within the designated amount.” With this diet you eat 500 calories a day twice per week. Women eat about 2,000 calories per day for the other five days, and men eat about 2,400 calories per day the other five days. Eating this way could encourage behaviors like binge eating and eating a lot of unhealthy foods, like high-calorie, high-fat ice cream, burgers, and fried foods. People may assume that just because they fast twice per week they can turn around and eat absolutely whatever they want the other five days, as long as they stay within their calorie ranges. In my opinion, this does not lend itself to a healthy relationship with food.” (Christy Shatlock , registered dietician : Florida)
  • The 5:2 and similar intermittent-fasting diets are said to be easier to follow than traditional calorie restriction, and an advantage is that you do not have to exclude any food groups.  Many see the eating regime less as a ‘diet’ and more as a way of life that can help them maintain their weight loss in the longer term. All the headlines for the 5:2 diet, and similar intermittent-fasting regimes, claim that calorie restriction may be linked with. (Kerry Torrens)
  • The Fast Diet is not recommended for diabetics or prediabetics because the drop in caloric intake could put them at risk for hypoglycemia, or low blood sugar. Also, diabetes medication would require adjustment on this diet, according to one expert.

The The Fast Diet is ranked #35 in Best Diabetes Diets.

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  • Experts noted their concern about the Fast Diet’s long-term sustainability and lack of guidance. Those who suffer from severe short-term calorie restriction might find it hard to follow. However, the diet could work for extremely busy people and those struggling to cut calories on a daily basis, said one expert, who called it “relatively easy to follow compared to the diets that required structured meal choices or significant food preparation.”

The The Fast Diet is ranked #22 (tie) in Easiest Diets to Follow.

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Findings on the ‘fast diet’ published in reputed journals:

  • A 2013 study in the journal Metabolism found that obese people who alternated days of fasting with either high-fat or low-fat diets lost weight and inches from their waist and reduced some heart disease risk factors.  (NCBI)
  • In a 2011 study published by the American Association for Cancer Research, researchers at Genesis Prevention Center at University Hospital in South Manchester, England tested the effects of three kinds of diets on 115 women. One diet looked like the Fast Diet (five days of normal eating and two days following a calorie-restricted, low-carb diet each week), another restricted carbs two days a week but had no calorie restrictions and a final group followed a calorie-restricted Mediterranean diet for all seven days of the week. After four months, participants following the intermittent low-carbohydrate diets lost an average of 9 pounds, while those on the Mediterranean diet lost an average of 5 pounds.
  • In a randomized trial of 107 overweight or obese premenopausal women, researchers found that participants who followed an intermittent food energy restriction plan (25 percent restriction two days a week) lost a comparable amount of weight to the participants who followed a continuous energy restriction plan. After six months, participants following the intermittent calorie restriction plan lost an average of 14 pounds each. Results were published in 2011 in the International Journal of Obesity.
  • A study published in the July 2013 issue of Physiology & Behavior doesn’t discuss intermittent-day fasting, but it addresses the concern of overeating after fasting. Researchers at Cornell University either fed breakfast to or withheld breakfast from a group of student volunteers. They found that those who skipped breakfast reported being hungrier than those who ate breakfast. They also ate more at lunch. Still, the amount they ate didn’t fully compensate for the missed meal. Volunteers who skipped breakfast consumed 408 fewer calories over the course of the day than those who ate breakfast.
  • Studies on every-other-day fasting show mixed results. One published in 2010 in the Nutrition Journal suggested that the technique was effective among a group of obese patients. A group of 16 participants ate only one meal – lunch – every other day, and they were limited to about 500 calories. That’s the same amount of calories women consume on the Fast Diet’s fasting days. On the days when the study participants were not fasting, they were not constrained to any rules. Over the course of eight weeks, the participants lost an average of 12 3/10 pounds.