Alternate-Day Fasting vs. Daily Caloric Restriction for Weight Loss

The quest for the perfect weight loss diet has led some to try alternate-day fasting—restricting calories on “fast” days, and not restricting calories on “feast” days. But is this method worth the sacrifice? Maybe not, according to research published in JAMA Internal Medicine. The research found that, while alternate-day fasting may yield the same weight loss as everyday calorie restriction, it may be harder to stick to in the long run.

The study included 100 participants between 18 and 64 years old who were obese but otherwise healthy. Researchers calculated how many calories each participant normally ate each day and considered this to be their baseline calorie intake. Then, they randomly assigned participants to one of two weight loss intervention groups or a control group: participants assigned to the alternate-day fasting intervention were instructed to eat 25% of their baseline calories on fast days and 125% of their baseline calories on feast days; participants assigned to the daily calorie restriction intervention were instructed to eat 75% of their baseline calories every day; and, the control group was instructed to eat normally, with no calorie restrictions. After six months, daily calorie intake levels were revised for the weight loss groups to instead support weight maintenance. At months six and twelve, researchers measured the participants’ weight loss and diet adherence, as well as health markers such as blood pressure, insulin resistance, and LDL cholesterol (“bad” cholesterol). At the end of the study, they found that:

  • The alternate-day fasting group and calorie restriction group lost similar amounts of weight after both six months and one year. At the end of the trial, they had lost 6% and 5.3% more weight, respectively, than the control group.
  • Participants in the alternate-day fasting group were less adherent to their intervention: on average, they ate more on fast days and less on feast days than they were instructed to eat, while the calorie restriction group generally ate as they were directed.
  • More participants dropped out of the alternate-day fasting group (38%) than out of the calorie restriction group (29%) or the control group (26%).
  • The alternate-day fasting group had increased levels of LDL-cholesterol compared with the calorie restriction group, but there were no significant differences in blood pressure, insulin resistance, or other health markers between the two groups.

These findings suggest alternate-day fasting and calorie restriction are likely to result in similar amounts of weight loss, but alternate-day fasting may be harder to maintain, and may even have a negative impact on LDL-cholesterol—a known cardiovascular risk factor. Nonetheless, alternate-day fasting may be a sound option for those who would benefit from weight loss but don’t fare well with daily calorie restriction. After all, there really isn’t a “one size fits all” diet.

Source: JAMA Internal Medicine

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