Nor is alternate-day fasting better — or worse — at improving risk factors for heart disease, such as blood pressure and cholesterol profiles.
But alternate-day fasting does appear to be a slightly more difficult diet to stick with.
These findings may be helpful to people who have struggled to lose weight on a conventional diet — one that requires them to limit how much food they eat each and every day. Alternate-day fasting, which requires restricting calories only every other day, may offer an alternative for losing weight — if you can stay on the diet, that is.
Indeed, several previous studies have suggested that alternate-day fasting is effective for losing weight. But those earlier studies followed people for only two to three months. The current study observed people for six months and then followed up with them after a “maintenance” period of another six months.
For the study, a team of researchers recruited 100 overweight or obese adults. Most of the participants (86) were women, and their mean age was 44.
The recruits ate normally for the first month (to assess how many calories they typically consumed). Then they were randomly assigned to one of three diets. One group was put on a calorie-restricted diet and told to consume no more than 75 percent of their normal daily intake of calories each day. The second group was assigned to alternate-day fasting. They were instructed to alternate between a day of consuming no more than 25 percent of their normal calorie intake (typically about 500 calories) and a day of consuming up to 125 percent (referred to as “feast day” by the researchers). The third (control) group was not given any instructions about counting their calories and continued eating as they had in the past.
After six months, the groups on the calorie-restricted diet and on the alternate-day fasting diet had both lost 6.8 percent more weight, on average, than those in the control group.
The researchers also found that the participants in the alternate-day fasting group consumed more calories than prescribed on their “fast” days and less than prescribed on their “feast” days, while those in the daily calorie-restricted group generally kept to their assigned calorie goals.
The participants were then instructed to maintain their weight for another six months. At the end of that period, everyone was re-weighed. The group on the calorie-restricted diet had lost an average of 5.3 percent more weight than the control group, while those on the alternate-day fasting group had lost an average of 6.0 percent more weight.
The researchers then looked at various risk factors for heart disease, including blood pressure, heart rate, cholesterol profiles and fasting glucose levels. They found no significant differences between the two intervention groups.
“The results of this randomized clinical trial demonstrated that alternate-day fasting did not produce superior adherence, weight loss, weight maintenance or improvements in risk indicators for cardiovascular disease compared with daily calorie restriction,” the study concludes.
Needed: a long-term solution
As the researchers point out, the study comes with many caveats. Most notably, it started with a relatively small number of participants (100), and then had a high dropout rate. Only 69 of the participants completed the study, and the dropout rate was highest (13 of 34) in the alternate-day fasting group (compared to 10 of 35 in the calorie restriction group and 8 of 31 in the control group).
It should also be pointed out that one of the authors has published a book that promotes an alternate-fasting diet.
Still, both intervention groups in this study did lose — on average, at least — more weight than the people who made no changes in their eating habits. So, doing something would appear to be better than not doing anything — at least, in the short run.
The challenge, as always with weight-loss diets, is keeping the weight off for longer than a year. And doing that requires more than just recommending a particular diet to individuals. It requires substantive changes in how we structure our society, particularly among disadvantaged populations — creating policies that reward the growing and marketing of healthful foods, for example, and the building of transportation infrastructure that enables people to be more physically active right in their own communities.
In other words, getting our national obesity rates down is going to require much, much more than a fad diet.
FMI: The study can be downloaded and read in full on the JAMA Internal Medicine website.