Can fasting keep the holiday pounds off?

    A lot of people gain weight over the holiday season. This study explored whether intermittent fasting may be useful in putting the brakes on holiday weight gain.


    The average adult gains between 0.5 to 1.0[1] kilograms per year. This can lead to weight accumulation and obesity over the course of many years. There has been some research that suggests that the majority of this weight gain occurs during the traditional holiday season between the months of November and December. For example, roughly 0.4 kilograms[2] of weight gain have been observed between mid-November to early January. Another study showed a 0.6 kilogram[3] increase during the weeklong period between Christmas and New Year’s Day. As you can see in Figure 1, this weight gain occurs roughly in the same time frame in both the U.S. and Germany, with Japan’s frame for weight gain shifted to after New Year’s Day. Furthermore, this holiday weight gain is not lost[2] in the subsequent spring and summer months. As such, finding ways to mitigate holiday weight gain may be an important aspect of reducing weight gain in an individual’s life, and thus, reducing their overall risk of obesity.


    One potential solution for the prevention of weight gain during the holiday period is the use of intermittent energy restriction (IER), defined as short periods of eating significantly below energy requirements, interspersed with regular eating periods. This differs from conventional energy restriction during which energy intake is chronically reduced below the amount normally consumed for long periods of time. One popular implementation of IER is known as the “5:2 diet.” This implementation is characterized by substantial caloric reductions for two days a week and normal intake for five days a week. On the two days of reduction, food can be reduced as low as zero to 500 calories per day. This approach has been shown to be an effective tool for weight loss in previous studies[4].

    The present study is a randomized controlled pilot trial designed to evaluate the effects of a modified 5:2 IER nutrition program to prevent weight gain in overweight healthy adults over the winter holiday period between Thanksgiving and New Year, compared with a control group following their habitual diet.

    Much of the yearly weight gain that occurs in adults occurs during the holiday season. Intermittent energy restriction (IER) has been shown to aid weight loss in previous studies, yet it has not been investigated as a tool to prevent holiday weight gain. The present study is a randomized controlled pilot trial designed to evaluate the effects of an IER nutrition program to prevent weight gain in overweight healthy adults over the holiday period.

    Who and what was studied?

    The study under review was a pilot randomized controlled study designed to investigate if a modified 5:2 intermittent energy restriction nutrition program can prevent holiday weight gain in overweight adults. The study was registered at[5].

    Participants were considered eligible if they were 21-65 years old, had a BMI between 25 and 29.9, and were weight stable (defined as +/- 3.0 kilograms) in the previous six months. Participants were excluded if they were diagnosed or received medical intervention for metabolic diseases (e.g. diabetes, dyslipidemia, impaired fasting glucose) or gastrointestinal disorders. Ultimately, 23 adults were randomized to the IER and control groups, with 22 completing the study.

    The interventions took place throughout the winter holiday season (November 13 through January 3). The IER protocol consisted of two consecutive days of energy intake reduction to 730 kilocalories per day provided via meal replacement shakes. On the remaining five days, participants were instructed to eat normally. The participants were also given several dietary supplements, including fish oil, prebiotic fiber, clove and turmeric extracts, white kidney bean, saffron, CoQ10, calcium, and a multivitamin. The control group was instructed to maintain their regular eating habits and take a multivitamin.

    The primary outcomes were changes in bodyweight, both within and between groups. The secondary outcomes were liver enzymes, blood lipids, fasting insulin, and HOMA-IR.

    This study randomized 22 men and women into an IER nutrition program or control for 52 days around the winter holidays. The IER nutrition program consisted of two consecutive days of 730 kilocalories per day followed by five days of ad libitum eating. Bodyweight, blood pressure, heart rate, and blood samples were collected at baseline and at the end of the study.

    What were the findings?

    There were no statistically significant differences between groups for changes in bodyweight over the 52-day intervention. However, the IER group lost a significant amount of weight from baseline (-1.3 kilograms) while the control group did not (-0.4 kilograms). There were no differences between sexes and no correlation between weight loss and starting bodyweight.

    For secondary outcomes, the IER group experienced statistically significant reductions in HOMA-IR, fasting insulin, and the total to HDL-C ratio compared to the control group. All of these markers increased in the control group and were reduced in the IER group. Additionally, the IER group experienced a non-significant drop in triglycerides and increases in HDL-C. The statistically significant secondary outcomes are plotted in Figure 2.


    Compliance, which was assessed using telephone interviews and email, was 98% throughout the entire study. There were no changes reported in blood pressure or heart rate in either arm during the study. A total of 69 adverse events were reported in the nutrition program arm of the study. However, the authors reported that only 10 of them were possibly related to the dietary intervention. Of these events, one participant reported a 13-day spell of nausea. Adverse events in the control group were not reported.

    There was modest weight loss in both arms of the study, with the nutrition program arm losing 1.3 kilograms and the control group losing 0.4 kilograms. There were statistically significant between group differences in markers of glucose and lipid metabolism, with minor differences in the total cholesterol:HDL-c ratio (about 0.5) and insulin levels (about 3.5 μIU/mL). Both the compliance (about 98%) as well as the total number of adverse events (69 events in total) were high, but only ten of the latter could reliably be ascribed to the IER intervention.

    What does this study really tell us?

    This single-center, parallel-group, randomized and controlled pilot study showed that a 5:2 IER nutrition intervention over the holidays may lead to very minor reductions in weight. However, these results were not significantly better than the control group’s.

    The study showed similar changes in bodyweight between groups, with the nutrition program group losing roughly a kilogram more than the control group. While this difference was not statistically significant, it is difficult to make a conclusion on the efficacy of this IER approach over this short time frame with such a small sample size. It is entirely possible that this one kilogram difference would be a statistically significant difference with a larger sample. Also, both groups lost weight, suggesting that they were both in a caloric deficit over the 52-day duration of the study. This is an important aspect of the study to keep in mind.

    There were minor between-group differences with regard to changes in serum lipids, insulin, and liver enzymes, but these differences do not amount to large, clinically meaningful differences. As such, these results should be interpreted as modest changes that may just be the result of minor weight loss.

    This study was a pilot study that was designed to provide data for power calculations and future studies with larger samples. As such, this study does come with limitations that need to be considered. First, as noted in the study, many of the participants were employees of the study sponsor, Life Extension, which is a health company. As such, these participants may have introduced confounding variables, such as engaging in additional weight loss behaviors outside the study protocol. The minor weight loss noted in the control group hints that this may have occurred. Even if the participants didn’t engage in these behaviors, it’s still open to question whether the study population is representative of the general population. Second, the study may have been underpowered, which is not surprising because it was a pilot study and no power analysis was performed a priori. Third, there was no reporting of dietary intake outside of the compliance for the two days of energy restriction.

    The IER nutrition program led to slightly greater weight loss than the no-intervention control. There was also little additional benefit on blood markers from the IER nutrition program. The study was likely underpowered and skewed by self-selection bias.

    The big picture

    The present study is not in concordance with previous literature, in that the control group lost weight (or did not gain weight) during the holiday season. A previous study[6] found that people gain weight over this season, and that exercise alone (about five hours per week) is not correlated with the prevention of weight gain. Another study[7] found that young adults gained half a kilogram over the Thanksgiving holiday. The finding of no weight gain in the control group in the present study may likely be due to self-selection bias, as the participants in the control group may have engaged in additional, “out of the norm” weight loss behaviors.

    Previous studies that have employed IER for weight loss have shown some success. For example, a previous study[8] that utilized alternate day fasting demonstrated that IER led to a 3.9 kilogram reduction in bodyweight in participants with obesity over eight weeks. Another study[9] that also used alternate day fasting found that IER led to a roughly five kilogram reduction in bodyweight after 12 weeks. Furthermore, a systematic review and meta-analysis[10] of IER interventions found that they tended to help people lose 5-13% of their starting weight. As you can see in Figure 3, IER wasn’t statistically better than continuous energy restriction. However, the error bar shows that the data is mostly compatible with IER outperforming it.


    The results from this pilot study are preliminary and are restricted by substantial limitations. There are also several aspects of IER that need to be considered before employing the strategies utilized in the study. Short periods of large caloric deficits can be helpful in offsetting the total caloric load of subsequent periods of higher caloric intake. However, IER approaches may be worse for managing hunger[11] than other forms of attempted caloric restriction (e.g. continuous, less aggressive caloric restriction). However, this is not a consistent finding. Furthermore, some evidence suggests that IER may lead to greater metabolic improvements[12] (e.g. fasting glucose, cholesterol, triglycerides) than continuous caloric restriction. However, it is difficult to isolate those effects from the often increased weight loss, and other evidence suggests that there is no additional metabolic benefit[13].

    The present study showed no weight gain among the control group, which conflicts with the larger body of literature. As such, the lack of effect found in the study under review should be taken with caution.. It’s possible that IER may be is a valid dietary tool for weight loss and weight management. Whether it is superior to other dietary interventions for weight loss or for metabolic improvements is equivocal.

    Frequently Asked Questions

    Q. What other forms of IER might be useful in this context?

    The 5:2 approach used in this study is one example of many approaches to IER. Alternate day fasting, which requires a significantly energy-restricted diet every other day, has been shown to aid weight loss[14] and weight management. Time restricted feeding, (i.e. shortening the feeding window during the day), has also been shown to help reduce bodyweight[15] and may hence be useful to prevent holiday weight gain, as well.

    Q. What’s the evidence base for IER extending life?

    There has been some early research and speculation that IER may be one way to improve longevity. Decades of research in model organisms has been conducted and the literature suggests that IER may improve lifespan, primarily through decreasing nutrient-sensing pathways[16]. However, whether this would translate to humans and meaningfully increase lifespan is still a very open question.

    If the use of an IER regimen helps people avoid holiday weight gain, the ensuing health benefits may very well translate into an increased lifespan, or at least healthspan, worldwide.

    What should I know?

    Holiday weight gain contributes to much of the average weight gain that occurs during the year for many people. IER has been shown to be a useful tool for weight reduction and weight maintenance in many contexts. However, it has not previously been studied as a weight gain prevention strategy during the holiday season.

    The present study was a randomized controlled pilot trial that examined the effect of IER compared to a control group on weight loss over the holiday season. In this study, the researchers found that the IER nutrition intervention over the holidays may lead to very minor reductions in weight. However, these results were not substantially better than a no-intervention control group, which—in contrast to previous research—lost a non-significant amount of weight during the winter holiday period. Furthermore, the IER group also received a supplement that included a variety of ingredients that may have confounded the intervention. These preliminary results need further investigation. However, other research indicates that IER is at least as effective as traditional continuous energy restriction for losing weight.