Newsletter #294

Conventional wisdom dictates that most people put on a few pounds during the holiday season. But is this true?

Well, the good news is that the amount of weight that you actually gain is probably less than you think. You might feel quite a bit heavier, but a lot of this can be attributed to water weight gain (more starches and sodium = water retention).

Yet, there is some bad news here. Research suggests that when we do gain a little bit of fat mass, it may hang around long after the holiday celebrations have ended. Furthermore, some of us might be more prone to gaining significant weight during the holidays.

Fortunately, recent studies also indicate that this is far from inevitable.

People often claim to have gained weight during Christmas and other festive periods, usually around five pounds or so. However, relying on self-report for body weight information is obviously fraught with issues.

To get around this limitation, researchers acquired body weight data from smart scales, which connect to wifi and transmit the information wirelessly. A total of 2924 participants from three different countries recorded daily body weight over a 12-month period. This included:

In all three countries, the participants’ weight rose within ten days after Christmas Day, as compared with ten days before Christmas Day.

And as you can see from the graph, significant weight gain was observed around major holidays in each country, including Golden Week in Japan, Easter in Germany, and Thanksgiving in the United States.

Compared to their lowest weight during the year, body mass increased by 0.7-1.0% during holiday seasons, which is less than two pounds. However, about half of that weight gain lingered until the summer months or even beyond.

So, on the one hand, the amount of weight that people actually gain during the holidays, on average, is much smaller than what they think.

However, that little bit of added weight seems to hang around long after the holidays have concluded.

Could this lead to a gradual accumulation of weight over the years?

On average, people put on a very small amount of weight during the holidays. However, the actual magnitude of this gain is likely to vary between individuals.

Researchers affiliated with the NIH recruited 195 healthy adults in Bethesda. Participants were not told that the study was designed to monitor weight fluctuations specifically — it was instead characterized as a study of "seasonal changes in vital signs."

Subjects visited the clinic on four different occasions to have measurements taken:

They were subsequently invited to return for two additional visits in the summer and fall in order to see how body weight might have changed across a full one year interval.

The researchers determined that study subjects had an average net weight gain of 1.05 lb over the course of a year. Importantly, more than half of this annual increase was attributable to a seasonal gain in body weight that occurred during the 6-week interval that encompassed the holiday season, which was not fully reversed thereafter.

Fewer than 10% of subjects gained more than five pounds, but those individuals were more likely to already be overweight or obese.

Finally, when the research team examined factors that predicted holiday weight gain, only one behavioral factor emerged: changes in physical activity. Those who reported much less physical activity gained the most during the festive period.

Accordingly, the researchers state, "The relationship we found between reported physical activity and weight change point to the need for further studies determining whether increasing physical activity can prevent holiday-related weight gain in at-risk individuals."

Holiday weight gain is typically attributed to greater intake of hyperpalatable food, and with good reason. But another potential source of fat gain is diminished physical activity. We know that people are less active in the winter than in any other season, suggesting that exercise could be useful to counteract weight gain associated with winter holidays.

And given that overweight/obese individuals appear to be more susceptible to significant weight gain, they likely stand to benefit more from such a preventive measure.

To assess the effects of exercise (and the lack thereof) on body weight and cardiometabolic health markers, Spanish researchers recruited 38 middle-aged men with overweight and metabolic syndrome. These volunteers were already undergoing a 3-month HIIT program, which was scheduled to conclude one week before Christmas.

The participants were randomly split into two groups. One group extended their HIIT program for three more weeks, and the other stopped training altogether for the same timespan.

Before and after, the research team measured body weight, insulin, arterial blood pressure, and blood lipids. They also assessed insulin resistance via the homeostasis model assessment of insulin resistance (HOMA-IR).

The results weren't super surprising. The group that stopped training gained weight. In line with the other studies we just talked about, this increase was statistically significant but fairly modest, amounting to only about 1.5 pounds.

This weight gain was accompanied by increases in mean arterial pressure (94.0 to 97.1 mm Hg), blood insulin (10.2 to 12.5 µIU·mL). Finally, they showed a significant increase in insulin resistance (from 3.2 to 4.1).

Meanwhile, the group that continued their exercise regimen did not gain any weight, and the aforementioned biomarkers were unaffected by Christmas and its immediate aftermath.

They even experienced a significant decrease in their LDL cholesterol through the feasting period (going from 104.8 mg/dL to 95.6 mg/dL), which is something that few of us are likely to see, based on prior research.

So the key takeaway here is that exercise not only prevents weight gain during the holidays in the most vulnerable people, but also maintains insulin sensitivity and other cardiometabolic markers closely tied to body mass.

This is supported by prior observational research indicating that sustaining a high volume of physical activity is one of the strongest predictors of weight maintenance. Self-monitoring in general seems to be key for weight control during the holidays and other high-risk periods, and it's possible that adhering to an exercise regimen is part of that.

🎅 Doctor Who Holiday Specials are associated with lower mortality rates.

The show Doctor Who has been broadcast for 60 years. Between 1963-2022, a new Doctor Who episode was broadcast during 31 holidays, including 14 episodes on Christmas Day.

In a newly published study, a statistician at the University of Birmingham analyzed how holiday episodes of the show correlated with subsequent age-standardized death rates in the UK, and found that episodes shown during this period were indeed associated with fewer deaths, with the strongest association seen for episodes shown on Christmas Day.

If you are trying to increase levels of physical activity throughout the day, some kind of movement tracker is basically a must. Can’t manage what you don’t measure, right? Pedometers have actually been around since the 1700s, but modern digital activity trackers obviously offer a lot of other benefits, such as heart rate monitoring, as well as a much cooler user interface. Fitbit has been one of the most popular for quite a while, and it is one that we continue to rely upon here. And of course, you can easily sync your Fitbit data to your humanOS Dashboard for a more complete view of your activity patterns over the course of time.

This week, we’d like to highlight one of the courses from the Ideal Weight Program, developed by Stephan Guyenet. There is abundant evidence that physical activity can help attenuate fat gain — although not necessarily in the way that most people tend to assume.

Moderate amounts of exercise do not usually burn a ton of calories (certainly not enough to balance out hardcore holiday feasting). However, there is abundant research indicating that physical activity indirectly reins in fat gain in other ways — for instance, exercise seems to help with appetite regulation, and may even reduce expression of genes that are associated with obesity. In particular, exercise seems to be crucial in weight maintenance (most of the successful maintainers in the National Weight Control Registry are highly physically active).

In this course, Stephan describes how physical activity patterns have changed in recent history, and how the relative absence of physical activity in our lives undermines our health and body composition goals. He then explains what you can do to naturally build more movement into your day.

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